Optimal selection of “zero liquid discharge” (ZLD) system using “analytical hierarchy process” (AHP) and “grey relational analysis” (GRA)

This article specifically presents three different zero liquid discharge (ZLD) options as “Desalination of industrial wastewater and associated rejects management” and deals with optimal selection of ZLD system using “analytical hierarchy process” and “grey relation analysis” (GRA). Commercially available ZLD systems, which differ from each other in some way or the other, were assessed for various factors. Hierarchy among the three factors, viz. economic, technical, and administrative criteria, was considered to arrive at the best treatment option. Each criterion again involved hierarchy of indices. The most suitable ZLD option was arrived at in two ways: 1) by comparing the commercially available treatment options and 2) by deriving the most suitable option based on the maximum beneficial unit operation and treatment process among all the options. A ZLD treatment system based on the combination of unit operation and processes of different treatment options was recommended since it provided maximum benefits. An assessment of annual expenditure on operation and maintenance of existing ZLD system revealed that there is an emergent need to develop more cost-effective techniques to make them environmentally and economically sustainable.