The suitability of fermenter liquor from MSW as an electron donor for hypersaline sulfate reduction

Liquor from the fermentation of the organic fraction of municipal solid waste (OFMSW) was tested as a carbon source for sulfate reducing organisms under saline to hypersaline conditions for treating acid mine drainage in arid climates. Two 1.4 L reactors were operated continuously, one as a control maintained at a salinity of 20 g NaCl/L, the other (the test reactor) operated at salinities up to 50 g NaCl/L. Both reactors were first fed a synthetic mix of VFAs (acetate, propionate, butyrate, and valerate) at a COD ratio of 2:1:3:0.5 and at an organic loading rate of 1.56 gCOD/L/d with sulfate supplied in excess as Na₂SO₄. The sulfate reduction rate (SRR) was unaffected by the salinity up to 35 g NaCl/L, but was adversely affected in hypersaline (>35 g NaCl/L) conditions. The stabilized SRR at 50 g NaCl/L was 0.43 ± 0.01 g SO₄-S/L/d compared to 0.66 ± 0.01 g SO₄-S/L/d in the control reactor. Upon replacing the VFA mixture in both reactors with fermenter liquor (a mixture of alcohols, VFAs, lactate and succinate and 29 ± 4 % of unidentified COD), at the same COD loading rate, the SRR recovered in the test reactor (50 g NaCl/L) to 0.56 ± 0.01 g SO₄-S/L/d with full utilisation of acetate by completely oxidizing sulfate reducers, no methane production and over 65 % utilisation of the un-identified COD fraction.