Characteristics of nitrate removal in a bio-ceramsite reactor by aerobic denitrification

A newly aerobic denitrifying bacterial strain, Pseudomonas sp. X31, which was isolated from activated sludge, was added to a newly developed aerobic denitrification bio-ceramsite reactor as an inoculum to treat nitrate-polluted water and the denitrification activities of this system under different air-water ratio, hydraulic loading, and C/N (carbon/nitrogen ratio) conditions were investigated. It demonstrated excellent capability for denitrification in the bio-ceramsite reactor at air-water ratios that varied from 6.5:1 to 8:1. The optimal hydraulic loading for the bio-ceramsite reactor was 0.75 m/h with the optimum denitrification efficiency of 95.18%. The optimal C/N was 4.5:1 with a maximum nitrate removal efficiency of 98.48%. COD could be completely removed under the most appropriate condition (air-water ratio 6.5:1-8:1, hydraulic loading 0.75 m/h, and C/N 4.5:1). The quantity of the biomass in the reactor decreased along with flow, which was in accordance with the variety of the available substrate concentrations in the water. However, the biofilm activity was not proportional to the biomass in the bio-ceramsite reactor, but increased with the quantity of the biomass up to a peak value and then decreased.