Effect of chromium on survival of heterotrophic bacteria in waste stabilization ponds

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University of Dar es Salaam
The effect of chromium on heterotrophic bacteria at varying pH was investigated in batch cultures. Samples were collected from the effluent of the primary facultative pond of the university waste stabilization ponds system and were doused with varying concentration of chromium in the laboratory. From the study of artificially changing pH in the laboratory at the range of 4 to 11, it was observed that the pH of 11 was significantly detrimental to the heterotrophic bacteria. The density of heterotrophic bacteria was higher at pH 7 than any other pH values for all concentrations, which confirms that the optimum pH for bacterial growth is near neutral pH. For a given pH, the mortality rate of heterotrophic bacteria increased as concentration increased. The decay rate of heterotrophic bacteria was mathematically developed, with reference to chromium concentration and pH. The predicted mortality rate obtained from these models compared well with the experimental data. The correlation coefficient R2 was 0.87. The model shows the hydrogen ion concentration is a strong inhibitor of growth of microorganism at pH values below 5.5 and above 9.5. The decay rate constant remains steady between pH 5.5 and pH 9.5. The steady rate values of mortality rate differ from one concentration to another.
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Sewage lagoons, Tanzania
Masoud, G. A. A. (1999) Effect of chromium on survival of heterotrophic bacteria in waste stabilization ponds, Masters’ dissertation, University of Dar es Salaam. Available at (