Economic and cross-media effect analyses of best available techniques for caustic recovery from mercerization textile wastewater

Caustic can be recovered from textile mercerization wastewaters by evaporation or membrane filtration. The main objective of this study was to evaluate and compare these two processes in environmental and economic terms, employing the methodology presented in the Integrated Pollution Prevention and Control (IPPC) Reference Document on Economics and Cross-Media Effects (ECM). Cross-media effects for caustic recovery alternatives were calculated on environmental themes including potentials of human toxicity (HTP), aquatic toxicity (ATP), global warming (GWP), acidification (AP), eutrophication (EP), ozone depletion (ODP), and photochemical ozone creation (POCP). For all the environmental themes, membrane filtration exhibited better environmental performance (lower environmental impact) than evaporation. Due to relatively dilute caustic solution to be obtained by membrane processes, ‘membrane filtration + evaporation’ option was also investigated. Findings showed that combination of membrane filtration and evaporation reduces the environmental benefits of membrane filtration alone. The cost-effectiveness values of evaporation and membrane filtration were calculated as 375–625 and 457–685 USD/ton caustic, respectively. Considering the mass of caustic recovered, unit total cost, net present value, internal rate of return, and payback period parameters, it was concluded that evaporation process is more cost-effective than membrane filtration with lower annual unit total cost and payback period. Evaporation may be preferred over membrane filtration in cases where concentrated caustic solution must be obtained for mercerization, although evaporation exhibits lower environmental performance. In cases where dilute caustic solution is adequate or the recovered dilute caustic is to be mixed with new concentrated caustic solution for further use in production processes, membrane filtration can be preferred over evaporation. Graphical abstract