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An important issue concerning performance of forward osmosis (FO) systems is salt accumulation in the retentate. This occurs due to the highly retentive FO membrane and reverse diffusion of draw solutes. In this study, experimental data from an osmotic membrane bioreactor (OMBR), which epitomizes a challenging application for FO, was analyzed to investigate longer term effects of the above issue. It was found that salt accumulation is controlled by three factors: membrane, influent, and process. The role of the membrane is application-dependent and significant only when influent osmotic pressure is smaller or in the same order of magnitude as the salt to water permeability ratio (B/A). The study also shows that an experimental duration of 3 × solids retention time (SRT) is necessary for adequate study of salt accumulation in FO systems. Analysis of the B/A ratio provided fundamental information into system behavior. A reducing B/A could be associated with the formation of a mild secondary foulant layer, whereas an increasing B/A was observed for more severe fouling cases and indicated further flux reducing mechanisms. The study makes clear that knowledge of factors affecting salt accumulation is essential for optimization of FO systems. [ABSTRACT FROM AUTHOR]

The integration of forward osmosis (FO) and biological process, known as the osmotic membrane bioreactor (OMBR), may be viewed as beyond the state of the art for used water treatment and water reclamation. While it is known that the OMBR is able to produce good product water quality in terms of total organic carbon (TOC) removal, limited information is available on the removal of organic micro-pollutants in relation to process performance under the concentrated environment. In this study, a novel OMBR system was continuously operated over 73 days, during which pharmaceuticals were dosed on two occasions into the system. It was found that while pharmaceutical removal was high (>96%), other process parameters in the form of TOC, mixed liquor suspended solids (MLSS) and extracellular polymeric substances (EPS) were unmistakably affected. The major portion of TOC that permeated the FO membrane was found to be low-molecular weight neutral compounds which were associated with the impaired biological process. Microbiological analysis confirmed shifts in microbial populations occurred due to the increased salinity and dosage of the pharmaceuticals. The study demonstrated the importance of the biological process for optimal OMBR system performance, and paves the way for further research in this direction. [ABSTRACT FROM PUBLISHER]