Novel design and operational control of integrated ultrafiltration —Reverse osmosis system with RO concentrate backwash

• Direct UF–RO integration was implemented through an advanced control scheme. • RO concentrate stream was utilized for UF backwash. • Pulse backwash significantly improved overall UF backwash effectiveness. • Self-adaptive UF backwash successfully retarded the progression of UF fouling.

A novel RO desalination system was developed that directly integrates UF pre-treatment of RO feed whereby UF backwash is accomplished using the RO concentrate. This direct integration reduces the overall system footprint through elimination of intermediate storage tanks and UF backwash pump which also reduces associated maintenance costs, while allowing for flexible and effective UF backwash strategies. Given the unique decoupling of the RO and UF systems control, RO productivity can be set independently of the UF system which is able to autonomously adjust and provide the RO system with the required RO feed and at the set inlet RO pump pressure. Self-adaptive backwash in the present system was implemented by integrating direct diversion of RO concentrate from the RO system for continuous and sequential backwash with pulse backwash using a hydraulic accumulator. It is noted that while self-adaptive backwash with RO permeate was somewhat more effective than with RO concentrate, this approach resulted in reduced permeate production (~35%) and higher (by ~ 40%) overall energy cost per volume of permeate product. Seawater desalination field studies demonstrated that triggering of UF backwash with RO concentrate, based on a membrane resistance threshold, was superior to fixed frequency backwash extending the projected UF operation from about 16 to 143 days before requiring CIP. The above results suggest that there is merit in exploring further enhancement of UF filtration and backwash effectiveness by integrating coagulation with the present self-adaptive UF backwash. Acknowledgments This work was funded, in part, through grants by the United States Office of Naval Research (N00014-11-1-0950 ONR and ONR N0001409-1-1132), the California Department of Water Resources (46-4120 and RD-2006-09), U.S. Bureau of Reclamation (R13AC80025), Naval Facilities Engineering Command (N62583-11-C-0630), and the UCLA Water Technology Research (WaTeR) Center. The authors would like to acknowledge the contributions of Dr. Richard Zhu, Dr. Alex Bartman, and John Thompson in the construction of the pilot. The authors also acknowledge contributions of equipment and materials by Danfoss Sea Recovery (Henrik Wendelboe and Christopher Okada), Inge GmbH (Peter Berg, Martin Heijnen, and Josef Wunram), George Fisher (Rick Hines), and Dow Water & Process Solutions (Michael Kim), Ahlstrom (Rod Komlenic and Denise Russell) for equipment contributions toward construction of the desalination plant. The personnel of the Seawater [1] S. Gray, R. Semiat, M. Duke, A. Rahardianto, Y. 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