The impact of different natural zeolite concentrations on the methane production in thermophilic anaerobic digestion of pig waste

The effect of natural zeolite on the thermophilic anaerobic decomposition of pig waste was investigated. In particular, the effect of adding different amounts of zeolite on the increase of methane production of waste was examined. Two sets of experiments were carried out in duplicate: one with a low initial concentration of organic matter and one with a high initial concentration of organic matter. These experiments were carried out in eight batch reactors at 55 °C. The doses of zeolite which were used for the experiments were 0, 4, 8, 12 g l−1 of waste. Methane production was significantly higher in treatments with natural zeolite at doses 8 and 12 g l−1 of wastes, compared to those without zeolite. Also in treatments with natural zeolite, the reduction of volatile solids and biological oxygen demand (BOD5) was statistically significant. The results appear to be caused by the addition of zeolite, which adsorbs ammonia, thus having an effect not only on the toxicity of ammonia and on the C/N proportion but also on the regulation of acidity (pH) of the pig wastes.