A Study On Nutrients Removal And Microbial Community Structure In Biofilm Reactors For Wastewater Treatment

In this paper, nutrients removal characteristics and microbial community structure in biofilm reactors were studied under different C/N/P (50/6.25/1,75/6.25/1and100/6.25/1) by routine water quality testing methods and molecular biology technique. The results sure the contribution of biofilm and suspended sludge to nitrogen and phosphorus removal in HBR; reveal C/N/P effect on the removal efficiencies of nutrients and analyze the changes of microbial communities in sequencing batch reactor (SBR), hybrid biofilm reactor (HBR) and sequencing batch biofilm reactor (SBBR), respectively.The influence of inoculated activated sludge amount on start-up of HBR was studied in four parallel reactors, Nv was0.8kgCODCr/(m3·d). The results showed that vaccinated moderate activated-sludge can shortcut set-up time and improved the activity of microbial in biofilm. The moderate activated sludge reactor (3#reactor) achived highest removal efficiency of CODCr and NH3-N up to93%and100%, respectively. The microbial activity namely the specific oxygen utilization rate of biofilm in3#reactor was58mgO2/(gMLSS·d), which was highest.The removal efficiencies of nitrogen and phosphorus in SBR, HBR and SBBR were tested under different C/N/P. The results indicated that HBR performed well on nitrogen and phosphorus removal. When C/N/P was100/6.25/1, HBR achived highest removal efficiency of NH3-N, TN and TP reach to96%,92%and94%, respectively. Sufficient organic carbon is a necessary condition for simultaneous nitrification and denitrification. In HBR system, suspended-sludge plays an important role in nitrification and biofilm in denitrification and phosphorus removal.The biofilm structure in SBBR and HBR was similar, which was mainly composed of extracellar polymeric substances (EPS), cell clusters, holes and channels. The biofilm structure was gradually dense, the holes and channels became more and small with C/N/P increased from50/6.25/1to100/6.25/1. The flora form of biofilm in HBR and SBBR was similar, which was mainly composed of cocci and bacilli, but more filamentous bacteria were presented in HBR biofilm than in SBBR, the size of cocci and bacilli in HBR biofilm were larger than in SBBR.The results of fluorescence in situ hybridization (FISH) showed that many phosphate-accumulating bacterias (PAO), ammonia-oxidizing bacterias (AOB) and nitrifying-oxidizing bacterias (NOB) existed on the surface of biofilm. The percentage of AOB was more than NOB. In HBR system, the presense of suspended micro-organisms, easier to intake corbon in wastewater, weakened the competitive relationship between glycogen-accumlating bacterias (GAO) and PAO in biofilm. Therefore, PAO were the dominant bacteria in HBR and GAO were the dominant bacteria in SBBR when C/N/P increased to100/6.25/1.The similarity and diversity of microbial community in biofilm were analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that microbial communities of biofilm were changed obvious with C/N/P increased from50/6.25/1to100/6.25/1in HBR and SBBR. However, C/N/P effect on the diversity of microbial communities in HBR was less than SBBR; it indicated that HBR has a strong adaptability to changes of external environment.