Self-adaptive cycle-to-cycle control of in-line coagulant dosing in ultrafiltration for pre-treatment of reverse osmosis feed water

Abstract

Real-time self-adaptive approach to in-line UF coagulant dosing was developed and field demonstrated for integrated UF-RO seawater desalination. A novel coagulant dose controller was designed and successfully implemented in a pilot UF-RO seawater desalination plant. The coagulant controller, which tracks the UF resistance during filtration and backwash, adjusts coagulant dose to the UF feed with the objective of reducing the incremental cycle-to-cycle UF post-backwash (PB) resistance change (i.e., Δn). Real-time tracking the above UF resistance metrics, as well as the rate of change of Δn with coagulant dose, enabled the controller to quantify the progression of both irreversible fouling and UF backwash effectiveness. The above information was then utilized by the controller to make the appropriate coagulant adjustment. Field tests of the proposed self-adaptive coagulant dosing approach demonstrated measurable coagulant dose reduction while maintaining robust UF operation even during periods of both mild and severe water quality degradation. The approach to real-time coagulant dose control developed in the present work should be suitable for both seawater and brackish water UF treatment and has the potential of providing both effective UF operation as well as reduction in coagulant use.