Simultaneous nitrogen and carbon removal from wastewater at different operating conditions in a moving bed biofilm reactor (MBBR): Process modeling and optimization

Abstract

In this study, a moving bed biofilm reactor (MBBR) was examined removing organic carbon and nitrogen from municipal wastewater through simultaneous nitrification and denitrification (SND) process. To assess the process performance, two numerical independent variables, hydraulic retention time (HRT) and dissolved oxygen (DO), and one categorical variable, type of packing media, were selected. The effects of the numerical variables were investigated at three levels, 4, 8 and 12 h for HRT and 2, 3 and 4 mg/L for DO, while two levels of the categorical variable (Ring form and Kaldnes-3) were examined. The packing media used were different in the structure and geometry but similar to specific surface area (500 m2/m3). The experiments were carried out at two parallel reactors. The process was analyzed and modeled by monitoring 10 dependent responses. Maximum COD removal efficiency was found to be 85 and 88%, respectively, for the system with Ring form and Kaldnes-3 at HRT of 12 h and DO of 4 mg/L. The results showed that the system with Ring form could achieve more TN removal efficiency than that of the process with Kaldnes-3, indicating that anoxic condition is favored with Ring form due to its structure geometry. In all the conditions tested, nitrite oxidizing bacteria (NOB) was dominant species. It implies more nitrite production from the ammonia oxidizing bacteria (AOB) activity which leads to increase NOB growth. The maximum denitrification rates for Ring form and Kaldnes-3 were obtained 90 and 70 mg N/L.d, respectively at DO of 3 mg/L and HRT of 8 h. Overall, the changes in the system with Ring form media at different conditions have been more compared to that in the system with Kaldnes-3, indicating more stability of the system operated with Kaldnes-3. As a conclusion, the biofilm in the Ring form showed lower stability compared to that of the system with Kaldnes-3.