Static optimal control of combined sewer networks under enhanced cost functions to minimize the adverse environmental effects

Capacity limitations of combined sewer systems lead overflows (CSOs) especially under intensified rain events. The socio-economic damage due to these CSOs on receiving water is immeasurable. Structural measures include enhancing the existing pipe network and introducing new sewer systems lead extra burden on the inhabitants due to new constructions. In addition, the taxpayers have to bear the construction cost. Optimal control of existing combined sewer systems is one of the non-structural solutions in minimizing the adverse impacts of CSOs; however, a holistic control algorithm based on water quality of the receiving water is yet to be developed. This paper develops an enhanced control algorithm based on the pollution load to the receiving water from CSOs. Unlike the previous studies, this paper looks at an enhanced cost function for one of the objective functions, which includes the pumping cost of combined sewer network. The control algorithm is generic; however, it is tested against a real world combined sewer network in Liverpool, United Kingdom. Optimal control settings of the combined sewer systems are found and further analysis shows that algorithm gives feasible solutions. Therefore, the results have proved the applicability of the newly developed optimization algorithm in control of combined sewer systems.