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Reliability Problems With Indicator Organisms for Monitoring Overland Flow Treated Waste Water Effluent¹

ABSTRACT

A 2-year study (1975–1976) on the response of indicator organisms in facultative lagoon waste water treated by overland flow was conducted in Utica, Mississippi. Overland flow plots of 4.55 by 45.5 m on 2% slope were established on a Grenada silty clay loam with an artificially established hard pan at 15 cm. The vegetation was a grass mixture dominated by reed canary grass (Phalaris arundinacea L.). Undisinfected waste water from a facultative lagoon was applied to the plots at a rate of 1.25 cm in 6 hours on 5 days a week. Fecal streptococci and fecal coliforms were enumerated in the waste water before it was applied to the plots, as it flowed down slope, and as it was discharged from the plots. Fecal streptococci were found to be poor indicators of the sanitary condition of effluent after overland flow treatment of waste water. Their numbers were consistently higher in the discharged effluent than in the waste water, even when only tap water was applied to the treatment plots. Fecal coliforms were questionable indicators of sanitary conditions in the discharged effluent during the summer when fecal coliform numbers were considerably higher in the discharged treated effluent than in the waste water coming directly from the lagoon. The extent of actual pathogen removal or growth on the soil surface during overland flow treatment was not assessed during this study. However, the use of fecal streptococci or fecal coliforms as indicators of pathogen removal by overland flow during the summer is seriously questioned. Disinfection after treatment by overland flow, at least during the summer, is suggested.

Key Words: fecal coliform • fecal streptococci • disinfection • growth • seasonal effect

¹ Contribution from the USDA-SEA-AR and the U.S. Army Corps of Engineers.

² Soil Scientist, AR, Florence, SC 29502; Research Agricultural Engineer, Biologist, and Research Soil Scientist, respectively, Environ. Lab., U.S. Army Engineer Waterways Exp. Stn., Vicksburg, MS 39180.

Received for publication November 4, 1978.