Water Science & Technology Vol 66 No 3 pp 517–524 © IWA Publishing 2012 doi:10.2166/wst.2012.148

Denitrification of nitrate-contaminated groundwater using a simple immobilized activated sludge bioreactor

Zhengfang Ye, Feng Wang, Haitao Bi, Zhongyou Wang and Guo-hua Liu

A simple anaerobic-activated sludge system, in which microorganisms are immobilized by a novel functional carrier, was used for removing nitrate in groundwater. The operating conditions, including hydraulic retention time (HRT), C/N ratio, temperature and NO₃⁻-N loading concentration were investigated. The NO₃⁻-N concentration, residual chemical oxygen demand (COD) and nitrite accumulation were used as indicators to assess the water quality of the effluent. The anaerobic biomass loading capacity in the carrier was 12.8 g/L and the denitrifying Pseudomonas sp. and Rhodocyclaceae bacterium were dominant among the immobilized microorganisms in the anaerobic-activated sludge. Under operating conditions of HRT= 1.5 h, C/N= 2–3 and T= 16.8–20 °C, the removal efficiency of NO₃⁻-N exceeded 93%, corresponding to a relatively high denitrification rate of 0.73 kg NO₃⁻-N m⁻³ d⁻¹, when the NO₃⁻-N loading concentration was 50 mg/L. The NO₃⁻-N concentration of the effluent always met regulatory criteria for drinking water (<10 mg/L) in the main developed and developing countries. The effluent COD was also below 10 mg/L. Although some nitrite accumulated (0–1.77 mg/L) during the operating period, it can be decreased through adjusting the operating pH and HRT. The immobilized activated sludge system may be useful for the removal of nitrate from groundwater.

Keywords: C/N ratio; denitrification; groundwater; HRT; immobilized microorganism

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