The fate of chlorinated volatile organic compounds in aeration basins using recirculated aeration: a pilot-plant evaluation.

The fate of chloroform, which was chosen to represent chlorinated volatile organic compounds sometimes found in publicly owned wastewater treatment works, has been followed in a pilot aeration basin utilizing aeration recirculation. Tests were conducted using real wastewaters spiked with two different concentration levels of chloroform and operated at conditions similar to those of a large-scale aeration basin of the Mill Creek Wastewater Treatment Plant in Cincinnati, Ohio. Aeration recirculation levels of 0, 25, 50, and 75% were used to evaluate the concept that aeration recirculation can be an effective method of reducing the release of these toxic compounds to the atmosphere. Data obtained demonstrated that the concentration of chloroform in the off-gas increased as the recirculation ratio increased, but that the total mass emission rate to the atmosphere decreased due to the decreased off-gas volumetric flow rate. Biodegradation in the pilot plant increased by 183% for the 75% recirculation level compared to 0% recirculation. Mass balance analysis results indicated that 60% of chloroform emissions could be reduced with 75% recirculation ratio with little or no effect of dissolved oxygen concentration.