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Title: Ammonium removal from landfill leachate by chemical precipitation
Authors: Li, Xiang-zhong
Zhao, Q. L.
Hao, X. D.
Subjects: Ammonium (NH₄⁺-N)
Landfill leachate
Magnesium-ammonium-phosphate (MAP)
Issue Date: Oct-1999
Publisher: Elsevier
Source: Waste management, Oct. 1999, v. 19, no. 6, p. 409-415.
Abstract: The landfill leachate in Hong Kong usually contains quite high NH₄⁺-N concentration, which is well known to inhibit nitrification in biological treatment processes. A common pre-treatment for reducing high strength of ammonium (NH₄⁺-N) is by an air-stripping process. However, there are some operational problems such as carbonate scaling in the process of stripping. For this reason, some technical alternatives for NH₄⁺-N removal from leachate need to be studied. In this study, a bench-scale experiment was initiated to investigate the feasibility of selectively precipitating NH₄⁺-N in the leachate collected from a local landfill in Hong Kong as magnesium ammonium phosphate (MAP). In the experiment, three combinations of chemicals, MgCl₂.6H₂O+-Na₂HPO₄.12H₂O, MgO+85% H₃PO₄, and Ca(H₂PO₄)₂.H₂O+MgSO₄.7H₂O, were used with the different stoichiometric ratios to generate the MAP precipitate effectively. The results indicated that NH₄⁺-N contained in the leachate could be quickly reduced from 5618 to 112 mg/l within 15 min, when MgCl₂.6H₂O and Na₂HPO₄.12H₂O were applied with a Mg²⁺:NH₄⁺:PO₄³⁻mol ratio of 1:1:1. The pH range of the minimum MAP solubility was discovered to be between 8.5 and 9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl₂.6H₂O and Na₂HPO₄.12H₂O, which may affect microbial activity in the following biological treatment processes. The other two combinations of chemicals [MgO+85% H₃PO₄and Ca(H₂PO₄)2.- H₂O+MgSO₄.7H₂O] could minimise salinity after precipitation, but they were less efficient for NH₄⁺-N removal, compared with MgCl₂.6H₂O and Na₂HPO₄.12H₂O. COD had no significant reduction during this precipitation. It was found that the sludge of MAP generated was easily settled within 10 min to reach its solids content up to 27%. The other characteristics including capillary suction time (CST) and dry density (DD) of the MAP sludge were also tested. The experimental results indicate that the settled sludge is quite solid and can be directly dumped at a landfill site even without any further dewatering treatment.
Rights: Waste Management © 1999 Elsevier Science Ltd. The journal web site is located at
Type: Journal/Magazine Article
DOI: 10.1016/S0956-053X(99)00148-8
ISSN: 0956-053X
Appears in Collections:CEE Journal/Magazine Articles

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