Ammonium removal from landfill leachate by chemical precipitation |
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| Institution: | 1. Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, PR China;2. School of Municipal and Environmental Engineering, Harbin University of Civil Engineering and Architecture, 202 Haihe Road, Nangang District, Harbin 15001, PR China;3. The Research Center of Ecological Economics and Environmental Technology, Shanxi University of Finance and Economics, 696 Wucheng Road, Taiyuan, Shanxi 030006, PR China;1. MEtRICs, Mechanical Engineering and Resource Sustainability Center, Department of Science and Technology of Biomass, FCT-NOVA, Campus de Caparica, 2829-516 Caparica, Portugal;2. CoLAB BIOREF - Collaborative Laboratory for Biorefineries, Rua Amieira Apartado 1089, 4466-901 S. Mamede Infesta, Portugal;3. CVR, Center for Waste Valorization, Campus de Azurém, 4800-058 Guimarães, Portugal;4. MEtRICs, Mechanical Engineering and Resource Sustainability Center, Mechanical Engineering Department, School of Engineering, Minho University, Campus de Azúrem, 4800-058 Guimarães, Portugal;5. LNEG – Laboratório Nacional de Energia e Geologia, I.P./Bioenergy and Biorefineries Unit, Estrada do Paço do Lumiar 22, 1649-038 Lisbon, Portugal;6. GreenCoLab - Green Ocean Technologies and Products Collaborative Laboratory, Centro de Ciências do Mar do Algarve, Universidade do Algarve, Portugal;1. Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043, United States;2. LG Electronics Inc., Englewood Cliffs, NJ 07632, United States;3. Department of Civil and Environmental Engineering, Lamar University, Beaumont, TX 77710, United States;4. Brown and Caldwell, Upper Saddle River, NJ 07458, United States;5. Microscopy and Microanalysis Research Laboratory, Montclair State University, Montclair, NJ 07043, United States;1. Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia;2. Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham Malaysia Campus, Jalan Broga, 43500, Semenyih, Selangor Darul Ehsan, Malaysia;3. Nanotechnology & Catalysis Research Centre, Deputy Vice Chancellor (Research & Innovation) Office, University of Malaya, 50603, Kuala Lumpur, Malaysia;4. Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, 701, Taiwan;5. Department of Chemical Engineering, National Cheng Kung University, Tainan, 701, Taiwan;6. Research Centre for Circular Economy, National Cheng Kung University, Tainan, 701, Taiwan;7. College of Engineering, Tunghai University, Taichung, 407, Taiwan;8. Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia;9. School of Chemical Sciences, University of Science, Malaysia, 11800, Pulau Pinang, Malaysia;10. School of Energy and Chemical Engineering, Xiamen University Malaysia, 43900, Sepang, Malaysia;1. ICSM, Institut de Chimie Séparative de Marcoule, UMR 5257, CEA/CNRS/ENSCM/UM, Bât 426, BP 17171, 30207 Bagnols-sur-Cèze cedex, France;2. SARPI VEOLIA, Direction Technique et Innovations, Zone portuaire de Limay-Porcheville, 427 route du Hazay, 78520 Limay, France;1. College of Chemical and Biological Engineering, Taiyuan University of Science and Technology, Taiyuan, 030024, China;2. College of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan, 030024, China;3. Instrumental analysis center, Taiyuan University of Science and Technology, Taiyuan, 030024, China;1. College of Ecological Environment and Urban Construction, Fujian University of Technology, Fuzhou, Fujian 350118, China;2. Fuzhou City Construction Design & Research Institute Co., Ltd., 350000, China |
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| 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% H3PO4 and 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. |
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