Effects of environmental conditions on the performance of nitrogen removal activated sludge systems

The aim of this paper was to evaluate whether reduced biomass production occurs when denitrification is incorporated into conventional activated sludge (AS) treatment systems. Furthermore, the effects of environmental conditions such as predation and temperatures on biomass production were examined. An additional goal of the research was to assess nitrification kinetics when denitrification is incorporated into conventional nitrifying AS treatment systems, including the effect of predation.; Nine sequencing batch reactors (SBRs) were used in parallel in order to investigate the effect of temperature and the incorporation of denitrification process on biomass production.; Based on the data obtained, it was concluded that incorporating denitrification into a conventional AS treatment system would not reduce biomass production. As to the effect of temperature on biomass production, none of the data sets showed a continuous trend of increasing or decreasing biomass production with decreasing range of temperature.; Nitrification rates in alternating SBRs were much greater than those in the aerobic reactors regardless of the presence of predation. It was concluded that predation does not have a significant impact on maximum nitrification rates and the decay rates of nitrifying bacteria. Alternating anoxic/aerobic conditions were found to impact both maximum nitrification rates and autotrophic decay, producing higher nitrification rates.; Based on the findings two theories were proposed to explain the mechanism responsible for higher nitrification rates under mixed oxidation-reduction potential (ORP) conditions. To evaluate the first theory, Fluorescence In Situ Hybridization (FISH) with rRNA-targeted oligonucleotide probes was used for the in situ identification and quantification of the nitrifier populations in aerobic and alternating anoxic/aerobic SBRs at 12 and 20°C. For the second theory, the Western blot immunochemical analysis method was used in order to compare the amount of the heat shock protein GroEL produced during aerobic and alternating anoxic/aerobic conditions. Quantification of nitrifiers using rRNA targeted oligonucleotide probes revealed that there were no significant differences in the nitrifier populations of aerobic and alternating anoxic/aerobic reactors, suggesting the hypothesis that alternating ORP conditions result in a change in nitrifier species to be rejected. Examination of GroEL in aerobic and alternating reactors led to the conclusion that alternating reactors have a more stressful environment than aerobic reactors, lending credence to the hypothesis that differences in nitrification rates are the result of the feast/famine relationship in the alternating system. (Abstract shortened by UMI.)...