Survival of Pathogenic Bacteria in Elevated Temperature Oxidation Ponds

Abstract

Oxidation ponds are commonly used as an inexpensive method for wastewater treatment. The overall treatment results are measured in terms of pH, oxygen concentration, number and type of algae, and order of magnitude of coliform bacteria reduction. It is often found that pond water temperatures, especially in the summer, reach levels which cause a rapid die-off of pathogenic bacteria. The purpose of the current study was to follow the die-off of pathogenic bacteria in an elevated temperature experimental oxidation pond. Raw wastewater was pumped from a suburban main sewer to the Environmental Engineering Department's pilot plant installations and was introduced daily into two experimental oxidation ponds to give a detention time of 10 - 12 days. One pond was held at 42 - 45°C whilst the other served as a control at ambient temperatures. Salmonellatyphimurium was introduced daily into the two ponds. In another set of experiments, the Salmonella were kept in dialysis bags placed in the ponds. The dialysis bags were filled with saline, control pond effluent, or raw wastewater. The results showed that it is very difficult to isolate the bacteria from the pond effluent. The number of Salmonella bacteria in the dialysis bags in the elevated temperature pond decreased by a few orders of magnitude within days. The Salmonella in the control pond survived for longer. It is thought that the high temperature and adverse environmental conditions caused the rapid die-off of the bacteria in the elevated temperature pond. Taking into account the fact that the numbers of the various pathogenic bacteria in nature are much smaller than the numbers introduced into the experimental ponds, it is thought that effluents from oxidation ponds operating at temperatures in the range 40 - 45°C will not contain any pathogenic bacteria.