膜分離活性汚泥法における膜の塩素洗浄による有機塩素化合物の生成

概要

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Chlorinated organic compounds formed in activated sludge by the addition of hypochlorite solution were analyzed. Although many types of chlorinated organic compound were detected, their concentrations were high particularly those of chloroform (CHCl3), chloral hydrate, dichloroacetonitrile (DCAN) and trichloroacetic acid. The mixed liquor of activated sludge was fractioned into supernatant, extracellular and intracellular fractions and the by-products (CHCl3 and DCAN) of each fraction was also investigated. CHCl3 and DCAN were related to the extracellular and intracellular fractions, respectively. To determine the precursor of DCAN, 23 N compounds were mixed with hypochlorite solution and the amount of DCAN formed was measured. DCAN was formed only from polypeptide and amino acid-containing cyclic N compounds. From this result, it was concluded that DCAN is formed mainly from cyclic N compounds in proteins in activated sludge. Clogged membrane modules in the laboratory experiments were cleaned using hypochlorite solution. The formation of CHCl3 and DCAN was detected in both cases: cleaning directly in the mixed liquor and cleaning in pure water. The amount of the by-product formed seems to be decreased by cleaning in pure water. The trihalomethane (THM) formed by membrane cleaning in existing wastewater treatment facilities was also analyzed. THM was detected in the penetrate of membrane after the cleaning.
2005-03-10