The effect of a renovated sewage treatment plant on the Cottonwood River, Kansas.

Abstract

The effect of a renovated sewage treatment plant on the environmental quality of the Cottonwood River in Emporia, Kansas. was investigated. Benthic macroinvertebrate community structure was analyzed by the species diversity index (d). Coliform bacteria populations were enumerated with membrane filter techniques and various physicochemical parameters were studied. During November and December, 1978, a poor quality of sewage effluent resulting from interruption of the secondary sewage treatment process at the Emporia, Kansas, Wastewater Treatment Plant caused a severe depression in species diversity (d) values at the sampling site below the plant outfall. The river recovered in March. 1979. after the secondary treatment process was restored. The river was clean to moderately stressed as indicated by d throughout the study. Although there were no significant differences in mean annual species diversity between the sampling station below the sewage outfall and those above the outfall. a marked difference was noted in benthic community composition. Stations upstream from the outfall were dominated by Trichoptera larvae while the station downstream from the outfall was Dipteran dominated. There were higher mean coliform populations below the sewage outfall but the differences were not significant. Fecal contamination was due to wastes from animals upstream from the outfall and from wastes of human origin below the outfall. Coliform populations increased considerably during periods of runoff. The sewage plant effluent did not significantly lower the dissolved oxygen values in the river 0.5 km downstream. The sewage treatment plant did contribute a significant amount of ammonium nitrogen which suggests that a significant oxygen depletion could have occurred further downstream due to nitrification related oxygen demand. Nitrate nitrogen, nitrite nitrogen and phosphate levels were generally higher downstream from the sewage plant but the differences were not significant. Nitrogen and phosphate levels increased considerably during periods of runoff.