Biological nutrient removal in a sequencing batch reactor using ethanol as carbon source

Background: When organic matter is limiting for biological nutrient removal (BNR) from wastewater, external organic carbon can be added to a wastewater treatment plant (WWTP). This increases the overall treatment cost, so the choice of substrate is critical. The effect of using ethanol as the carbon source for BNR is investigated. Results: The results clearly showed that using ethanol as a carbon source is a promising strategy for removing nutrients from wastewater. Effluent concentrations of 3.0 mg total nitrogen (TN) L^-1 (96% N removal efficiency) and 0.05 mg phosphate (P-PO₄) L^-1 (99.9% P removal efficiency) were obtained. Furthermore, tests performed in order to identify the carbon source used by polyphosphate-accumulating organisms (PAOs) showed that the phosphorus release/carbon uptake ratio using ethanol (0.41 mmolP mmol^-1 C) was slightly lower than that with acetate (0.50 mmolP mmol^-1 C) but close to that with propionate (0.42 mmolP mmol^-1 C). Conclusion: Therefore, taking into account the results presented for ethanol-acclimatised biomass and the fact that the cost of ethanol is lower than that of acetate or propionate, ethanol can be considered as an alternative carbon source if one is needed in a WWTP.