聚羟基烷酸脂论文：两段式和三段式工艺制取聚羟基烷酸酯的试验研究

聚羟基烷酸脂论文：两段式和三段式工艺制取聚羟基烷酸酯的试验研究【中文摘要】聚羟基烷酸酯(PHA)是一类羟基脂肪酸的聚合物,当外界环境较恶劣时,部分微生物可以在体内以内碳源的形式贮存PHA。PHA具有生物相容性和可生物降解性,同时根据单体组分的不同还可以具有同石化塑料相类似的多种物理性质,可以代替现行的难降解塑料,以此可缓解环境固体废弃物污染。然而目前PHA商业化生产都采用纯菌发酵的方式,成本较高,阻碍了PHA的大规模应用。采用活性污泥混合菌群生产PHA可以采用廉价的有机废物为底物,有望大大降低PHA的生产成本。两段式PHA生产工艺包括有机废物厌氧酸化和PHA生产两步,后者在时间上分为污泥适应阶段和PHA积累阶段,适应阶段采用均衡营养比例而PHA积累阶段则限制进水中营养元素。本研究发现在PHA积累阶段一步减少进水中80%(相对于均衡比例)的氨氮,比逐步减少可以更有效的促进PHA积累;在每周期底物都可以消耗完毕的条件下,无论底物为乙酸钠还是污泥水解液,该阶段反应器厌氧-好氧运行与好氧运行得到的结果几乎没有区别;研究还发现适应期污泥龄较长时可以保证反应器长时间的稳定运行,而污泥龄较短时易引发污泥膨胀,污泥龄低于5天引发的污泥膨胀会使得污泥产PHA能力下降。以污泥水解液为底物时,其中VFAs可以得到的快速的吸收,PHA积累与其中氨氮水平有很大关系。三段式PHA生产工艺包括有机废物厌氧酸化、菌群富集和PHA积累,其中菌群富集是最重要的一步。本研究以乙酸钠为底物考察以SBR富集产PHA菌群时,发现反应器易于发生污泥膨胀。在污泥龄为1天、底物负荷较高(6.6gCOD/L/d)时,反应器膨胀非常严重,大量泡沫产生,污泥很快丧失了产PHA能力;而污泥龄为10天、负荷较低(2.7gCOD/L/d)条件下得到的膨胀污泥则具有较高的PHA合成能力,好氧SBR运行102天时污泥积累PHA最大含量达到了53%,PHA平均积累速率为0.19mgCOD/mgX/h,PHA产率为0.76mgCOD/mgCOD,而与此SBR同步运行的厌氧-好氧SBR则运行55天左右后突然崩溃,污泥浓度甚至不足500mg/L。以蔗糖模拟糖蜜废水经厌氧酸化用于PHA合成时,产酸反应器启动运行1个月后逐渐稳定为乙醇型发酵,此时出水经中空纤维膜过滤后用于SBR富集产PHA混合菌群和PHA积累,实现了生物制氢与PHA合成系统的耦合。SBR运行负荷为4.2-4.5gCOD/L/d,污泥龄为10天,启动运行1个月内污泥浓度从3300mg/L增大到8000mg/L以上,尽管底物充盈时溶解氧控制于3.0mg/L左右,然而30天时SBR依然发生了污泥膨胀,这可能是污泥浓度过大导致的。对比发现,膨胀后的污泥在底物吸收、PHA合成以及生长方面比非膨胀污泥快了1倍左右。本实验在SBR运行25天时,系统每消耗1kgCOD的蔗糖,约生产16L氢气和0.1kgCOD的PHA,其中单体HV质量比约占24%左右。【英文摘要】Polyhydroxyalkanoates(PHAs)areaclassofpolymers,whichcanbeaccumulatedasinternalcarbonsourcesbypartmicroorganismsunderadversecircumstances.PHAsarebiocompatibleandbiodegradableandcanalsopossessthesimilarpropertieswiththepetromadeplastics,whichenablesthemtosubstitutethecurrentplasticstoreducesolidwastes.However,PHAsinmarketareallcommerciallyproducedbypurecultures,whichbringabouthighcostsandhamperedtheirlarge-scaleapplication.PHAproductionbymixedmicrobialculturescanbecompletedinopenreactorsandfuturemore,morecheaporganicwastescanbeused.Thiswouldmakecostreductionpossible.Two-stagePHAproductionprocessincludesacidogenicfermentationoforganicwastesandPHAproduction,andthelatteriscomposedbysludgeacclimationandPHAaccumulation.Insludgeacclimation,nutrientsarebalancedwhileinPHAaccumulation,nutrientsareunbalanced.Inthisstudy,resultsshowedthatdirectlimitationofammoniaby80%(comparedwithbalancelevel)ininfluentcouldbetterstimulatePHAaccumulationthangraduallimitation.Whentherewasnosubstrateleftineverycycle,littledifferencewasobservedinPHAaccumulationbetweenanaerobic-aerobicandaerobicoperationwithsubstrateasacetateorsludgealkalinefermentationliquids.Itcanalsobedrawnthatlongsludgeretentiontimewouldguaranteelongtermstabilityofthereactor,whilelowsludgeretentiontimewouldbringaboutsludgebulking.Especially,whensludgeretentiontimewaslowerthan5days,thePHAstoragecapacitywouldbedamaged.VFAscouldbeuptakenrapidlyandthePHAaccumulationdependedhighlyonthelevelofammoniawhenthesubstratewassludgealkalinefermentationliquids.Three-stagePHAproductionprocessincludesacidogenicfermentationoforganicwastes,cultureselectionandPHAaccumulation,andstageofcultureselectionisthemostimportant.ItwasobservedthatbulkingsludgewaseasilyestablishedwhenselectingculturesinSBRwithactateassubstrate.UnderSRTof1dandhighorganicloadingrate(6.6gCOD/L/d),thebulkingwasmoreseverewithagreatdealoffoamandpoorPHAstorageability.While,underSRTof10dandloworganicloadingrate(2.7gCOD/L/d),bulkingsludgepossessedhighPHAstoragecapacity.After102days’operation,sludgefromSBRcouldaccumulatePHAto53%ofTSS,underammoniastarvation,withaveragestoragerateof0.19mgCOD/mgX/handyieldof0.76mgCOD/mgCOD.However,anotherSBRoperatedinparallelwithanaerobic-aecobicpatternsuddenlyfailedafter55days’operation.Whenusingcanesugartosimulatemolassessasthesubstrate,afteranaerobicfermented,forPHAproduction,theCSTRgraduallystablizedtowardsethonal-typefermantationonemonthafterstartup.TheeffluentwasclarifiedwithhollowfibermembraneandthenwasusedforcultureselectionandPHAaccumulation,thuscouplingbio-hydrogenproductionwithPHAproductionsystemwasachieved.TheTSSinSBRriseduptomorethan8000mg/Lfrom3300mg/Lwithorganicloadingrateof4.2-4.5gCOD/L/dandSRTof10d.AlthoughDOwasmaintainedabove3mg/Linfeastphase,sludgebulkingstillhappenedafter30days’operation.Thismaybecausedbyhighsludgeconcentration.Bulkingsludgeexhibitedhigherratesinsubstrateuptake,PHAstorageandbiomassproliferationthanwell-settlingsludge,about2timesthanthelatter.WhenSBRrun25daysafterinoculation,thewholesystemcouldproduce16LH2and0.1kgCODPHAusing1kgCODcanesugar.TheHVweightproportionofPHAwas24%approximately.【关键词】聚羟基烷酸脂混合菌群污泥膨胀生物制氢PHA合成【英文关键词】polyhydroxyalkanoatesmixedmicrobialculturesludgebulkingbio-hydrogenproductionPHAsynthesis【目录】两段式和三段式工艺制取聚羟基烷酸酯的试验研究摘要4-6Abstract6-7第1章绪论11-311.1课题背景11-121.1.1课题来源111.1.2课题研究目的和意义11-121.2PHA概述12-191.2.1PHA结构与性质12-141.2.2细胞储存PHA的微生物学意义14-151.2.3微生物合成PHA的代谢机制15-181.2.4PHA的提取回收18-191.3混合菌群合成PHA国内外研究现状19-291.3.1底物选择19-201.3.2工艺流程20-221.3.3工艺运行策略22-251.3.4影响因素25-291.4主要研究内容29-31第2章实验材料与方法31-362.1实验装置及运行工况31-332.1.1实验装置31-322.1.2主要设备仪器32-332.2检测方法33-362.2.1PHA的检测332.2.2乙醇-VFAs的检测33-342.2.3气体成分检测342.2.4其他常规指标的测定与分析方法34-36第3章两段式PHA制取工艺优化36-493.1氨氮限制方式对PHA积累的影响36-393.1.1实验工艺控制36-373.1.2污泥性状的变迁37-383.1.3限制进水氨氮下PHA的循环积累38-393.2PHA积累期厌氧-好氧与好氧运