Combined anaerobic-aerobic sbr for the treatment of piggery wastewater

Biological treatment of a piggery wastewater for organic carbon and nitroge n removal in a combined anaerobic-aerobic system was investigated using two laboratory-scale sequencing batch reactors. The cycle length was 24 h. In the anaerobic reactor. fed with raw wastewater and recycling from the aerob ic reactor, denitrification followed by anaerobic digestion of organic carb on was observed. In the aerobic reactor, more organic carbon removal and am monia oxidation to mainly nitrite occurred. Denitrification was also observ ed in the aerobic reactor during the filling period, when mixed liquor diss olved oxygen concentration was very low. Three recycle-to-influent ratios f rom 1 to 3 were tested. Average performances of the overall process, in the different conditions tested, were a TOC removal of 81 to 91% and 85 to 91% of TKN. 10 to 25% of the initial TKN was discharged as N-NOx because of th e low recycle-to-influent ratios used. The higher the recycle-to-influent r atio, the lower the concentrations of nitrogen oxides in the final effluent . However, the effect of this ratio was attenuated by the phenomenon of den itrification in the aerobic reactor which increased the performances of the process. (C) 1999 Elsevier Science Ltd. All rights reserved.