Simultaneous degradation of waste phosphogypsum and liquid manure from industrial pig farm by a mixed community of sulfate-reducing bacteria

The utilization of pig manure as a source of nutrients for the dissimilatory reduction of sulfates present in phosphogypsum was investigated. In both types of media used (synthetic medium and raw pig manure) increased utilization of sulfates with growing COD/SO₄²⁻ ratio in the medium was observed. The percent of sulfate reduction obtained in synthetic medium was from 18 to 99%, whereas the value for cultures set up in raw liquid manure was from 12% (at COD/SO₄²⁻ of 0.3) up to as high as 98% (at COD/SO₄²⁻ equal 3.80). Even with almost complete reduction of sulfates the percent of COD reduction did not exceed 55%. Based on the results obtained it was concluded that the effectiveness of removal of sulfates and organic matter by sulfate-reducing bacteria (SRB) depends to a considerable degree on the proportion between organic matter and sulfates in the purified wastewaters. The optimal COD/SO₄²⁻ ratio for the removal of organic matter was between 0.6 and 1.2 whereas the optimal ratio for the removal of sulfates was between 2.4 and 4.8.