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Improving Anaerobic Methane Production from Ammonium-rich Piggery Waste in a Zeolite-fixed Bioreactor and Evaluation of Ammonium Adsorbed on Zeolite A-3 as Fertilizer

Cang Yu, Dawei Li, Qinghong Wang, Zhenya Zhang and Yingnan Yang

To mitigate ammonia inhibition and enhance methane production, a zeolite-fixed bioreactor was developed for anaerobic digestion of ammonium-rich piggery wastes. Ammonium adsorption on zeolite A-3 fitted with the pseudo-second-order kinetic model and can be described by both Langmuir and Freundlich isotherms. Desorption of ammonium from saturated zeolite fits the first-order reversible reaction kinetic. The zeolite-fixed bioreactor with zeolite loading rate of 10 g l-1 showed the shortest startup period of 13 days and achieved the highest methane yield of 354.2 ml g-1-VS and the largest COD removal rate of 75.37%. Due to the effective mitigation of ammonia inhibition and enhancement of methane production, zeolite-fixed bioreactor is a good option for practical anaerobic digestion of ammonium-rich piggery wastes. Ammonium saturated zeolite can be directly used as fertilizer to decrease annual production of nitrogen fertilizer. Besides, regeneration of zeolite using Na2SO4 solution also obtained a (NH4)2SO4 by-product, which is nice nitrogenous fertilizer.