Abstract
Carbon to nitrogen ratio (C/N) is not the lone limiting factors in biological nutrient removal from municipal wastewaters, but readily biodegradable to slowly biodegradable COD ratio (rbCOD/sbCOD) inter alia governs the process of nutrient removal. An intermittent aeration pre-anoxic sequencing batch reactor was operated at C/N ratio of 3, 7.5, and 10 and at rbCOD/sbCOD ratios of 0.1, 0.25, and 0.5 at different sludge internal recirculation ratios. The increasing trend in nitrogen removal was observed with above mentioned operating parameters.
At high C/N and rbCOD/sbCOD ratio of 10 and 0.5 the maximum total nitrogen (TN) removal was 90.7% giving 3.8 mg/L TN in the effluent out of 30 mg/L in the influent. At average sewage quality consisting of C/N and rbCOD/sbCOD ratio of 7.5 and 0.25; the TN removal was not more than 83%. The specific nitrate removal rate varied from 0.010 to 0.022 gNO(3)(-)/gVSSa.d (0.015 +/- 0.0013) at C/N ratio of 3.0, 0.013-0.018 gNO(3)(-)/gVSSa.d (0.017 +/- 0.0011) at 7.5 and 0.013-0.015 gNO(3)(-)/gVSSa.d (0.014 +/- 0.001) at 10. The increase in specific nitrate removal rate was coherent to high rbCOD/sbCOD ratio but as the C/N increased to 10 this effect was nullified. The result conformed to defined stoichiometric model based on C/N, rbCOD/sbCOD and sludge internal recirculation ratios. It will help in further effluent polishing with respect to nutrient removal to achieve desired treated wastewater quality. (C) 2017 Elsevier Ltd. All rights reserved.