In this paper, we review the latest developments in biological methods used in the removal of hydrogen sulphide, present in the liquid phase in anaerobic reactors. The toxicity of H₂S to methane-forming microorganisms and the problems caused by the presence of this compound in the biogas generated during this process, as well as the main causes of hydrogen sulphide generation in anaerobic processes of wastes are also reviewed. We especially discuss the fundamentals in applying micro-aerobic conditions to remove dissolved hydrogen sulphide from the aqueous phase of an anaerobic reactor. The alternative technology of simultaneous removal of sulphide, nitrate, and organic matter is under recent investigation. Therefore, this review paper includes a study and analysis of the microbiological basis of this technology, the physical and chemical factors that influence the process and the potential application of this technology on different types of wastewaters and situations. Also considered are the fundamentals of both biofilm reactors and microbial fuel cells desulphurization. Because relatively few studies on modeling desulphurisation processes are available, we discuss the advances made in that area.

The influence of initial pH and sulfate concentration on the anaerobic digestion of tannery wastewater was studied using the specific methanogenic activity (SMA) test. The SMA tests were performed with a chemical oxygen demand (COD) concentration of 6.5 g/L and SO⁻² ₄ concentrations of 1.95, 3.90, 6.50, 8.45 and 10.4 g/L. The effect of pH was studied at pH 6.8; 6.4 and 6.1. It was found that methane production took place under all conditions, but the use of SO⁻² ₄ concentrations higher than 8.45 g/L and initial pH levels lower than 6.4 caused a decrease of up to 73% of methane production. The influence of pH was significant only for SO⁻² ₄ concentrations lower than 8.45 g/L, with up to 50% inhibition. Specific methanogenic activity for COD/SO⁻² ₄ ratios lower than 0.77 depends basically on this ratio and not on the initial pH value under the conditions of the study.

Thermoelectric fly ash was used as a micronutrient source for microorganisms in the anaerobic digestion process of thermally-pretreated (1 hour, 120 °C) secondary sludge. The obtained result suggest that fly ash improve the methane generation not only in the conversion of volatile fatty acids into methane, also the results show a new observation, the fly ash contributes in the particulate organic solubilization. The maximum methane production rate increased from 6.52 mL/L/d to 22.59 mL/L/d when fly ash was added at a dosage of 150 mg/L in biochemical methane potential tests compared with tests with no added ash. Additionally, the kinetic constants of the hydrolysis of particulate organic matter were obtained in both cases (with and without added ash) in batch reactors using a first-order kinetic model; in the case of no addition, the first-order kinetic parameter was 0.019 ± 0.002 d⁻¹, while with ashes this value increased to 0.045 ± 0.000 d⁻¹. Therefore, the addition of fly ash improves methane generation and hydrolytic kinetics in different order of magnitude.