Title: Evaluating the effects of pH and temperature on sulphate-reducing bacteria and modelling of their effects in stirred bioreactors
Abstract:
Sulphate (SO4) abundance in the earth’s crust contributes largely to industrial wastewater contamination lowering the pH, which exuberates the dissolution of metals forming acidic drainages. Biological sulphate reduction as a remediation process can be affected by factors such as pH, temperature and high sulphide concentrations. In this study, sulphate-reducing bacterial community enriched from mine wastewaters was applied in semi-automated bioreactors to assess the effects of these factors on microbial sulphate reduction capacities. Low pH (3.5) and temperature (10°C) were observed to promote the toxicity of sulphur-reduced species on the consortium while mesophilic temperature (25°C) and near neutral pH (6.2) were observed to induce optimum SO4 reduction attaining a maximum of 95% SO4 reduction. It was confirmed that low pH exerts a higher inhibitory effect than low temperature with evidence that different SO species affect bacteria differently under varied environmental conditions. Obtained SO4 reduction dynamics data was then applied in formulating a unique non-competitive inhibition equation that models biogeochemical events during SO4 reduction under varied pH and temperature conditions and predicts the efficacy of a bioremediation system. Although the model fits well with the experimental data, it had limitations that needed to be optimized further by additional experiments that encompasses other factors such as O2 concentration, specifically defined bacterial groups, metals associated with SO4 contamination in water. Finally, it was possible to determine that optimizing environmental conditions, such as pH and temperature through adjusting the physicochemical parameters using a stirred tank reactor, can induce the effectivity of a bioremediation systems. Application of the predictor model can be used to make decisions in planning and implementing bioremediation systems in pilot-scale experiments.
Keywords: bacterial consortium, biogeochemical modelling, bio-precipitation, bioreactors, bioremediation, sulphur reduction, water contamination.
