Discharge Of Organic Contaminants To Rivers WithTreated Municipal Wastewaters

In this study organic solutes in final clarifier effluents of a rural and an urban wastewater treatment plant discharged to German rivers were analyzed: COD, DOC, free fatty acids, triacyl glycerols, carbohydrates, proteins, humic acids, anionic and nonionic detergents, hydrocarbons, AOX as well as gas chromatographically detectable substances. To the rural sewer no significant industrial effluents were discharged while about 30 % of the wastewater treated in the urban plant were estimated to be of industrial origin. In the investigated effluents 30 to 40 % of DOC could be related to classes of organic compounds measured as sum parameters. In the urban effluent DOC and COD were lower, but concentrations of gas chromatographically detectable substances were higher (about 1.8 % of DOC) than in the rural effluent (about 0.7 % of DOC). Hydrocarbons, ethers/alcohols (mainly oxaalkanes and oxaalkanols) and esters were the predominant groups of gas chromatographically detectable organic solutes in both effluents. The urban effluent additionally exhibited relatively high concentrations of gas chromatographically detectable carboxylic acids. Among the 22 organic compounds identified in the urban effluent there were 4 substances with genotoxic and/or carcinogenic potential discussed in the literature: 2-ethylhexanoic acid, phthalic acid diethyl ester, caffeine, and phosphoric acid 2-chloroethyl ester. In the rural effluent only 8 dissolved organics were identified, among them also phthalic acid diethyl ester, caffeine, and phosphoric acid 2-chloroethyl ester. The analyzed polar oxaalkanes and oxaalkanols may enter drinking water resources. A derivative of benzenesulfonamide also showed drugs to be relevant solutes of treated municipal wastewaters. Transactions on Ecology and the Environment vol 14, © 1997 WIT Press, www.witpress.com, ISSN 1743-3541