Bioremediation of arsenic contaminated water by SRB could be a cost-effective process, especially if a suitable carbon source and support matrix were available. To these ends, the chemical composition of molasses was investigated as a candidate for the former purpose while pine bark, sand and polystyrene were assessed as support matrices. Batch culture studies were carried out to assess 1, 2.5 and 5 g l~(-1) molasses as suitable concentrations for SRB growth. The results show that all concentrations supported SRB growth, the response being dependent on the amount present; however, growth on molasses was not as good as that obtained when lactate was used. Biofilm formation on the matrices was evaluated in batch cultures in flasks containing Postgate medium B. The inherent ability of these matrices to support growth of the organisms was evaluated on the basis of pH and redox potential change and the levels of sulphate removal and sulphide production occurring. Environmental scanning electron microscopy (ESEM) was used to characterise the matrix surfaces. A consortium of SRB growing on polystyrene caused a 49% removal of the original sulphate present whereas on sand a 36% reduction occurred. With pine bark as support matrix no significant sulphate removal occurred. Polystyrene was further examined for its durability as a long-term support material for the growing of SRB in the presence of As(III) and/or As(V) at concentrations of 1, 5 and 20 mg l~(-1). An immobilised mixed culture of SRB with molasses as carbon source and polystyrene as support matrix was grown in laboratory-scale bioreactors to investigate the treatment of synthetic groundwater containing either As(III) or As(V) at initial concentration of 20, 10, 5 and 1 mg l~(-1). Percentage removal of As(III) improved from about 10% to 47% when the concentration was reduced from 20 to 1 mg l~(-1) whereas the corresponding improvement for As(V) was from 39% to 92% during the 14-day experiment.
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