Abstract
Phosphorous, which is extracted from non-renewable rock reserves found in select countries, is a valuable resource for food production. With the increasing demand for food production, it is projected that the rock reserves will be exhausted within the century. Sustainable alternatives should be explored to satisfy the global demand of future generations. Nitrogen and phosphorous are required nutrients for crop growth. These nutrients can be found in wastewater which can be recovered using nutrient recovery technologies in sewage treatment plants (STPs) and subsequently transformed into valuable fertiliser. This approach can reduce the dependence on costly commercial fertilisers and help STPs comply with stringent effluent standards. A sewage treatment plant requires multiple treatment levels before the wastewater is discharged to receiving water bodies. The performance of a technology to remove nutrients from wastewater depend on several factors like influent characteristics and operating conditions. The challenge is in determining the appropriate series of treatment technologies which maximises P-removal while also reducing total annualised costs (TAC). This study develops a lexicographic e-constraint optimisation model with TAC and overall phosphorous removal efficiency to address this problem. In comparison to most previous studies, the study also considered that the effluent may be used for irrigation provided that the effluent characteristics satisfy the standards for irrigation. The model was implemented to determine the optimal series of technologies for a 10,000 m3/d STP with medium-strength influent characteristics and subject to regulatory standards for discharge and reuse applications. Using lexicographic e-constraint method, the optimal superstructure utilises MBR with an overall phosphorous efficiency of 100 % and cost of USD 49,877,190,000.
