This study consisted of two stages. The first stage was to cultivate denitrifying biofilm with a simplified UCBR while the second stage was to investigate the performance of a standard UCBR for nitrate removal. The volumetric nitrate-N conversion rate increased steadily from less than 0.5 kg/m3.d to about 2.5 kg/m3.d towards the end of Stage 1. Reactor instability and poor biofilm morphology had led to a relatively low nitrate-N conversion rate during stage 1 of operation. In Stage 2, the conversion rate increased rapidly to 6.5 kg/m3.d within 4 days and increased steadily to 10.5 kg/m3.d, thereafter. The biofilm formation in Stage 2 was better than that attained in Stage 1. Biofilm density and biomass concentration in the reactor were in the range of 20.5 to 29.0 g/L and 1 to 3 g/L, respectively. The specific growth rate of the denitrifiers (μ) and the observed biomass growth yield coefficient (Yobs) in the reactor varied within the ranges of 1.5-4.2 d-1 and 0.20-0.65 g biomass/g nitrate-N, respectively. The specific nitrate-N conversion rate (γ) was within the range of 1.8-3.8 g nitrate-N/g biomass.d.

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