title: Efficiency of biological treatment affected by high strength of ammonium-nitrogen in leachate and chemical precipitation of ammonium-nitrogen as pretreatment.
abstract: Leachate samples with a high strength of ammonium-nitrogen (NH4+-N) were collected from a local landfill site in Hong Kong. Two experiments were carried out to study (1) the inhibition of microbial activity of activated sludge by NH4+-N and (2) the chemical precipitation of NH4+-N from leachate as a preliminary treatment prior to the activated sludge process. The experimental results demonstrated that the efficiency of COD removal decreased from 97.7% to 78.1%, and the dehydrogenase activity of activated sludge decreased from 9.29 to 4.93 microg TF/mg MLSS, respectively, when the NH4+-N concentration increased from 53 to 800 mg/l. The experiment also demonstrated that the NH4+-N in the leachate can be quickly precipitated as MgNH4PO4 x 6H2O after addition of MgCl2 x 6H2O + Na2HPO4 x 12H2O. The NH4+-N concentration was reduced from 5618 to 112 mg/l within 15 min when a molar ratio of Mg2+:NH+:PO4(3-) = 1:1:1 was used. The optimum pH to reach the minimum solubility of MgNH4PO4 x 6H2O was found to be in the range of 8.5-9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl2 x 6H2O + Na2HPO4 x 12H2O, which may affect microbial activity in the following biological treatment processes. Using two other combinations of chemicals [MgO + 85%H3PO4 and Ca(H2PO4)2 x H2O + MgSO4 x 7H2O] could minimise salinity generation after precipitation, while they were less efficient for NH4+-N removal.
authors: Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon. cexzli@polyu.edu.hk
authors: X Z
authors: XZ
authors: Li
authors: Q L
authors: QL
authors: Zhao
mesh_terms: D006863:Hydrogen-Ion Concentration; D017895:Manganese Compounds / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry*; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010710:Phosphates / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012037:Refuse Disposal / Q000379:methods*; D012965:Sodium Chloride; D012988:Soil Microbiology; D012995:Solubility
chemical_list: D017895:Manganese Compounds; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; C024788:ammonium phosphate; D012965:Sodium Chloride; D010088:Oxidoreductases; D009584:Nitrogen; D010100:Oxygen