Early detection of preferential channeling in reverse electrodialysis

Membrane applications often experience fouling, which prevent uniform flow distribution through the feed water compartments, i.e. preferential channeling may occur. This research shows the effect of preferential channeling on energy generation from mixing salt water and fresh water using reverse electrodialysis (RED). The experimentally obtained power density, electrical resistance and pressure drop are evaluated for artificially controlled preferential channeling. The obtained power density decreases significantly when part of the feed water compartment is inaccessible for flow; a blockage of only 10% of the feed water compartments decreases the net power density by approximately 20%. When 80% of the feed water channels is inaccessible, the net power densities are only marginally positive. This decrease in power density is due to an increase in non-ohmic resistance, which is related to the concentration changes in the feed water compartments when ions are transported from the seawater to the river water side. Chronopotentiometric measurements show that the typical response time to establish a non-ohmic overpotential is an even more sensitive and easily scalable parameter to detect preferential channeling (and the presence of possible fouling) in an early stage. In practical applications, this response time can thus be used as an indicator for preferential channeling and serve to decide on and selectively apply cleaning in RED and other applications

Reverse electrodialysis for salinity gradient power generation:challenges and future perspectives

\u3cp\u3eSalinity gradient energy, which is also known as Blue energy, is a renewable energy form that can be extracted from the mixing of two solutions with different salinities. About 80% of the current global electricity demand could potentially be covered by this energy source. Among several energy extraction technologies, reverse electrodialysis (RED), using anion and cation exchange membranes for ionic transport that is converted into an electrical current at the electrodes, is most promising. This study provides a brief overview of recent advances in RED technology. Furthermore, it discusses future research directions and prospects to expand the true potential of this technology for power generation. Major emphasis should be on the development of task-specific membranes and stacks, the control of fouling and the design of new applications and hybrid processes.\u3c/p\u3

Gas-liquid membrane contactors for CO2 removal

\u3cp\u3eIn the present work we use a membrane contactor for the separation of CO\u3csub\u3e2\u3c/sub\u3e from CH\u3csub\u3e4\u3c/sub\u3e and we systematically investigate the influence of both the type of membrane and the different process parameters on the overall process performance (permeability and selectivity). This work is important because it reports real process performance data (permeances and selectivities) for the total process consisting of absorption and desorption under practical conditions using feed mixtures. Commercially available porous PP hollow fiber membranes and asymmetric PPO hollow fiber membranes have been applied and MEA was used as absorption liquid in the membrane contactor. The proposed approach allows us to identify the operating window and potential of the process. Although the performance of the PP membranes outperforms the performance of the PPO membranes in terms of productivity and selectivity, the PP fibers are extremely sensitive to only small variations in the feed pressure, resulting in severe performance loss. In addition to that, extremely high liquid losses are observed for the PP fibers especially at elevated temperatures. Factors that are significantly reduced when asymmetric PPO membranes with a dense, ultrathin top layer are used, which thus improves the performance and significantly increases the operating window and potential of the membrane contactor process.\u3c/p\u3

Fouling in reverse electrodialysis under natural conditions

Renewable energy can be generated from mixing salt water and fresh water in reverse electrodialysis. The potential for energy generation from mixing seawater and river water is enormous. To investigate the effect of fouling when such natural feed waters are used, the performance of three different setups for reverse electrodialysis was evaluated for 25 days using seawater and river water as feed water, with no other (pre-)treatment than a 20 μm filter. Due to the absence of other anti-fouling treatments, a mixture of fouling is observed on the membranes, composed of remnants of diatoms, clay minerals, organic fouling and scaling. The fouling type was dependent on the different membrane types. The anion exchange membranes attract mainly diatoms and clay minerals, whereas scaling was only found on the cation exchange membranes. As a reference, plastic sheets without charge were used, which results in significant cleaner surfaces. Additionally, the setups without spacers in between the membranes (i.e. profiled membranes) appear significant less sensitive to fouling. This was quantified by the pressure drop over the feed waters and the power density obtained from the membrane piles. The pressure drop increases four times slower and the power density remains higher when profiled membranes are use instead of flat membranes with spacers. Although the obtained power density reduced with approximately 40% in the first day under these conditions, caused by organic fouling, several strategies are available to maintain a high power output using reverse electrodialysi

Removal of aqueous nC\u3csub\u3e60\u3c/sub\u3e fullerene from water by low pressure membrane filtration

\u3cp\u3eThe potential environmental and health risks of engineered nanoparticles such as buckminsterfullerene C\u3csub\u3e60\u3c/sub\u3e in water require their removal during the production of drinking water. We present a study focusing on (i) the removal mechanism and (ii) the elucidation of the role of the membrane pore size during removal of nC\u3csub\u3e60\u3c/sub\u3e fullerene nanoparticle suspensions in dead-end microfiltration and ultrafiltration mimicking separation in real industrial water treatment plants. Membranes were selected with pore sizes ranging from 18 nm to 500 nm to determine the significance of the nC\u3csub\u3e60\u3c/sub\u3e to membrane pore size ratio and the adsorption affinity between nC\u3csub\u3e60\u3c/sub\u3e and membrane material during filtration. Experiments were carried out with a dead-end bench-scale system operated at constant flux conditions including a hydraulic backwash cleaning procedure. nC\u3csub\u3e60\u3c/sub\u3e nanoparticles can be efficiently removed by low pressure membrane technology with smaller and, unexpectedly, also by mostly similar or larger pores than the particle size, although the nC\u3csub\u3e60\u3c/sub\u3e filtration behaviour appeared to be different. The nC\u3csub\u3e60\u3c/sub\u3e size to membrane pore size ratio and the ratio of the cake-layer deposition resistance to the clean membrane resistance, both play an important role on the nC\u3csub\u3e60\u3c/sub\u3e filtration behaviour and on the efficiency of the backwash procedure recovering the initial membrane filtration conditions. These results become specifically significant in the context of drinking water production, for which they provide relevant information for an accurate selection between membrane processes and operational parameters for the removal of nC\u3csub\u3e60\u3c/sub\u3e in the drinking water treatment.\u3c/p\u3

Pushing the limits of block copolymer membranes for CO2 separation

\u3cp\u3eThe current work describes the synthesis and mass transport properties of a series of blend membranes based on a highly permeable polyether based segmented block copolymer and a poly(ethylene glycol) based additive. This series of polymers integrates the knowledge of molecular design and molecular blending and presents CO\u3csub\u3e2\u3c/sub\u3e permeabilities currently unknown to any polyether based block copolymer (system) known in literature. The concept presented is not limited to this specific case and hence opens a window of opportunity for further development of highly permeable block copolymer systems for CO\u3csub\u3e2\u3c/sub\u3e separation and in particular for use in post-combustion CO\u3csub\u3e2\u3c/sub\u3e capture.\u3c/p\u3

Mixed matrix for process intensification in electrodialysis of amino acids

Amino acids are valuable intermediates in the biobased economy for the production of chemicals. Electro-membrane processes combined with enzymatic modification have been investigated as an alternative technology for the fractionation of a mixture of amino acids with almost identical charge behavior. Up to now, the modification and subsequent separation were performed in two separate reactors. An interesting approach is the integration of both unit operations into one single device using mixed matrix membranes (MMMs) as platform for enzymatic conversio

Mitigation of the effects of multivalent ion transport in reverse electrodialysis

\u3cp\u3eReverse electrodialysis (RED) is a sustainable method to harvest energy using the salinity gradient between fresh and seawater. RED technology is developing but efficiencies are still limited when using natural feed water sources. One significant constraint is induced by the presence of multivalent ions in sea and river water (i.e. Mg\u3csup\u3e2+\u3c/sup\u3e, Ca\u3csup\u3e2+\u3c/sup\u3e, SO\u3csub\u3e4\u3c/sub\u3e \u3csup\u3e2-\u3c/sup\u3e). Uphill transport and an increase in membrane resistance in the presence of magnesium ions significantly reduce the power density output obtainable. The choice of cation exchange membrane determines the magnesium transport and as such the power density. Here we investigate four cation exchange membrane types and relate their properties to the stack performance using three different magnesium concentrations on either river and/or seawater side: 1) a highly cross-linked styrene-divinyl benzene monovalent selective cation exchange membrane (Neosepta CMS); 2) a monovalent selective cation exchange membrane that contains a thin polyethyleneimine (PEI) anion exchange layer (Selemion CSO); 3) a multivalent ion (e.g. magnesium) permeable cation exchange membrane with an engineered molecularly open structure facilitating the transport of multivalent ions as recently developed (T1 Fujifilm); 4) a standard cation exchange membrane (Type I Fujifilm (reference)). The first two membranes both retain magnesium ions, while the other two membranes are considered permeable for magnesium ions. The results show that power density strongly depends on the composition of both river and seawater. Power density decreases in the presence of magnesium, an effect being strongest with magnesium at both river and seawater side, followed by the river water side and the seawater side. The negative effect of multivalent ion transport against the concentration gradient, so called uphill transport, in RED can be significantly minimized when monovalent selective membranes such as the highly cross-linked Neosepta CMS membrane or the AEM coated Selemion CSO membrane are used. However, the use of such membranes directly results in a strong increase in membrane resistance due to the lower ion mobility of magnesium ions inside these membranes. As a consequence, power densities in RED are not improved. Especially at high magnesium concentrations, this effect is very strong at higher concentrations, the membranes are no longer able to retain magnesium ions effectively. More beneficial is the application of multivalent permeable membranes with a more ‘open’ structure that allow the free movement of both sodium and magnesium ions through the membrane. Maybe somewhat counter intuitively, such membranes (especially the Fujifilm multivalent permeable T1 membrane) have low resistance values combined with reasonable OCV values leading to high power densities under almost all magnesium concentrations, especially at long term applications. Highest power densities well exceeding 0.3 W/m\u3csup\u3e2\u3c/sup\u3e are still obtained when only sodium is present. However, when magnesium ions are present power densities in the order of 0.2–0.25 W/m\u3csup\u3e2\u3c/sup\u3e can still be obtained for these membranes.\u3c/p\u3

Effect of multicomponent fouling during microfiltration of natural surface waters containing nC\u3csub\u3e60\u3c/sub\u3e fullerene nanoparticles

\u3cp\u3eTo understand and mitigate the role of surface water composition and associated membrane fouling in the removal of nC\u3csub\u3e60\u3c/sub\u3e nanoparticles by low-pressure membranes, experiments were carried out with microfiltration membranes using natural feed waters, mimicking separation in real industrial water treatment plants. The effects of water composition, the presence of nanoparticles, and membrane fouling were investigated with a dead-end bench-scale system operated under constant flux conditions including a hydraulic backwash cleaning procedure. nC\u3csub\u3e60\u3c/sub\u3e nanoparticles can be efficiently removed by microfiltration and the removal efficiency is found to be independent of the water surface composition. However, the water composition controls the extent of fouling occurring during filtration. A synergistic effect on membrane fouling between nC\u3csub\u3e60\u3c/sub\u3e and surface water constituents such as natural organic matter (NOM) and its fractions is observed: the synergistic effect resulted in a transmembrane pressure (TMP) increase always higher than the sum of the TMP increase due to the filtration of nC\u3csub\u3e60\u3c/sub\u3e in ultrapure water and the TMP increase due to the surface water without nC\u3csub\u3e60\u3c/sub\u3e.\u3c/p\u3