Designing an AnMBR-based WWTP for energy recovery from urban wastewater: The role of primary settling and anaerobic digestion

•An anaerobic membrane bioreactor (AnMBR) for energy recovery was designed.•The role of primary settling (PS) and anaerobic digestion (AD) was assessed.•High- and low-sulphate urban wastewater (UWW) at 15 and 30°C were considered.•AnMBR without PS and without AD was the most economic option for low-sulphate UWW.•AnMBR with PS and AD was the most economic option when treating sulphate-rich UWW. The main objective of this paper is to assess different treatment schemes for designing a submerged anaerobic membrane bioreactor (AnMBR) based WWTP. The economic impact of including a primary settling (PS) stage and further anaerobic digestion (AD) of the wasted sludge has been evaluated. The following operating scenarios were considered: sulphate-rich and low-sulphate urban wastewater (UWW) treatment at 15 and 30°C. To this aim, the optimum combination of design/operating parameters that resulted in minimum total cost (CAPEX plus OPEX) for the different schemes and scenarios was determined. The AnMBR design was based on both simulation and experimental results from an AnMBR plant featuring industrial-scale hollow-fibre membranes fed with UWW from the pre-treatment of a municipal WWTP located in Valencia (Spain). AnMBR without PS and AD was identified as the most economic option for an AnMBR-based WWTP treating low-sulphate UWW (minimum cost of €0.05 per m3 and a maximum surplus energy of 0.1kWh per m3), whilst AnMBR with PS and AD was the optimum option when treating sulphate-rich UWW (minimum cost of €0.05 per m3 and a maximum surplus energy of 0.09kWh per m3).