Investigation of Suitable, Readily Available, Sources of Sulfate-Reducing Bacteria Inoculum, and Evaluation of Sulfate Reduction Rates Achieved at Different pHs

Abstract

This study investigated the suitability of readily available and naturally occurring sources of microorganisms (inoculum) to use for the cultivation of sulphate-reducing bacteria (SRB) for acid mine drainage (AMD) remediation. The selected inocula included AMD water (AMD), mud (MUD) and reed-bed mud (RM) from the AMD surrounds, mealworms (MW), cow dung (CD) and raw sewage sludge (RS). The suitability of the different inoculum sources was evaluated by comparing the SO₄²⁻ reduction and sulfide (S²⁻) production rates at three different pHs. Experimental results showed that the AMD, MW, MUD and CD inoculum did not produce appreciable reduction of SO₄²⁻ to S²⁻ and were unsuitable sources of SRB inoculum. The inoculum evaluated in pH 2 media did not achieve SO₄²⁻ reduction. Of the inoculum assessed in pH 4 media, only the RM inoculum achieved SO₄²⁻ reduction (40%) with S²⁻ production (36 mg/L). In contrast, a notable S²⁻ production, RS (114 mg/L) and RM (99 mg/L), accompanied the SO₄²⁻ reduction achieved in the pH 7.5 RS (44%) and RM (30%) samples. The improved S²⁻_produced/SO₄²⁻_removed conversion ratios for samples pH 7.5 RS (0.14) and pH 7.5 RM (0.17) are indicative of increased SRB activity and the suitability of these inoculum as SRB sources.