Ultrafiltration after primary settler to enhance organic carbon valorization: Energy, economic and environmental assessment

Abstract

A membrane-based alternative consisting of introducing an ultrafiltration step after the primary settler of the Carraixet WWTP (Valencia, Spain) is analyzed. This alternative aim at increasing the organic carbon valorization in the anaerobic digestion and reducing the aeration requirements in the biological reactor. A comparison is made between the current WWTP and the membrane-based alternative based on their energy balances and applying the life cycle costing and life cycle assessment methodologies. Assessment of the membrane-based alternative shows a reduction in the energy demand of 0.053 kWh per kg of COD removed due to a decrease of the aeration needs and a higher methane production in the anaerobic digestion. However, a bypass stream of 25 % to the reactor is needed to guarantee enough COD for a proper nitrogen removal to accomplish with discharge limits. The improvement in the energy balance allowed a reduction in OPEX of €0.013 per kg of COD removed, while the implementation of the membrane system represents CAPEX of €0.105 per kg COD removed. Finally, membrane-based alternative shows a better environmental performance in all the categories evaluated with ReCiPe 2016. Specifically, lower N2O emissions allowed a reduction of 0.3 kg CO2eq per kg of COD removed.