Micropollutants Produced by Disinfection of Wastewater Effluents*

Abstract

The principal objective of this research program was to examine the effects of disinfection by chlorine, ozone, and ultraviolet light (uv) irradiation on nonvolatile organic constituents relative to chemical effects and the formation of micropollutants. In a comparative study of highly concentrated samples of effluents from nine wastewater treatment plants, it was determined that disinfection with chlorine or ozone both destroys and produces nonvolatile organic constituents including mutagenic constituents. The chemical effects of disinfection by uv irradiation were relatively slight, although the mutagenic constituents in one effluent were eliminated by this treatment. The nine wastewater treatment plants were selected by using the following criteria: disinfection method, nature of wastewater source, type of wastewater treatment, standards for quality of treatment, and geographical location. The treatment plants varied from pilot plant and small plants [0.05 m3/s (1 Mgd)] treating principally domestic waste to large plants [4.4 m3/s (100 Mgd)] treating principally industrial waste. Four plants used only chlorine for disinfection, four used ozone for disinfection, and one used uv irradiation for disinfection. Eight treatment plants used conventional secondary or more advanced wastewater treatment, and one plant used primary treatment. The following methodology was used in this investigation: grab sample collection of 40-L samples of undisinfected and disinfected effluents; concentration of the effluents by lyophilization; high-pressure liquid chromatographic separation of nonvolatile organic constituents in effluent concentrates using uv absorbance, cerate oxidation, and fluorescence detectors; bacterial mutagenicity testing of concentrates and chromatographic fractions; and identification and characterization of nonvolatile organic constituents in mutagenic HPLC fractions. With these procedures, over 100 micropollutants were identified in the wastewater effluent concentrates. Interplant comparison revealed considerable variability in the presence of mutagenic nonvolatile organic constituents in the undisinfected effluent concentrates as well as much variability in the destruction of the mutagenic constituents and the formation of other mutagenic constituents as a result of disinfection. Moreover, the effects varied on samples collected at the same wastewater treatment plant at different periods. No micropollutants known to be mutagens were identified in the mutagenic HPLC fractions separated from the undisinfected, chlorinated, and ozonated effluent concentrates. The mutagenic activity of the nonvolatile organic constituents in one chlorinated effluent concentrate was not attributable to organic chloramines. Most of the mutagens detected in effluent concentrates are direct acting and do not require metabolic activation. Both base-pair substitution mutagens and frame-shift mutagens occurred in the wastewater concentrates, but the former type was more frequent. For many of the compounds in effluents, strain TA-1535 was more sensitive than strain TA-100 in detecting base-pair substitution mutagens. *Research sponsored by the U.S. Department of Energy and the U.S. Environmental Protection Agency. The work was carried out at the Oak Ridge National Laboratory, which is operated by the U.S. Department of Energy under contract W-7405-eng-26 with the Union Carbide Corporation.