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A study on the utilization of zeolite for ammonia removal from composting leachate Liu, Chuan-hsia

Abstract

This thesis studied the feasibility of using zeolite to remove ammonia in the treatment of composting leachates. Composting is considered to be one of the best treatment methods for biological solid wastes. However, the leachate resulting from the composting process has the potential to impact seriously on the environment if it is not handled properly. This is due to the presence in composting leachates of high levels of nutrient contaminants, especially nitrogen. The main purpose of this study was to investigate the potential use of applications of the Canadian zeolite, clinoptilolite, in the removal of ammonia from composting leachate. Zeolite is considered to have potential use in efficient and cost effective treatment of composting leachate because of its affinity for ammonia and its capacity as a selective ion exchanger. Adsorption capacities, the effect of adsorption on initial solution concentrations, contact time and zeolite particle sizes were the parameters analyzed during batch studies. Adsorption capacities of zeolite ranged from 14.35-17.81 mg N/g. The Langmuir isotherm was found to describe the equilibrium better than the Freundlich model for this study. Particle diffusion was identified as the rate-controlling mechanism at the beginning of contact between zeolite and the wastewater. A batch-scale system using coarse zeolite packed columns was operated to investigate the continuous removal of ammonia from composting leachate. The effects of hydraulic retention time, operating adsorption capacities and regeneration efficiency were measured. A hydraulic retention time of 6 hours was found to be optimal for ammonia removal, which yielded an operating capacity of 1.31 mg N/g zeolite. Over 98% of the ammonia in the wastewater influent was consistently removed by the zeolite columns over approximately 5 bed volumes (BV) of leachate pass through. A 0.6M NaCl regenerating solution at a flow rate of 1 BV/ hr was preferred for the regeneration process. More than 95% of adsorbed ammonium ions were recovered in the effluent. In both the batch and column experiments, the presence of very high concentrations of potassium in the composting leachate meant that potassium acted as a competitive ion. This meant a reduction in the overall performance of the zeolite both in terms of ammonia removal and in terms of column regeneration efficiency. This study concluded that using zeolite as an ion exchanger has potential for increasing the efficiency of ammonia removal from composting leachates.

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