Wednesday, November 10, 2010: 10:30 AM
253 B Room (Salt Palace Convention Center)
Reverse Osmosis (RO) membrane desalination of inland brackish water is a proven technology for the development of new water resources from brackish, wastewater, groundwater, and high salinity agricultural drainage water. Brine management is a key factor affecting the practical and economic feasibility of implementing inland water desalination. In order to implement technically feasible, low cost concentrate (brine) management strategy, deployment of inland water RO desalination requires high recovery operation. However, in many inland locations, product water recovery is often limited due to membrane scaling by sparingly soluble mineral salts (e.g., calcium carbonate, calcium sulfate and barium sulfate). Suppression of mineral scaling can be accomplished to some extent with the addition of antiscalants to the feed water, but RO recovery is still limited since antiscalant addition adds to the cost of desalination and they can also contribute to membrane biofouling. Operation of RO desalting in a feed flow reversal (FFR) mode was recently proposed as an alternative, non-chemical method for retarding mineral scale development on RO membranes. This RO process operation relies on periodic reversal of the feed flow direction, exposing each end of the RO membranes bank alternatively to the undersaturated feed solution in order to dissolve any mineral crystals that may have formed. In this approach, 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. However, for FFR to be practical in full-scale RO desalting operation, effective feedback control of FFR is needed. Accordingly, this work demonstrates the integration of a sensitive real-time mineral scale membrane monitor (MeMo) with a novel automated Mini -Modular-Mobile (M3) “Smart” RO water desalination pilot system. The M3 has an advanced dynamic control system to enable optimal triggering of FFR cycles. FFR was evaluated in the M3 pilot system using model feed solutions containing calcium, sodium, sulfate and chloride ions. To demonstrate multi-cycle FFR operation, the M3 system was operated with automatic feedback control at a recovery level up to 77% with feed water of high calcium sulfate scaling propensity. The membrane monitor system was configured to automatically trigger flow reversal in the M3 system once a specific scaling threshold (quantified by percent surface area coverage by mineral scale) was reached in the MeMo cell. M3 operation was accomplished over an extended period of time, through periodic dissolution of any formed scale, thereby maintaining overall system permeate flux. In the present approach the FFR operation did not interrupt the RO system operation and continuous permeate productivity was maintained without the use of antiscalants.