Abstract
Anaerobic biotechnology using sulfate-reducing bacteria (SRB) is a promising alternative for reducing long-term stockpiling of phosphogypsum (PG), an acidic (pH ~3) by-product of the phosphate fertilizer industries containing high amounts of sulfate. The main objective of this study was to evaluate, for the first time, the diversity and ability of anaerobic marine microorganisms to convert sulfate from PG into sulfide, in order to look for marine SRB of biotechnological interest. A series of sulfate-reducing enrichment cultures were performed using different electron donors (i.e., acetate, formate, or lactate) and sulfate sources (i.e., sodium sulfate or PG) as electron acceptors. Significant sulfide production was observed from enrichment cultures inoculated with marine sediments, collected near the effluent discharge point of a Tunisian fertilizer industry (Sfax, Tunisia). Sulfate sources impacted sulfide production rates from marine sediments as well as the diversity of SRB species belonging to Deltaproteobacteria. When PG was used as sulfate source, Desulfovibrio species dominated microbial communities of marine sediments, while Desulfobacter species were mainly detected using sodium sulfate. Sulfide production was also affected depending on the electron donor used, with the highest production obtained using formate. In contrast, low sulfide production (acetate-containing cultures) was associated with an increase in the population of Firmicutes. These results suggested that marine Desulfovibrio species, to be further isolated, are potential candidates for bioremediation of PG by immobilizing metals and metalloids thanks to sulfide production by these SRB.
Highlights
Phosphogypsum (PG) is the main by-product of the production of phosphate fertilizers
This study demonstrates that MS microbial communities, cultivated in microcosms under laboratory conditions and fed with different electron donors, can efficiently convert sulfate contained in PG into H2S
The type of electron donor to be used in such process was found as key criterion influencing H2S production from enriched microbial communities
Summary
Phosphogypsum (PG) is the main by-product of the production of phosphate fertilizers. It is produced by the economic wet process, which generates a large amount of PG (Tayibi et al, 2009; Gennari et al, 2011). Worldwide PG production is estimated to be around 100–280 million tons per year (Mt/year; Tayibi et al, 2009), but only a small part is reprocessed (15%), and the majority is stockpiled. In Tunisia, one of the main phosphate producing countries in the world, the phosphate fertilizer plants are mainly located around the Gulf of Gabes and produce 1–10 Mt/year PG (Ajam et al, 2009). In the Sfax and Skhrira plants, the PG is stockpiled for long-term storage without further treatment
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