Abstract: In view of the high concentration of nitrate nitrogen (higher than 600 mg/L) contained in photovoltaic wastewater, continuous flow biofilm method was used for denitrification of wastewater, and continuous flow activated sludge method was set as a comparison. Firstly, the operating conditions of continuous flow denitrification were optimized. The effects of different carbon nitrogen ratios (3∶1, 3.5∶1 and 4∶1) on denitrification were studied by adjusting the carbon source, and the hydraulic retention time (8 h, 10 h and 12 h) of continuous flow was changed to find a sufficient effective reaction time. The ratio of carbon to nitrogen and hydraulic retention time were kept, and the influent nitrate concentration was gradually increased under the optimal operating conditions. The results showed that the best operating conditions of continuous flow denitrification were C/N ratio of 3.5 and HRT of 12 hours. Under this operating condition, the total nitrogen removal rate of wastewater with influent nitrate concentration of 600 mg/L, 1 200 mg/L and 1 500 mg/L reached 96.69%, 92.95% and 90.93%, respectively. The experiment showed that compared with continuous flow activated sludge process, continuous flow biofilm process had higher total nitrogen removal rate and lower nitrite nitrogen accumulation rate for the treatment of wastewater with high nitrate concentration, which can provide not only reference for the optimization of high concentration wastewater treatment, but also basic data for the operation of photovoltaic wastewater with high concentration of nitrate nitrogen in the future.

Key words: high nitrate nitrogen, photovoltaic wastewater, biofilm process, activated sludge process, continuous flow, best working condition