Monitoring of pathogenicity of effluents from the UASB based sewage treatment plant

The microbial profile of an Upflow Anaerobic Sludge Blanket Reactor based sewage treatment plant located at a suburb of Delhi, India, and possible risk due to the pathogenicity of the treated wastewater was investigated. Frequency of occurrence of Salmonella, Shigella and Vibrio was 100% at all the stages of sewage treatment. However, recovery of Vibrio was the highest among all the pathogens. The order of removal of all the pathogens was same at the different stages of the treatment. Ratio of counts of fecal coliforms (FC) and fecal streptococci (FS) at different stages of treatment showed the origin of contamination was from the human source. The average density of FC in the treated sewage was 4.6 x 10(5) MPN/100 ml, which exceeds the prescribed limit of 1,000 MPN/100 ml for the FC. The proposed national standard were evaluated with the help of potential risk on the basis of indicator to pathogen ratio, and the concept of Infective Dose (ID(50)) causing infection in 50% exposed population. The analysis showed that the proposed microbial standards could adequately safeguard the risk against wastewater pathogenicity.