A new ecosystem model was developed to predict the effects of pH variation on the microbial community in freshwater lakes by using the features of three existing models: an ecosystem model, a pH simulation model, and a cardinal temperature and pH model. Data for validation were obtained by conducting the following experiment. Circumneutral lake water, collected from Lake Inawashiro in Fukushima Prefecture, Japan, was mixed with acidic river water to prepare water samples with three pH values: 6.5, 5.5, and 4.5. Transparent acrylic tanks were filled with prepared water and placed in a sunny place for 24 days, during which time pH and dissolved oxygen content were continuously measured. The biomass of phytoplankton, zooplankton, and bacteria was measured on the first and last day. Hourly calculated values of pH and DO were in excellent agreement with observed values in the tanks. The simulation of the change in biomass of alkaliphilous, circumneutral, and acidophilous phytoplankton species for three different levels of pH over the course of 24 days also agreed with observations. The examination of fundamental model response also showed that the new ecosystem model is applicable to actual lake environments, where acidification or alkalization in pH is observed, by continuously changing the total alkalinity and incorporating sediment respiration.

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Bacterial communities of activated sludge were analyzed monthly for one year by using FISH method with 33 kinds of genus specific probes. These obtained FISH data were also analyzed with cluster analysis. Activated sludge were taken from 9 trains in 5 sewage treatment plants in Japan. These were classified into following 5 treatment processes; Conventional activated sludge process, Oxidation Ditch process, Pre-Denitrification process, Anaerobic-Anoxic-Oxic process and Modified Bardenpho process. As the results, following things were found. When the bacterial communities were compared with 9 trains, it was suggested that these were different from each other. The occupation ratios of genus Nitrospira and genus Ethanoligenens were observed as the highest group in many trains. In the same sewage treatment plant, it was suggested that the bacterial communities obtained from different treatment trains were similar to each other. In all of 4 treatment processes of K plant, the occupation ratio of phylum proteobacteria and nitrogen removal bacteria were higher than other kinds of bacteria. In conventional process and oxidation ditch process, the occupation ratio of phylum Bacteroidetes were higher than other bacterial groups. In Pre-Denitrification process, A2O process and Modified Bardenpho process, the occupation ratio of phylum Proteobacteria were higher than other bacterial groups.According to comparison of classification of treatment processes, it was suggested that a high / low of phosphate removing bacteria affected on the bacterial communities.In these results, it was indicated that the possibility that bacterial community can be used as an index of activated sludge.

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The single-stage nitrogen removal by anammox and partial nitritation (SNAP) process was evaluated for tolerances to fluctuations in pH (5.6 to 8.9), temperature (15 to 35 ℃), and dissolved oxygen (DO) concentration (2 to 5 mg/l) using large-scale (80－l) reactors. The nitrogen removal rate (NRR) increased with increases in DO concentrations up to 5 mg/l, indicating oxygen supply enhanced the specific activity of the ammonia-oxidizing bacteria (AOB) without inhibiting the anammox activity. Additionally, the NRR was stable at pH levels of 6.1 to 8.6; however, the NRR decreased at pH 5.6 with the occurrence of NH₄⁺－N accumulation due to a decrease in AOB activity, but was then quickly restored after adjusting the reactor pH to 7.5. Furthermore, the NRR decreased at pH levels over 8.9, as evidenced by increases in effluent NH₄⁺－N and NO₂^－－N concentrations; in this case, though, a long time was required to recover from this deleterious effect of pH on the core anammox activity. Finally, a high NRR could be maintained over a temperature range of 15 to 35 ℃, indicating the feasibility of the SNAP process over a substantial range of environmental conditions.

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