Sustainable growth of industries in fast developing but water-scarce countries like Kenya can only be achieved by optimizing water usage and reducing wastewater discharge. Besides internal recycling, industries can greatly reduce their freshwater intake by exchanging wastewater streams with neighboring industries and creating symbiosis relations. Previous studies have attempted to design an optimal network of water exchange streams in industrial parks by applying a global multi-objective optimization approach (e.g., [1]). However, only a few have considered the complexity of used water streams in terms of flow rate variation [2] and number of significant pollutants [3].
In this study, we present the outcome of the optimization analysis, covering the above-mentioned knowledge gaps, for water exchange between 10 companies in an industrial park in Ruaraka, Nairobi. A combination of clarification, physico-chemical, membrane-based (Inside® by Aquaporin A/S, Denmark) and disinfection treatments was considered in the optimization exercise as decentralized fit-for-purpose treatment units. Information on volumes and quality of water usage and wastewater discharge was gathered through on-site visits and interviews. The analysis forms part of a research project, Gecko (Green and Circular Innovation for Kenyan Companies), investigating circular solutions within water, materials and energy by specifically focusing on wastewater reuse and targeting industrial symbiosis potentials.
The formulation of the water reuse network is shown in the superstructure (an example for three processes) in Figure 1 using a series of multiple treatment units prior to reuse. The multi-objective evolutionary algorithm NSGA II [4] was applied, considering (i) an economic objective (i.e. capital and operational cost of treatment, piping cost and freshwater consumption volume); (ii) an environmental objective (i.e. CO2 emission, wastewater discharge pollution load); (iii) social constraints, considered as a matrix of collaboration interests among industries (as gathered during on-site surveys). Life
Cycle Assessment (LCA) was performed on the applied water treatment processes, as well as post-optimization evaluation of multiple optimum solutions.
Preliminary optimization results show the potential of 10% economic and 20% environmental improvements in the industrial park through a water exchange network among the considered companies. More detailed analysis on the optimization objectives including fresh water saving and wastewater discharge, as well as LCA of optimum solutions will be presented later. The water network will be expanded to up to 32 companies in the same industrial park. The presented methodology can also be used to perform uncertainty and flexibility assessments of water reuse networks