Enrichment Of Anaerobic Ammonium Oxidizing-bacteria

Anerobic ammonium oxidation (ANAMMOX) is one of the most promising wastewater biological nitrogen removal methods. In this study, both MBR and SBR were applied to enrich and culture ANAMMOX bacteria. In enrichment process, we attempt to assess the nitrogen removal rate, detect ANAMMOX bacteria and the changes of microbial population communities, analyze key ecological factors for each reactors. By these analytical methods, we soundly compared the merits and demerites of both MBR and SBR on enrichment of ANAMMOX bcateria. In addition, different strategies were applied to start up the MBRs in order to find the way to speed up the start-up process.For the first time, anaerobic external MBR was applied to enrich and culture ANAMMOX bacteria, inoculated with activated sludge from a WWTP. Also we choose SBR to enrich and culture ANAMMOX bacteria from aerbic granular sludge. Beside the ordinary methods of water and wastewater measurement, molecular biology methods such as polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), 16S rDNA and fluorescence in situ hybridization (FISH) were used to study the changes of microbial population community and detect ANAMMOX bacteria. In addition, electronic pressure sense and scanning electron microscope (SEM) were used to messure the TMP changes and analyze membrane fouling of the MBRs.Results showed that both MBR and SBR were appropriate for ANAMMOX bacteria enrichment, but SBR is obviously better than MBR from the view of start-up efficiency and ANAMMOX bacteria content. After long time enrichment (8 months for MBR and 7 months for SBR), the ANAMMOX activity of MBR sludge was increased by 50%, and the ANAMMOX activity of SBR sludge was 12 times higher than that at start-up period. All the molecular biology methods proved the higher content and wider distribution of ANAMMOX bacteria in SBR, also the existence of Brocadia and Kuenenia in each reactor. Two identical MBR systems were applied with different start-up strategies: sludge wash-out strategy was applied to 2# MBR, also the liquid from above the settled sediment and biomass was drew off every day from day 1 to day 10, while nothing special strategy was applied to 1# MBR. Such start-up strategy did not benefit ANAMMOX bacteria enrichment, contrarily, 2# MBR expressed lower enrichment and nitrogen removal efficiency of 20%～25% than 1# MBR, and 1 time longer start-up period than 2# MBR. However, 2# MBR showed advantages on membrane fouling control: the fouling phenomenon of 1# MBR was severer than 2#, and the effective life-span of the 1# membrane was 1/3 shorter than that of 2# membrane. At last, we discuss the ecological impact factors of ANAMMOX bacteria: dissolved oxygen (DO), metal (Fe, Mg and Ca) and antibiotics (amoxicillin, chloramphenicol, and oxytetracycline). Low level of DO enhanced the nitrogen removal capacity (especially for nitrite removal) of the MBR. Fe, Mg and Ca accumulated in the MBR, and batch tests showed that the ANAMMOX activity decreased with the increase of iron concentration. Oxytetracycline showed obvious inhibition on ANAMMOX bacteria, and then is chloramphenicol. Amoxicillin almost had no inhibirory effect on ANAMMOX bacteria. Hence, chloramphenicol and amoxicillin could possibly be used to fast screen ANAMMOX bacteria from mixed cultures.