Systematic comparison framework for selecting the best retrofitting alternative for an existing WRRF

A systematic comparison framework for selecting the best retrofitting alternative for a water resource recovery facility (WRRF) is proposed in this work. The procedure is applied comparing different possible plant configurations to retrofit an existent anoxic/oxic (A/O) WRRF (Manresa, Spain) aiming to include enhanced biological phosphorus removal (EBPR). The framework for comparison was built on system analysis using a calibrated IWA ASM2d model. A multicriteria set of performance variables, as the operational and capital expenditures (OPEX and CAPEX, respectively) and robustness tests for measuring how fast the plant configuration refuses external disturbances (like ammonium and phosphate peak loads), were used for comparison. Starting from the existent WRRF, four plant configurations were tested: single A ²/O (only one anoxic reactor converted to anaerobic), double A ²/O (two anoxic reactors converted to anaerobic), BARDENPHO, and UCT. The double A ²/O plant configuration was the most economical and reliable alternative for improving the existent Manresa WRRF capacity and implementing EBPR, since the effluent quality increased 3.8% compared to the current plant configuration. In addition, the double A ²/O CAPEX was close to €165,000 which was at the same order of the single A ²/O and lower than the BARDENPHO and UCT alternatives. Practitioner points: Four configurations including EBPR were evaluated for retrofitting an A/O WRRF. A new multicriteria comparison framework was used to select the best configuration. Up to 13 criteria related to effluent quality, robustness and costs were included. A single function based on the combination of all the criteria was also evaluated.