Source and Composition of Organic components in treated wastewater

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Although biological wastewater treatment is very efficient in removing organic pollutants in wastewater, there still remains trace level of roganic materials in treated wastewater. The trace organic materials can affect water environmtent if the source of a water body is mainly treated wastewater, where the watershed is densely populated. While the origin of the organic materials in treated wastewater is partly attributed to hardly biodegradable materials in influent wastewater, microorganisms used for wastewater treatment might be contributing as a source of organic materials in treated wastewater. Thus in the present study, we investigated the contribution of microorganisms in activated sludge to the organic materials in the treated wastewater. Activated sludge processes were operated with synthetic wastewater with simple orgnaic composition, and the organic materials in the treated wastewater was analyzed in detail.In the former part of the study, trace organic materials in the effluent were analyzed. Organic materials in the treated wastewater was extracted with dichloromethane, concentrated, and directly analyzed by gas chromatography/mass spectrometry. Fourtyeight organic materials were identified. While most part of the compounds were identified as aliphatic fatty acids, aromatic compounds were also found. The organic material detected changed significantly even for the same reactor if the sampling date was different.In the latter part of the study, the behavior of protein and carbohydrates in the treated wastewater was investigated. Protein and carbohydrates explained almost 70% of the organic materials in treated wastewater. It was estimated that about half of organic materials in treated wastewater in actual wastewater treatment plant is coming from activated sludge. The fluctuation of effluent dissolved organic carbon had high correlation with carbohydrates, but not with protein.