Evaluating resource recovery potential and process feasibility of direct membrane ultrafiltration of municipal wastewater at demonstration scale

The aim of this work was to assess the feasibility of applying ultrafiltration membranes for the direct filtration of municipal wastewater. The effect of different influents (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) and operating solids concentration (about 1, 2.6, 6 and 11 g L−1) was evaluated. Increasing the operating solids concentration sharply reduced membrane fouling, achieving a minimum of about 0.55 mbar per day when operating above 6 g L−1. Filtering raw municipal wastewater also had a beneficial effect on the filtration performance, although only when operating at a low solids concentration (under 2.6 g L−1). High quality permeates were obtained regardless of operating conditions, meeting European discharge requirements for no sensible environments. High resource recoveries were achieved thanks to the direct filtration of wastewater, capturing about 80-85 and 20%–40% of the influent COD and nutrients, respectively. The energy and carbon footprint balances showed promising results, achieving energy recoveries and carbon footprints of about 0.46-0.40 kWh per m3 of influent municipal wastewater and -[0.19-0.16] kg CO2-eq per m3 of influent municipal wastewater when considering the process energy demands and potential energy recovery. Additionally, profits can be obtained from MWW treatment by this alternative, achieving about €0.035–0.021 per m3 of influent MWW when operating at a flux of 10 LMH which entail a payback period for the initial membrane acquisition of 12.3–20.1 years.