Reactor Configuration on the Nitrifier Community and Kinetics of Activated Sludge Process

Both a nitrifying sequencing batch reactor (SBR) and a completely stirred tank reactor (CSTR) were operated under aerobic conditions. Microbial populations of both reactors were examined via fluorescent in situ hybridization (FISH) and kinetic properties such as ammonium/nitrite utilization rate and half-saturation constants (K-S) were investigated. In the SBR, dominant ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were rapid growth r-strategists (Nitrosomonas europaea and Nitrobacter). However, in the CSTR, the dominant AOB and NOB were slow growth K-strategists (Nitrosospira and Nitrospira). The half-saturation constants of AOB and NOB were 3.01 +/- 0.97 and 4.22 +/- 0.64 mg/L, respectively, for the SBR and 0.43 +/- 0.19 and 2.15 +/- 0.64 mg/L, respectively, for the CSTR. The nitrification rate of the SBR was 63% higher than that in the CSTR. The reactor configuration shows an evident selectivity for K/r-strategists. Thus, the difference in nitrification rates between the SBR and CSTR are likely caused by the combination of chemical reaction engineering kinetics and nitrifier communities.