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The focus of whey processing has been changed from waste treatment to the production of valuable products owing to the advancement of membrane technology. Producing high quality whey products at low energy consumption entails novel techniques for whey concentration. This study proposes forward osmosis (FO) as a potential approach to concentrate whey protein solutions, which is superior to the concentration via reverse osmosis (RO), mainly owing to the low hydraulic pressure during FO process. In particular, this work validated the feasibility of FO-based whey concentration using high-performance hollow fiber membranes that were fabricated in-house. The investigation focused on the effects of various operating conditions on the concentration performance. The experimental results reveal that optimal concentration efficiency would be achieved by appropriately choosing the cross-flow velocity, draw solution concentration and the maximum attainable concentration of whey protein solution. Especially, the flux decline behaviour as a function of the whey protein concentration in the feed solution indicated rapid formation of a polarized or gel foulant layer at the membrane surface. The proposed mechanism was supported by the investigation of physical cleaning with water, showing that the post-process cleaning after the concentration cycle was able to recover the membrane performance, whereas the intermediate cleaning during one concentration cycle had little impact on the concentration efficiency enhancement. This study has practical significance for the application of FO in the concentration of dairy streams and other liquid foods. [ABSTRACT FROM AUTHOR]

Abstract: Novel osmotic membrane bioreactors (OMBRs) have been recently reported in the literature. An OMBR uses a dense salt-rejecting forward osmosis (FO) membrane, which exhibits high retention of organic matter and various other contaminants. Meanwhile, the high rejection nature also leads to the accumulation of salts in the bioreactor, which can adversely affect the biological activities as well as the FO water flux. A salt accumulation model is developed in the current study. Our model suggests that both the bioreactor salt concentration and the FO water flux are controlled by membrane properties (water permeability A, salt permeability B, mass transfer coefficient K m, and membrane orientation relative to the draw solution) and the OMBR operational conditions (salt concentration of the influent wastewater, draw solution concentration, hydraulic retention time (HRT), and sludge retention time (SRT)). The salt accumulation is contributed by both the influent wastewater and the reverse diffusion of solutes from the draw solution, and is directly proportional to the volumetric concentration factor (i.e., the SRT/HRT ratio). The relative importance of reverse diffusion over contribution from influent solutes is governed by the membrane selectivity. For a relatively selective membrane (B/A ≪the osmotic pressure of the influent water), solute reverse diffusion has negligible effect on OMBR performance. In contrast, the salt accumulation and FO water flux reduction are governed by reverse diffusion for B/A greater than the osmotic pressure of the influent water. The current study reveals the critical importance of the B/A ratio and HRT/SRT ratio for optimized OMBR operation. [ABSTRACT FROM AUTHOR]

Abstract: Forward osmosis (FO) is attracting increasing interest for its potential applications in water and wastewater treatment and desalination. One of the major drawbacks of FO is internal concentration polarization (ICP), which significantly limits the FO flux efficiency. In addition, FO membrane flux can be adversely affected by membrane fouling. The effects of ICP and fouling on FO flux behavior were systematically investigated in the current study. Both theoretical model and experimental results demonstrated that the FO flux was highly non-linear with respect to the apparent driving force (the concentration difference between the draw solution and the feed water) as a result of ICP. ICP played a dominant role on FO flux behavior at greater draw solution concentrations and/or greater membrane fluxes due to the exponential dependence of ICP on flux level. Compared to the active layer facing draw solution (AL-facing-DS) configuration, more severe ICP was observed when the membrane active layer faced the feed water (AL-facing-FW) as a result of dilutive ICP in the FO support layer. Interestingly, the AL-facing-FW configuration showed remarkable flux stability against both dilution of the bulk draw solution and membrane fouling. In this configuration, any attempt to reduce membrane flux was compensated by a reduced level of ICP. The net result was only a marginal flux reduction. In addition, foulant deposition was insignificant in this configuration. Thus, the AL-facing-FW configuration enjoyed inherently stable flux, however, at the expense of severer initial ICP. In contrast, the AL-facing-DS configuration suffered severe flux reduction as porous membrane support faced the humic acid containing feed water. The flux loss in this configuration was likely due to the combined effects of (1) the internal clogging of the FO support structure as well as (2) the resulting enhanced ICP in the support layer. The latter was caused by reduced porosity and reduced mass transfer coefficient of the support. The pore clogging enhanced ICP mechanism probably played a dominant role in FO flux reduction at higher flux levels. To the authors’ best knowledge, this is the first study to systematically demonstrate the coupled effects of ICP and fouling on the FO flux behavior. [Copyright &y& Elsevier]