Automated Feed Flow Reversal Operation in a 'Smart' RO Pilot System with Real-Time Mineral Scale Monitoring

摘要

Reverse Osmosis (RO) membrane desalination of inland brackish water is a viable technology for generation of local water resources from brackish groundwater, desalting and reuse of high salinity agricultural drainage water and in wastewater reuse applications. Inland water deployment of RO requires high recovery operation in order to enable technically and economically feasible concentrate management. However, in many inland locations, product water recovery is often limited due to membrane scaling of sparingly soluble mineral salts (e.g., calcium carbonate, calcium sulfate and barium sulfate). Although suppression of mineral scaling can be accomplished, to some extent, with antiscalant feed treatment, recovery is limited even with the use of antiscalants [1]. Recently, RO operation in a feed flow reversal (FFR) mode was proposed as an alternative, non-chemical method for retarding the mineral scale development in RO membranes [2, 4]. This approach is based on the fact that, mineral crystals can be dissolved when exposed to an undersaturated solution. In the membrane feed channel, mineral supersaturation increases in the axial flow direction and thus periodic reversal of the flow direction will reverse the mineral saturation profile in the RO elements. When the RO feed is undersaturated with respect to the mineral salt of concern, flow reversal alternately exposes each end of the RO membranes bank to undersaturated solution conditions. In this case, membrane scaling can be suppressed by timing the flow reversal period to be less than the crystallization induction time at each end of the RO retentate fluid channel [2, 3]. For FFR to be practical in full-scale RO desalting operation, effective feedback control of FFR is needed. This requires the integration of a sensitive real-time mineral scale detection system is needed. Such a scale detection/monitoring system has to be integrated with the RO system control system to enable optimal triggering of FFR cycles.