嫌気性ろ床法における外来性懸濁物質蓄積の影響評価モデル

概要

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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.