Application of DN/CN Enhanced Nitrogen Removal Technology in Upgrading and Reconstruction of Wastewater Treatment Plant

The effluent contained high nitrate concentration of a bioreactor in a municipal wastewater treatment plant was treated by a process of denitrification and nitrification biofilters (DN/CN), the effects of carbon to nitrogen (C/N) ratio, influent load and temperature on total nitrogen removal were investigated. When C/N ratio increased by 3.6 and hydraulic load was no more than 9.44 m ³ /(m²·h) ［the maximum nitrate load was 4.8 kg/(m³·d)］, the effluent TN met the national standard requirements (≤10 mg/L). Removing per unit mass TN required 3.7 times COD, and insufficient carbon source would lead to accumulation of nitrite and increase of carbon source per unit consumption. TN removal efficiency at 14 ℃ decreased by about 15% compared with that at 19 ℃. A corresponding relationship between pH increment and TN removal amount was developed, which could be used to assist in estimating the treatment efficiency of the denitrification filter.