COMPARISON OF CARBON ENERGY AND COMPLEX NITROGEN-SOURCES FOR BACTERIAL SULFATE-REDUCTION - POTENTIAL APPLICATIONS TO BIOPRECIPITATION OF TOXIC METALS AS SULFIDES/

Detailed nutrient requirements were determined to maximise efficacy of a sulphate-reducing bacterial mixed culture for biotechnological remo val of sulphate, acidity and toxic metals from waste waters. In batch culture, lactate produced the greatest biomass, while ethanol was more effective in stimulating sulphide production and acetate was less eff ective. The presence of additional bicarbonate and H-2 only marginally stimulated sulphide production. The sulphide output per unit of bioma ss was greatest using ethanol as substrate. In continuous culture, eth anol and lactate were used directly as efficient substrates for sulpha te reduction while acetate yielded only slow growth. Glucose was utili sed following fermentation to organic acids and therefore had a delete rious effect on pH. Ethanol was selected as the most efficient substra te due to cost and efficient yield of sulphide. On ethanol, the presen ce of additional carbon sources had no effect on growth or sulphate re duction in batch culture but the presence of complex nitrogen sources (yeast extract or cornsteep) stimulated both. Cornsteep showed the str ongest effect and was also preferred on cost grounds. In continuous cu lture, cornsteep significantly improved the yield of sulphate reduced per unit of ethanol consumed. These results suggest that the most effi cient nutrient regime for bioremediation using sulphate-reducing bacte ria required both ethanol as carbon source and cornsteep as a complex nitrogen source.