Brine pre-treatment technologies for zero liquid discharge systems

The management of brine produced by the reverse osmosis process is challenging due to its high salt and organic content. Limitations in brine disposal options sometimes necessitate the use of zero liquid discharge (ZLD) approach. ZLD systems may include a membrane process - which is used to recover water and to further concentrate brine - followed by thermal treatment. In such systems, a high-water recovery rate is difficult to achieve due to the early onset of membrane scaling and fouling. Brine pre-treatment is therefore necessary to protect the membrane and facilitate ZLD. Literature shows that the most common brine pre-treatment process, chemical precipitation, is generally costly because of high chemical consumption and hazardous sludge production. Moreover, its performance may be hindered by the temporal fluctuations in brine chemistry and the occurrence of residual antiscalants in the brine. A critical evaluation of alternative pre-treatment options was performed. It was found that electrocoagulation and nanofiltration processes have promising performance in terms of hardness and organic removals. Meanwhile, coagulation and adsorption processes show potential for organic removal. Further studies should be performed on process optimization and cost analysis to determine the feasibility of applying these technologies in ZLD systems.