Simulation of denitrification in groundwater from Chaohu Lake Catchment, China

The eutrophication of Chaohu Lake in China is mainly attributed to nitrate inflow from non-point sources in the lake catchment. In this study,biological nitrate reduction from groundwater in the Chaohu Lake Catchment was investigated under laboratory conditions in a continuous upflow reactor. Sodium acetate served as the carbon source and electron donor. Results showed that a carbon-to-nitrogen(C/N) molar ratio of 3:1 and hydraulic retention time(HRT) of 8 d could achieve the most rapid nitrate nitrogen(NO~--N) depletion(from 100 mg/L to 1 mg/L within120 h). This rate was confirmed when field groundwater was tested in the reactor, in which a NO~--N removal rate of 97.71% was achieved(from60.35 mg/L to 1.38 mg/L within 120 h). Different levels of the initial NO~--N concentration(30, 50, 70, and 100 mg/L) showed observable influence on the denitrification rates, with an overall average NO~--N removal efficiency of 98.25% at 120 h. Nitrite nitrogen(NO~--N)accumulated in the initial 12 h, and then kept decreasing, until it reached 0.0254 mg/L at 120 h. Compared with the initial value, there was a slight accumulation of 0.04 mg/L for the ammonia nitrogen(NH4-N) concentration in the effluent, which is, however, less than the limit value.These results can provide a reference for evaluating performance of denitrification in situ.