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Title: Map precipitation from landfill leachate and seawater bittern waste
Authors: Li, Xiang-zhong
Zhao, Q. L.
Subjects: Landfill leachate
Magnesium ammonium phosphate (MAP)
Crystallization and precipitation
Issue Date: Sep-2002
Publisher: Selper Ltd.
Source: Environmental technology, Sept. 2002, v. 23, no. 9, p. 989-1000.
Abstract: The leachates generated at Hong Kong landfill sites contain high strength of ammonium-nitrogen (NK₄⁺-N) over 3,000 mg 1⁻¹ and are generally inhibitive to most biological treatment processes. To remove the NK₄⁺-N from the landfill leachates and also recover the nitrogen as a struvite fertilizer, a lab-scale study was performed to investigate the feasibility of NH₄⁺-N removal and struvite crystallization using different magnesium sources. Three combinations of chemicals, MgCl₂·6H₂O+Na₂HPO₄·12H₂O, MgO+H₃PO₄and MgSO₄·7H₂O+Ca(H₂PO₄)·H₂O, were first used at different molar ratios to precipitate NH₄⁺-N from the leachate. The experimental results indicated that NH₄⁺-N was removed by 92%, 36% and 70% respectively at pH 9.0 and a molar ratio of Mg:N:P = 1:1:1. Two synthetic seawater bittern wastes containing Mg²⁺ at 9,220 mg 1⁻¹ and 24,900 mg 1⁻¹ respectively were then used as a magnesium source, while 85% H₃PO₄, chemical was used as a phosphorus source. The results revealed that NH₄⁺-N was removed by 80% and 72% respectively, while a molar ratio of Mg:N:P = 1:1:1 was applied. In the final stage of experiments, the magnesium-ammonium-phosphate (MAP) precipitates were examined by SEM, EDS and XRD. The SEM micrographs of the MAP precipitates showed a typical morphology of elongated tubular and short prismatic crystals. The EDS and XRD results indicated that the chemical composition of the MAP precipitates depended on the chemicals used and experimental conditions. The study confirmed that the recovery of NH₄⁺-N from landfill leachate and seawater bittern wastes could be effectively achieved by MAP precipitation to obtain struvite crystals with a composition of 5.1%N, 10.3%Mg and 16.5%P.
Rights: Environmental Technology © 2002 Selper Ltd. This is an electronic version of an article published in Environmental Technology, 23(9),989-1000. Environmental Technology is available online at:, and the open URL of the article:
Type: Journal/Magazine Article
DOI: 10.1080/09593332308618348
ISSN: 0959-3330
Appears in Collections:CEE Journal/Magazine Articles

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