Abstract
We surveyed THM (trihalomethanes) and TOX (total organic halides) concentrations in the chlorinated effluents from 55 domestic wastewater treatment facilities ; 53 middle or large scale gappei-shori johkasous (wastewater purifying facilities) and 2 rural sewerage systems, and examined whether operation and maintenance of the facilities had an influence on the formation of THM and TOX.The THM concentrations ranged from 0 to 56.1 μg·l-1, but it was lower than 2 μg·l-1 at 65% of the facilities, while the TOX concenrations ranged from 55 to 612 μg·l-1. Both the THM and TOX concentration correlated with free residual chlorine. More than 20 μg·l-1 of THM was detected in 3 facilities where free residual chlorine was higher than 2.5mg·l-1. The facilities with high concenration of THM showed the following features : (1) BOD and NH4-N were low, that is, water qualities were good, or (2) the water amounts of influent were extremely small.Since a small amount of free residual chlorine may result in insufficient disinfection performance while more than 2mg·l-1 causes high concenration of THM or TOX, it was proved that the maintenance of facilities and the improvement of disinfection equipment should be performed accoding to volume and quality of the biologically treated wastewater.
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