Concentrate Volume Minimization for Impaired Water Treatment with Reverse Osmosis

Concentrate minimization is critical to future success and development of desalination technology for both wastewater reuse and drinking water applications. The overall objective of this work was to advance desalination by developing an innovative approach for concentrate minimization. The approach comprises a dual membrane system constituting a primary desalting step with reverse osmosis (RO), intermediate chemical precipitation of RO concentrate, and subsequent treatment with electrodialysis (ED) and/or electrodialysis reversal (EDR) stages. Results indicate that chemical precipitation can reduce sparingly soluble ions of concern in RO concentrate such that subsequent ED/EDR can recover approximately an additional 80 percent of water. For a RO system operating at a recovery of about 80 percent, this would result in an overall recovery of about 95 percent. Conceptual cost estimates indicate that the innovative configuration is cost-competitive, and has likely cost advantages compared to alternative concentrate minimization schemes including brine concentrator or zero-liquid-discharge. Depending on the source water quality, the innovative hybrid concentrate minimization approach developed in this work is estimated to achieve a 10 percent to 20 percent recovery enhancement compared to the conventional RO configuration. It is noted that if easy access to sewer or surface water disposal were available, the total cost of conventional RO would most likely be lower than for the innovative hybrid approach; however, other, non-economic drivers (e.g. regulatory requirements, water resource limitations, wastewater plant capacity limitations for concentrate disposal, public perception, etc.) could still dictate that an approach including concentrate minimization be considered. Source: WEFTEC 2009 Proceedings