Worker exposure to chlorinated organic compounds from the activated-sludge wastewater treatment process

The objective of this research was to investigate some of the potentially controlling factors influencing the atmospheric releases of volatile organic chlorinated compounds from the activated-sludge sewage treatment process. The field study was designed to evaluate the wastewater and airborne concentrations of six chlorinated compounds: hexachlorobicycloheptadiene (hex-BCH), heptachlorobicycloheptene (Hex-VCL), chlordene, chloroform (CHCl3), carbon tetrachloride (CCl4) and tetrachloroethylene (TCE). Analysis of samples consisted of saturating 5 mL aliquots with sodium chloride, extracting with an equal amount of petroleum ether (PE) and subsequent analysis using a gas chromatograph. The air samples collected on Chromsorb 102 were desorbed with 2 mL PE. The study revealed that the highest wastewater concentrations for the water-insoluble hex-BCH, hex-VCL and chlordene were found in the aeration basins, which suggests adsorption of these compounds to the biomass. The plant effluent wastewater concentrations were reduced because of airborne release and suspended solids separation in the clarifiers. In contrast, the wastewater concentrations for the more water-soluble CHCl3, CCl4 and TCE were significantly reduced in the aeration basins. This is because of aerial stripping at the grit-chamber weir. This study suggests that the water-insoluble compounds have prolonged aerial release from the aeration basins. The water-insoluble compounds adhere to the biomass, which is recycled through the plant. The aerial release of these water-insoluble compounds was enhanced by increased aeration rate but depressed by higher suspended solids concentrations.