Microbial Quality of Human Wastes and Treatment Plant Effluent

Abstract

In order to evaluate the microbial quality of human wastes and effluents from treatment processes, the microbial flora of samples was examined. Total coliforms, fecal coliforms and fecal streptococci were used as indicator micro-organisms, and Vibrio cholerae non O-1, Salmonella, Staphylococcus aureus and Welchii (Clostridium perfrigens) were selected as pathogenic organisms. Salmonella was detected in only the water samples from the night soil treatment plant, while Staphylococcus aureus was detected in the night soil and the samples from the night soil purification tanks. Vibrio cholerae non 0-1 was not detected in any samples, but Welchii existed in almost all samples. Generally, the density levels and distribution patterns of the indicator micro-organisms were similar to those in the raw wastewaters. The microbial flora was not changed remarkably after the primary sedimentation process and the biological treatment process. After the chlorination process, total colonies, spore-forming bacteria, Welchii, moulds and fecal streptococci could survive, and spore-forming bacteria formed the majority of the total colonies in the well-chlorinated effluents. Welchii at the level of 103/100 ml can be used as the indicator micro-organism to ensure a sanitary safe discharge, because it can survive at the level of 103−104/100 ml even if other indicators and pathogenic micro-organisms are inactivated completely by the chlorination process.