Fate of Indicator Microorganisms During Primary and Secondary Wastewater Treatment Processes

The removal of human enteric viruses, indicator bacteria, coliphages (phages of E. coli), and Salmonella phages by primary sedimentation, activated sludge, and trickling filters was evaluated at a large wastewater treatment facility. Results indicate that primary sedimentation reduced coliform bacteria by 86%, coliphage by 56%, Salmonella phage by 19%, and enteric virus by 11%. Trickling filters reduced coliform by 69%, coliphage by 73%, and Salmonella phage by 48%. No significant reduction in the concentration of enteric virus was observed by trickling filter treatment. Activated sludge reduced coliform, coliphage and enteric viruses by at least 96%, but no significant reduction in the number of the Salmonella phage was observed. With the exception of the removal of enteric virus and Salmonella phage by trickling filters, the efficiency of removing all the tested organisms are within the ranges reported in the literature.