| With the rapid development of economy and population explosion,thephenomenon of eutrophication is increasingly serious in China in recent years, and thebasic reson is excessemission of nitrogen and phosphorus.There has been3515municipal wastewater treatment plants in China by the end of2013.The totaltreatment capacity reached149million cubic metre per day. And more than90percentof these plants adopt activated sludge process.However, the process appears somebottlenecks including low operation stability and low efficiency of nitrogen andphosphorus removal especially at low temperature.So it is urgent to develop a newremoval technology of nitrogen and phosphorous.Composite ferric enzymatic activated sludge process is aimed at enhancingmicrobial activity.It is used to strengthen the participation of ferric in electrontransport system and activationof ferric in enzyme catalyzed reaction by getting ferricinvolved in biochemical reaction including substance and energy metabolism.It couldalso optimize activated sludge flocculate structure to improve the ability of microbialresistance to the change of external environment.It has solved many questions thatbiological nutrient removal exists.This study was to uncover the reason why composite ferric enzymatic activatedsludge could enhance biological removal of nitrogen by analyzing the nitrifyingbacteria in the system.The study was mainly divided into three parts.The first part wasto research the proportion of AOB and NOB in the composite ferric enzymaticactivated sludge system and its diversity of community structureat low temperature byReal-Time PCR and RFLP.The second part was to study the effect of ferric on thegrowth and functional gene expression of AOB and NOB at different temperature byMicrobiology Reader Bioscreen C and Real-Time PCR.The third part was to analyzethe effect of ferric on maximum specific growth rate of AOB and NOB at differenttemperature. The results proved:(1)Composite ferric enzymatic activated sludge system could improve theproportion of nitrifying bacteria,which was the direct reason why it had highernitrification performance.Treating synthetic wastewater and real domestic wastewater,the proportion of AOB in the composite ferric enzymatic activated sludge was2.544%and0.281%respectively, while it was only1.678%and0.173%inconventional activated sludge.Treating synthetic wastewater,the dominant bacteria ofNOB was Nitrospira,and the proportion of it was2.834%in composite ferricenzymatic activated sludge,while it was only1.693%in conventional activatedsludge.Treating real domestic wastewater,the dominant bacteria of NOB wasNitrobacter,and the proportion of it was1.968%in the composite ferric enzymaticactivated sludge,while it was only1.414%in conventional activated sludge.(2)Treating synthetic wastewater, the richness index of AOB clone library in theconventional activatedsludge systemand in the composite ferric enzymatic activatedsludge system was1.55and1.03respectively, and the richness index of the clonelibrary of Nitrobacter which was the dominant bacteria of NOB was3.62and3.10respectively.Treating real domestic wastewater, the richness index of AOB clonelibrary in the composite ferric enzymatic activated sludge systemand in theconventional activated sludge systemwas2.84and2.58,and the richness index of theclone library of Nitrospira which was the dominant bacteria of NOB was2.07and0.77respectivelyat.That may be the reason why the composite ferric enzymaticactivated sludg had higher nitrification performance from the point of the diversity ofnitrifying bacteria.(3)The community structure of AOB was changed in the compositeferricenzymatic activated sludge system.Treating synthetic wastewater and real domesticwastewater,the proportion of the bacteria which was represented by OTU A-1and hada higherability of ammoxidation was increased from39.58%to67.67%and from39.58%to60.42%respectively,and the proportion of the bacteria which was represented by OTU A-2and had a poorer ability of ammoxidation was decreasedfrom45.85%to22.92%and from20.83%to8.33%respectively.In addition,treatingsynthetic wastewater and domestic wastewater,four and eight speciesrepresented byOTUs were appearedmerely in the composite ferric enzymatic activated sludgesystem respectively,and twoand seven species were appreared merely in theconventional activated sluge system respectively.(4)The community structure of NOB was changed in the composite ferricenzymatic activated sludge system.Treating synthetic wastewater,the proportion of thebacteria which was represented by OTU L-1and was the dominant bacteria ofNitrospira which was the dominant bacteria of NOB was increased from39.58%to58.33%.In addition,ten species represented by OTUs were appeared merely in thecomposite ferric enzymatic activated sludge system,and eight species were appearedmerely in the conventional activated sludge system.Treating real domesticwastewater,the proportion of the bacteria which was represented by OTUG-1and wasthe dominant bacteria of Nitrobacter which was the dominant bacteria of NOB wasincreased from48.94%to68.90%.In addition,five species represented by OTUs wereappeared merely in the composite ferric enzymatic activated sludge system.(5)Ferric could promote the growth of AOB and NOB.The more the content offerric was in the medium, the high the growth rate of the bacteria was within therestriction of100mg/L.(6)Ferric could promote the nitrification of AOB and NOB, especially at lowtemperature.The specific nitrification rate of AOB and NOB was increased by38.7%、118.5%、174.5%、186.4%and64.4%,152.6%,160.1%,181.1%respectively in thecomposite ferric enzymatic activated sludge system than that in the conventionalactivated sludge system.(7)Ferric could promote the functional gene expression of AOB andNOB,especially at low temperature.The relative amoA mRNA expression of AOB inthe medium with ferric than that without ferric was1.647,1.765,1.803,2.014at the temperature of21℃,18℃,15℃,12℃respectively.The relative NxrA mRNAexpression of NOB in the medium with ferric than that without ferric was2.014,2.676,2.732,2.868at the temperature of21℃,18℃,15℃,12℃respectively.(8)Ferric could promote the maximum specific growth rate of AOB and NOB,especially at low temperature.The maximum specific growth rate of AOB in themedium with ferric and without ferric was0.956d-1、0.729d-1、0.555d-1、0.406d-1、0.284d-1and0.828d-1、0.626d-1、0.440d-1、0.333d-1、0.180d-1respectively at thetemperature of26℃,21℃,18℃,15℃,12℃.The maximum specific growth rate ofNOB in the medium with ferric and without ferricwas1.540d-1,0.835d-1,708d-1,0.498d-1,0.411d-1and1.392d-1,0.751d-1,0.576d-1,0.415d-1,0.348d-1respectively at the temperature of30℃,21℃,18℃,15℃,12℃. |
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