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Feasibility of an AnMBR demonstration plant treating urban wastewater (UWW) at temperatures around 25-30 °C was assessed during a 350-day experimental period. The plant was fed with the effluent from the pre-treatment of a full-scale municipal WWTP, characterized by high COD and sulfate concentrations. Biodegradability of the UWW reached values up to 87%, although a portion of the biodegradable COD was consumed by sulfate reducing organisms. Effluent COD remained below effluent discharge limits, achieving COD removals above 90%. System operation resulted in a reduction of sludge production of 36-58% compared to theoretical aerobic sludge productions. The membranes were operated at gross transmembrane fluxes above 20 LMH maintaining low membrane fouling propensities for more than 250 days without chemical cleaning requirements. Thus, the system resulted in net positive energy productions and GHG emissions around zero. The results obtained confirm the feasibility of UWW treatment in AnMBR under mild and warm climates.

Highlights

This study aimed to evaluate the feasibility of degassing membrane (DM) technology for recovering dissolved methane from AnMBR effluents. For that purpose, a PDMS membrane module was operated for treating the effluent from an AnMBR prototype-plant, which treated urban wastewater (UWW) at ambient temperature. Different transmembrane pressures and liquid flow rates were applied for evaluating methane recovery efficiency. Maximum methane recoveries were achieved when increasing the vacuum pressure and reducing the liquid flow rate, reaching a maximum methane recovery efficiency of around 80% at a transmembrane pressure (TMP) of 0.8 bars and a treatment flow rate (Q_L) of 50 L h⁻¹. The results revealed that the combination of PDMS DMs and AnMBR technology would allow to reduce the energy demand of UWW treatment, achieving net energy productions while reducing greenhouse gas emissions. Optimum operation was determined at a TMP of 0.8 bars and a Q_L of 150 L h⁻¹ when combining energy, environmental and economic targets. Under these operating conditions, the combination AnMBR + DM resulted in energy requirements and greenhouse gases emissions of −0.040 kWh and 0.113 kg of CO₂-eq per m³ of treated water, respectively, resulting in a DM payback period of around 10.5 years.

• PDMS membranes allow a suitable methane capture from AnMBR effluents.

• AnMBR energy efficiency can be improved by employing PDMS membranes.

• Greener wastewater treatments can be reached by coupling PDMS membranes with AnMBR.

• PDMS membranes showed a feasible potential for full-scale applications.

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