Dewatering Reverse Osmosis Concentrate from Water Reuse Applications Using Forward Osmosis
Samer Adham, Ph.D., MWH
Reverse osmosis (RO) is an effective barrier in water production systems when removal of dissolved contaminants or salts is needed to achieve high finished water quality. RO concentrate usually comprises 10–30% of the influent for surface water and 50–75% of the influent for seawater. While coastal communities can utilize the ocean to discharge the RO concentrate, inland facilities must rely upon more problematic conventional alternatives, such as surface water or sanitary sewer discharge, evaporation ponds, deep well injection, and land applications. These options are costly, not environmentally sustainable, and increasingly difficult to permit. Thus, proper handling and disposal of the RO concentrate have become a critical environmental issue, particularly for an inland community.
A novel process of dewatering RO concentrate is forward osmosis (FO). FO is defined as the net movement of water across a selectively permeable membrane driven by a difference in osmotic pressure across the membrane. FO has been studied for a variety of applications such as volume minimization of sanitary landfill leachate, concentration of fruit juices, and desalting emergency water supplies for homeland security operations. The main advantage of using FO in water and wastewater treatment is the very low energy consumption rate, since no external pressure is required while rejecting a wide range of contaminants with possibly a lower membrane-fouling propensity than pressure-driven membrane processes have. The main challenges, however, exist in the manufacture of high-performance FO membranes, the selection of easily separable draw solutions with a high osmotic pressure, and the optimization of process configurations to minimize concentration polarization (CP).
As a proof of concept, this study focuses on exploring innovative draw solutions, commercially available FO membranes, and the feasibility of applying FO to dewater RO concentrate.
(2007, 52 pages, 05-009-1)
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