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. Biolog ical processes are normally sensitive to temperature and therefore tem perature fluctuations can affect the process. Experiments were conduct ed 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 effec t of temperature on process kinetics showed that the specific growth r ates of the acidophilic as well as less acidophilic bacteria varied wi th the sludge pH at a particular temperature, with the degree of varia tion dependent on the temperature. Although lower pH occurred at highe r temperatures (as microbial activity and sulfate concentration increa sed), it was found that at constant pH, metal solubilization was the s ame regardless of the temperature.