COMPREHENSIVE IMPACT OF CARBON TO NITROGEN RATIO, DISSOLVED OXYGEN AND TEMPERATURE ON ADVANCED PHOSPHORUS AND NITROGEN REMOVAL EFFICIENCIES IN SEQUENCING BATCH BIOFILM REACTOR (SBBR) SYSTEM

Comprehensive effect of carbon to nitrogen ratio (C/N), dissolved oxygen (DO) and temperature on phosphorus and nitrogen removal efficiency were identified using response surface methodology in a sequencing batch biofilm reactor (SBBR), aiming to develop high-standard urban sewage treatment technology based on the non-engineering measures. Total nitrogen (TN) and phosphate (PO₄^3--P) removal rates were taken as the dependent variables, while C/N (A), DO (B) and temperature (C) were taken as independent variables. The Box-Benhnken (BBD) experimental design method and the quadratic polynomial model were applied. Results in response surface equations was illustrated as η(TN)=-70.76+7.58A+52.81B-0.36C+0.22AB-0.12AC+0.58BC-0.35A²-7.94B²+0.01C², η(PO₄^3--P)=-119.59+10.93A+72.91B+2.26C-1.50AB+0.05AC-0.13BC-0.33A²-6.86B²-0.07C². Further analysis by ANOVA method proved that DO and temperature significantly affected both the phosphorus and the nitrogen removal rates whilst C/N had a remarkable effect on nitrogen removal efficiency. The impact degree of three parameters was DO, temperature and C/N, successively. The interaction of DO with temperature significantly affected the nitrogen removal rate. Moreover, PO₄^3--P removal rate was obviously influenced by the interaction of C/N and DO. The quantifications of relation between operating parameters and system performance were achieved by the response equations, and the optimum working condition and efficiency of the model were verified by experiment, which could be used to guide the optimization of operating parameters in SBBR system for advanced phosphorus and nitrogen removal. The effluent NH₄⁺-N, TN, PO₄^3--P and COD concentration of the SBBR were 3.9, 5.0, 0.4, 40 mg/L respectively, under the condition of temperature of 23℃, C/N of 9.5 and DO of 4 mg/L, which reached the high standard treatment better than Grade I-A standard in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002).