Treatment of high TDS liquid waste: Is zero liquid discharge feasible?

A zero liquid discharge treatment system for the disposal of saline industrial liquid waste was proposed and evaluated in this study. Microfiltration was selected as a pretreatment process after a qualitative assessment against ‘conventional’ options. Two reverse osmosis (RO) membranes were examined for the pre-concentration of liquid waste using a laboratory scale membrane rig. The results were used to validate the use of the ROSA simulation package. ROSA simulation was conducted with liquid waste having a range of salinity of up to 100,000 ppm of total dissolved solid (TDS). Results reported here indicated that RO membranes were highly suitable for liquid waste of up to 25,000 ppm of TDS. Several techniques suitable for the treatment of RO concentrate were also identified and evaluated. These include spray dryers, scraped surface evaporators and forced circulation crystallisers/evaporators. Overall, the treatment train was deemed to be preliminarily feasible based on the robust and modular nature of the design, the theoretical ability to achieve the desired output, and the relatively economical use of the integrated membrane system for pre-concentration, reducing dryer/evaporator capital and operational expenditure.