Extracellular polymer (ECP) formation and the effect on the surface charge of anaerobic sludge was investigated using each sludge which degraded glucose, propionate, butyrate, or acetate as a single organic substrate. The effect of ECP accumulation on surface charge of the sludges was also discussed in relation to sludge flocculation.
ECP contents in sludge were measured with time during each substrate degradation test using glass vials. The accumulation ratio of ECP-protein exceeded that of ECP-carbohydrate for all cases. The highest accumulation ratio was observed for the glucose degradation test. The calculation from COD balance on substrate revealed that several percents of the substrate utilized for growth was taken to form ECP. As more ECP was accumulated, the sludge surface was more negative in charge except the case of acetate. The increasing negative charge could be neutralized by added divalent cations such as calcium to promote floculation of anaerobic sludges.

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The effect of temperature on the characteristics of substrate degradation and bacterial population in a single and two phase anaerobic digestion was investigated using anaerobic chemostat-type reactor fed with soluble starch as a substrate. Three series of reactors were used for investigation. One of the reactors was a single phase anaerobic reactor and two other series were two phase reactors. Temperature was decreased from 30°C to 20°C over 8 hours and thereafter maintained at 20°C in a single phase reactor and two phase anaerobic reactors. In the other methanogenic phase reactor, temperature was maintained at 30°C as a control. The degradation efficiency of the substrate decreased by about 4% after 5 days in a single phase anaerobic digester, about 20% after 7 days in the acidogenic reactor of two phase anaerobic digestion, but no significant impact was observed in methanogenesis. Steady state condition in a single phase anaerobic digestion was established after about 60 days, and in two phase anaerobic digestion, after about 30 and 60 days in acidogenesis and methanogenesis, respectively. The n-butyrate was accumulated most highly in the temperature stressed digester. The methanogenesis was not significantly affected by rapid temperature change in the acidogenesis of two phase anaerobic digestion in spite of significant effect observed in the acidogenesis. The rapid change in temperature did not have a significant impact on the acidogenic bacteria, home-acetogenic bacteria, acetate-consuming methanogenic bacteria and H₂-consuming methanogenic bacteria in a single phase anaerobic digestion. In two phase anaerobic digestion, however, the number of acetate-consuming methanogenic bacteria significantly decreased, but no impact was observed in other bacteria enumerated.

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Simulation model for assessing the effects of organic suspended solids (SS) in wastewater on the performance of anaerobic filter was developed. The model considered the changes in the condition of anaerobic filter with accumulation of SS, i.e. 1) decrease in hydraulic retention time (HRT) ; 2) increase in release amount of dissolved organic matter (DOC) by hydrolysis of accumulated SS ; 3) decrease in DOC removal rate by inhibition to methanogenesis. Parameter values for the model were determined according to the results of laboratory study using synthetic wastewater with BOD 200 mg·l^-1 containing rice bran as SS.
Calculation results by the model showed that DOC removal rate would decrease markedly when accumulated SS concentration became more than 10,000-20,000 mg·l^-1 at HRT 20 h. Sensitivity analysis showed that holding rate of SS and anaerobic bacteria in anaerobic filter was the most influential factor in DOC removal efficiency. DOC removal rate by methanogenic bacteria was considered to be rate-limiting step in DOC removal process in anaerobic filter. Therefore, holding rate of methanogenic bacteria in anaerobic filter resulted in the most influential factor. Calculation results for gray water treatment showed that increase in HRT may be effective for improving DOC removal.

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Wastewater from the production of semiconductor, printed circuits, and IC parts contains chemically stable COD components and chelating heavy metals shch as lead borofluoride [Pb (BF₄)₂]. As conventional treatments of those components by neutralization, coagulation and biological methods are not efficient enough, we examined a treatment by oxidation together with hydrolysis. The subject is oxidized by hydrogen peroxide with iron powder catalyst and hydrolyzed by aluminium sulfate.
The article reports the results of our laboratory and field experiments. With iron powder catalyst, the subject water (COD : 4,500mg·l^-1) was oxidized up to 160mg·l^-1 in COD value, while the subject was oxidized only up to 270mg·l^-1 in COD value with ferrous sulfate catalyst. The oxidation with iron powder is considered to be efficient since the amount of Fe-ions from iron powder was less than half of that from ferrous sulfate.
Consequently, with the iron powder catalyst, the volume of sludge from Fe-ions reduced to half of that from process with ferrous sulfate, which will contribute to reducing the volume of industrial waste. The hydrolysis of borofluoric acid with aluminium sulfate removed F^- ions up to 1mg·l^-1.

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