Abstract
Compared to the linear economy, the circular economy promotes the minimization of fresh resources through the recovery of the applicable items. The concept of the circular economy can be implemented at the industrial level through the process systems engineering approach. A single element or multiple elements nexus can be developed in order to obtain an integrated optimal network. For a tripartite energy-water-waste nexus, focusing the wastewater as the subject of study, the optimization effort may not only be limited to the economic aspect, but it may also include the need to maximize the recovery of resource and the need to reuse and reclaim the wastewater stream. This will require the multi-objective optimization approach. In this study, a multi-objective optimization exercise to develop an integrated energy-water-waste is performed based on the fuzzy optimization constraints method. Three types of objective functions are assessed, namely to maximize profit, to maximize the amount of recovered resources, and to maximize the recovery of water. The mixed-integer non-linear programming (MINLP) model is formulated for such purposes. A case study conducted provides the solution that compromises the trade-off between the objective functions. An annual profit of 1.2 M USD/y, plus the recovery of biogas, struvite, metal hydroxides, and solid sludges, as well as the reuse and reclamation of 574 m3/h of water can be achieved. The model offers a perspective on how the economics and the environmental considerations can be optimized simultaneously.
