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.
[1]
D. Orhon,et al.
Ammonia removal by magnesium ammonium phosphate precipitation in industrial wastewaters
,
1997
.
[2]
David Jenkins,et al.
The viability and activity of activated sludge
,
1971
.
[3]
H. Siegrist.
Nitrogen removal from digester supernatant - comparison of chemical and biological methods
,
1996
.
[4]
Erhard Hoffmann,et al.
Chemical Water and Wastewater Treatment VII
,
2002
.
[5]
H. Siegrist,et al.
Nitrogen Elimination from Digester Supernatant with Magnesium-Ammonium-Phosphate Precipitation
,
1992
.
[6]
G. Bitton,et al.
ATP, oxygen uptake rate and INT-dehydrogenase activity of actinomycete foams
,
1985
.
[7]
R. Schulze-Rettmer,et al.
The Simultaneous Chemical Precipitation of Ammonium and Phosphate in the form of Magnesium-Ammonium-Phosphate
,
1991
.
[8]
M. Zdybiewska,et al.
Removal of Ammonia Nitrogen by the Precipitation Method, on the Example of Some Selected Waste Waters
,
1991
.