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Phosphorus removal from municipal wastewater is primarily accomplished through a combination of biological uptake and chemical precipitation. This study examines the capital and operating costs of four strategies for phosphorus removal: conventional activated sludge (CAS), CAS followed by sand filtration, CAS followed by membrane filtration, and membrane bioreactors (MBR). The cost-effectiveness of these four strategies to achieve three target levels of effluent total phosphorus is contrasted: 2.0, 0.3, and 0.1 mg/L. The impact of simultaneously achieving biological nitrogen removal in the system to achieve 10 mg/L total nitrogen is also considered. This study, which is balanced carefully to try to ensure a ‘level playing field’, reveals that MBR facilities are cost-competitive with CAS facilities when tertiary media filtration or tertiary membrane filtration is required for achieving moderate to high levels of phosphorus removal, particularly when simultaneous nitrogen removal is required.

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Previous studies have investigated capital and operating cost comparisons between membrane bioreactors and conventional treatment technologies for particular treatment scenarios. This study expands on prior work with the development of an Excel and Biowin based tool to compare the capital and operating costs of equivalent size greenfield wastewater treatment facilities using membrane bioreactor (MBR) vs. conventional activated sludge (CAS) processes based on identical influent loading conditions, variable temperature and flow peaking factors, and varying levels of effluent treatment objectives. The resulting capital and operating cost tables developed using this tool indicate which system is most cost-effective for each scenario evaluated. The tool can also be used to easily compare the 20-year Present Worth cost impacts of changing input variables such as the cost of concrete, land, chemicals, or electricity.

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