Science Letters

Effect of Reflux Ratios for Anoxic Digestion of Sewage during A2O Process

Haq Nawaz Abbasi 1,2, Xiwu Lu 1*

1 School of Energy and Environment, Southeast University, Nanjing, China

2 Department of Environmental Science, FUUAST, Karachi, Pakistan

Abstract

Anaerobic/anoxic/oxic (A2O) process has been proven to be effective for wastewater treatment, especially for nutrient removal. In this study, effect of N/S, C/N and hydraulic retention time (HRT) on anoxic digestion during A2O process was evaluated. The study was carried out for a whole year and covered summer, autumn and winter seasons. The results showed that sulfide and threshold odor number (TON) removal was increased with the increase of S/N ratio; however, nitrate removal was decreased. The optimum S/N ratios were 0.6, 1.0 and 1.5 during summer, autumn and winter, respectively. Whereas, with the increase of C/N ratio nitrate removal was increased and sulfide and TON removal was decreased. The optimum C/N ratio was 6.00 for summer, 4.00 for autumn, and 3.50 for winter. During the whole study period, removal rate for all three parameters was increased with the increased of HRTs. The optimum HRTs were 5h, 7.5h and 8.5h for summer, autumn and winter, respectively. The experiment showed that anoxic digestion is influenced by the reflux ratio and it should be optimized to promote complete anoxic digestion during A2O process.

Keywords A2O; sulfate reduction; nutrient removal, anoxic digestion; C/N ratio

Received March 28, 2016 Accepted May 29, 2016 Abstract Published June 20, 2016 Manuscript Published August 15, 2016

*Corresponding author Xiwu Lu E-mail xiwulu@seu.edu.cn