Effect of Australian zeolite on methane production and ammonium removal during anaerobic digestion of swine manure

Anaerobic digestion is one of the most effective methods for treating swine manure by converting it into green energy, and efficiently reducing methane (CH₄) emission to the atmosphere. Low C/N ratio of swine manure and the production of high levels of total ammoniacal nitrogen (TAN) during acidogenesis due to the high N contents of swine manure considerably reduce CH₄ yield. The reduction of N during anaerobic digestion by the addition of zeolite improves CH₄ production and reduces potential environmental threats associated with ammonia (NH₃) emissions from anaerobic digestion of swine manure. The main objective of this study was to determine the optimum Australian zeolite dose that produces maximum NH₄ ⁺ recovery at optimum CH₄ production. In laboratory experiments, swine manure was treated with natural and sodium zeolites at 0, 10, 40, 70, 100 mg/L and digested anaerobically for 60 days. Natural zeolite at a dose of 40 g/L resulted in the largest increase (29%) in total CH₄ yield from swine manure compared to the nil zeolite treatments. The lag phase of digestion was decreased with increasing zeolite doses up to 100 g/L. Natural and sodium zeolites at a dose of 100 g/L reduced NH₄ ⁺ by 50% and 52% in the media, respectively, compared to the nil zeolite treatments. However, the increases in CH₄ yield of natural and sodium zeolites at a dose of 100 g/L were only 10% and 12%, respectively. Variations of cation concentrations in the digesters caused by adding zeolite at different rates might be a reason for variation of biogas and CH₄ productions from various rates of zeolites digesters.