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Water Science & Technology Vol 49 No 5-6 pp 105 - 112 © IWA Publishing 2004 Removal of high NO3Ð concentrations in saline water through autotrophic denitrification by the bacterium Thiobacillus denitrificans strain MPJ.-D. Gu*, W. Qiu**, A. Koenig*** and Y. Fan*****Laboratory of Environmental Toxicology, Department of Ecology and Biodiversity, The University of Hong Kong, Pokfulam Road; and The Swire Institute of Marine Science, The University of Hong Kong, Shek O, Cape d'Aguilar, Hong Kong, China (E-mail: jdgu@hkucc.hku.hk) ABSTRACT Autotrophic denitrification by Thiobacillus denitrificans MP isolated from mangrove was investigated in both a sulphur-limestone column reactor and a fermenter. More than 97.5% of the nitrate (NO3-) in the 250 mg NO3--N/L strong influent was removed after 14.3 hours in the column reactor. Influent NO3- was completely depleted in the lower part of the column as the hydraulic retention time increased and a slight pH drop was also observed along the reactor column due to the exhaustion of the buffering ability of the limestone. Trace amounts of oxygen present in the lower part of the reactor column resulted in the accumulation of nitrite and subsequent inhibition of further denitrification. The species composition of the bacterial community in the higher parts of the reactor column was morphologically more diverse than in the lower part. Denitrification by T. denitrificans MP reached an optimal level when the dissolved oxygen was maintained between 1.5-2% of saturation level in the automated fermenter. The stoichiometric ratios of ΔSO42- produced/ΔNO3--N removed were 6.81 and 9.32 in the reactor column and fermenter, respectively. This study suggests that efficient removal of high NO3Ð concentrations in water or wastewater can be achieved using autotrophic bacteria immobilized on surfaces of sulphur granules in the column system. eProduct: Buy this article for £24.00 (IWA MEMBER PRICE: £18.00) All prices include VAT. For customers where VAT should not be applied, the VAT amount will be removed upon payment |
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