太空生存太空生存太空生存 (7).pdf

《太空生存太空生存太空生存 (7).pdf》由会员分享，可在线阅读，更多相关《太空生存太空生存太空生存 (7).pdf（11页珍藏版）》请在得力文库 - 分享文档赚钱的网站上搜索。

1、Electricity generation directly using human feces wastewater for lifesupport systemDu Fangzhou,Li Zhenglong,Yang Shaoqiang,Xie Beizhen,Liu Hong?Laboratory of Environmental Biology and Life Support Technology,School of Biological Science and Medical Engineering,Beihang University,Beijing 100191,China

2、a r t i c l e i n f oArticle history:Received 30 July 2009Received in revised form15 December 2009Accepted 18 December 2009Available online 18 February 2010Keywords:Microbial fuel cell(MFC)Life support systemHuman feces wastewaterElectricity generation capacityWastewater treatmenta b s t r a c tWast

3、ewaterreuseandpowerregenerationarekeyissuesintheresearchofbioregeneration life support system(BLSS).Microbial fuel cell(MFC)can generateelectricity during the process of wastewater treatment,which might be promising tosolve the two problems simultaneously.We used human feces wastewater containingabu

4、ndant organic compounds as the substrate of MFC to generate electricity,and thefactors concerning electricity generation capacity were investigated.The removalefficiency of total chemical oxygen demand(TCOD),Soluble chemical oxygen demand(SCOD)and NH4reached 71%,88%and 44%,respectively with two-cham

5、ber MFC whenit was fed with the actual human feces wastewater and operated for 190h.And themaximum power density reached 70.8mW/m2,which implicated that MFC technologywas feasible and appropriate for treating human feces wastewater.In order to improvethe power generation of MFC further,human feces w

6、astewater were fermented beforepoured into MFC,and the result showed that fermentation pretreatment could improvethe MFC output obviously.The maximum power density of MFC fed with pretreatedhuman feces wastewater was 22mW/m2,which was 47%higher than that of the controlwithout pretreatment(15mW/m2).F

7、urthermore,the structure of MFC was studied andit was found that both enlarging the area of electrodes and shortening the distancebetween electrodes could increase the electricity generation capacity.Finally,anautomatic system,controlled by time switches and electromagnetic valves,wasestablishedtopr

8、ocessonepersonsfeceswastewater(1L/d)whilegeneratingelectricity.The main parts of this system comprised a pretreatment device and 3 one-chamber air-cathode MFCs.The total power could reach 787.1mW and power densitycould reach the maximum of about 240mW/m2.&2010 Elsevier Ltd.All rights reserved.1.Intr

9、oductionIn manned space activity,the life support system playsan important role to allow astronauts to survive in outerspace.Water reuse and power supply are critical tech-nologies of the system.There are many water resourceswhich can be recovered and reused in manned spaceactivity,such as human fec

10、es wastewater,urine,gray waterand so on.These kinds of wastewater can be purified by thewater cycle regeneration system and then reused as potablewater or domestic water 1.Although the treatmenttechnology of human feces wastewater and urine has madea certain achievement,the process is complicated,no

11、tstable and with high energy consumption.Microbial fuel cell(MFC)is an emerging technology inthe field of environmental protection and power genera-tion.It makes use of microbial metabolization underanaerobic condition to convert the chemical energyContents lists available at ScienceDirectjournal ho

12、mepage: Astronautica0094-5765/$-see front matter&2010 Elsevier Ltd.All rights reserved.doi:10.1016/j.actaastro.2009.12.013?Corresponding author.Tel./fax:+861082339837.E-mail address:LH(H.Liu).Acta Astronautica 68(2011)15371547contained in the organics to electricity,so that waste-water disposal and

13、power generation take place simulta-neously in normal condition.Theoretically,almost allthe substrates that can be metabolized by microorgan-isms are able to act as the fuel of MFC 2,such assimple molecules,urban sewage,food industry waste-water and so on.Moreover,it has been reported thatswine wast

14、ewater can feed MFC 3.Therefore,MFC hasspecial features and advantages suitable for life supportsystem.Human feces wastewater contains abundant organics4,which can be degraded to small organic moleculesapplicable for MFC.Disposing human feces via MFC canpurify water quality and recover the power in

15、them at thesame time.This will be a great of help for power andwater supply in life support system.In this paper,wefocused on the feasibility and improvement of MFC fed byhuman feces,and then we constructed an automatichuman feces MFC system to recover energy and disposethe feces produced by one ast

16、ronaut in one day.2.Materials and methods2.1.Activated sludgeThe inoculating sludge was obtained from the anaero-bic digester of sewage treatment plant,and its MLSS andMLVSS were 27g/L and 14g/L,respectively.The pH valuewas around 7.2.2.Experimental wastewater and culture mediumThe glucose culture m

17、edium,mineral solution andvitamin solution were prepared as Liu and Lovley hadreported 5,6.Phosphate buffer contained 4.22g/L NaH2PO4?2H2Oand 2.75g/L Na2HPO4?12H2O.Human feces wastewater were obtained from theseptic tank.Firstly,we filtered the human feces waste-water to remove the insoluble matter,

18、and then dilutedthe solution according to the requirement of experiment.Artificial human feces wastewater was composed of8g starch,2.5g casein,5g oleic acid,4.97g NaH2-PO4?2H2O,2.75g Na2HPO4?12H2O,0.31g NH4Cl,0.13gKCl,per liter 7.Add 12.5mL mineral solution andvitamin solution per liter.2.3.MFCs2.3.

19、1.Two-chamber MFCAs shown in Fig.1,carbon paper(6cm?8cm)servedas the anode,and carbon paper(4cm?5cm)with 40%platinum served as the cathode.The volume of anode andcathode chamber were 1L each(10cm?10cm?10cm),and they were separated by PEM(6cm?6cm,Nafion117).During the experiment,the cathode-chamber w

20、asaerated by air to keep dissolved oxygen(DO)at a highlevel.2.3.2.One-chamber MFC with two membrane electrodeassemblies(MEAs)The membrane electrode assembly(MEA)is a kind ofelectrode,whose anode,PEM and cathode are pressedtogetherto makethedistance between anodeandcathode as small as possible.Two ME

21、As covered bothsides of the anode-chamber and acted as electrodes in theone-chamber MFC(Fig.2).And baffle plates were fixes inthe chamber to make the mass in the chamber mix fullyduring the continuous-flow operation.The details of thisMFC were described in Table 1.2.3.3.One-chamber MFC with one MEAI

22、t was described in Table 1 and Fig.3.2.3.4.Adjustable two-chamber MFCTwo column chambers with actual volume of 628mLwere separated by PEM(4.9cm2).The length of the bridgeconnecting them was adjustable so that the distancebetween anode and cathode could vary from 4 to 24cm.Carbon paper with 40%platin

23、um served as the cathode(4cm?5cm)and carbon paper served as the anode(9cm?6cm)(Fig.4).2.4.Fermentation pretreatment deviceThe column reactor was made of PMMA,and its actualvolume was 2.5L.There was a blender system for stirring(Fig.5).Fig.1.Two-chamber MFC schematic diagram.Fig.2.One-chamber MFC wit

24、h two MEAs(1-Fender;2-MEA).F.Du et al./Acta Astronautica 68(2011)1537154715382.5.Experimental2.5.1.Feasibility of human feces MFCA two-chamber MFC was inoculated with anaerobicsludge(terminal concentration was 5g/L),the anode andcathode chamber were filled with glucose culture med-ium and phosphate

25、buffer,respectively,during the startupphase.The data acquisition system(Personal Measure-ment Device,PMD-1608FS,USB-1608FS,US)was used totest the output voltage of the MFC every one minute andrecord those data.We operated the MFC in batch modeandrefreshedtheanolyteaftertheoutputvoltagedecreased obvi

26、ously.After the MFC worked steadily,10fold diluted human feces wastewater took the place of theglucose culture medium in the anode chamber.The waterquality and pH were tested during the MFC was running.The batch mode was also chosen in this phase and thepolarization curve of the MFC was determined w

27、hen theMFC came to a stable performance.2.5.2.Startup of other kinds of MFCsAll MFCs,including one-chamber MFC with one or twoMEAs and adjustable two-chamber MFC,were started upin the same way as just mentioned above.2.5.3.Fermentation pretreatmentA cylindrical reactor as shown in Fig.5 was designed

28、for the fermentation pretreatment of artificial humanfeces wastewater.Anaerobic sludge was the inocula andits terminal concentration was maintained at 5g/L.Theartificial human feces wastewater were treated in thisTable 1Structure and running parameters of MFC.One-chamberMFC withtwo MEAsOne-chamberMF

29、C withone MEAActual volume(mL)1500425Total electrode area(cm2)32025Surface-to-volume ratios ofanode(m2/m3)21.35.6CathodeCarbon paper with 40%platinumMembranePEM(Nafion 117),320cm2PEM(Nafion117),25cm2Fig.3.One-chamber MFC with one MEA.Data Acquisition System pH&Temperature Detecor Cathode AnodePEMRes

30、istorFig.4.Adjustable two-chamber MFC.Fig.5.Fermentation pretreatment device 8.(1outlet,2samplingPort,3blender,4inlet)F.Du et al./Acta Astronautica 68(2011)153715471539reactor and then injected into the experimental MFC.Thebest HRT of pretreatment was determined according tothe change of pH value in

31、 the device.Two adjustable two-chamber MFCs(the electrodedistancewasfixedat4cm),respectively,actedasexperimental and control MFC in this part.The pretreatedartificial human feces wastewater served as the experi-mental anolyte and artificial human feces wastewaterwithout pretreatment served as the co

32、ntrol anolyte.Allthe other parameters of the two MFCs were same.Theoutput voltage,internal resistance and polarization curveof the MFCs were monitored.2.5.4.Factors influencing MFC output(1)Electrode area:One-chamber MFCs with one or twoMEAs,whose electrode areas were different,were oper-ated in the

33、 same condition to investigate the effect ofelectrode area on electricity generation capacity.(2)Distance between electrodes:The adjustable two-chamber MFC was employed in this part.The performanceand internal resistance of MFC with different electrodedistance were tested.2.5.5.Automatic human feces

34、 wastewater MFC systemBased on the above research,an automatic humanfeces wastewater MFC system was designed and con-structed for the purpose of disposing feces produced byone person one day(1L)and generating electricitysimultaneously.The whole system was composed offermentation pretreatment device,

35、MFC stack with threeair-cathode MFCs,time switches,flow controllers andperistaltic pumps.We tested the output voltage,polariza-tion curve and internal resistance of the MFCs to estimatethe performance of the system.2.6.Analysis and calculationThe concentration of NH4,F?and SO2?4was measuredby Ion Ch

36、romatography(792 Basic IC,Metrohm).Andwe also use salicylate-hypochlorous acid method forNH4+N measurement to approve the result of the ionchromatography.Coulombic efficiency Ecwas calculated by formula(1).EcCpCTi?100%1In formula(1),Cpand CTi(coulomb)represented actualand theoretical electric quanti

37、ty,respectively.Cpwasworked out by integrating the total current over timeaccording to formula(2).CpZtitoUiRdt2And CTiwas calculated from formula(3),where F(C/molelectron)is the Faraday constant.CTiFbiSiVMi3biis the theoretical mole number of electrons generatedby one molar substrate(biof glucose is

38、 24 and biofwastewater is 4).Si(g/L)is the substrate concentration.V(L)is the volume of reaction system.Mi(g/mol)is themolar mass of substrate,which is 32g/mol when waste-water acts as the substrate 9,10.3.Results and discussion3.1.The feasibility of human feces MFCThe steady performance of MFC with

39、 glucose indicatedthat the anode biofilm had formed successfully.Then weused human feces wastewater to take the place of glucoseculture medium.And the output voltages with 1000Oexternal resistance was tested(Fig.6a).The peak outputvoltage could reach 548mV.And a single electricitygeneration cycle co

40、uld be divided into 3 phases:risingphase,stable phase and decline phase,which was similarto many other kinds of MFCs 11.Different external resistances were connected into theMFC circuit and the polarization curve was tested(Fig.6b).When the current density came to 208.6mA/m2(300Oexternal resistance)

41、,the power density reached the highestpoint,70.8mW/m2,which meant the internal resistance ofMFC was about 300O.The wastewater purification efficiency of the two-chamber MFC with human feces wastewater is shown inFig.7a.After 190h operation,the removal efficiency ofTCOD was 71%.This low COD removal r

42、ate may be dueto the complex human feces wastewater composition,ofwhichthecellulose,fat,proteinandothermacromolecules are the dominant parts.They cannot bemetabolized easily by the microorganisms in the anode-chamber.The concentration of different ions which are consid-ered as pollutant changed much

43、 more complexly(Fig.7b).The removal efficiency of NH4N was 44%,from 51.8 to28.9mg/L.F?concentration decreased from 49 to 8mg/L,corresponding 84%removal.After the treatment of MFC,the F content of the human feces wastewater had met theintegrated wastewater discharge standard of China.Themicrobes in t

44、he anode chamber could make use of thoseions by the way of absorbing the ions to their bodies andconverting the ions to insoluble forms to fix them in thecells.This might be the mechanism of the removal ofthese pollutant ions.In a single cycle,the pH in anode-chamber decreasedat first and then went

45、back.H+was consumed by O2toform water in the cathode-chamber,which drove H+tomove from anode-chamber to cathode-chamber to keepelectroneutrality.However,othercationscouldpassthrough the PEM,too.And the speed of H+transfer waslower than other cations such as K+,Na+and so on sincethe concentration of

46、H+was lower than them.Thisprocess made the H+accumulate in the anode-chamber12.In addition,at the beginning of MFC operation manyorganics was degraded to acids,and the speed of theconsumption of them was not as high as they wereproduced,causing the pH value decreasing.While in alongtimeoperation,H+w

47、asfinallytransferredtocathode-chamber and the production speed became lowerso that the pH value increased.F.Du et al./Acta Astronautica 68(2011)153715471540Although the two-chamber MFC could generate powerfrom human feces wastewater,aeration to catholytewhich caused extra energy consumption was nece

48、ssaryto increase the dissolved oxygen in long time operationfor a stable output.Therefore,the one chamber air-cathode MFC is more promising,especially for space use.The different performances of one-chamber MFC withglucose culture medium(1124mg/L)and human feceswastewater(10-time diluted)are shown i

49、n Fig.8.Theoutputvoltagedeterioratedobviouslyafterhumanfeces wastewater substituted for glucosefrom 653 to341mV as the peak point.The maximum power densitydecreased from 133 to 8.5mV/m2and the internalresistance changed from 100 to 480O.In addition,thestable phases of each cycle with human feces was

50、tewatershrankalotcomparedtoglucose-fedMFC.Thisdepravation may be also due to the complex com-position of human feces wastewater.The change ofanolyte and biochemical reaction resistance resulted inthe alteration of internal resistance,and finally affectedthe performance of MFC.Whats more,the composit