Effects of phosphate addition on methane fermentation in the batch and upflow anaerobic sludge blanket (UASB) reactors.

Abstract

Ammonia inhibition of methane fermentation is one of the leading causes of failure of anaerobic digestion reactors. In a batch anaerobic digestion reactor with 429mM NH3-N/L of ammonia, the addition of 25mM phosphate resulted in an increase in methane production rate. Similar results were obtained with the addition of disodium phosphate in continuous anaerobic digestion using an upflow anaerobic sludge blanket (UASB) reactor. While methane content and production rate decreased in the presence of more than 143mM NH3-N/L of ammonium chloride in UASB, the addition of 5mM disodium phosphate suppressed ammonia inhibition at 214mM NH3-N/L of ammonium chloride. The addition prevented acetate/propionate accumulation, which might be one of the effects of the phosphate on the ammonia inhibition. The effects on the microbial community in the UASB reactor was also assessed, which was composed of Bacteria involved in hydrolysis, acidogenesis, acetogenesis, and dehydrogenation, as well as Archaea carrying out methanogenesis. The change in the microbial community was observed by ammonia inhibition and the addition of phosphate. The change indicates that the suppression of ammonia inhibition by disodium phosphate addition could stimulate the activity of methanogens, reduce shift in bacterial community, and enhance hydrogen-producing bacteria. The addition of phosphate will be an important treatment for future studies of methane fermentation.