LAUSR

Abstract The concept of circular economy has received much attention due to growing global concern on resource depletion and environmental protection. There are studies to minimize freshwater reduction via mathematical modelling methods. However, study to explore possibilities of combining both domestic and industrial wastewater regeneration, reuse, and resource recovery in a centralised facility is yet to be made. This study develops a non-linear programming (NLP) model that could optimise water regeneration and reuse network, as well as biogas generation from the selected wastewater streams. The main objective is to maximize profit from the network established. A superstructure that consists of sources, regeneration units, outsourced water, freshwater, mixers-demands, and biogas systems is developed. The sources are from domestic and industrial wastewaters. A combination of the sources, regenerated sources, outsource water, and freshwater is performed in the mixers, subject to the demands’ flowrate and contaminant properties, namely Chemical Oxygen Demand (COD), Total Dissolved Solids (TDS), Total Suspended Solid (TSS), Nitrogen (N), and Phosphorus (P). The formulations also incorporate the techno-economic elements such as mass balance and equipment cost. The processing fee and selling price items are also introduced in the model to ensure that the participants (the sources providers, the centralized water utility facility provider, and the demands) obtain benefits from the integration works. The case study results show that the reused water can be mixed with the freshwater for the boiler feed water and cooling water application with a total supply of 656 m3/h. Connection cost and nanofiltration (NF) cost contribute in a relatively large portion of the annual cost. The selling price of the supplied water is the most important factor that determines the overall systems’ economics compared to other items. The annual profit obtained is USD 1,015,784 and the payback period obtained is 3.13 years. Total freshwater consumption is reduced by 34 %. This model provides insights on how both domestic and industrial wastewaters can be symbiotically integrated in a centralized facility.