Optimizing nitrogen removal in a hybrid oxidation ditch

Wastewater treatment plants are now facing the challenges of high cost, high energy consumption, while effluent quality is relatively poor with total nitrogen concentration exceeding the requirement of reuse. This study investigated the performance of contaminants removal, especially nitrogen by a hybrid oxidation ditch (H-OD) which is based on the theory of integrated fixed-film activated sludge under different control factors. The aeration rate, return ratio and hydraulic loading were controlled at 0.4 m(3)/h, 100% and 0.55 m(3)/m(3) h, respectively as the optimized control parameter values. Under the optimized conditions, the effluent concentrations of chemical oxygen demand and ammonium were 35.8 mg/L, 1.04 mg/L, respectively, while the suspended solid was below 10 mg/L. The average removal rate of total nitrogen was 72.8%, and simultaneous nitrification and denitrification (SND) was achieved at 42.7%. Besides, when the carbon/nitogen ratio was maintained from 2.12 to 5.56, the complete nitrification and denitrification was obtained. The results showed that the H-OD was suitable for nitrogen removal and SND was very attractive for practical engineering applications.