Sulfate reduction from phosphogypsum using a mixed culture of sulfate-reducing bacteria [An article from: International Biodeterioration & Biodegradation]

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Description:
Phosphogypsum (CaSO"4), a primary by-product of phosphoric acid production, is accumulated in large stockpiles and occupies vast areas of land. It poses a severe threat to the quality of water and land in countries producing phosphoric acid. In this study, the potential of sulfate-reducing bacteria for biodegradation of this sulfur-rich industrial solid waste was assessed. The effect of phosphogypsum concentration, carbon and nitrogen sources, temperature, pH and stirring on the growth of sulfate-reducing bacteria was investigated. Growth of sulfate-reducing bacteria was monitored by measuring sulfide production. Phosphogypsum was shown to be a good source of sulfate, albeit that the addition of organic carbon was necessary for bacterial growth. Biogenic sulfide production occurred with phosphogypsum up to a concentration of 40gL^-^1, above which no growth of sulfate-reducing bacteria was observed. Optimal growth was obtained at 10gL^-^1 phosphogypsum. Both the gas mixture H"2/CO"2 and lactate supported high amounts of H"2S formation (19 and 11mM, respectively). The best source of nitrogen for sulfate-reducing bacteria was yeast extract, followed by ammonium chloride. The presence of nitrate had an inhibitory effect on the process of sulfate reduction. Stirring the culture at 150rpm slightly stimulated H"2S formation, probably by improving sulfate solubility.