Effect of Chromium on the Survival of Heterotrophic Bacteria in Waste Stabilization Ponds

Abstract

Based on experimental work, the effect of pH on heterotrophic bacteria enumeration was studied in batch cultures tests conducted under different chromium concentrations. Samples were collected from the effluent of the primary facultative pond of the University of Dar es Salam (Tanzania) waste stabilization ponds system. The enumeration of heterotrophic bacteria was investigated at different pH values. The density of bacteria was higher at pH 7 than any other pH values for all concentrations. At this pH, the number varied between 1,450,000 to 280,000 at 12 and 108 hours after addition of 5 mg/l chromium concentration. In case of 50 mg/l and pH 7 the number reduced dramatically to 98 to 0 at 12 and 108 hours respectively. It was observed that, the pH of 11 was significantly detrimental to the heterotrophic bacteria. The number ranged between 4000 to 500 in case of 5 mg/l after 12 and 108 hours. Only 13 heterotrophic bacteria were counted after 12 hours when 50 mg/l of chromium concentration was added.