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 degrees 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 epsilon 0.05 per m(3) and a maximum surplus energy of 0.1 kW h per m(3)), whilst AnMBR with PS and AD was the optimum option when treating sulphate-rich UWW (minimum cost of (sic)0.05 per m(3) and a maximum surplus energy of 0.09 kW h per m(3)). (C) 2015 Elsevier B.V. All rights reserved.