Effects of PH and enumeration conditions on the survival of heterotrophic bacteria in waste stabilization ponds

It is known that the microorganisms, in particular bacteria present in raw wastewater, are reduced considerably during treatment using both conventional and unconventional methods. Several hypotheses have been put forward as to the cause of great reductions of bacteria in stabilization ponds. The potential causes, just to mention the few, include the presence of anti-bacterial substances produced by algae, the high PH levels that are common in the ponds, the depletion of nutrients, microbial antagonism, and the high oxidation-reduction potentials established in intensely propagating algal cultures. In this work, the effects of PH and enumeration conditions on the survival of heterotrophic bacteria in waste stabilization pond are presented. Samples for the study were collected from waste stabilization ponds at the University of Dar es Salaam. Samples were analyzed for heterotrophic bacteria by try tone glucose extract agar in triplicate. For the study of incubation conditions to be applied, samples were incubated against time and colony forming curves were drawn, maximum number of colonies formed after 5 days was found for incubation temperature of 35oc, and the lag time for colony formation was longer at 20oc. Sample incubated at 35oc for 72 h gave 85% of the maximum colony cell able to be formed. Incubation condition of 35oc for 48 h gave only 60%. Samples for enumeration of heterotrophic bacteria collected from waste stabilization ponds were recommended to be incubated at 35oc for 72 h. From the study of naturally changing PH in the field and artificially changing PH in the laboratory it was observed that the Ph in the laboratory it was observed that the Ph of around 10.5 were significantly detrimental to the heterotrophic bacteria. It was observed in this study that up to a Ph of 12 the heterotrophic bacteria were not completely eliminated and were reduced only to 10/ml from 10/ml at Ph 10. However, the ph values in the ponds are rarely exceeding 10.5. Thus, ph was not found to be the main cause of reduction of heterotrophic bacteria in waste stabilization ponds.