KINETICS OF HEAVY-METAL BIOLEACHING FROM SEWAGE-SLUDGE .3. TEMPERATURE EFFECTS

Heavy metals present in sewage sludge can be leached out using sludge-indigenous sulfur oxidizing bacteria (Thiobacillus spp.). The process depends on the growth of and acid production by these bacteria. Biological processes are normally sensitive to temperature and therefore temperature fluctuations can affect the process. Experiments were conducted to examine these effects in the temperature range of 7-42 degrees C. It was found that lower temperature resulted in slower accumulation of acid and thereby slower pH reduction. Investigations into the effect of temperature on process kinetics showed that the specific growth rates of the acidophilic as well as less acidophilic bacteria varied with the sludge pH at a particular temperature, with the degree of variation dependent on the temperature. Although lower pH occurred at higher temperatures (as microbial activity and sulfate concentration increased), it was found that at constant pH, metal solubilization was the same regardless of the temperature.