Enhanced coagulation and nitrification for nitrogen and phosphorus removal from corn starch wastewater

Considering the limit-exceeding problems of nitrogen and phosphorus in current cornstarch wastewater treatment, two solutions were put forward: one is to remove some pollutants by enhanced flocculation at the pretreatment stage; the other is to utilize the effluent of primary sedimentation tank as a carbon source for denitrification. The wastewater was treated by ferric chloride, aluminum sulfate, chitosan, and sodium alginate as flocculants, and optimum conditions were determined by single factor coagulation tests. The results showed that the ferric chloride was the suitable flocculant for treatment of cornstarch wastewater. When the dosing quantity of ferric chloride coagulant was 0.40 g/L, pH was 4, temperature was 35 ℃, the removal rates of TP, SS, TN and COD_Cr were 93.5%, 94.8%, 10.8% and 10.7%, respectively. The pollutant degradation characteristics and dynamic characteristics were studied by sequencing batch reactor with the effluent of primary sedimentation tank as the carbon source for denitrification, and Monod equation and piecewise zero-order kinetic model were used to fit the experimental data. The results showed that $NO_{2}^{-}$-N accumulation was found in the denitrification process, and the accumulation rate was 61%. The predicted values of simulation parameters using Monod equation fit well with the measured data, and the maximum degradation rates of $NO_{3}^{-}$-N、$NO_{2}^{-}$>-N and $NO_{x}^{-}$-N were 24.21, 12.78 and 15.97 mg/(g MLVSS·h) respectively. The concentrations of $NO_{x}^{-}$-N was also fit well by piecewise zero-order kinetic model and the denitrification rates of stage 1 and 2 were 16.09 and 8.71 mg/(g MLVSS·h) respectively.