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Integrated CO2 capture, wastewater treatment and biofuel production

Integrated CO2capture,wastewater treatment and biofuel production

by microalgae culturing—A review

Shaikh A.Razzak a,Mohammad M.Hossain a,Rahima A.Lucky b,Amarjeet S.Bassi b,

Hugo de Lasa b,n

a Department of Chemical Engineering,King Fahd University of Petroleum&Minerals,Dhahran31261,Saudi Arabia

b Department of Chemical and Biochemical Engineering,The University of Western Ontario,London,Ont.,Canada N6G5B8

a r t i c l e i n f o

Article history:

Received8June2012

Received in revised form

22May2013

Accepted26May2013

Available online7August2013

Keywords:

Microlgae

Biofuel

Digester ef?uent

Photobioreactor

Transesteri?cation

CO2capture

Wastewater treatment

a b s t r a c t

Algae have recently received growing attention given its prospects as a source of renewable energy and

its potential for CO2capture.Algae culture is of increasing value given that:(i)algae can be cultivated on

non-agricultural land using wastewater,(ii)algae can provide a high yield on a per unit of light irradiated

area,(iii)algae growth requires CO2and nutrients that can be obtained from wastewater and fossil fuel

combustion and(iv)algae contains high oil and starch making possible the production of high quality

biodiesel.Thus,algae culture can contribute to CO2?xation,wastewater treatment and can be a source of

bioenergy.This article presents a critical review,focusing on various microalgae species that consume

CO2and nutrients from wastewater,and provide high quality biofuel.In this respect,a number of

relevant topics are discussed in this review:(a)the media for algae culture,(b)the photobioreactor,

(c)the associated wastewater treatment processes,(d)the CO2capture mechanism and(e)microalgal

harvesting.This review also considers various aspects of the biomass processing such as(a)lipid

extraction,(b)thermodynamics of the produced biomass conversion,(c)biomass gasi?cation,

(d)biodiesel production,(e)catalysts,(f)reaction pathways/mechanisms and(g)reaction kinetics.

Contents

1.Introduction (623)

2.Algae species (625)

3.Microalgae cultivation system-photobioreactor technology (626)

3.1.Open system (626)

3.1.1.Unstirred ponds (627)

3.1.2.Raceway pond (627)

3.1.3.Circular pond (627)

3.1.4.Limitations of open pond systems (627)

3.2.Closed system (627)

3.2.1.Tubular photobioreactor (627)

3.2.2.Plastic bag photobioreactor (629)

3.2.3.Airlift photobioreactor (629)

3.2.4.Flat plate photobioreactor (629)

4.CO2capture (630)

4.1.Photosynthesis (630)

4.1.1.Light dependent reaction (630)

4.1.2.Light independent reaction (631)

4.2.CO2sources (631)

4.3.CO2?xation (631)

5.Wastewater treatment (632)

Contents lists available at ScienceDirect

journal homepage:https://www.sodocs.net/doc/2b5937375.html,/locate/rser

Renewable and Sustainable Energy Reviews

https://www.sodocs.net/doc/2b5937375.html,/10.1016/j.rser.2013.05.063

n Correspondence to:Chemical and Biochemical Engineering,Western University,London,ON,Canada N6A5B9.Tel.:+15196612144;fax:+15198502931.

E-mail address:hdelasa@fes.engga.uwo.ca(H.de Lasa).

Renewable and Sustainable Energy Reviews27(2013)622–653

5.1.Microalgal nutrition (632)

5.2.Nitrogen (632)

5.3.Phosphorous (632)

5.4.Wastewater components (632)

5.5.Anaerobic digested dairy wastewater treatment (633)

5.6.Municipality wastewater treatment (634)

5.7.Industrial wastewater treatment (637)

6.Algae growth/cultivation (637)

6.1.Effects of solar irradiation (638)

6.2.Effects of CO2concentration (640)

6.3.Effects of temperature (640)

6.4.Effects of pH and media composition (640)

7.Growth kinetics (640)

8.Algae harvesting (642)

9.Lipid extraction and analysis (643)

9.1.Lipid extraction (643)

9.1.1.Mechanical extraction (643)

9.1.2.Chemical/solvent extraction (644)

9.2.Lipid analysis (644)

10.Biofuel production (645)

10.1.Chemical conversion (645)

10.1.1.Transesteri?cation (645)

10.1.2.Esteri?cation (646)

10.2.Thermochemical conversion (647)

10.2.1.Gasi?cation (647)

10.2.2.Pyrolysis (647)

10.2.3.Liquefaction (647)

10.3.Biochemical conversion (648)

10.3.1.Interesteri?cation (648)

10.3.2.Fermentation (648)

10.3.3.Anaerobic digestion (649)

11.Conclusions (649)

Acknowledgments (649)

References (650)

1.Introduction

Global energy demand is drastically increasing due to the growing world population and the improvement of the quality of human life.Conventionally,fossil fuels have been the main source of worldwide energy.However,the continued use of fossil fuels is now commonly considered as unsustainable.This leads to both depleting non-renewable energy reserves and many envir-onmental issues related to fossil fuel combustion.

Combustion of fossil fuels releases large amounts of CO2into the atmosphere.This is a major source of greenhouse gases, contributing to the global warming[1].Statistics indicate that fossil fuel based power generation contributes to about one-third of the total CO2released from fuel combustion[2].A number of international accords such the one of the Kyoto Protocol in1997 set the stage for worldwide efforts to reduce CO2emissions.In order to achieve these ambitious targets,it is required to mitigate the footprints of energy generation using multi-faceted approaches that include nuclear,solar,hydrogen,wind,geother-mal,fossil fuels with carbon sequestration/use,and biofuels. Biofuels derived from bio-resources can be classi?ed using the phase they are produced in,by solid,liquid and gas[3].These fuels are renewable and designated as green energy sources,given their net zero CO2emission.

Currently,countries including USA and Brazil produce biodiesel and bioethanol employing human food chain raw materials such as corn,sugarcane,sugar beet,sorghum and wheat.However,the food chain based biofuel industries are receiving increased criti-cism.This is due to the competing demands of the same sources for human consumption as food.As an alternative,there are other types of biofuels originating from non-food feedstocks such as agricultural wastes,municipal wastes,microalgae and other microbial sources[3].These alternative feedstocks are more attractive and more acceptable.Their direct or after processing utilization leads to products unsuitable for human consumption. The use of these bio-wastes also help with disposal issues of waste and improve CO2emission reduction efforts[4].For example,the cultivation of microalgae consumes CO2that can be traced back to fossil fuel combustion processes[5,6].

Nowadays,the use of microorganisms and their metabolic products by humans is one of the most signi?cant?elds of biotechnology.Biotechnology deals with the use of microorgan-isms for the conversion of certain substances into others of greater added value of relevance is the possibility of using a wide variety of substrates for viable products and sub-products,which enables a rational and balanced use of natural resources[7].

Algae may range from single-cell microalgae species to com-plex multi-cellular giant bladder kelp species.There exists a diverse aquatic family of photosynthetic eukaryotes[8].Micro-algae are microscopic organisms that typically grow suspended in water and are driven by the same photosynthetic process adopted by higher plants.However,unlike higher plants,algae do not require a vascular system to transport nutrients.In addition,and given that every cell is photoautotrophic,they can directly absorb dissolved nutrients[9].These eukaryotics are sunlight-driven cell factories that can convert carbon dioxide into raw materials for biofuels,animal food chemical feedstocks and high-value bioactive products[10].Microalgae are amenable to genetic engineering and exploitation in mass cultures for both biomass production and carbon sequestration[11].For these reasons,microalgae have

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found numerous bene ?cial applications including animal food fertilizer,food stocks for pharmaceutical industry,pollution con-trol,water treatment,dyes,agar manufacturing and production of a second generation biofuel [12].Speci ?cally,their ability to capture CO 2makes microalgae cultivation an attractive alternative for CO 2sequestration.This capture of CO 2that can be traced to fossil fuel power plant gas ef ?uents contribute to the reduction of green house gas emissions [4].

Interestingly,unicellular microalgae can grow in waste water containing high nutrient concentrations,helping with water treatment.The treatment of livestock ef ?uents from dairy farms with microalgae has also received increasing attention.This is due to the fact that the uncontrolled nutrient discharges coming with dairy waste may cause severe problems in aquatic ecosystems and pollute strategic groundwater resources [13].Conventional aerobic treatment methods,such as activated sludge processes,involve oxygen supply which are energy demanding.These processes also entail the impractical recycling of valuable nutrients contained in dairy ef ?uents [14,15].Anaerobic digestion is generally applied in a variety off-forms and scales to stabilize the organic matter in wastewater.These processes can be effective for organic matter and pathogen reduction.They can generate biogas as well,which can be used as a fuel [15].

However,ef ?uents of anaerobic digestion of dairy wastewaters are characterized by a high ammonia content that must be pretreated before further processing [16].During storage and usage,digester ef ?uents may lead to large amounts of nitrogen escaping into the atmosphere due to ammonia volatilization [17].In this respect,environmentally friendly and economically sound

manure management in dairy farms is vital to their sustainability and to the minimization of losses of valuable plant nutrients.Microalgae and cyanobacteria offer low cost processes.They can be utilized as bioremediation agents to remove inorganic nutrients from wastewaters and to improve water quality due to their high capacity of nutrient uptake [18].Microalgae that are produced in the bioremediation of dairy wastes can be further processed into different types of biofuels such as biodiesel,jet fuel,biogas and biohydrogen [19–25].

Fig.1displays a simpli ?ed process ?ow diagram of an inte-grated microalgae culture-wastewater treatment-biofuel produc-tion process.It shows that microalgae grow using nutrients of the wastewater and CO 2from a combustion process.Finally,the cultivated microalgae can be employed to produce energy and food supplements for humans and animals.Thus,one can notice that commercial scale CO 2capture with wastewater treatment and biofuel production using microalgae culturing entails a holistic approach.This approach requires that various process steps will be integrated effectively in the context of a single industrial facility.Thus,the cultivation of microalgae offers the following three important advantages:

(i)capture of CO 2emitted from fossil fuel based power generat-ing stations,

(ii)treatment of wastewater,

(iii)production of renewable energy.

Keeping these advantages in mind,research studies are cur-rently being developed to establish processes and technologies

for

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624

application at the industrial scale.This review article focuses on the current state-of-the-art and recent developments of technol-ogies dealing with microalgae culturing for CO 2capture,waste-water treatment and biofuel production.A valuable example of the commercial prospects of this technology is the “Solutions4CO2”plant being established in Sarnia,Ontario.This 50,000square foot plant captures carbon dioxide and combines it with wastewater which is high in nitrogen.The plant ef ?uent is used to grow algae under enhanced conditions.The produced algae can be used to make biopharmaceuticals,like the Omega 3and biofuels [26].

2.Algae species

As mentioned earlier,algae are a diverse family of photosyn-thetic eukaryotes species.Most of these species are aquatic.Numerous types of algae accumulate oil and lipids have a density lower than water.This lower density helps with their ?otation in ponds and lagoons.Over 36,000different species of algae are available in the natural ecosystem.Algae species can be classi ?ed as red algae,green algae,brown algae,diatoms,blue green algae (prokaryotes)or dino ?agellates.Many of these algae have found various bene ?cial uses including animal food,fertilizer,pharma-ceutical drugs production,pollution control,water treatment,dyes,agar manufacture and as source for bioenergy [27].

In early research initiatives,culture systems of microalgae were investigated in a detailed manner as an alternative to protein sources for human consumption.Recently,the focus has been shifted to the use of microalgae culturing for CO 2capture and biofuel production.Microalgae can capture emitted CO 2from a variety of sources and can convert CO 2into biomass with the help of sunlight and photosynthesis.Moreover,microalgae produced can be further processed to manufacture biofuels [28].Microalgae have the ability to grow rapidly.Microalgae also can synthesize and accumulate large amounts (approximately 20–50%of dry weight)of neutral lipid stored in cytosolic lipid bodies.As a result,a successful and economically viable algae based biofuel industry mainly depends on the selection of appropriate algal strains [29,30].

Table 1reports the general chemical composition of different microalgal species that were reported in the literature [31].One can easily notice from this table that most of the algae contain large amount of proteins,dominantly enzymatic proteins or crude proteins.These proteins,mainly amino acids,provide high quality nutrients commonly found in foods and feeds for animals.

To grow the algae species,carbon dioxide,water,nutrients and suitable temperature control are needed.Wastewater contains signi ?cant amounts of nutrients that are suitable for algae growth.Table 2summarizes the algal species that have been studied for the removal of nitrogen and phosphorous containing chemical species such as ammonia,nitrates and phosphates from the wastewaters.As can be seen in this table,Chlorella vulgaris and Phormididium laminosum are two main types of algae species that have been widely studied.Other species studied includes Anabaena doliolum ,Chlorella emersonii ,Chlamydomonas reinhardtii ,Scenedesmus bijugatus and Scenedesmus obliquus .

In order to achieve the maximum bene ?t from microalgae culture,it is essential to pay attention to the selection of adequate species or strains.Microalgae culture consists of a single speci ?c strain precisely selected for producing the desired product and the most bene ?cial outcome of the culture process.It is also

important

Fig.1.Simpli ?ed process ?ow diagram envisioned for algae wastewater treatment with CO 2mitigation and biofuel production (adapted from [7]).

Table 1

General composition of different microalgae in percentage of dry weight basis (adapted from [31]).Microalgae species Protein Carbohydrates Lipids Anabaena cylindrica

43–5625–304–7Aphanizomenon ?os-aquae 62233Chlamydomonas rheinhardii 481721Chlorella pyrenoidosa 57262

Chlorella vulgaris 51–5812–1714–22Dunaliella salina 57326

Euglena gracilis

39–6114–1814–20Porphyridium cruentum 28–3940–579–14Scenedesmus obliquus 50–5610–1712–14Spirogyra sp.

6–2033–6411–21Arthrospira maxima 60–7113–166–7Spirulina platensis 46–638–144–9Synechococcus sp.

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to observe that required culture conditions are (a)water media at the adequate pH and temperature,(b)necessary contained nutri-ents and (c)CO 2dosed in a controlled manner in presence of sunlight.In order to ensure the proper growth of microalgae,the necessary nutrients must be provided.Nutrients can be classi-?ed into the following categories:(i)carbon source from CO 2,(ii)energy source from sunlight,(iii)nitrogen source (e.g.ammo-nia,nitrates)from wastewater or other culture media,(iv)other minerals from culture media and (v)potentially added vitamins.

3.Microalgae cultivation system-photobioreactor technology There is in the scienti ?c literature,a wide range of the microalgae cultivation systems reported.These microalgae culture

systems differ mainly depending on (a)the cost,(b)the type of desired products,(c)the source of nutrients and (d)the CO 2capture.The culture systems are generally classi ?ed according to their design conditions as “open ”or “closed ”systems.The “open ”systems are outdoor facilities that include ponds,lagoons,deep channels,shallow circulating units and others,while the “closed ”systems are vessels or tubes with walls made of transparent materials located in outdoors facilities under sunlight irradiation or indoor facilities under arti ?cial irradiation.

Due to their technical complexity,photobioreactors have been considered for a long time as the antithesis of open ponds technology.It is only recently and as a result of the operational dif ?culties with open ponds that closed bioreactors are being considered as providing useful methods of algal mass culture.The increasing interest in this technology is leading algal culture towards great developments involving quick technical progress [53].Generally,sophisticated photo-bioreactors are more versatile but such reactors are expensive and dif ?cult to operate and control.Some studies suggest,however,that the use of photobioreactors is a more feasible and practical option,especially for the removal of CO 2,and for wastewater treatment applications [6,14,20].

3.1.Open system

Open ponds have long been used for large scale microalgae cultivation given their simple construction and relatively easy operation.Such cultivation systems can be classi ?ed as (i)natural water systems such as lakes,lagoon,ponds and (ii)arti ?cial water systems such as arti ?cial pond,tanks and containers.Depending on the applications,different shapes,sizes and types of open systems (agitated,inclined and others)have been investigated [54].

Fig.2illustrates various ponds that have been reported in the technical literature.Among them,non-stirred ponds (Fig.2a and c)are the most economical,being the simpler to https://www.sodocs.net/doc/2b5937375.html,mer-cial non-stirred ponds are built in natural water ponds with less than half of meter in depth.However,this type of pond is very limited in its applications given that algae species cannot survive under frequently poor growth conditions.

One can record,however,an evolution of open systems,with this being the result of trying to address mixing issues in ponds,

Table 2

Summary of algal species for the removal of nitrogen and phosphorus containing compounds.

Microalgae species Removal of

References Anabaena doliolum Nitrogen and phosphorous [32]Chlorella emersonii Phosphorous

[33]Chlorella kessleri

Nitrogen and phosphorous [34]Chlamydomonas reinhardtii Nitrogen and phosphorous [35]Chlamydomonas reinhardti Nitrogen and phosphorous [36]Chlorella vulgaris Nitrogen and phosphorous [37]Chlorella vulgaris Nitrogen and phosphorous [38]Chlorella vulgaris Nitrogen and phosphorous [32]Chlorella vulgaris Nitrogen and phosphorous [39]Chlorella vulgaris Nitrogen and phosphorous [40]Chlorella vulgaris Nitrogen and phosphorous [41]Dunaliella salina

Nitrogen and phosphorous [42]Phormidium laminosum Nitrogen and phosphorous

[43]Phormidium laminosum Phosphorous containing species [44]Scenedesmus bijugatus Nitrogen and phosphorous [45]Scenedesmus rubescens Nitrogen and phosphorous [38]Scenedesmus bicellularis Nitrogen and phosphorous [46]Scenedesmus intermedius Nitrogen and phosphorous [47]Scenedesmus obliquus Nitrogen [48]Scenedesmus obliquus Nitrogen

[49]Scenedesmus quadricauda Nitrogen and phosphorous [50]Spirulina maxima

Nitrogen and phosphorous

[51,52

]

Fig.2.Open cultivation systems:(a)open unstirred pond for chlorella culture by Solix Biofuel,Colorado,USA.(b)Paddle wheel raceway pond at Carbon Corporation,California,USA.(c)Red algae culture at the San Francisco Bay,California,USA.(d)Circular Ponds in Taiwan (BEAM).

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626

preventing algae sedimentation and enhancing light utilization. Thus,in open ponds,mixing is of great signi?cance with this having an impact on operating costs and productivity.Signi?cant constraints also affect open pond operation.For instance,in high cell-density culture systems,light gradients inside the algae can be seldom prevented,given media,light absorption and cell shading. Furthermore,biomass productivity is not only dependent on the total amount of solar energy penetrating the culture surface,but also on the quantity of energy available at the cell level.This leads to various possible design regimes and operating parameters such as‘light regime’and‘light per cell’as proposed by Richmond[55].

Given all the described matters,the pro?table implementation of open culture systems has been limited to very special cases such as production of specialties foods with claimed health bene?ts [56].For example,production costs in Japan have been in the range of10–20$/kg for Chlorella sp.[57].However,in open ponds, until today,only a few species of microalgae have been found to grow well at a commercial scale.

3.1.1.Unstirred ponds

Unstirred ponds provide an economical and simple way for operating a pond facility.Unstirred ponds are commercially used for some microalgae species cultures such as Dunaliella salina[58]. Borowitzka et al.[59]reported that these types of large unstirred open ponds are of simple construction.For example,natural water ponds with less than half a meter in depth can be used.Similar small ponds are shallow water surfaces covered with plastic?lms[57].Lee [60]reported that in South-East Asia,over30t per year of dried microalgae biomass were harvested from unstirred natural lakes. Unstirred open ponds are,however,limited to growing microorgan-isms under poor environmental conditions being exposed to the concurrent growth of protozoa,bacteria and viruses[53].

3.1.2.Raceway pond

The most popular open culture system being currently used is the“stirred paddle wheel open pond”or“raceway pond”(Fig.2b) [54,61].This type of open pond is usually shallow and commonly in between15and25cm in depth.Raceway ponds are usually constructed as either a single channel or as groups of channels that are built by joining individual raceways together.In raceway ponds,the productivity of the biomass has been shown to be as high as60–100mg dry weight L?1d?1[54,57].Raceway ponds are mostly used for the commercial culturing of four species of microalgae:Chlorella sp.,Spiriluna platensis,Hematococcus sp.and D.salina[62].

Different designs of raceway ponds,especially the paddle wheel mixed type,have been used commercially over the last30 years.The circulation of the cultured media in the raceway pond loop is helped by a paddle.This circulation generates the water velocity required to avoid the deposition of settling cells or the aggregation of cells via?occulation[63].Many ponds are operated with a liquid velocity of more than30cm/s.In many cases, dif?culties are encountered with solid deposition in stagnant areas.In raceway ponds,biomass concentrations of up to1g dry weight/L and60–100mg dry weight/L d productivities are typi-cally obtained[57,60].

3.1.3.Circular pond

Circular ponds(central pivot)have primarily been used for large-scale cultivation especially in South-East Asia for the culture of Chlorella sp.[64].Circular ponds are the oldest large-scale algae cultivation open ponds.The depth of these ponds is about 25–30cm.Microalgae are usually grown in concrete circular ponds up to45m in diameter,with agitation by a rotating arm(resem-bling a clock dial with the second rotating hand running around).A20–30cm thick layer of inorganic nutrient solution with algae, exposed to sunlight and bubbled by CO2,is continuously moved by means of paddle wheels(Fig.2d).

3.1.

4.Limitations of open pond systems

The major limitations in open systems include the following: (a)poor light utilization by the cells,(b)signi?cant evaporative losses,(c)limited diffusion of CO2from the atmosphere,and (d)large areas of land are required[65].In addition,contamination is another major problem of open systems with large-scale micro-algal production.Unwanted algae,mold,fungi,yeast and bacteria are the common biological contaminants often found in these open systems[57].To overcome the above limitations,simple plastic covers or green houses over the open ponds have been proposed [66].Plastic covers also allow extension of the growing period.A permeable plastic cover also facilitates transfer and supply of carbon dioxide and the maintenance of mild temperatures over night hours. It has been reported that the covering of open ponds provides an improvement of biomass productivities[67].Unfortunately,however, contamination issues still remain unresolved.In addition to that, capital costs,maintenance and overheating make open ponds covered with translucid plastics is impractical with this being especially true for large size units.

3.2.Closed system

Closed systems,mainly known as photobioreactors,can address some of the problems associated with open pond systems.The major advantages of the closed systems are as follows:(a)minimization of water evaporation and(b)reduction of the growth of competitive algal weeds,predators and pathogens that may kill the desired microalgae.It is important to acknowl-edge that although photobioreactors signi?cantly reduce the growth of competitive algal weeds,they cannot completely elim-inate the growth of contaminants[54].A detailed comparison of different closed photobioreactor systems and their biomass pro-ductivities are reported in Table3.

3.2.1.Tubular photobioreactor

Given the several mentioned disadvantages of open systems, closed systems have been receiving great attention.Several tubu-lar photobioreactors have been studied and developed since the pioneering work of Tamiya et al.[84].Tubular photobioreactors are made with transparent materials and are placed in outdoors facilities under sunlight irradiation(Fig.3a).A gas exchange vessel where air,CO2and nutrients are added and O2is removed is connected to the main reactor[85].One of the basic characteristics of these cultivation vessel designs is their large surface area per unit volume.This is done to maximize exposure of the microalgae to sunlight.Tube sizes are generally less than10cm in diameter to secure sunlight penetration.In a typical tubular microalgae culture system,the medium is circulated through the tubes,where it is exposed to sunlight for photosynthesis.The medium is circulated back to a reservoir with the help of a mechanical pump or an airlift pump.The pump also helps to maintain a highly turbulent?ow within the reactor,preventing the algal biomass from settling[1].

A fraction of the algae is usually harvested after it circulates through the solar collection tubes,making the system a contin-uous operation.Until today,most of the tubular photobioreactors, studied in presence of arti?cial light have been developed at small/ laboratory scale(0–20L capacities).There is,in this respect,a limited number of studies reporting data for large-scale closed photobioreactors.

James and Al-Khars[74]studied the growth and the produc-tivity of Chlorella and Nannochloropsis in a translucent vertical

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airlift photobioreactor.They obtained productivities between 109and 264g/m 3d for Nannochlropsis and between 32.5and 95.3g/m 3d for the Chlorella strain.Miyamoto et al.[76]used a vertical glass tube with 5cm diameter and 2.3m height (4.5L).This is a bubble column unit with good light penetration.Its implementation at full commercial scale-up still seems challenging.The Monoraphidium productivity in such reactor has been reported as 23g/m 3d.

In these tubular type photobioreactors,tube bundles used as solar irradiation captors are made out of (a)polyvinylchloride (50mm in diameter)or (b)polycarbonate (32mm in diameter).

Table 3

Comparison of different closed photobioreactor systems.Closed system photobioreactor type Light source Capacity (L)Algal strain

Biomass conc.(g/L)Biomass conc.(g/m 3d)

References Tubular

Arti ?cial 5.5Spirulina platesnsis

0.62[68]Sun 200Phaeodactylum tricornutum 1.19[69]Sun 75Phaeodactylum tricornutum 1.38

[70]Sun

10000

Spirulina

[71]Airlift

Arti ?cial 3Haematococcus pluvialis 4.09[72]Arti ?cial 170

Chaetoceros

0.80

[73]Arti ?cial Nannochloropsis 32.5–95.3[74]Arti ?cial Chlorella

109–264

[74]Bubble column

Arti ?cial 170Chaetoceceros 3.31[73]Arti ?cial 1.9Phaeoductylum -[75]Arti ?cial 4.5Monoraphidium 23

[76]Arti ?cial 1.8Cyanobium sp.0.071[77]Arti ?cial 3.5Spirulina 4.13

[78]Sun

64Monodus 0.03–0.20[79]Arti ?cial 1.8Sc.obliquus

2.12[78]Arti ?cial 1.8Chlorella vulgaris 1.41[78]Flat plate

Articial 3.4Dunaliella

1.5[80]Sun 5Phaeodactylum 1.38[81]Sun 200Nannochloropsis

0.225[82]Sun 440Nannochloropsis sp.0.27

[82]Sun 25,000

10.2[68]Plastic bag

Sun

Tetraselmis

20–30

[83]

Fig.3.Closed cultivation system:(a)horizontal tubular photobioreactor at Varion Aqua Solution Ltd.,UK.(b)Bubble column air-lift photobioreactor,BBSRC,UK.(c)Helical –tubular photobioreactor.(d)Large-scale plastic bag photobioreactors.

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These type of tube bundles were used for algae culturing by Torzillo et al.[71].The rate of?ow in these tubes ranged between 30and50cm/s.From this study,it was concluded that,when the tube diameter is reduced from50mm to32mm,the optimum population density of Spirulina platensis and Anabaena siamensis increases,resulting in a higher productivity per culture volume. Torzillo et al.[71]also studied a comparable closed pilot scale photobioreactor(100m2,10m3of culture)initially made of ?exible polyethylene tubes(14cm in diameter)and later of methyl polymethacrylate tubes(13cm in diameter).The pumping of the culture medium is of the intermittent type in order to maintain an adequate medium?ow rate inside the tubular photobioreactor.

A diaphragm pump raised the culture media to a feed tank that allowed an intermittent discharge using a siphon into the photo-bioreactor.At intervals of4min.,about350L of culture suspension were discharged into the photobioreactor,thus moving the culture in the tubes at a rate of0.26m/s.This regime of circulation was obtained by adjusting the?ow rate of the pump to4000L/h.The result was better than with continuous circulation at the same ?ow rate of the pump.The maximum productivities of Spirulina were25g/m2d.

In some photobioreactors,the tubes are coiled spirals forming helical–tubular photobioreactors(Fig.3c).Usually,these types of reactors are suitable for the culture of microalgal species in presence of sunlight.Despite this,these systems sometimes require arti?cial illumination as well as natural light to enhance the microalgae growth.However,the introduction of arti?cial light adds to production costs,making the helical–tubular bioreactor only adequate for the manufacturing of high-value added pro-ducts.Another category of closed systems is the airlift photobior-eactor.In this reactor,liquid motion is characterized by large circulatory currents in a heterogeneous?ow regime[86].

Anderson and Eakin[87]designed a tubular photobioreactor with the capacity to produce polysaccharides using Porphyridium cruentum microalgae.The system has a modular design,resem-bling a solar collector with a photodetector placed at a strategic location for angular adjustment of the glass surface position.The polysaccharide productivities published by the authors ranged from20to25g/m2d.

3.2.2.Plastic bag photobioreactor

There are studies which suggest that microalgae can be produced in transparent polyethylene bags,as shown in Fig.3d. Generally,these bags are either hung or placed in a cage under the sunlight irradiation.In such arrangements,the algae cultures are mixed with air at the bottom of the bags[54].Transparent

polyethylene sleeves sealed at the bottom in a conical shape which are used to prevent cell settling are also widely https://www.sodocs.net/doc/2b5937375.html,ing 50L polyethylene bag cultures operated as turbidostats,Trotta[83] obtained yields of20–30g/m3d for Tetraselmis.

3.2.3.Airlift photobioreactor

In airlift photobioreactors(Figs.3b and4),the?uid volume of the vessel is divided into two interconnected zones using a baf?e or a draft tube.Liquid movement is characterized by large circulatory currents in the heterogeneous?ow regime[86].Airlift photobioreactors are sometimes dif?cult to scale-up given their complex?ow pattern[88].

Vertical bubble columns and airlift cylinders can attain sub-stantially increased radial movement of?uid,with high cycling of medium between the irradiated and the dark zones.These reactor designs have a low surface/volume ratio.However,they can provide a substantially greater gas hold-up than horizontal reac-tors with a potentially greater segregated gas–liquid?ow[89].

Other researchers claimed that advantages for these units included(a)high mass transfers,(b)good mixing with low shear stress,(c)low energy consumption,(d)relatively easy to work under sterile conditions,(f)good for the immobilization of algae on moving particles.In these units,cultures suffer less from photo-inhibition and photo-oxidation,being subject to cycling effects occurring between lighter and darker zones.Limitations include (a)higher manufacturing and maintenance cost,(b)smaller irradiation per unit surface area,(c)more sophisticated construc-tion materials,(d)higher shear stress on algal cultures,and (e)larger number of units are needed to build a commercial plant given the diameter to height cannot be increased signi?cantly. 3.2.4.Flat plate photobioreactor

Vertical plate photobioreactors(Fig.5)mixed by air bubbling, seem to be even better than bubble columns in terms of produc-tivity and ease of operation.Flat-plate photobioreactors allow the following:(a)large irradiated surface area,(b)suitable for

outdoor Fig.4.Air-lift photobioreactor(Adapted from[90]

Fig.5.Flat panel photobioreactor(Adapted fromhttp://www.ruhr-unibochum.de/ h2design/pro?le/main.de.html,June02,2012).

S.A.Razzak et al./Renewable and Sustainable Energy Reviews27(2013)622–653629

cultures,(c)good for algae immobilization and(d)good biomass productivities.These photobioreactors are relatively cheap and easy to clean[89].Vertical?at plates can be accommodated in 1000–2000L volume capacity units that were successfully oper-ated for long time periods(be speci?c,e.g.several days).Thus, these are fully scalable photobioreactor units[67].

Closed?at panels mixed by bubbling air can potentially achieve high overall ground–aerial productivities in terms of volume cultivation.There are500L with440L culture volume capacity units with0.27g/L d using?at plate glass photobioreactor[82]. Major limitations include(a)dif?culty of controlling culture temperature,(b)limited degree of grow that the near wall region, (c)possibility of hydrodynamic stress,and(d)algal strains are subjected to important hydrodynamic stresses[82,89].

Flat plate photobioreactors are recommended for mass produc-tion of microalgae in outdoor and indoor culture systems given the

following:(a)high irradiation of plate surface,(b)small accumula-tion of dissolved oxygen while compared to horizontal tubular photobioreactors and(c)convenient modular design for scale-up. Pulz et al.[91]described an optimized large-scale?at plate photobioreactor module of6000L.This double layer panel (8m2)is laid on the ground.One of the layers is used for the circulation of the culture,while the other is utilized for circulation of the temperature-controlled water.Tredici et al.[92]and Tredici and Materassi[93]developed a vertical alveolar panel(2.2m2) based on the same type of material.Flat panels can be used at variable equinoxial orientation with respect to the sun's rays. Mixing and deoxygenation processes of the culture suspension are affected by continuously bubbling air at the bottom of the https://www.sodocs.net/doc/2b5937375.html,parable designs with pump and with airlift circulation are also under development[94].In all cases,high productivities were obtained given the high surface/volume ratio.However, biomass output could be limited by photo-inhibition and tem-perature control issues.

4.CO2capture

Growing industrialization and urbanization are considered to be a major source of CO2and it is one of the most important atmospheric pollutants contributing to green house gases.According to the Kyoto Protocol(1997)signed by more than170countries, greenhouse gas emissions should be reduced by5.2%on the basis of the emissions in1990[95].Since then,there are numerous research and development studies that have been undertaken around the world aiming to achieve CO2mitigation.Widely studied techniques have included physical,chemical,and biological methods[96–99]. Among these attempts,the biological method using microalgal photosynthesis is believed to be an effective approach to biological CO2?xation[95,100].Microalgal biomass contains approximately50% carbon by dry weight[101].All of this carbon is typically derived from carbon dioxide.Producing100t of algal biomass?xes roughly183t of carbon dioxide.Carbon dioxide must be fed continuously during daylight hours.Control of CO2feeding can be helped with pH measurements.pH measurements minimize carbon dioxide losses. Thus,biodiesel production using microalgae culture with carbon dioxide emitted from power plants can reduce the environmental impact of burning fossil fuels[20,96,98,102].

4.1.Photosynthesis

Biological processes provide a promising approach to capture CO2in the form of microalgal biomass via photosynthesis.Photo-synthesis is the process used by plants to convert water,CO2and sunlight with the help of chlorophyll into carbohydrates(Fig.6).

In microalgae,photosynthesis releases oxygen.This is why it also called"oxygenic photosynthesis".Since CO2is converted into lipids and other hydrocarbons in this process,this explains the designation of“CO2?xation process”.In oxygenic photosynthesis, water is the electron donor and after hydrolysis it releases oxygen. The general equation for photosynthesis can be written as

H2OtCO2tphotons-?CH2O ntO2

The overall reaction is separated into two pathways:(i)light reaction and(ii)dark or light independent reaction.Photosynth-esis takes place in chloroplasts which are enclosed by a mem-brane.This membrane contains an aqueous?uid called stroma. This stroma contains stacks of?attened disks bounded by mem-brane called thylakoids,which are the active sites of photosynth-esis.The sites for photosynthesis are thylakoids membranes which contain protein complexes including pigments(e.g.β-carotene, xanthophylls)that absorb light energy.These pigments are embedded in microalgae in special antenna proteins.This protein is also called“the light harvesting complex”[103].

Photosynthetically active radiation,often abbreviated as“PAR”, designates the spectral range of solar radiation from400to 700nm that photosynthetic organisms are able to use in the process of photosynthesis.Due to the low absorption capacity of the culture media at450–650nm,chlorophyll is able to capture about30–40%of PAR.Microalgae can optimize the capturing of light by changing the quantity by additional light capturing pigments.The photosynthetically active range of the chlorophyll spectrum lies at and between680and700nm.The photon energy captured at shorter wavelengths can be transferred to the680–700nm longer wave length region.During this photon transfer process from high-energy and shorter wavelength photons to lower energy and longer wavelength photons,signi?cant energy losses occur.As a result,there is a net loss of about21%of the original light sun energy[104].

4.1.1.Light dependent reaction

The light dependent reaction involves both photochemical and redox reaction steps.In the thylakoids membranes of the chlor-oplasts,chlorophyll pigments absorbs light energy/photons and release electrons.The overall equation for the light-dependent reactions is[105]

2H2Ot2NADPtt3ADPt3Ptlight-2NADPHt2Htt3ATPtO2 Light energy is used to synthesize ATP(adenosine tripho-sphate)and NADPH(nicotinamide adenine dinucleotide phos-phate).Synthesis can take place in two forms:in cyclic or in non-cyclic pathways.Microalgae and cyanobacteria mainly use light energy in a non-cyclic reaction.In the non-cyclic pathway, light-harvesting antenna complexes(chlorophyll and other acces-sory pigments)of photosystem II capture

photons.

Fig. 6.Schematic diagram of photosynthesis process(Adapted fromhttp://en. https://www.sodocs.net/doc/2b5937375.html,/wiki/Photosynthesis,June02,2012).

S.A.Razzak et al./Renewable and Sustainable Energy Reviews27(2013)622–653 630

Electrons are transported to a primary electron acceptor molecule.This happens when a chlorophyll molecule at the core of the photosystem II reaction center obtains suf?cient excitation energy from the adjacent antenna pigments.The Z-scheme initially generates a chemiosmotic potential across the membranes.An ATP synthase enzyme uses the chemiosmotic potential to make ATP during photophosphorylation.On the other hand,NADPH is a product of the terminal redoxreaction in the Z-scheme.In Photo-system I,the electron enters a chlorophyll molecule and gets excited due to the light absorbed by the photosystem.A second electron carrier accepts the electron and passes it down,lowering energies of electron acceptors.Hydrogen ions move across the thylakoid membrane into the lumen through the in?uence of the energy created by the electron acceptors.

The cyclic reaction is similar to that of the non-cyclic,but differs in the form that it generates only ATP,with no reduced NADP(NADPH)being formed.The cyclic reaction takes place only in photosystem I.Once the electrons are displaced from the photosystem,the electrons are passed down the electron acceptor molecules and returns to photosystem I,from where they were originally emitted.

4.1.2.Light independent reaction

In the light-independent reactions or dark reactions,the enzyme RuBisCO captures CO2from the atmosphere.This process requires the newly formed NADPH,and is called the Calvin–Benson Cycle[104].

To be more speci?c,carbon?xation produces an intermediate product,which is then converted to the?nal carbohydrate products. The carbon skeletons produced by photosynthesis are then used in a variety of ensuing processes forming other organic compounds. An example of this process is the formation of cellulose,which is the precursor for lipid and amino acid biosynthesis,or a fuel for respir-ation.The overall equation for the light-independent reactions is[105]

3CO2t9ATPt6NADPHt6Ht-C3H6O3?phosphatet9ADPt8P t6NADPtt3H2O

The?xation or reduction of carbon dioxide takes place by combining carbon dioxide with a?ve-carbon sugar,ribulose1,5-bisphosphate(Ru5BP).This yields two molecules of a three-carbon compound,glycerate3-phosphate(GP),also known as3-phos-phoglycerate(PGA).In the presence of ATP and NADPH(from light-dependent stages),GP is reduced to glyceraldehyde3-phosphate(G3P).

This product is also referred to as3-phosphoglyceraldehyde (PGAL)or even as triose phosphate.Most(5out of6molecules)of the G3P produced is used to regenerate Ru5BP so that the process can continue.The1out of6molecules of the triose phosphates is not“recycled”and often condenses to form hexose phosphates, which ultimately yields sucrose,starch and cellulose.The sugars produced during carbon metabolism yield carbon skeletons that can be used for other metabolic reactions like the production of amino acids and lipids.

4.2.CO2sources

Microorganisms formed via photosynthesis,such as microal-gae,use CO2as a carbon source.No growth can occur without it. Insuf?cient supply of CO2is often the limiting factor of productiv-ity.Based on the average chemical composition of microalgae biomass,approximately1.8t of CO2are required to produce1t of biomass.Microalgae can also produce proteins,fatty acids and dietary supplements for humans and animals.Furthermore,lipids from microalgae are chemically similar to those in common vegetable oils and are good potential sources for biodiesel.The microalgae-based biodiesel,in contrast to the one derived from fossil fuels,is renewable,biodegradable,and produced with low pollutant emissions[1].Thus,reducing the atmospheric CO2by microalgal photosynthesis is considered safe and advantageous for the human ecosystem.

4.3.CO2?xation

Most of supply of the CO2emissions can be traced to the?ue gases produced by different industries.CO2can only be?xed on algae during the day time.Microalgae can eventually produce some CO2overnight as it happens with other plants.There is however and as a result a net positive CO2uptake.

In outdoor culture systems or open systems,an extra amount of ?ue gas supply is needed to provide the required amount of CO2. Outdoor culture systems are limited by microalgal growth.These systems are not easy to control showing low productivity as a result of variability of the following:(a)environmental tempera-tures,(b)system circulation and(c)light utilization.In comparison with open culture systems,a closed photobioreactor is easy to control and can achieve high growth rates.A closed photobior-eactor can be considered a bioscrubber for waste gas treatment. The microalgal cells cultured in this photobioreactor convert the CO2from the waste gas into biomass in an energy-ef?cient and economical manner[6].

The CO2?xation rate is related directly to light utilization ef?ciency and to the cell density of microalgae.Microalgal CO2?xation involves photoautotrophic growth in which anthropogeni-cally derived CO2may be used as a carbon source.Therefore, biomass measurements or growth rate evaluations are critical in assessing the potential of a microalgal culture system for direct CO2removal[106,107].

The effects of CO2concentrations in air on microalgae growth have been evaluated in several studies in photobioreactors.The goal has been to consider CO2capture from waste gases at high CO2concentrations[78,108–113].With this end,different air and CO2feed compositions were fed into the photobioreactor.This research has allowed the study of microalgal growth and CO2?xation,with this information being valuable to determine CO2 removal ef?ciency.In spite of this,there is still lack of agreement on the optimum CO2concentration for various algal species.

The CO2removal ef?ciency in a photobioreactor with micro-algal culture can be determined as the difference of CO2concentra-tion of the incoming and outgoing ef?uents.The removal ef?ciency (%)can be thus determined using the following formula[5]: Influent of CO2?Effluent of CO2

?100%

The ef?ciency of CO2removal or?xation in a closed culture system depends on(a)microalgal species,(b)CO2concentration, (c)photobioreactor design and(d)operating conditions[78,106]. Cheng et al.[106]observed in a membrane photobioreactor,a maximum CO2removal ef?ciency of55.3%at0.15%CO2with a reduction of80mg/L h at1%CO2in a C.vulgaris culture.In a three serial tubular photobioreactor,27–38%and7–13%of CO2was?xed by Spirulina sp.and S.obliquus,respectively,in cultures aerated with6%CO2.

On the other hand,in treatments with12%CO2aeration,CO2?xation ef?ciency was only7–17%for Spirulina sp.and4–9%for S.obliquus[78].In other words,there is a species dependence on the CO2ef?ciency removal or?xation.This may be due to physiological conditions of microalgae,such as potential for cell growth and CO2metabolism.

In studies by Yun et al.[102],the CO2?xation rate was determined from the carbon content of algal cells.The growth

S.A.Razzak et al./Renewable and Sustainable Energy Reviews27(2013)622–653631

rate was established as follows:

R CO

2?C C?μL?M CO2

where R CO

andμL are the?xation rate(g CO2/m3h)and the volumetric growth rate(g dry weight/m3h),respectively,in the linear growth phase.M CO

and M C represented the molecular weights of CO2,and elemental carbon,respectively.The average carbon content(C C measured by an elemental analyzer)(CHNS-932,Leco)was0.507g carbon/g dry cell weight.The algal growth rate was determined in the linear growth regime given that most of the algal growth occurred during this phase.

Due to climatic,land and water restrictions,it is challenging to collect and utilize microalgae directly on site.However,it is possible to increase the economics of microalgae utilization by using a two-stage process.In such a process,the CO2from a power generating stations or other source is?rst scrubbed(e.g.amine scrubber)and concentrated with a conventional process[114,115]. The resulting and concentrated CO2is then transported to a suitable site for microalgae production.This can be compared to the economics of other more“conventional”CO2capture process where CO2capture involves a separation process,followed by transportation and?nally disposal in deep oceans,and/or deple-tion in gas wells.

One should mention that in this respect,some microalgae species are tolerant to relatively high temperatures(close and above301C).This type of microalgae can be cultured in conjunc-tion with the usage of high temperature?ue gases from industrial neighboring sites[95].These thermo tolerant strains may also simplify species-control.This is the result that that the optimum temperature of most microalgal species growth is in the20–301C range.For instance,several unicellular green algal strains,identi-?ed as a species of Chlorella,were isolated from hot springs in Japan.These strains grew at temperatures of up to421C and in air containing more than40%CO2.Their tolerance to both high temperatures and high CO2content makes them potentially appropriate microbial cells for photobioreactors involved in CO2 capture from?ue gases[95].

Table4reports the microalgae species identi?ed as tolerant to moderate to high CO2concentrations and20–301C temperatures. It is interesting to note that Chlorococcum littorale,a marine algae, showed exceptional tolerance to high CO2concentrations of up to 40%[116].de Morais and Costa[78]reported that microalgae S.obliquus,Chlorella kessleri and Spirulina sp.also exhibited good tolerance to high CO2contents(up to18%CO2).This indicates their great potential for CO2?xation from CO2-rich streams.For Spirulina sp.,the maximum speci?c growth rate and maximum productivity were0.44d?1and0.22g/L d respectively,with both using6%and12%CO2concentrations(v/v).The maximum cell concentration was3.50g/L(dry basis)at both CO2concentrations. For S.obliquus,the corresponding maximum growth rate and maximum productivity were0.22and0.14g/L d.Murakami and Ikenouchi[116]developed an extensive screening,of more than10 strains of microalgae with high capability of?xing CO2.Two green algal strains,Chlorella https://www.sodocs.net/doc/2b5937375.html,001and Chlorococcum littorale, showed high CO2?xation rates exceeding1g CO2/L d.

5.Wastewater treatment

5.1.Microalgal nutrition

Algae are important bioremediation agents.They are already being used by many wastewater facilities.The potential for algae in wastewater remediation is however much wider in scope than its current role.Microalgae contain higher nitrogen and phos-phorus contents,approximately10–11%,respectively,on a dry weight basis.These types of nitrogen and phosphorous levels are several times greater than that of plants.Microalgae have also been used extensively to remove heavy metals from wastewater even though these could not compete commercially with ion exchange resins[117].The use of microalgae has also attracted attention because microalgae have the ability to remove both CO2 and NO x during their growth[118].Microalgae can also produce,as stated in the previous sections,potentially valuable biomass, which can be used as an animal feed additive,slow-release fertilizer and biodiesel feedstock[119,120].

5.2.Nitrogen

Nitrogen in the form of nitrates and ammonia is the most commonly found nitrogen containing chemical species.Ammo-nium is among the most common chemical forms of nitrogen that can be readily absorbed by microalgae.In this respect,a cheap source of nitrogen can be a used as a wastewater stream or as secondary treated wastewater.

5.3.Phosphorous

Phosphorus is also an important element required for cell growth and microalgae metabolism.Phosphorus is an essential element included in DNA,RNA and ATP,and cell membrane materials.In the photophosphorylation process,phosphorus is an essential element contributing as ATP.As a result,phosphorus availability has a large impact in microalgae growth as it is considerably affected in photosynthesis.Lipid accumulation may occur in the culture media under phosphorus starvation condi-tions.Phosphorus is usually available in the wastewater as inorganic anions species such as H2PO4?and HPO42?[121].

5.4.Wastewater components

Many species of microalgae are able to effectively grow in wastewater conditions due to the abundance of nutrient inorganic species.A major requirement for wastewater treatment(aside from sludge removal via conventional processes,such as activated sludge)is the need of removing high concentration of nutrients. This is true in particular for nitrogen(N)and phososphorus (P)species.Not doing so leads to eutrophication with nutrients accumulation in rivers,lakes or ponds.In the conventional

Table4

Microalgae strains studied for CO2bio-sequestration(adapted from[95]).

Microalgae sp.CO2

(%)Temperature

(1C)

Biomass

productivity

(g/L d)

CO2?xation

rate(L/d)

Chlorococcum

littorale

4030N/A 1.0 Chlorella kessleri18300.0870.163 Chlorella https://www.sodocs.net/doc/2b5937375.html,0011535N/A41 Chlorella vulgaris Air250.0400.075a Chlorella vulgaris15–N/A0.624 Dunaliella3270.170.313 Haematococcus

pluvialis

16–34200.0760.143 Scenedesmus

obliquus

Air–0.0090.0160 Scenedesmus

obliquus

18300.140.26 Spirulina sp.12300.220.413

activated sludge process,phosphorus removal is particularly challenging[122].

Microalgae are ef?cient species in removing nitrogen,phosphorus and other toxic materials from wastewater.As a result,microalgae can play an important role during the?nal steps of wastewater treatment when nitrogen,phosphorous and chemical oxygen demand(COD) have to be reduced.Indeed,algae-based treatments have been found to be equally ef?cient at removing P species from wastewater,as compared to chemical processes[123].

The treatment of livestock ef?uents is also receiving increasing attention.Uncontrolled nutrients discharges have caused severe episodes of eutrophication in aquatic ecosystems and pollution of strategic groundwater resources[124].Intensive farming together with the high carbon and nutrient concentration of livestock waste-waters(two orders of magnitude higher than domestic wastewaters) has surpassed the natural capacity of the surrounding environment to cope with these ef?uents[125].Table5provides a comparison of municipal and livestock wastewater data[126].

The development of cost-effective and environmentally friendly methods for the treatment of livestock ef?uents is,thus, required.In this context,the algal–bacterial system application for the recovery of livestock ef?uents provides an in situ microalgal-O2production.This occurs via photosynthesis and through nutri-ents recycling with N and P assimilation into the algal–bacterial biomass[127].Thus,when irradiated with natural light,micro-algae produce the O2needed by aerobic bacteria to mineralize organic matter and oxidize NH4+.In turn,microalgae can consume the CO2released by bacteria,which mitigates CO2emissions [128,129].

5.5.Anaerobic digested dairy wastewater treatment

Treatment of livestock ef?uents is receiving increasing atten-tion[131,132].Biogas is derived through anaerobic digestion of biomass,such as animal wastes,municipal wastewater,and land-?ll waste.Anaerobic digestion is themicrobially mediated bio-chemical degradation of complex organic material into simple organics and dissolved nutrients.Digesters are physical structures that facilitate anaerobic digestion by providing an anaerobic environment for the organisms responsible for digestion.Proces-sing livestock manure through anaerobic digesters captures methane,which can be used as an energy source while reducing emissions of this greenhouse gas[133].

Lansing et al.[133]studied12in?uent and ef?uent wastewater parameters to determine their statistically trends.This study was conducted-using seven digesters to assess variability within these systems.These digesters were identical in construction materials,but differed in length,wastewater management styles,wastewater sources,and hydrologic loading.During the digestion process,all of the organic matter and solid variables showed important reductions(Table6).The average chemical oxygen demand (COD)of the in?uent wastewater decreased by84.1%from 2970mg/L to472mg/L,while the biological oxygen demand (BOD)decreased by79.4%to96.2mg/L.The average turbidity decreased by90.5%from1820NTU(Nephelometric Turbidity Unit) to172NTU,and the total suspended solids(TSS)concentration decreased by85.6%L to319mg/L(Table2).Dissolved nutrient (PO4–P,NH4–N)concentrations and conductivity increased as the wastewater moved through the digester(Table6),with the NH4–N concentration increasing by78.3%to82.2mg/L.The dissolved oxygen(DO)concentration slightly increased in the digester,but both the average in?uent(0.21mg/L)and ef?uent(0.54mg/L)DO concentrations were anaerobic.The average pH decreased from 7.34to6.64.

It was shown that the digester ef?uent wastewater contains an important amount of colloidal solid particles/organic matters which are dif?cult to oxidize biologically[134,135].These sus-pended colloidal particles also reduce the opacity of the cultured media.Thus,to slowly remove biodegradable COD,other treat-ment strategies should be applied.In this respect,coagulation is a very well-known process of removing colloidal particles present in wastewater,in order to achieve the aggregation of suspension particles by sedimentation or?otation.To facilitate the use of coagulant agents,aluminum or iron salt can be employed[16].

Dosta et al.[16]reported experiments for the reduction of COD (suspended solids)in aerobically digested ef?uent wastewater. Various FeCl3dosages(0–2500mg/L)were added to the ef?uent. These authors performed coagulation/?occulation tests in a Jar-Test device(Flocculator2000,KEMIRA Kemwater)involving a vigorous mixing period(30s),a low mixing phase(15min)and a?nal settling period(20min).Both coagulant(FeCl3)and ?occulent agents were added to the desired concentration at the beginning of the?rst step(vigorous mixing period).The effective-ness of the coagulation/?occulation was evaluated by means of chemical oxygen demand(COD)and suspended solids(SS)reduc-tion.Fig.9reports the average COD reduction yields obtained in those experiments.When FeCl3was dosed,suspended solids reduction yields were in the range of8–10%.Due to the acidity of the FeCl3,the pH change was also observed in Fig.7.

Recovery of nutrients from the digester ef?uent wastewaters with the help of microalgal culturing has been investigated by a number of researchers.Wang et al.[135]studied the nutrient removal in a dairy farm(Haubenschild Farm)ef?uent wastewater. It was found that algal growths need a minimum level of light in the culture media to grow ef?ciently.Wang et al.[135]measured

Table5

Initial wastewater characteristics comparison between dairy/livestock wastewater and municipal wastewater[130].

Wastewater characteristics Dairy wastewater Municipal

wastewater 10%

dilution

20%

dilution

No dilution

TSS(mg/L)28313593 VSS(mg/L)22012058

pH7.97.77.2 Ammonium as N(mg/L)30.516.339 Nitrate as N(mg/L)0.010.05o0.01 Nitrite as N(mg/L)o0.010.04o0.01 Organic nitrogen(mg/L)50.720.212 TKN(mg/L)81.036.551 Total nitrogen(mg/L)81.036.651 Phosphate as P(mg/L) 2.6 1.8 2.1Table6

Average in?uent and ef?uent data7SE(n)for seven farm digesters[133].

Average

in?uent

Average

ef?uent

Percent decrease/

increase Temperature(1C)26.270.2(74)26.170.1(80)0.4%decrease Conductivity

(mS/cm)

1.5970.1(74) 1.7370.1(80)8.8%increase

pH7.3470.1(74) 6.6470.04(80)9.5%decrease

DO(mg/L)0.2170.1(73)0.5470.1(80)157%increase BOD(mg/L)467740(74)96.2711(80)79.4%decrease COD(mg/L)29707260(73)472740(79)84.1%decrease Turbidity(NTU)18207200(73)172715(80)90.5%decrease TSS(mg/L)22107223(72)319756(80)85.6%decrease NO x–N(mg/L)0.9270.2(71)0.1870.03(80)80.4%decrease PO4–P(mg/L)13.371.7(74)15.471.4(80)15.8%increase NH4–N(mg/L)46.175.1(72)82.275.0(79)78.3%increase TKN(mg/L)306728(35)166713(37)45.7%decrease

the optical density at 680nm in 10?,15?,20?and 25?diluted digester ef ?uents.Fig.8reported the wild isolated Chlorella sp.growth in all four diluted samples.

Comparing between them,they found that algae grew faster in the 20?and 25?diluted samples during the ?rst 7days.The 10?sample increased the rate of growth after 12days.Authors reported that the speci ?c growth rates of the Chlorella sp.in those four speci ?c samples were 0.282.,0.350,0.407and 0.409g DW d ?1.

Most of the nitrogen in the dairy manure is found in the form of ammonium (NH 4+),nitrate (NO 3?)and nitrite (NO 2?).Results from the four dilution cases are reported by Wang et al.[129]as shown in Fig.9.Total nitrogen was greatly reduced by 75–83%with,however,a fraction still remaining.This shows the presence of organic species left that could not be converted into ammonia and nitrogen associated species.A signi ?cant amount (62–75%)of total phosphorus was also found in all four samples.Concerning manure CODs,they are utilized to some extent by algae as carbon sources (27.4–38.4%)but not as ef ?ciently as nitrogen and phos-phorus are employed.These experiments were performed under axenic conditions and therefore,the reduction of COD could only be attributed its consumption by algae (Wang et al.[129]).

Treatment of livestock manure wastewater after being digested is necessary.This is due to the high waste water content of nitrogen,phosphorus and soluble total organic compound (TOC).From the above ?ndings,it can be concluded that one can use microalgae in biological treatments of wastewater and that the ?nal outcome is the production of a large amount of biomass.5.6.Municipality wastewater treatment

Water used in our daily life goes down the drain and into the sewage domiciliary collection system.This waste water is normally

designated as municipal wastewater.This includes water from baths,showers,sinks,dishwashers,washing machines,toilets and others.Small businesses and industries located in the urban areas also often contribute with large amounts of wastewater to sewage collection systems.Very frequently,large industries treat their own industrial wastewater.Therefore,industrial wastewaters remain contained in the industrial facilities and do not contribute to the municipal wastewater.

Most of the municipal wastewater treatment plants perform primary wastewater treatment systems consisting of (i)a screen-ing chamber to get rid of large solids from the wastewater,(ii)grit chambers to remove the grit and (iii)settling tanks to allow the deposition of most of the particles at the bottom.Fig.10shows a typical wastewater treatment plant.Sludge from the settling tank is then sent to the digester plant for further treatment and for solid disposal.The remaining waste water is then further directed to the secondary treatment plant.In the secondary treatment plant,waste water is ?ltered further using a trickle ?lter.Following this step,wastewater is directed to the sedimentation tank or treatment ponds/lagoons.Relatively clear water from the sedi-mentation tanks is then sent to tertiary/advanced treatment units.Most of the tertiary treatment units are of the biological treatment type.

As mentioned,water from the secondary treatment processes is sent for a tertiary treatment to remove nutrients such as ammonia,nitrate and phosphate as well as some organic compounds.Tertiary biological wastewater treatment can be achieved using conven-tional aerobic treatment methods such as activated sludge.These processes are energy intensive given the need of O 2supply.

Furthermore,they do not offer the opportunity for recycling the valuable nutrients present in wastewater [137].On the other hand,although energetically more favorable than their aerobic counterparts,anaerobic processes are often limited by low ambi-ent temperatures and the poor reduction of nitrogen and phos-phorus [138].

Aerobic wastewater treatment processes are energy intensive given the need of mechanical aeration to provide oxygen to aerobic bacteria consuming organic matter.Aeration accounts for 45–75%of a wastewater treatment plant 's total energy costs.In clear contrast with this,in algae based wastewater treatment,the cultivating algae provide the oxygen necessary for the aerobic bacteria.Thus,cultivation of algae can provide an ef ?cient way to consume nutrients and provide the aerobic bacteria with the needed oxygen through photosynthesis.It is estimated that 1kg of BOD removed in an activated sludge process requires 1kWh of electricity for aeration with this producing 1kg of fossil fuel derived CO 2for power generation [139].

Wang [135]and his coworkers investigated the effects of green algae Chlorella sp.culture on the nutrient removal from four

different

Fig.7.Percentage of COD removal (▲)and ef ?uent pH (O)during the jar-test using several FeCl 3(Adapted from [16]

Fig.8.Growth curve of Chlorella sp.in digested dairy manure with different dilution multiples (Adapted from [129]).

wastewater samples collected from St.Paul,MN,USA,Metropolitan wastewater treatment facilities.At ?rst,they analyzed the water samples collected from different treatments units of the existing facilities.The analysis results are listed in Table 7.One can see from this table that the chemical characteristics of the wastewater leaving the primary settling unit remain similar to the one of the incoming wastewater.

However,the chemical composition of the water leaving both the aeration tank and the centrate from the sludge centrifuge is signi ?-cantly different than those of the inlet streams of the respective units.One can note that the ef ?uents are stabilized by the activated sludge process in which ammonium is oxidized to nitrate,phosphorus is absorbed,and COD is signi ?cantly reduced.The ef ?uents in this case can be discharged with further disinfection such as chlorination being required.The centrate is generated using a physical separation process in the sludge centrifuge,with this liquid stream retaining high levels of ammonium,phosphorous,and COD.

Wang et al.[129]used green algae Chlorella sp.culture to remove nutrients from the waste water samples collected from different treatment process locations zones as reported in Table 7.It was reported that green algae Chlorella sp.successfully grew in all of the studied samples.From this study,it was concluded that green algae Chlorella sp.consumed ammonium or nitrate.These are two primary nitrogen nutrient sources already available in the wastewater samples.

Table 7summarizes the nutrient removal from each waste-water sample after treatment with green algae Chlorella sp.From this table,it can be concluded that NH 4–N,the major nitrogen bearing inorganic compound species in the wastewaters before and after primary settling and centrate,was signi ?cantly reduced.In fact,removal for #1,#2,and #4were 82.4%,74.7%,and 78.3%,respectively.Reduction of phosphorus was up to 90%(Table 7)in wastewater #1,#2,and #4.This shows the effectiveness of algae growth as an effective removal system.However,only 4.7%phosphorus was removed from the ef ?uent of #3.

Table 8shows that up to 90%of phosphorus was removed from wastewater #1,#2and #4by algae growth.If one compares the inorganic N/P ratios for the four wastewaters treated,before and after algal cultivation (Tables 7and 8),one can see that there is optimal inorganic 6.8–10N/P ratio for algae growth,with this ratio dropping from 52.3to 20.8.At the end of the experiment,one can expect severe phosphorus content limitations for algal culture.However,the unbalanced N/P ratio of the centrate did not affect nitrogen or phosphorous removal.This suggests that the N/P ratios and the absolute levels of N and P for both algal growth and ef ?uents from wastewater should be considered when evaluating the nutrient composition effects on algal growth.

Arbib et al.[140,141]studied the algal growth rate and nutrient removal along with carbon dioxide bio ?xation using S.obliquus and Chlorella stigmatophor .These species were cultivated in urban wastewater at different nitrogen and phosphorus ratios,ranging from 1:1to 35:1.These authors found that the nitrogen to phosphorus ratios ranging between 9and 13(263and 322mg/L d respectively)are very important to achieve optimum batch biomass productivity.Renuka et al.[142]worked with different microalgae groups.Their ?ndings showed highest dry cell weight (0.97mg/L)using Calthrix sp.with 57–58%NO 3–N,44–91%PO 4–P removal from sewage wastewater.

Woertz et al.[143]conducted algal growth experiments using wastewater samples collected from the ef ?uent of a secondary treatment facility at the San Luis Obispo,California,municipal wastewater treatment plant.Before adding the wastewater into the algae culture system,it was ?rst circulated through a ?lter screen with 196-μm openings.This allowed removing micron

size

Fig.9.(a)Initial and ?nal ammonium concentrations and removal rates;(b)initial and ?nal total Kjehldahl nitrogen (TKN)concentrations and removal rates;(c)initial and ?nal total phosphorus (TP)concentrations and removal rates and (d)initial and ?nal chemical oxygen demand (COD)concentrations and removal rates (Adapted from [129])

particles.Collected wastewater was then allowed to ?ow over a wedge-wire inclined screen to remove other ?ne solids.Finally,the water was treated in an anaerobic digester before being used in the algae culture experiments.

For the municipal wastewater,the culture volume in each Roux bottle was 800mL.Wastewater was introduced into the bottles with a daily draw-?ll procedure at the end of the light period.Three daily hydraulic loading rates were tested as follows:200,267,and 400mL of primary ef ?uent to achieve 4-,3-,and 2-day hydraulic residence time (HRTs),respectively.For the air –CO 2sparge treatments,each HRT was run with duplicates.For the air-only treatment,the 3-day HRT was run over 99%ammonium.Orthophosphate removal was achieved in the CO 2-sparge treat-ment with both 3-and 4-day HRTs as reported by Woertz et al.[143](Table 9).To determine the fate of the removed ammonium and to validate the results,a nitrogen balance was done on four occasions over 10days of operation.

A recent study characterized a Chlorella species called Chlorella minutissima which was identi ?ed in wastewater treatment oxida-tion ponds in India [144].C.minutissima was able to grow well in high concentrations of raw sewage and dominated the subsequent pond stages in the oxidation pond system.Analysis has found

that

Fig.10.Typical wastewater treatment process (Adapted from [136])

Table 7

Characteristics of four wastewater samples from the St.Paul Metropolitan Wastewater Treatment Plant [135].Parameters Wastewater before primary settling Wastewater after primary settling Ef ?uent from aeration tank Centrate from sludge centrifuge NH 3–N (mg/L)33.470.6

32.270.4ND

71.871.1NO 3–N (mg/L)ND (not detected)ND 16.9570.07ND NO 2–N (mg/L)ND

0.07470.003ND

TP (mg/L) 5.6670.08 6.8670.050.3270.04201.5710.6TN (mg/L)40.6570.0738.9571.9119.170.1131.572.1COD (mg/L)231.074.2224.074.242.271.92250.0799.0Inorganic N/P

5.9

4.7

53.2

0.36

this species can grow heterotrophically in the dark,and mixotro-phically in the light utilizing a variety of organic carbon substrates, over a wide pH range.Furthermore, C.minutissima can utilize either ammonia or nitrate as an N source.The growth of these algae was shown to be highest under mixotrophic(photohetero-trophic)conditions with biomass productivity of379mg/L after10 days of growth compared to biomass of73.03mg/L under photo-autotrophic conditions[135].C.minutissima could,therefore,be a good candidate for high biomass productivity in a wastewater high-rate pond system.All of these experiments further demon-strate that chlorophytic microalgae such as Chlorella can grow well even in very raw wastewater environments.

Based on the above reviews and on the research done so far regarding the biological municipal wastewater treatments,it can be concluded that mass culture of microalgae in the presence of N and P in the municipality wastewater can convert N and P into algal biomass.

5.7.Industrial wastewater treatment

The composition of the industrial wastewaters differs from one disposal site to another and considerably from domestic waste composition.Table10shows the typical range of the biochemical oxygen demand(BOD)and the total suspended solids(TSS)load in industrial wastewaters.

Industrial wastewaters contain heavy metals such as cadmium, chromium,zinc and others.Furthermore,they contain organic chemical toxins such as hydrocarbons,biocides and surfactants. Ef?uents from textile,leather,tannery,electroplating and other metal processing industries have considerable amounts of toxic metal ions.These types of toxic elements are both harmful to the ecosystem and unsafe for humans.The conventional methods of industrial wastewater treatments involve precipitation,ion exchange,electrowinning(electroextraction)and electrochemical methods[146].

Due to generally low nitrogen and phosphorous concentrations and high toxin levels,algal growth rates are lower in many industrial wastewaters while compared with their growth in municipal domiciliary wastewaters.Consequently,there is less potential for utilizing industrial wastewaters for algal culture. Industrial wastewaters contain chemicals and pigments.These wastewaters also contain metals,P and N,at low concentrations and are able to support algal growth with B.braunii and Chlorella saccharophila,and a marine alga Pleurochrysis carterae[147].

6.Algae growth/cultivation

Microalgae culture offers important advantages to improve utilization ef?ciency of solar energy and CO2?xation.Since the culture can be operated in continuous mode,it allows maximum annual productivity.The cells structures of microalgae are rela-tively small and the growth rate of microalgae is much faster than other crops.Thus,the harvesting time of microalgae is pretty short which allows faster CO2capture.For an equivalent amount of microalgae production,much smaller areas of land are required as compared to other crops.Therefore,microalgae are unique because they combine the capturing ability of photosynthesis with the high yield of controlled microbial cultivation[148].

The optimization of strain-speci?c growth/cultivation is a complex topic with many interrelated factors affecting it.These include among others,the following reaction engineering para-meters:(a)light(day–night cycle and irradiation intensity), (b)temperature,(c)nutrient concentration,(d)O2,(e)CO2,(f) pH,(g)salinity,(h)water quality,(i)mineral and carbon regula-tion/bioavailability,(j)cell fragility,(k)cell density and(l)growth inhibition.

Furthermore,there are other culture growth,reactor design and operation issues that affect growth such as(a)mixing,(b)?uid dynamics and hydrodynamic stress,(c)culture depth,(d)gas bubble size and distribution,(e)gas exchange,(f)mass transfer, (g)dilution rate,(h)toxic chemicals and pathogens(bacteria, fungi,viruses)and(i)competition by other algae and harvest frequency.Thus,for large scale cultivation,algae should have desirable features.These are summarized in Table11[149].

High cell density cultures can be achieved using microalgae biotechnology with proper reactor design and process optimiza-tion.For this reason,it is important to develop the general knowledge in this?eld,with emphasis on the most critical scale-up and operational parameters such as(a)light irradiation, (b)mass transfer,(c)shear forces and(d)mixing rate.These

Table8

Nutrient removal rates by algal growth in four wastewater samples from the St.Paul Metropolitan Wastewater Treatment Plant[135].

Parameters Wastewater

before primary

settling(%)Wastewater

after primary

settling(%)

Ef?uent from

aeration tank

(%)

Centrate from

sludge

centrifuge(%)

NH3–N82.474.7–78.3 NO3–N––62.5–NO2–N––?6.297–PO4–P83.290.6 4.6985.6 TN68.468.550.882.8 COD50.956.5?22.783.0 Inorganic

N/P

6.212.7720.80.538

Table9

Nutrient removal of municipality wastewater cultures[143].

Total ammonia nitrogen(mg/L)Phosphate as P(mg/L)

In?uent Ef?uent%

Removal In?uent Ef?uent%

Removal

CO24-day

HRT

39.0o0.02499 2.1o0.02499

CO23-day

HRT

39.0o0.02499 2.1o0.02499

Air3-day HRT 39.0 6.1

(70.89)

84 2.1o0.02499

CO22-day HRT 39.00.6

(70.57)

98 2.10.15

(70.15)

Table10

Typical range of BOD and TSS load in industrial wastewaters.

Source:Industrial wastewater treatment plants self-monitoring manual,Chapter2,

2002[145].

Origin of waste Biochemical oxygen demand

(BOD)(kg/ton)

Total suspended solids(TSS)

(kg/ton product)

Dairy industry 5.3 2.2

Yeast industry12518.7

Starch and

glucose

industry

13.49.7

Fruits and

vegetable

industry

12.5 4.3

Textile industry30–31455–196

Pulp and paper

industry

4–13011.5–26

Beverage industry 2.5–220 1.3–257

Tennary industry48–8685–155

parameters are closely interrelated and they determine the pro-ductivity and ef?ciency of a speci?c reactor unit.

Moreover,the maximization of the algal productivity also implies optimizing algae culture;maximizing CO2capture and wastewater treatment.One of the major issues in the industrial scale-up of microalgae culture is related to algae culture in open ponds under uncontrolled conditions.It is only recently that closed bioreactors have been considered complementary to algal mass culture in open systems.The following are the key aspects of the closed system reactor design:(i)light source and orientation; (ii)algae circulation(iii)materials of construction,(iv)CO2feed and O2removal and(v)pH and temperature control.

6.1.Effects of solar irradiation

Ef?cient utilization of solar irradiation by cells is one of the major objectives of an economically viable microalgae culture system.A cost-effective system whether open or closed,is char-acterized by a high surface area as well as by volumetric produc-tivity.This can be achieved by establishing an optimal solar irradiation regime in the culture.

Table12summarizes the light penetration rate in the culture of Nannochloropsis sp.at different wavelength ranges of incident light [150].From this table,one can see that the light penetration into the culture decreases exponentially as the cell density increases. Generally,the light penetration is expressed as a percentage of total incident irradiation impinging on the culture surface.Two light zones are thereby affected in the photobioreactor:(a)the illuminated volume in which light supports photosynthesis,and (b)the dark volume,in which light intensity is below the compensation point and net photosynthesis cannot take place. One can note that the higher the algae population density,the smaller the light path and the more complex it becomes to attain ef?cient utilization of solar irradiation,(i.e.an even distribution of light to all cells in the reactor).

In this respect,one should mention that algae have developed several mechanisms like plants,to adjust to changes and quality of the light and intensity.However,the adjustment capacities vary from species to species.Algae with phycobilisomes may prefer low light intensities(i.e.,～10mmol photons m?2s?1).Some other algal strains(e.g.,most dino?agellates)often need higher light intensities(～60–100mmol photons m?2s?1).Colorless algae such as astasia,polytomella and prototheca are best kept in a closed cupboard.These algae have otherwise the same maintenance requirements as their photoautotrophic relatives.To develop a culture of organisms from extreme environments,specialized literature should be consulted[151].Standard light intensities between10–30mmol photons m?2s?1have proven to be appro-priate in combination with temperatures commonly used for long-term culturing of most microalgal species.One should note, however,that over-illumination is a widespread misunderstanding for sustainable maintenance of cultures.Not only can excessive irradiation result in photo-oxidative stresses in some algae,but localized heating may also be a problem.Moreover,light and dark photoperiods are required for the maintenance of most cultures. Some algae(e.g.many tropical open-ocean coccolithophorids)may be destroyed by continuous irradiation[152].In most algal cultures,light/dark periods are required to vary from12/12to 16/8hours of light to hours of darkness[153].Inappropriate hours of light to hours of darkness may lead to unwanted photoperiodic effects.For example,short day length periods may cause cyst formation in marine dino?agellates like Lingulodinium polyedrum. These cysts are germinate with dif?culty under standard culture conditions[154].

Regarding the way that light affects mass cultures of phototrophic microorganisms,growth response of mass cultures has been erro-neously described using the so-called‘light curve’[155].This provides a generalized shape of the light response curve,relating the photosynthetic or growth rate of the culture to the intensity of the light source(i.e.the photon?ux density(PFD)impinging on the culture surface).The light source is thus considered as the sole rate-limiting factor in an irradiation limited system.This relationship, however,is only correct for optically thin cultures,of low density population where the cell mutual shading is essentially absent.In reality,however,mass cultures exposed to high irradiation density cannot be maintained in optically thin concentrations with no mutual shading.This is true since PFD is much higher outdoors,up to an order of magnitude or more,than the photosynthetic saturating light intensity.Excess light may cause photo inhibition followed by culture death.The most practical approach by which to cope with this phenomenon is to increase cell density to the point at which mutual shading causes cells to receive strong light intermittently.

Table11

Desired characteristics of algae for mass culturing[149].

Algae characteristic Advantages Disadvantages

(1)Growth in extreme environments Reduced problems with competing species

and predators

Only limited numbers of species available.Culture dif?cult to maintain on a large scale

under extreme environments(i.e.cold weather)

(2)Rapid growth rate Provides competitive advantage over competing

species and predators.It has a reduced pond

area required Growth rate is usually inversely related to cell size;i.e.fast growing cells are usually very small in size

(3)Large cell size,colonial

or?lamentous

morphology

Reduces harvesting costs Large cells usually grow slower than smaller size cells

(4)Wide tolerance of environmental conditions Less control of culture conditions required for reliable culture

(5)Tolerance of shear force Allows cheaper pumping and mixing methods

to be used

(6)High cell product content Higher value of biomass Products are usually secondary metabolites(not directly involved in normal growth).

High concentrations of secondary metabolites normally mean slower growth

Table12

Light penetration depth a(cm)into cultures of Nannochloropsis sp.as effected by the concentration of cell mass[150].

DW(g/L)21050

Blue(410–450nm)0.960.190.04 Green(580–600nm)9.43 1.890.38 Red(670–678nm) 1.250.250.05

a To the depth in which light energy is10%incident light

The high PFD prevailing outdoors is thereby 'diminished 'or ‘diluted ’for the individual cells.Light energy reaching each individual cell during a long exposure time is thus not only a function of the light source intensity,but is also and often more so,dependent on cell density.Thus,changes in growth rate may indeed be manifested in a culture as a response to a given intensity of light [155].A major parameter in mass culture is the output rate of cell mass.This output rate of cell mass in continuous cultures at steady-state is a function of both the growth rate and cell density.In this respect,inadequate selection of optical path and culture density may yield output rates signi ?cantly below maximal values.

As in any biological phenomenon related to optimal exploita-tion of resources per unit irradiation area,there is a certain optimal algal content which may lead to a highest output rate.De ?nition of this parameter involves an ‘optimal cell density ’(OCD,g/L),this optimal cell density is system speci ?c and is required to be maintained in a culture media to exploit sun irradiation most ef ?ciently [150].

The growth rate,k ,can be calculated from the integrated growth equation proposed by Sorokin and Kraus [156]:k ?log 2

O :D :1O :D :0?1

where O.D.0and O.D.1are optical densities at the beginning and end of the time interval,t .

By using a base 2logarithm and the day unit of time,the growth constant,k ,becomes equivalent to the number of dou-blings per day.At least ?ve readings need to be taken during exponential growth in each experiment at a particular light intensity.Reproducibility of the rate in at least two subsequent experiments is required.It is recommended to calculate the logarithmic growth rate for each light intensity as an average from two experiments,with each experiment conducted induplicate.

Fig.11shows the effect of light intensities on the growth of different algae species as reported by Sorokin and Kraus [156].The growth effect can be categorized in three distinct regimes:(i)a light dependent regime in which growth rate increases,(ii)a light independent regime where the growth rate stabilizes,(iii)a light independent regime where growth rate declines.In this respect,a high algae growth rate was found when using low light

intensities.Thus,microalgae are suitable for culturing in shaded areas.

Irradiation ef ?ciency must also be considered when predicting mass culture yields.This is due to algal population density often limiting light intensities penetrating into the algal culture.Further-more,the transition from a light dependent growth regime to alight independent growth phase may be signi ?cantly affected when changing the type of microalgae.

The light-independent plateau for the van Niel strain of C.pyrenoidosa and Scenedesmus extended from 500to about 2000ft-cd.Chlamydomonas however,stretched out in shorter strands from 500to 1000ft-cd.A short plateau extending from 250or 300ft-c to not more than 600ft-c was also observed,with this plateau being characteristic of C.vulgaris [156].Low light-saturating intensity and negative low intensity effects to strain growth are characteristic features also observed in shade plants [156].

In Fig.12,the growth curves of four different municipal wastewater samples are reported as shown by Wang et al.[135].

Table 8shows the different characteristics of the samples collected from the municipal wastewater treatment plant at St Paul,Minnesota,USA.The optical density of the four samples was established at 680nm.Wang et al.[135]cultured Chlorella sp.in those four speci ?c samples under axenic conditions.It was noted that Chlorella sp.,survived in all four cases.Similar growth patterns in the ?rst 3days were followed by an exponential phase lasting 1extra day.This behavior took place before entering the secondary growth phase.One can note that algae in the four wastewater samples before and after primary settling displayed growth curves close to each other.The growth curve of the wastewater from sludge centrifuge was found to be higher than all other three culture systems.This behavior was assigned to the similar chemical composition type,as reported in Table 8.More-over,algal growth was signi ?cantly enhanced in the centrate media due to the much higher nitrogen and phosphorous available and due to the higher COD level.The average speci ?c growth rates in the ?rst 3days were 0.412,0.429,0.343,and 0.948d ?1in wastewaters before and after primary settling,in ef ?uent and in centrate,respectively.

Xue et al.[157]used vertically installed optical ?bers to monitor the culture ?ow direction.A light source was placed inside the set up to promote a “?ashing light effect ”(FLE)on microalgae,so as to obtain high light ef ?ciency.Three types of optical-?ber photobior-eactors involving FLE of microalgae were studied,i.e.air-driven panel,pump-driven panel and stirred tank type reactors.Results demonstrate that with light/dark 10Hz frequency cycles,the microalgae productivity was increased by 43%and 38%for Spirulina platensis and Scenedesmus dimorphus

respectively.

Fig.11.The growth rates of four species of algae at 251C measured at limiting,saturating,and inhibiting light intensities.The symbols are as follows:Chlorella pyrenoidosa (van Niel),circles;Chlorella vulgaris ,crosses;Scenedesmus obliquus ,triangles;and Chlamydomonas reinhardti,squares.Open symbols show growth under ?uorescent light;closed symbols show growth under incandescent light (Adapted from [156]

Fig.12.Algae growth curves in the four wastewaters (Adapted from [135])

6.2.Effects of CO 2concentration

The effect of CO 2concentration on the growth of C.vulgaris was studied by Yun et al.[4].The inoculums were prepared by bubbling air.The growth was somewhat inhibited at 15%(v/v)CO 2with air.However,when the inoculums were adapted to 5%(v/v)CO 2with air,best growth was achieved [4],

Since the typical concentration of CO 2in ?ue gas is around 15%(v/v),adaptation of C.vulgaris to higher CO 2concentrations is needed for the direct use of ?ue gas.Moreover,it was found in a separate experiment that the gradual increase of CO 2concentration gave even better growth at CO 2concentrations of up to 30%2(v/v).

6.3.Effects of temperature

After light,temperature is the most important factor for microalgae culturing for both open and closed culture systems [158–160].Like other microorganisms,microalgae have an opti-mum growth temperature,where maximum growth rate can be achieved.The growth rate dependency on temperature varies from species to species [161].Some species can grow successfully at higher temperatures while others can tolerate very low tempera-tures.Microalgae can tolerate a range of temperatures and their response to temperature variations can affect the following (i)nutritional requirements,(ii)rates and nature of metabolism and (iii)cell compositions [162].Usually,most of the microalgae species can tolerate temperatures up to 151C lower than their optimal temperature.However,exceeding the optimum tempera-tures by only 2–41C may result in the total culture loss [162].

Torzillo et al.[159],reported that laboratory experiments have shown that the maximum biomass yield occurred when the tempera-ture of spiriluna (algal species)was 351C.These authors carried out experiments outdoors from May to September and analyzed tempera-ture effect on growth rate.During this period,the average biomass productivity was found to be 14%superior at 351C versus the growth rate observed at 251C (refer to Fig.15).It is also shown in Fig.13that in the culture grown at 251C average biomass productivity decreases and biomass loss during the night was signi ?cantly higher (7.6%dry weight)than in the culture grown at 351C.This biomass loss accounts for the marked difference in the net biomass productivity of the two cultures (23%average).

6.4.Effects of pH and media composition

The pH is an important factor in culture media.In fact,common problems associated with culture media are the use of an inade-quate pH and high levels of precipitate resulting from incorrectly formulated media,including omission of vital ingredients (e.g.,silicon for diatoms,vitamins)[163].Most algae are tolerant of fairly large changes in pH.However,if the inoculums vigor is suboptimal,then poor or no growth can result.In most cases,freshwater eukaryotic algae prefer acidic environments (pH 5–7),whereas cyanobacteria prefer alkaline environments (pH 7–9).Furthermore,high levels of precipitate can result in nutrient limitation and osmotically stressful microenvironments [163].Rachlin and Grosso [163],measured the percentage of con-trolled growth of C.vulgaris incubated for 96-h at various pHs,as shown in Table 13.It can be seen that for the acidic and neutral pHs,the pH remained relatively constant over the 96-h incubation period.However,for alkaline pHs (pH 7.5and greater)cell growth appeared to change the pH reducing it to 7.0–7.9,with this change being a function of the initial pH.In this respect,one should notice that at alkaline pHs microalgae cell growth during 96-h incubation periods (Table 13)is higher than the acidic media.

Table 13shows that the pH control at 6.9gave the 100%reference growth.Table 13also shows that under acidic conditions (pH 3.0–5.0),C.vulgaris growth is reduced to 27.3–55%with respect to the growth at 6.9pH.As well at the alkaline pH of 8.3–9.0,growth is reduced from 46%to 37.2%of the growth reference values of particular interest is that at the alkaline pHs of 7.5and 8.0,the growth exceeds reference growth,indicating an optimum growth conditions within this narrow pH range.

7.Growth kinetics

The algae growth rate is a function of (a)the light intensity (I ),(b)the temperature,(c)the nutrients and (d)the pH [155].Thus,a speci ?c growth rate of algae in outdoor cultures can be de ?ned

Fig.13.In ?uence of temperature on the productivity of Spirulina platensis during (a)the daylight period and (b)24h day –night cycles (Adapted from [159]).

Table 13

Percentage of controlled growth of Chlorella vulgaris after 96h exposure to pH modi ?ed Bristol 's Medium [163].Initial pH %Growth Final pH 3.027.370.16 2.84.036.370.17 4.05.055.670.18 4.96.291.970.10 6.26.9100

6.9

7.5124.970.20 6.9

8.0120.070.187.88.346.170.187.98.54

9.770.188.19.0

37.2.070.17

8.5

Goldman[155]as

μ?ln2?1dX

in whichμis the speci?c growth rate[T?1],ln2is the natural logarithm of2,g is the cell generation period[T],X is the biomass concentration[M L?3],and dX/dt is the change in biomass con-centration with respect to time,or the biomass productivity per unit volume[ML?3T?1].

Algal productivity can be normalized on a per unit area basis by considering the culture volume V[L3]with the culture area A[L2] and depth d[L].The total production of biomass B(XV)[M]per unit time is dB/dt[MT?1].This later term can be divided by the area A[L2]to give P,the per unit areal yield[ML?2T?1]

P?1

?μXd

Nutrient effect on algal growth rates using the Monod model has been successfully tested by some research groups,as reported by Goldman and Carpenter[161].The main basic assumption using the Monod model is that the growth rate of algae is solely dependent on the concentration of the limiting nutrient.Based on this assumption, the Monod model as de?ned by Goldman and Carpenter[161]is as follows:

μ?feST?^μS

K StS

where S is a the limiting nutrient concentration and K S is the half saturation coef?cient,mg/L.

The Monod model does not explicitly include other effects such as light intensity or temperature.Goldman and Carpenter[161] considered,in this respect,that the^μmaximum growth rate in the Monod equation is not affected by nutrient concentration.

The^μmaximum growth rate is a function of other environ-mental variables such as light and temperature.When light intensity is held constant then the growth rate becomes solely a temperature function following an Arrhenius equation:

^μ?Ae?E=RT

where A is a constant in d?1;E is an activation energy in cal mol?1; R is the universal gas constant in cal K mole?1and T is the temperature in Kelvin.

By substituting this equation into above equation,as proposed by Goldman and Carpenter[161],one can conclude the following:

μ?Ae?E=RT S

K SeTTtS

Fig.14a shows the increase of S nutrient concentration with temperature and light intensity held constant.This yields an algal growth rate augmenting?rst and reaching a plateau later.In this respect,Goldman[155]showed that growth is a?rst order function μ?γS S at low nutrient levels becoming of zero orderμ≈^μat higher nutrient concentrations.The intersection of the linear approximation for the?rst order portion of the growth curve with the horizontal asymptote gives^μand K S.K S represents the half-saturation coef?cient, or the nutrient concentration?0:5^μ.

Fig.14b describes the effect of increasing light intensity while keeping nutrient concentration and temperature constant.The growth rate also displays a?rst orderμ?γI I at low light intensity becoming of zero orderμ≈^μat high irradiation.Regarding the I K parameter,one can observe that it represents K S.Based on the Goldman and Carpenter[161]an Arrhenius type empirical equa-tion is suitable for representing temperature effects:

^μ?e1:8?1010Te?6842=T

where T is the absolute temperature in Kelvin

units.

Fig.14.The general functionality between algal growth rate(μ)and environmental parameters is conveyed through four different scenarios shown in the above graphs representing the following:(a)nutrients(S)are increased while temperature(T)and light intensity(I)held constant,(b)I is increased while T and S are held constant,(c)T is increased while S and I are kept constant,(d)S held constant and I being changed for various temperatures(Adapted from[155]).

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22104030施工质量控制的内容和方法复习要点 1．施工质量控制的基本环节和一般方法 (1)施工质量控制的基本环节包括事前、事中和事后质量控制。 (2)施工质量控制的依据分为共同性依据和专门技术法规性依据。 (3)施工质量控制的一般方法包括质量文件审核和现场质量检查。现场质量检查的内容包括开工前的检查；工序交接检查；隐蔽工程的检查；停工后复工的检查；分项、分部工程完工后的检查以及成品保护的检查。检查的方法主要有目测法、实测法和试验法。试验法又分为理化试验和无损检测。 2．施工准备阶段的质量控制 (1)施工质量控制的准备工作包括工程项目划分与编号以及技术准备的质量控制。 (2)现场施工准备的质量控制包括工程定位和标高基准的控制以及施工平面布置的控制。 (3)材料的质量控制要把好采购订货关、进场检验关以及存储和使用关。 (4)施工机械设备的质量控制包括机械设备的选型、主要性能参数指标的确定以及使用操作要求。 3．施工过程的质量控制 (1)技术交底书应由施工项目技术人员编制，并经项目技术负责人批准实施。交底的形式有：书面、口头、会议、挂牌、样板、示范操作等。 (2)项目开工前应编制测量控制方案，经项目技术负责人批准后实施。 (3)施工过程中的计量工作包括施工生产时的投料计量、施工测量、监测计量以及对项目、产品或过程的测试、检验、分析计量等。其主要任务是统一计量单位制度，组织量值传递，保证量值统一。 (4)工序施工质量控制主要包括工序施工条件质量控制和工序施工质量效果控制。 (5)特殊过程是指该施工过程或工序的施工质量不易或不能通过其后的检验和试验而得到充分验证，或万一发生质量事故则难以挽救的施工过程。其质量控制除按一般过程质量控制的规定执行外，还应由专业技术人员编制作业指导书，经项目技术负责人审批后执行。(6)成品保护的措施一般包括防护、包裹、覆盖、封闭等方法。 4．工程施工质量验收的规定和方法 (1)工程施工质量验收的内容包括施工过程的工程质量验收和施工项目竣工质量验收。(2)施工过程的工程质量验收，是在施工过程中、在施工单位自行质量检查评定的基础上，参与建设活动的有关单位共同对检验批、分项、分部、单位工程的质量进行抽样复验，根据相关标准以书面形式对工程质量达到合格与否做出确认。 (3)施工项目竣工验收工作可分为验收的准备、初步验收(预验收)和正式验收。一单项选择题

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通信电子线路课程设计中波电台发射系统与接收系统设计学院：******* 专业：******* 姓名：**** 学号：******

一．引言这学期，我们学习了《通信电子线路》这门课，让我对无线电通信方面的知识有了一定的认识与了解。通过这次的课程设计，可以来检验和考察自己理论知识的掌握情况，同时，在本课设结合Multisim软件来对中波电台发射机与接收机电路的设计与调试方法进行研究。既帮助我将理论变成实践，也使自己加深了对理论知识的理解，提高自己的设计能力二．发射机与接收机原理及原理框图 1.发射机原理及原理框图发射机的主要任务是完成有用的低频信号对高频载波的调制,将其变为在某一中心频率上具有一定带宽、适合通过天线发射的电磁波。通常，发射机包括三个部分：高频部分，低频部分，和电源部分。高频部分一般包括主振荡器、缓冲放大、倍频器、中间放大、功放推动级与末级功放。主振器的作用是产生频率稳定的载波。为了提高频率稳定性，主振级往往采用石英晶体振荡器，并在它后面加上缓冲级，以削弱后级对主振器的影响。低频部分包括话筒、低频电压放大级、低频功率放大级与末级低频功率放大级。低频信号通过逐渐放大，在末级功放处获得所需的功率电平，以便对高频末级功率放大器进行调制。因此，末级低频功率放大级也叫调制器。发射机系统原理框图如下图：设计指标：设计目的是要求掌握最基本的小功率调幅发射系统的设计与安装调试。技术指标：载波频率535-1605KHz，载波频率稳定度不低于10-3，输出负载51Ω，总的输出功率50mW，调幅指数30％~80％。调制频率500Hz~10kHz。本设计可提供的器件如下，参数请查询芯片数据手册。所提供的芯片仅供参考，可以选择其他替代芯片。高频小功率晶体管3DG6 高频小功率晶体管3DG12 集成模拟乘法器XCC，MC1496 高频磁环NXO-100 运算放大器μA74l 集成振荡电路E16483 原理及原理框图接收机的主要任务是从已调制AM波中解调出原始有用信号，主要由输

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6、已知谐振功率放大器工作在欠压状态，为了提高输出功率可将负载电阻Re 增大，或将电源电压Vcc 减小，或将输入电压Uim 增大。 7、丙类功放最佳工作状态是临界状态，最不安全工作状态是强欠压状态。最佳工作状态的特点是输出功率最大、效率较高 8、为了有效地实现基极调幅，调制器必须工作在欠压状态，为了有效地实现集电极调幅，调制器必须工作在过压状态。 9、要产生较高频率信号应采用LC振荡器，要产生较低频率信号应采用RC振荡器，要产生频率稳定度高的信号应采用石英晶体振荡器。 10、反馈式正弦波振荡器由放大部分、选频网络、反馈网络三部分组成。 11、反馈式正弦波振荡器的幅度起振条件为1 ，相位起振条件 A F （n=0,1,2…）。 12、三点式振荡器主要分为电容三点式和电感三点式电路。 13、石英晶体振荡器是利用石英晶体的压电和反压电效应工作的，其频率稳定度很高，通常可分为串联型晶体振荡器和并联型晶体振荡器两种。 14、并联型石英晶振中，石英谐振器相当于电感，串联型石英晶振中，石英谐振器相当于短路线。

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计算你的生命数字 Company Document number：WUUT-WUUY-WBBGB-BWYTT-1982GT

计算你的生命数字每个数字从 1 到 9，都有它形而上的特殊意义；毕氏相信人生就是学习，而轮回也是存在的，如果人清楚了解他在这一世努力的方向，那么藉由每世不同的数字，我们便学习人所该学到的所有课程。至于我们的生命数字该怎么算呢只要将你的公历生日所有数字加在一起即可。换算公历数字则为公元 1981 年 10 月 15 日，1+9+8+1+1+0+1+5 等于 26，因位超过十位数，所以继续运算 2+6 则为8，因此他的生命数字即为 8！生命数字１的人：他的爱很深、很真，期待你视他为生命中的第一生命数字１的人，天生就是领袖，他们非常独立，不轻易相别人。根据圣经，上帝创造的第一个人亚当就是典型的代表，他所有的事都得自己来，他可以自我照顾得很好，而他也没有与人分享的概念。由于太独立又不太在意别的结果，显得灵数１的人有些自私，希望大家都听他的，他们做起事来，也彷佛这世界就没有其它人一样；他们常给人一种冷冷的、不太在乎你、甚至有些距离的感觉。生命数字１的人中，他的人生课题是要学习谦虚，试着敞开自己，信任别人，多与人沟通互动，并和他人分享自己的感觉。

在感情上，灵数１的人的特点是他们可以爱得很真，很深，只可惜他们不会表达，这是由于灵数１的人总是希望别人都听他的，也都照他的话去做，他们期望你待他们如国王、王后一样，不会告诉你他的感觉，而你也别无选择，除了加倍努力取悦他、宝贝他之外，否则他就会不信任你，甚至以为你是在利用他。因此如果你的另一半是灵数是１的话，你最好花时间去投其所好，像是不停地赞美恭维他、搂他抱他、给他最爱吃的东西等，某些程度上来说，如果你是个好演员的话，他们是很容易被摆布的，只要你视他如生命中的「第一」即可，但是千万留意；他可不认为他也得如此待你，你自己的头脑可得想清楚。换句话说，在情爱关系上，灵数１的人是不公平的，因此双方得多花时间共处、沟通，而两人在人生目标上也必须明确，相合。最好两人都选择爱情为人生目标的第一顺位，事业等皆为其次；如果这点共识清楚，那么一切就容易得多，彼此也更能了解对方，满足双方需求；否则迟早就会有问题引爆得不可收拾。生命数字２的人：很能享受亲密关系恨极独处很会挑剔伴侣，遭拒就泄气生命数字２的人，天生敏感，擅长分析，由于对照与比较能力突出，使得生命数字２的人成为一流的批评家。一般说来，灵数２的人，个性较强而且呈两极的刚柔兼具。灵数２的女性，性格中稍带男性阳刚特质，而灵数２的男性则具备了女性阴柔的一面，也许您从外型上，就很容易察觉出来。另外，灵数２的人，还有一种双重性格，那就是他们可以在极端独立和极度依赖中任意游离。我们可以从圣经中，亚当和夏娃的依存关系而清楚了解这点。

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二○○九～二○一○学年第二学期电子信息工程系课程设计报告书班级：学号：姓名：课程名称：通信电子线路学时学分：1周1学分指导教师：二○一○年三月十五日

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? 谐振回路品质因数Q 与通频带和选择性有什么关系？提高谐振回路的Q 值，在电路上主要采用什么手段。 Q ↑,选择性好，但通频带窄；提高Q 值，在电路上可采用部分接入的方式，包括信号源和/或负载部分接入谐振回路。 ? 小信号调谐放大器在性能上存在什么矛盾，解决该矛盾有什么途径。高频小信号谐振放大器存在通频带和选择性的矛盾。选择性越好，通频带越窄，选择合适的Q 值，尽可能兼顾两者；当不能兼顾时，可采用耦合谐振回路的方式，即两个单谐振回路通过互感或电容临界耦合，获得理想的矩形系数。 ? 影响小信号谐振放大器稳定性的因素是什么？可采用何措施来提高稳定性。影响小信号谐振放大器稳定性的因素是晶体管存在内部反馈即方向传输导纳y re 的作用。它把输出电压可以反馈到输入端, 引起输入电流的变化, 从而可能引起放大器工作不稳定。可采用中和法和失配法来消减其影响；其中前者是在电路中引入一反馈，来抵消内部反馈的作用，达到放大器单向化的目的；而后者是通过牺牲增益来换取稳定，通过增大放大器的负载电导，使之与放大器输出电导不匹配，即失配，导致放大器放大倍数降低，以减小内部反馈的影响。采用失配法时为保证增益高的要求，常采用组合放大电路。 ? 如图所示电路中，电感L 的铜损电阻忽略不计，Rs=30k Ω，电感量为100uH ，R L =5k Ω。 i s =1cos(2π×5 ×105t )mA 。若要求回路的有载Q 为50，确定C 1和C 2的值，并计算输出电压。由I S 的表示式可知信号频率f0=5×105Hz,故谐振回路总电容 pF L f C C C C C 10001010010541 416 10222022121=????==+= -ππ (1) L R Q L 0ω∑= Ω=??????==∴∑K L Q R L 15.710100105250-6 50πω 又L s L s R R R R R '+'=∑ Ω='-='∴∑∑K R R R R R s s L 32.94 则接入系数p C 应满足 3896.0211 ='= += L L c R R C C C p (2) 由(1)和(2)可得pF C pF C 1637,256712==

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英汉数字的文化差异与翻译财富)、the seven corporal works of mercy(七大肉体善事)、the seven spiritual works of mercy(七大精神善事)、the seven sacraments(七大圣礼)。此外,人们也视“七”为吉数,在生活中有“lucky seven”的说法,即“幸运之七”。英语中有“seven”的习语很多,如:Keep a thing seven years and you will find a use for it.(东西保存时间长,终会派上好用场。) Seven hours? sleep will make a clown forget his design.(睡七小时的觉,小丑把花样都忘掉。) A man may lose more in an hour than he can get in seven.(得之艰难失之易) to be in the seventh heaven(极其快乐)等。 (三)、“四”与“十三” 1、“四” 在中国“四”被视为一个不吉祥的数字,但在古代人们对于“四”并无特别的忌讳。这主要是因为随着科技的发展,人们生活中越来越多地使用到数字,如门牌号、手机号码、车牌号等。而因为“4”的发音与“死”谐音,所以车牌号码、电话号码等尾数有四的就不受欢迎。人们尤其要避开“14”(谐音“要死”)、“514”(谐音“我要死”)、44、444、4444等数目字。在习语中,数字“四”常常与“三”在一起,常带有贬义。如:七个铜钱放两处——不三不四;七个仙女争面脂——香三臭四;七根竹竿掉进猪圈里——横三竖四。虽说在音乐中4的发音与“发”相似,但还是很少有人愿意使用带4的车牌、电话号码等。不过时下年轻男女很喜欢根据数字的谐音来传递信息。这种数字信息并不会排斥4,因为4除了可以是“死”的谐音,也可以是“是” 或“世” 等字的谐音。如1314(一生一世)、0451(你是我要)、7564335(请无聊时想想我)、456(是我拉)、25184(爱我一辈子)、0594184(你我就是一辈子)、3456(相思无用)、246(饿死了)、246437(爱是如此神奇)、73748096,13148687(今生今世伴你左右,一生一世不离不弃)、740(气死你)、74839(其

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值为o Q ，则：R L Q o o ω= 值，则：设接入信号源内阻和负载电阻的Q 为L Q R R R R Q R R R L Q L s L ++=++=1L s o L ω 其中R 为回路本身的损耗，R S 为信号源内阻，R L 为负载电阻。由此看出：串联谐振回路适于R s 很小（恒压源）和R L 不大的电路，只有这样Q L 才不至于太低，保证回路有较好的选择性。对于并联谐振电路（如下图所示）：设接入信号源内阻和负载电阻的Q 值为L Q 由于没有信号源内阻和负载接入时的Q 值为由式（2-31）可知，当R s 和R L 较小时，Q L 也减小，所以对并联回路而言，并联的电阻越大越好。因此并联谐振回路适于恒流源。 2-6已知某电视机一滤波电路如题图2-2所示，试问这个电路对什么信号滤除能力最强，对什么信号滤除能力最弱，定性画出它的幅频特性。 V1=V2? 题图2-2题图2-3 2-7已知调谐电路如题图2-3所示，回路的谐振频率为465kHz ，试求：（1）电感L 值；（2）L 无损耗时回路的通频带；（3）L 有损耗（Q L =100）回路的通频带宽度。左侧电路的接入系数： 25.040120401=+= T T T p 右侧电路的接入系数：25.040120402=+= T T T p 等效电源： s s i p i 1' = 等效阻抗：Ω=Ω + Ω+Ω= k k p k k p R p 67.265.21601 101 2 221 等效容抗：2 22 1' 16?10p pF p pF C ?++?= 电容值未知 2-8回路的插入损耗是怎样引起的，应如何减小这一损耗？由于回路有谐振电阻R p 存在，它会消耗功率因此信号源送来的功率不能全部送给负载R L ，有一部分功率被回路电导g p 所消耗了，这就是插入损耗。增大回路本身的Q 值可以减小插入损耗。 2-9已知收音机某中放的负载回路如题2-4所示，回路的f 0=465kHz ，电感的Q 0=100，要求回路的带宽B=20kHz ，试求：（1）电感L 值；（2）回路插入损耗；

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体中所占的重要程度，具有较强的说服力，被广泛应用于确定改革的主要目标和效果、调查产生缺陷及故障的原因。因此，企业管理人员必须掌握排列图的绘制，并将其应用到质量过程中去。一般说来，绘制排列图的步骤如图7-1所示，即：确定调查事项，收集数据，按内容或原因对数据分类，然后进行合计、整理数据，计算累积数，计算累积占有率，作出柱形图，画出累积曲线，填写有关事项。图7-1 排列图的绘制步骤排列图的应用实例某化工机械厂为从事尿素合成的公司生产尿素合成塔，尿素合成塔在生产过程中需要承受一定的压力，上面共有成千上万个焊缝和焊点。由于该厂所生产的十五台尿素合成塔均不同程度地出现了焊缝缺陷，由此对返修所需工时的数据统计如表7-1所示。表7-1 焊缝缺陷返修工时统计表序号项目返修工时fi 频率 pi/% 累计频率 fi/% 类别 1焊缝气孔14860.460.4A 2夹渣5120.881.2A 3焊缝成型差208.289.4B 4焊道凹陷15 6.195.5B 5其他11 4.5100C 合计245100 缝成型差、焊道凹陷及其他缺陷，前三个要素累加起来达到了89.4%。根据这些统计数据绘制出如图7-2所示的排列图：横坐标是所列举问题的分类，纵坐标是各类缺陷百分率的频数。

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摘要反馈振荡器是一种常用的正弦波振荡器，主要由决定振荡频率的选频网络和维持振荡的正反馈放大器组成。按照选频网络所采用元件的不同，正弦波振荡器可分为LC振荡器、RC振荡器和晶体振荡器等类型。本文介绍了高频电感三点式振荡器电路的原理及设计，电感三点式容易起振，调整频率方便，变电容而不影响反馈系数。正弦波振荡器在各种电子设备中有着广泛的应用。例如，无线发射机中的载波信号源，接收设备中的本地振荡信号源，各种测量仪器如信号发生器、频率计、fT测试仪中的核心部分以及自动控制环节，都离不开正弦波振荡器。根据所产生的波形不同，可将振荡器分成正弦波振荡器和非正弦波振荡器两大类。前者能产生正弦波，后者能产生矩形波、三角波、锯齿波等。本文将简单介绍一种利用一款名为Multisim 11.0的软件作为电路设计的仿真软件，电容电感以及其他电子器件构成的高频电感三点式正弦波振荡器。电路中采用了晶体三极管作为电路的放大器，电路的额定电源电压为5.0 V，电流为1~3 mA，电路可输出输出频率为8 MHz（该频率具有较大的变化围）。关键词：高频、电感、振荡器

和数字有关的常识

【五脏】心、肝、脾、肺、肾【六腑】胃、胆、三焦、膀胱、大肠、小肠【七情】喜、怒、哀、乐、爱、恶、欲【五常】仁、义、礼、智、信【五伦】君臣、父子、兄弟、夫妇、朋友【三姑】尼姑、道姑、卦姑【六婆】牙婆、媒婆、师婆、虔婆、药婆、稳婆【九属】玄孙、曾孙、孙、子、身、父、祖父、曾祖父、高祖父【五谷】稻、黍、稷、麦、豆【中国八大菜系】四川菜、湖南菜、山东菜、江苏菜、浙江菜、广东菜、福建菜、安徽菜【五毒】石胆、丹砂、雄黄、矾石、慈石【配药七方】大方、小方、缓方、急方、奇方、偶方、复方【五彩】青、黄、赤、白、黑【五音】宫、商、角、徵、羽【七宝】金、银、琉璃、珊瑚、砗磲、珍珠、玛瑙【九宫】正宫、中吕宫、南吕宫、仙吕宫、黄钟宫、大面调、双调、商调、越调【七大艺术】绘画、音乐、雕塑、戏剧、文学、建筑、电影【四大名瓷窑】河北的瓷州窑、浙江的龙泉窑、江西的景德镇窑、福建的德化窑【四大名旦】梅兰芳、程砚秋、尚小云、荀慧生【六礼】冠、婚、丧、祭、乡饮酒、相见【六艺】礼、乐、射、御、书、数【六义】风、赋、比、兴、雅、颂

【八旗】镶黄、正黄、镶白、正白、镶红、正红、镶蓝、正蓝【十恶】谋反、谋大逆、谋叛、谋恶逆、不道、大不敬、不孝、不睦、不义、内乱【九流】儒家、道家、阴阳家、法家、名家、墨家、纵横家、杂家、农家【三山】安徽黄山、江西庐山、浙江雁荡山【五岭】越城岭、都庞岭、萌诸岭、骑田岭、大庾岭【五岳】〖中岳〗河南嵩山、〖东岳〗山东泰山、〖西岳〗陕西华山、〖南岳〗湖南衡山、〖北岳〗山西恒山【五湖】鄱阳湖〖江西〗、洞庭湖〖湖南〗、太湖〖江苏〗、洪泽湖〖江苏〗、巢湖〖安徽〗【四海】渤海、黄海、东海、南海【四大名桥】广济桥、赵州桥、洛阳桥、卢沟桥【四大名园】颐和园〖北京〗、避暑山庄〖河北承德〗、拙政园〖江苏苏州〗、留园〖江苏苏州〗【四大名刹】灵岩寺〖山东长清〗、国清寺〖浙江天台〗、玉泉寺〖湖北江陵〗、栖霞寺〖江苏南京〗【四大名楼】岳阳楼〖湖南岳阳〗、黄鹤楼〖湖北武汉〗、滕王阁〖江西南昌〗、大观楼〖云南昆明〗【四大名亭】醉翁亭〖安徽滁县〗、陶然亭〖北京先农坛〗、爱晚亭〖湖南长沙〗、湖心亭〖杭州西湖〗【四大古镇】景德镇〖江西〗、佛山镇〖广东〗、汉口镇〖湖北〗、朱仙镇〖河南〗【四大碑林】西安碑林〖陕西西安〗、孔庙碑林〖山东曲阜〗、地震碑林〖四川西昌〗、南门碑林〖台湾高雄〗【四大名塔】嵩岳寺塔〖河南登封嵩岳寺〗、飞虹塔〖山西洪洞广胜寺〗、释迦塔〖山西应县佛宫寺〗、千寻塔〖云南大理崇圣寺〗【四大石窟】莫高窟〖甘肃敦煌〗、云岗石窟〖山西大同〗、龙门石窟〖河南洛阳〗、麦积山石窟〖甘肃天水〗【四大书院】白鹿洞书院〖江西庐山〗、岳麓书院〖湖南长沙〗、嵩阳书院〖河南嵩山〗、应天书院〖河南商丘〗

通信电子线路课程设计

通信电子线路课程设计学院信息工程学院班级通信0711 姓名邱加钦学号 2007830029 成绩指导老师马中华陈红霞 2010年 1 月 4 日

通信电子线路课程设计报告一设计名称：调频无线话筒的设计二设计时间：2010年1月1日~1月5日三设计地点：集美大学信息工程学院通信实验室四指导老师：马中华、陈红霞五设计目的： 1，了解无线话筒的发射原理； 2，熟练掌握protel设计； 3，完成简单的无线话筒制作； 4，通过制作和检测无线话筒，加深对放功率放大器的认识。六设计原理调频无线话筒是一种可以将声音或者歌声转换成88~108MHz的无线电波发射出去，距离可以达到30~50m，用普通调频收音机或者带收音机功能的手机就可以接收。将声音调制到高频载波上，可以用调幅的方法，也可以用调频的方法。与调幅相比，调频具有保真度好，抗干扰性强的优点，缺点是占用频带较宽。调频的方式一般用于超短波波段。 1、调频无线话筒的框图如下： T2 图1 调频话筒框图 2、设计原理图：

图2 试验原理图晶体管T1和其周围的电路构成高频振荡器，振荡频率由L、C4、C5、T1的结电容决定。加至T1管基极的音频信号电压，会使c-b结电容随它变化，从而实现调频。 C4可改变中心频率的选择(88~108MHz)。 T1输出调频信号，通过C7耦合到T2管的基极，经过T2管放大后从天线辐射出去。T2管构成高频放大器，还有缓冲作用，隔离了天线对高频振荡器的影响，使振荡频率更加稳定。七设计内容 1，protel设计（1）电路原理图设计。按设计原理图进行电路原理图的绘制。如图3示。

通信电子线路课程设计题目及答案(正式版)

1.请问本机振荡电路的类型并估算电路的振荡频率？答：本振的类型为Clapp 振荡器，它是电容三端式振荡器的一种变形。振荡电路的振荡频率近似等于其选频回路的谐振频率，即： f= 2.影响振荡频率的元件有哪些？答：如下图：如图红色椭圆标注所示，振荡频率由这些元件决定。 3.天线信号接收选频网络的作用？答：其作用是选频，通过可变电容选择希望听到的广播信号。 4.混频电路射极电阻的作用？答：该电阻是用于稳定混频管静态工作点而使用的电流负反馈电阻。 5.混频电路输入输出信号波形特征？答：混频电路有两路输入信号：天线信号，其波形是疏密相间且等幅的调频信号；本振信号，其波形是高频正弦信号。混频电路输出信号：载波为中频的调频信号，其波形特征与天线信号一致，是疏密相间且等幅的调频信号。 6.混频电路集电极选频网络的作用？答：从混频后的信号中用该选频网络滤出中频信号。 7.中频放大电路陶瓷滤波器的作用？答：陶瓷滤波器的作用是进一步滤出中频信号，因为陶瓷滤波器的矩形系数一般要比LC谐振回路好，即具有较好的选择性。 8.检波电路中中周的作用及选频网络的中心频率是多少？答：该中周的作用是将信号中频率的变化转化为电压的变化。选频网络的中心频率是：

10.7MHz 9. 低频放大电路的输出是如何调整的？答：通过调整低放输入端可变电阻实现 10. 如何保证中频放大电路的频率是10.7MHz ？答：要保证中放的频率是10.7MHz ，我们在电路中需要注意：中放管输出端的陶瓷滤波器要选择中心频率为10.7MHz 的产品 11. 混频级与中放级电路静态计算答：混频级和和中放级电路的直流静态工作点分析如下：设Tr1和Tr2的直流放大倍数分别为1β、2β，基极电流、集电极电流和发射极电流分别为i Ib 、 i Ic 和i Ie ，1,2i =，总电流为I 。根据三极管的电流放大特性有： i i i Ic Ib β= （1） (1)i i i Ie Ib β=+ （2）设Tr1和Tr2的基极电压分别为1Vb 、2V b ，那么 1120.7Vb Ie R =+ （3） 2240.7Vb Ie R =+ （4）此外，

通信电子线路习题解答

关于《通信电子线路》课程的习题安排：第一章习题参考答案： 1-1 1-3 解： 1-5 解：第二章习题解答： 2-3 解： 2-4 由一并联回路，其通频带B 过窄，在L 、C 不变的条件下，怎样能使B 增宽？答：减小Q 值或减小并联电阻 2-5 信号源及负载对谐振回路有何影响，应该如何减弱这种影响？答： 1、信号源内阻及负载对串联谐振回路的影响：通常把没有接入信号源内阻和负载电阻时回路本身的Q 值叫做无载Q （空载Q 值）如式通常把接有信号源内阻和负载电阻时回路的Q 值叫做有载QL,如式为空载时的品质因数为有载时的品质因数 Q Q Q Q L L <可见结论：串联谐振回路通常适用于信号源内阻Rs 很小 (恒压源）和负载电阻RL 也不大的情况。 2、信号源内阻和负载电阻对并联谐振回路的影响 o o Q R L Q ==ωL S L R R R L Q ++=0ωL p s p p p p p p p 11R R R R Q Q G C LG Q L ++= ==故ωω同相变化。与L S L R R Q 、Θ性。较高而获得较好的选择以使也较大的情况,很大，负载电阻内阻并联谐振适用于信号源L L S Q R R ∴

2-8 回路的插入损耗是怎样引起的，应该如何减小这一损耗？答：由于回路有谐振电阻R p 存在，它会消耗功率因此信号源送来的功率不能全部送给负载R L ，有一部分功率被回路电导g p 所消耗了。回路本身引起的损耗称为插入损耗，用K l 表示无损耗时的功率，若R p = ， g p = 0则为无损耗。有损耗时的功率插入损耗通常在电路中我们希望Q 0大即损耗小，其中由于回路本身的L g Q 0p 01ω= ，而 L g g g Q 0L p s L )(1 ω++= 。 2-11 2-12 解： 2-13 时，电路的失调为：66.65 5 .0*23.33f f 2Q p 0 ==?=ξ 2-14 解：又解：接入系数p=c1/（c1+c2）=，折合后c0’=p2*c0=,R0’=R0/ p2=20k Ω,总电容C=Ci+C0’+C1C2/(C1+C2)=,回路谐振频率fp=，谐振阻抗Rp=1/（1/Ri+1/Rp0+1/R0’）,其中Rp0为空载时回路谐振阻抗，Rp0=Q0*2π*fp*L=Ω，因此，回路的总的谐振阻抗为：Rp=1/ 11P P K l '=率回路有损耗时的输出功率回路无损耗时的输出功L 2L s s L 201g g g I g V P ????? ??+==L 2 p L s s L 211g g g g I g V P ?? ??? ??++=='2 0L 1 111?? ? ? ?? ??-='=Q Q P P K l

数字的含义

数字的含义 1：代表单独或个体，此人非常独立、专注、诚实，而且意志坚定，定了目标就勇往直前的去实现它，他们不喜欢和别人一同工作，也不愿意发号施令，他们可能会以自我为中心，比较任性，而且作威作福，通常都是独来独往的人 2、代表互动与双向沟通、合作与平衡的能力，此人非常有想象力和创造力，个性柔顺、自然、平和，有很好的协调性，忠诚并勇于承担责任，而且非常公正。但会很矛盾，是正反两面的混合体（白天和黑夜、正义和邪恶），此人可能比较内向、孤僻、喜怒无常、优柔寡断、比较自省。 3、代表完整和完成的概念，它包括了开始、中间、结尾。代表了天才、能量、艺术方面的修养和才华、幽默感和社交能力。此人非常平易近人且富有，取得成功的概率很大，但不能专注于某事，容易觉得受到冒犯而且比较注重表面。

4、代表了稳定和坚实，是勤恳工作的代表，非常注重实际、实效，让人觉得值得信赖，他们喜欢逻辑思维和推理，不喜欢虚幻的东西，很有组织能力，能确保工作的顺利完成，此人没有任何悬念可言，行动是可以猜得到的，但比较固执、爱猜疑，让人觉得过于注重实效，经常疲劳过度，在2的矛盾性上在加倍表现。 5、代表不稳定性和不均衡性，揭示着改变和不确定性。此人往往会被寻多事吸引，但最终只会选一件，喜欢冒险、敢作敢为、旅行、愿意结交朋友，但不喜欢在一个地方停留太久，爱逞能、责任感不强而且脾气比较暴躁，没有什么耐心 6、代表了和谐、友谊和家庭观念，此人是忠诚的有责任感和爱心、很好的适应环境能力，喜欢传闲话、沾沾自喜，被认为是一个完美的数字（1*2*3=6、1+2+3=6）。

7、认知能力强、聪明切有悟性，喜欢努力工作和挑战，通常都很严肃、学究气质，觉得神秘的事情比金钱和财富更有吸引力。但有悲哀、喜欢讽刺和缺乏安全感的特性，被认为是神秘、有魔力的数字（一先前有7天，古代有7大行星）。 8、代表商业上的成功，此人非常实际、胸怀大志、勇于承担责任而且工作认真负责，但爱嫉妒、贪婪、喜欢发号施令，对权利非常渴望，被认为是无法预测的数字（既代表顶峰也代表了谷低）。 9、代表着完成和圆满的成就，此人愿意向其他人提供服务，意志坚定，工作起来勇往直前，从不觉得疲惫，也常常给人带来启迪，但比较傲慢、自以为是。塔罗牌里的10：命运之轮塔罗牌大阿卡那的第10张是“命运之轮”，象征时运的逆转，除了变动本身，世上并没有真正恒常不变的真理。这张牌显示了喜欢赌博的倾向，它会使生命因此起伏不定。事实上，人生不管成功或失败都与命运之轮紧紧相系；所以，生命中的成败输赢都不会是永久固定的。数字在西方各自的含义分别是什么? 悬赏分：0 |解决时间：2007-11-13 02:24 |提问者：X罐最佳答案 “1”——在西方，它表示完美、独尊、起始，代表概念世界的一，一产生多，因而是世界的象征。一产生多，一不是数，没有性的特征，属于太阳的领域。西方命理认为，生日带“1”的人，是一个有野心，喜欢站在颠峰的人，不喜欢受人指使，喜欢依照自己的意愿行事。具有领导能力，容易获得成功，兼且能得到别人的信任。塔罗牌里的1：魔术师就象数字“1”代表“万物之始”的意义，这张牌象征着宇宙创造万物的力量，隐藏在起点的能量。牌面上画的“魔术师”代表：掌管精神面和物质面的三大力量——“出发、创造、发现”。诉说着从“无”到“有”的过程中，蕴藏着无限大的万能力量。

通信电子线路作业参考答案

第2章 2-3 已知串联谐振回路的谐振频率f 0＝30MHz ，电容C ＝80pF ，谐振阻抗R 0＝5Ω，试求：电感L 和回路品质因数Q 0。解：1、求L 根据公式：LC 10=ω得： H H C L μ≈????π=ω=-35.01080103041112 6220 2、求Q 0 根据公式：Q 0 = 1/(ω0CR 0) =ω0L/R 0得： Q 0==1/(ω0CR 0) =1/(2π×30×106×80×10-12×5)=1/(24π×10-3)≈ 13. 27 或：Q 0==ω0L/R 0 =(2π×30×106×0.35×10-6)/5≈ 13. 20 2-5 题图2-5是单调谐放大器的交流通路，当谐振频率等于10MHz 时，测得晶体管的Y 参数为：y re ＝0；y ie ＝2＋j0.5 (mS)； y fe ＝20＋j5 (mS)；y oe ＝20＋j40 (μS)。放大器的通频带为300kHz ，谐振电压增益为50，试求：电路元件C 、L 的参数值。题图2-5 解：已知P 1＝1，P 2＝1，f 0=10MHz ，B=2Δf 0.7=300 kHz ,500 =u A 根据∑-=g y p p A fe u 210 ,∑-=g y p p A fe u 210 得： mS A y g u fe 41.050520220 ≈+==∑ 根据Q f Q 2B 00=πω= 得：Q L = f 0/2Δf 0.7 =33.33 根据ω0C oe =40(μS)得：C oe =40×10-6/(2π×10×106)≈ 0.637pF ，根据ie 22oe 21C p C C p C ++=∑ 和C Σ = g ΣQ L /ω0得：C= C Σ-C oe ≈217.6－0.637 ≈217pF 根据LC 10= ω得：L ≈1.15μH 2-8 如题图2-8所示。已知C i ＝5pF ，R i ＝10k Ω，L ＝0.8μH ，C 1＝C 2＝20pF ，C L ＝20pF ，R L ＝5k Ω，空载品质因数Q 0＝100。试计算回路谐振频率、谐振阻抗（不计R i 、R L 时）、有载品质因数Q L 和通频带。 C L 题图2-8

通信电子线路题库,答案版

复习题一、选择题 1.二极管峰值包络检波器适用于哪种调幅波的解调（C）。 A 单边带调幅波 B 抑制载波双边带调幅波 C 普通调幅波 D 残留边带调幅波 2.欲提高功率放大器的效率，应使放大器的工作状态为（C）。 A 甲类 B 乙类 C 丙类 3.变容二极管调频器实现线性调频的条件是变容二极管的结电容变化指数n为（C）。 A 1/3 B 1/2 C 2 D 4 4.某超外差接收机的中频为465kHz，当接收550kHz的信号时，还收到1480kHz 的干扰信号，此干扰为（B）。 A 干扰哨声 B 镜像干扰 C 互调干扰 D 交调干扰 5.某单频调制的普通调幅波的最大振幅为10v，最小振幅为6v，则调幅系数m a为（C） A 0.6 B 0.4 C 0.25 D 0.1 6.以下几种混频器电路中，输出信号频谱最纯净的是（A） A 二极管混频器 B 三极管混频器 C 模拟乘法器混频器 7.某丙类谐振功率放大器工作在临界状态，若保持其它参数不变，将集电极直流电源电压增大，则放大器的工作状态将变为（C） A 过压 B 临界 C 欠压 8.鉴频的描述是（ B ） A 调幅信号的解调 B 调频信号的解调 C 调相信号的解调 9.下图所示框图能实现何种功能？ ( C ) 其中u s(t)= U s cosωs tcosΩt， u L(t)= U L cosωL t A 振幅调制 B 调幅波的解调 C 混频 D 鉴频 10.在超外差式调幅收音机中，混频器的输出谐振回路应调谐在什么频率上？( D ) A 载波频率f c B 本机振荡频率f L C f c + f L D f c - f L 11.图1所示的检波电路适于对哪种已调信号进行检波？ ( C ) A 抑制载波的双边带调幅波 B 单边带调幅波 C 普通调幅波 D 调相波 12.调频波的瞬时附加相位与什么成正比？ ( A ) A 调制信号的积分 B 调制信号的微分 C 调制信号的瞬时值 D 调制信号的频率 13.在谐振功率放大器中，为了提高谐波抑制能力，谐振回路的Qe值（A） A越大越好B越小越好C无关 14.为了实现丙类工作，基极偏置电压应设置在功率管的（B） A 放大区 B 截止区 C 饱和区 15.某调频波，其调制信号频率F＝1kHz，载波频率为10.7MHz，最大频偏Δf m＝10kHz，若调制信号的振幅不变，频率加倍，则此时调频波的频带宽度为（B） A 12kHz B 24kHz C 20kHz D 40kHz 16.双边带调制信号和单边带调制信号的载波被（C） A变频B搬移C抑制 17.双边带调制信号和单边带调制信号的包络是否反映调制信号的变化规律。（B） A反映B不反映C双边带调制信号反映 18.为提高振荡频率的稳定度，高频正弦波振荡器一般选用（ B ）

通信电子线路部分习题解答(严国萍版)

《通信电子线路》课程的部分习题答案第一章习题参考答案： 1-1： 1-3：解： 1-5：解：

第二章习题解答： 2-3, 解： 2-4，由一并联回路，其通频带B 过窄，在L 、C 不变的条件下，怎样能使B 增宽？答：减小Q 值或减小并联电阻 2-5，信号源及负载对谐振回路有何影响，应该如何减弱这种影响？答： 1、信号源内阻及负载对串联谐振回路的影响：通常把没有接入信号源内阻和负载电阻时回路本身的Q 值叫做无载Q （空载Q 值）如式通常把接有信号源内阻和负载电阻时回路的Q 值叫做有载QL,如式为空载时的品质因数为有载时的品质因数 Q Q Q Q L L <可见 o o Q R L Q ==ωL S L R R R L Q ++=0ω

结论：串联谐振回路通常适用于信号源内阻Rs 很小 (恒压源）和负载电阻RL 也不大的情况。 2、信号源内阻和负载电阻对并联谐振回路的影响 2-8，回路的插入损耗是怎样引起的，应该如何减小这一损耗？答：由于回路有谐振电阻R p 存在，它会消耗功率因此信号源送来的功率不能全部送给负载R L ，有一部分功率被回路电导g p 所消耗了。回路本身引起的损耗称为插入损耗，用K l 表示无损耗时的功率，若R p = ∞， g p = 0则为无损耗。有损耗时的功率插入损耗通常在电路中我们希望Q 0大即损耗小，其中由于回路本身的L g Q 0p 01 ω=，而 L g g g Q 0L p s L )(1ω++= 。 2-11, L p s p p p p p p p 11R R R R Q Q G C LG Q L ++===故ωω同相变化。与L S L R R Q 、性。较高而获得较好的选择以使也较大的情况,很大，负载电阻内阻并联谐振适用于信号源L L S Q R R ∴11P P K l '=率回路有损耗时的输出功率回路无损耗时的输出功L 2L s s L 201g g g I g V P ????? ??+==L 2p L s s L 211g g g g I g V P ????? ??++=='20L 1111????? ? ??-='=Q Q P P K l

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