Methanogens’ Death Induced by Sulphide and its Kinetic Modelling

This study is aimed at investigating the poisoning effect of sulphide on methanogenic cultures. Using cultures enriched with either acetate or formate as a sole electron donor, sets of 1-week batch inhibition tests were performed to analyse the dynamic change of the living microorganism concentrations under the varied sulphide concentrations between zero and 400 mg-S L−1. In both cultures, the cellular decay was doubled when the cultures were placed in 100 mg-S L–1 of total sulphide. When the cultures were exposed to higher sulphide, higher specific decay rates were obtained. Because of the low correlations of the unionised sulphide concentrations to the specific decay rates, the total sulphide concentration was thought to be the dominant inhibition factor rather than its unionised form. To express the acceleration of cellular decay, a mathematical model was developed. Since the decay phenomena of both cultures were quite similar to each other, a culture-wide empirical formula was obtained to calculate the specific decay rate. In the model equation, the specific decay rate of the methanogenic cultures was linearly expressed with a coefficient of 0.30∙10−3 ± 0.05∙10−3 mg-S−1 L d−1 for sulphide concentration and a coefficient of 0.044 ± 0.013 d–1 for the inherent specific decay rate.