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Rhodopseudomonas sp. was immobilized in three supports(agar, k-carrageenan, and PVA) in order to remove nitrate in wastewater coming from fish farm. Among them 3% agar was the most suitable support when denitrification rate and bead durability were tested. Optimum bead size was 4mm-diameter when the substrate transfer into the bead and shear stress for bead were considered, and optimum cell loading was 25mg dry cells/㎤ gel. Ethanol was the best as a carbon source, and optimum C:N ratio, temperature and pH were 1.5:1, 31℃, and 6, respectively. Under these conditions the maximum denitrification rate in synthetic wastewater was 345 ㎖ N2/㎤ gel·hr and that in modified MYC medium was 450 ㎖ N2/㎤ gel·hr.
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