Ammonia removal from leachate solution using natural Chinese clinoptilolite

Abstract

This paper assesses the potential of natural Chinese clinoptilolite for ammonia removal from the leachate solution of sewage sludge. In batch study the effects of relevant parameters, such as contact time, initial ammonia concentration and particle size of clinoptilolite, were examined respectively. The results show that the data obtained from batch studies were fit to Langmuir and Freundlich isotherms and the Langmuir isotherms reflect more reasonable for ammonium ion uptake onto clinoptilolite; the clinoptilolite adsorption process has been proved effective, at laboratory scale, the maximum adsorption capacity of the clinoptilolite, for ammonium concentration ranging from 11.12 to 115.16 mg NH₄–N L⁻¹ in leachate solution, was about 1.74 mg NH₄–N g⁻¹; the time to adsorption equilibrium was 2.5 h in leachate solution and 1.5 h more than for in NH₄Cl synthetic solution; ammonium adsorption increased with decreasing clinoptilolite particle size; the ammonia removal capacity of clinoptilolite increased with increasing initial ammonia concentration. It is believed that as adsorption agent for NH₄–N removal from sludge leachate, natural Chinese clinoptilolite can be feasible.

Introduction

Today, our society generates substantial amounts of sewage sludge. As reported by Zorpas et al. [1], at Psittalia, approximately 750,000 m³ day⁻¹ of mainly municipal wastewater along with industrial wastes are subjected to primary treatment in China, producing approximately 250 tonnes day⁻¹ of dewatered anaerobically stabilized primary sewage sludge.

With the dramatic development of economy and improvement of human life, much more wastewater will be produced in China. On the other hand, people are concerned about environmental protection more than ever and relevant legislation or regulation is becoming more critical. The amount of wastewater treated and therefore the sewage sludge produced could increase rapidly in China [2]. Sewage sludge represents major byproducts of wastewater treatment. At a conventional sewage plant, sewage is first treated mechanically and then biologically. Then the sludge that was formed is further processed.

A variety of pollutants can be removed from the sewage by biological and chemical degradation, sorption to sludge or volatilisation [3]. So sewage sludge usually contains high proportions of organic matter and plant nutrients, but it also contains harmful elements, such as heavy metals, ammonium–nitrogen [4], [5], [6]. The major disposal options for sewage sludge include application to agricultural land, incineration, land reclamation, landfilling and so on. Considering both environmental and economical feasibility, sanitary landfilling is the most common disposal method for sewage sludge in China. Because of the initial moisture content of the sludge and other water inputs, such as raining, the leachates containing a range of soluble organic and inorganic contaminants are generated. One of the major environmental concerns associated with landfill of sewage sludge is related to the discharge of leachate into the environment, which may cause serious pollution and eutrophication of the groundwater aquifers as well as adjacent surface water.

The leachates generated from sewage sludge have high concentrations of organic compounds, a low pH value, high ammonia concentrations and high concentrations of heavy metals. Therefore, the leachate would lead to serious environmental problems if it was not properly treated. High ammonia concentration can cause various serious problems, such as eutrophication. Ammonia nitrogen contributes to BOD in water due to its biologic oxidation by nitrifying bacteria, which can have a significant dissolved oxygen requirement for the breakdown of NH₃ into NO₃⁻. In addition to the presence of nitrates, the principal end product of nitrification, stimulates algal growth and eutrophication in waterways. Therefore, a simple, efficient and economical treatment method for the leachate is needed.

Removal of ammonium can be accomplished through the use of air stripping, breakpoint chlorination, ion exchange, and biological nitrification–denitrification. The efficiency of the process of air stripping, biological nitrification and denitrification are significantly impaired by low temperature in winter. Ion exchange, therefore, is more competitive because of little influences of the low temperature during the winter in northern China, and particularly its relative simplicity and economy in application and operation. Clinoptilolite, one of natural zeolites, has been found very effective in removing ammonia from water by means of its excellent ion exchange capacity since the 1970s of last century. Many researchers have investigated ammonia removal from water by ion exchange [7], [8], [9], [10], [11]. Koon and Kaufman [7] studied ammonia removal from municipal wastewaters by clinoptilolite. Jorgensen et al. [8] investigated the dependence of the efficiency and capacity of a European clinoptilolite on different parameters. Klieve and Semmens [9] examined the effect of pretreatments on the performance of clinoptilolite for ammonia removal from wastewaters. Booker et al. [11] studied the value of a natural Australian clinoptilolite as an efficient alternative to existing treatment processes of ammonia removal.

The purpose of this study is to consider a kind of Chinese clinoptilolite, to determine the adsorption capacity of the zeolite and examine the effects of particle size, ion concentration and contact time on the adsorption capacity of the zeolite to ammonium ions in the leachate solution.