Totally found 814 items.

  • [期刊] Enhancing the performance of a bioelectrochemically assisted osmotic membrane bioreactor based on reverse diffusion of organic and buffering draw solutes
    By combining the merits of bioelectrochemical systems and osmotic membrane bioreactors (OMBRs), bioelectrochemically assisted OMBRs (BEA-OMBRs) can achieve simultaneous water/electricity recovery and salinity mitigation. One of the key challenges is reverse solute flux (RSF). The "negative effect" of RSF was turned into a "beneficial effect" by using a reverse-fluxed draw solute (DS) as a buffering agent or a carbon source supplement. The reverse-fluxed anions from the alkaline buffering DSs (NaHCO3 and PBS) stabilized the anolyte pH and had a positive effect on system performance, such as a high total Coulomb of 278.16-289.80C, a high recovered water of 261.64-277.80 mL, and a high COD removal of 90.91-91.61%. The reverse-fluxed cations from the acidic buffering DS (NH4Cl) promoted the accumulated ammonium to diffuse from the feed/anode to the cathode side due to the production of ammonia gas in the alkaline catholyte. The organic DS exhibited a lower RSF and a lower anolyte conductivity of 5.12-8.49 mS cm(-1). However, the reverse-fluxed organic DSs (glucose and NaOAc) had a negative effect on the electricity generation due to carbon source competition. These results have demonstrated the advantages of the reverse-fluxed DS to enhance the system performance and to encourage further development of BEA-OMBR technology.
  • [期刊] Developments and future prospects of reverse electrodialysis for salinity gradient power generation: Influence of ion exchange membranes and electrodes
    Salinity gradient power can be a very attractive renewable energy system because electricity is generated by salt concentration difference between two solutions without any pollutant emission. The representative example of salinity gradient power is reverse electrodialysis (RED), in which there are many variables such as ion exchange membrane (IEM), electrode, stack configuration, the structure of flow pathway, spacer, and solution concentration. This paper focuses on IEMs and electrodes that have not been covered in the previous review papers, as well as on the fundamental of the RED system and plant development for commercialization. In the part of IEM, the characteristics that need to be intensively studied are analyzed and the studies have been conducted to improve membrane property are summarized. In addition, the properties of major commercial IEMs and tailormade membranes are compared and analyzed, and the relationship between properties affecting membrane performance is studied. In the part of the electrode, the main issues and materials of the electrode part in the RED system are presented, and the recent researches related to the electrode of a large-scale RED system for commercialization are summarized. Finally, this review suggests the future prospects and expectations for salinity gradient power using the RED system.
  • [期刊] Risk evaluation of large-scale seawater desalination projects based on an integrated fuzzy comprehensive evaluation and analytic hierarchy process method
    Desalination projects play a vital role in the water supply of coastal regions with scarce water resources. The risks associated with desalination projects are worth investigating, especially for large-scale projects. This paper presents the risk identification and evaluation processes of large-scale desalination projects. Two levels of risk indicators are identified and the first-level risks include water intake and outfall risk, processing risk, financial risk and circumstance risk. With the identified risk indicators, an integrated fuzzy comprehensive evaluation (FCE) and analytic hierarchy process (AHP) method is introduced to conduct quantitative risk evaluations for large-scale desalination projects. Twenty experts in desalination-related fields are invited to vote to determine the weighting vectors for the FCE through the AHP. They also participate in deciding the membership matrixes in the FCE for three practical desalination projects. The evaluation results indicate that the overall risks of all the considered projects are at the "Very low" level. Finally, to diminish the potential risks, several instructions and recommendations are suggested that depend on the evaluation outcomes. It is expected that the current risk evaluation research will make remarkable contributions to the risk management and control of large-scale desalination projects and further promote the development of the desalination industry.
  • [期刊] In-situ covalently bonded supramolecular-based protective layer for improving chlorine resistance of thin-film composite nanofiltration membranes
    To improve the chlorine resistance of the polyamide-based NF membranes, ferric ion and tannic (Fe-III-TA) networks were grafted onto the polyamide membrane surface via an in-situ modification strategy. The separation performance tests by a cross-flow NF system showed that the grafted membrane (TFC-n) possesses an obviously improved rejection for the selected salts, dyes, and micropollutants with only similar to 10.0% decrease in water permeability. The chlorination experiments under various pH values demonstrated that the TFC-n membrane presents much superior chlorine resistance than that of the control membrane. Importantly, the grafting layer was also applied to a commercial NF 270 membrane, and the Fe-III-TA grafted NF 270 membrane exhibited much higher chlorine resistance than that of the bare NF 270 and polyvinyl alcohol (PVA) coated NF 270 membranes. The greatly enhanced chlorine resistance can be ascribed to the combined effects of enhanced size exclusion, additional protection, and sufficient radical scavenging originated from the grafted Fe-III-TA networks. The high-performance of the grafted membrane highlight the feasibility of Fe-III-TA networks as a promising material for the construction of chlorine resistant interfaces for environmental nanocomposites.
  • [期刊] Performance enhancement of a conventional multi-effect desalination (MED) system by heat pump cycles
    Multi-effect desalination (MED) systems are highly promising for high salinity seawaters at large scales, and hence are used broadly in desalination plants. Despite the fact that the MED systems can be driven by various renewable or waste heat energies, many of the available renewable technologies are expensive in some parts of the globe. Hence, proposing and developing high-efficient mechanical-based MED units can be an encouraging alternative. In pursuance of this objective, two innovative mechanical-driven MED units are devised, simulated and the results are compared with those of the conventional MED-MVC (mechanical vapor compression) unit. For this aim, absorption-compression heat pump (ACHP) and vapor compression heat pump (VCHP) systems are used for integrating with the MED unit. Under a constant input power of 1845 kW it is found that proposing the MED-VCHP system instead of the conventional MED-MVC system improves gain-output-ratio (GOR), performance ratio (PR), freshwater rate, specific work consumption (SWC), exergy efficiency, exergy destruction rate, and exergy of loss by 1%, 12.86%, 12.64%, 11.45%, 10.78%, 3.3%, and 10.86% respectively. However, the unit cost of distilled water (UCDW) of the MED-VCHP system is around 6.7% higher than that of the MED-MVC system. Also, the MED-VCHP system uses less exergy of fuel than the MED-MVC system due to its high seawater exergy. Furthermore, it is found that one can decrease the overall exergy loss rate from 145.4 kW to 129.6 kW when the MED-VCHP system is used instead of the MED-MVC system.
  • [期刊] Surface modification of thin-film composite forward osmosis membranes with polyvinyl alcohol-graphene oxide composite hydrogels for antifouling properties
    In this study, the polyamide (PA) layers of commercial thin-film composite (TFC) forward osmosis (FO) membranes were coated with glutaraldehyde cross-linked polyvinyl alcohol (PVA) hydrogel comprising of graphene oxide (GO) at various loadings to enhance their fouling resistance. The optimal GO concentration of 0.02 wt% in hydrogel solution was confirmed from the FO membrane performance, and its influence on membrane antifouling properties was studied. The properties of the modified membranes, such as surface morphology, surface charge and wettability, were also investigated. PVA/GO coating was observed to increase the smoothness and hydrophilicity of the membrane surface. The foulant resistances of the pristine, PVA-coated and PVA/GO-coated membranes were also reported. PVA hydrogel-coated TFC membrane with a GO loading of 0.02 wt% showed a 55% reduction in specific reverse solute flux, only a marginal reduction in the water flux, and the best antifouling property with a 58% higher flux recovery than the pristine TFC membrane. The significant improvement in the selectivity of the modified membranes meant that the hydrogel coating could be used to seal PA defects. The biocidal GO flakes in PVA hydrogel coating also improved the biofouling resistance of the modified membranes, which could be attributed to their morphologies and superior surface properties.
  • [期刊] Accelerated chemical conversion of metal cations dissolved in seawater-based reject brine solution for desalination and CO2 utilization
    A new desalination and carbon utilization method was developed using all of three major cations dissolved in seawater-based industrial wastewater (i.e., calcium, magnesium, and sodium). Here, three types of metal-based inorganic substances could be produced and utilized without additional energy requirements for precipitation reactions. Calcium and magnesium were separated in the form of hydroxide precipitates. Using a 30 wt% aqueous monoethanolamine (MEA) solution, carbon dioxide was captured and reacted with the hydroxides to produce calcium carbonate and magnesium carbonate. After Ca2+ and Mg2+ separation, sodium chloride was used to produce sodium bicarbonate based on the characteristics of primary alkanolamines mixed with a high concentration of sodium ions. The entire process produced 0.3819, 0.2549, and 0.4579 mol of calcium carbonate, magnesium carbonate, and sodium bicarbonate, respectively. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted to investigate their crystal structure. Moreover, FT-IR spectroscopy was utilized to investigate the ionic species under Na+-rich conditions.
  • [期刊] Surface modification of thin-film composite forward osmosis membranes with polyvinyl alcohol-graphene oxide composite hydrogels for antifouling properties
    In this study, the polyamide (PA) layers of commercial thin-film composite (TFC) forward osmosis (FO) membranes were coated with glutaraldehyde cross-linked polyvinyl alcohol (PVA) hydrogel comprising of graphene oxide (GO) at various loadings to enhance their fouling resistance. The optimal GO concentration of 0.02 wt% in hydrogel solution was confirmed from the FO membrane performance, and its influence on membrane antifouling properties was studied. The properties of the modified membranes, such as surface morphology, surface charge and wettability, were also investigated. PVA/GO coating was observed to increase the smoothness and hydrophilicity of the membrane surface. The foulant resistances of the pristine, PVA-coated and PVA/GO-coated membranes were also reported. PVA hydrogel-coated TFC membrane with a GO loading of 0.02 wt% showed a 55% reduction in specific reverse solute flux, only a marginal reduction in the water flux, and the best antifouling property with a 58% higher flux recovery than the pristine TFC membrane. The significant improvement in the selectivity of the modified membranes meant that the hydrogel coating could be used to seal PA defects. The biocidal GO flakes in PVA hydrogel coating also improved the biofouling resistance of the modified membranes, which could be attributed to their morphologies and superior surface properties.
  • [期刊] Water distillation performance of carbon nanotube membrane: Non-equilibrium molecular dynamics simulation
    Carbon nanotube (CNT) has a great potential as membrane material for water distillation because of its smooth and hydrophobic surface. We numerically investigated the distillation performance of CNT membrane for direct contact membrane distillation using non-equilibrium molecular dynamics (NEMD) simulation by varying diameters and lengths of the CNT and system operating conditions such as temperature, temperature difference between feed (hot) and permeate (cold) reservoirs, and sodium chloride (NaCI) concentration in the feed reservoir. It was found from the NEMD simulations that the distillation performance is enhanced by increasing system temperature, reservoir temperature difference, and CNT diameter, and decreasing CNT length, atomic attraction strength between water molecules and CNT, and NaCI concentration. The NEMD simulation overpredicts the water vapor transport by approximately an order of magnitude as compared with the results from the Knudsen diffusion model. The simulated flooding pressure is in good agreement with the theoretical prediction by the Young-Laplace equation using the MD-calculated contact angle. Most importantly, the permeability of the CNT membrane is two orders-of-magnitudes higher than a common polymer-based membrane made of Polytetrafluoroethylene (PTFE) due to almost two order-of-magnitude higher Knudsen diffusion of the CNT membrane than that of the PTFE membrane.
  • [期刊] Enhanced performance of a direct contact membrane distillation (DCMD) system with a Ti/MgF2 solar absorber under actual weather environments
    In this study, we report on a solar membrane distillation (MD) system with a 5-stack Ti/MgF2 solar absorber adapted as a heat source under actual weather conditions. The 5-stack Ti/MgF2 solar absorber showed light absorption of 85% over the wavelength range from 0.3 to 2.5 mu m. This consequently induced greater heat and a two-fold greater water heating capability up to 80 degrees C for water in a closed water tank without insulation under a 1-sun illumination. The enhanced solar absorption of the Ti/MgF2 solar absorber showed a 12% improvement in permeate flux of the integrated MD system compared with a system without a solar absorber. Under actual weather conditions, the solar DCMD system with the Ti/MgF2 solar absorber successfully produced distillate water in the range of 0.51-4.78 L/m(2).day depending on weather conditions. Despite unfavorable solar irradiance conditions in autumn, the integrated DCMD system with the Ti/MgF2 solar absorber proved superior to a conventional commercial evacuated-tube solar collector in terms of daily production of distillate water and solar energy requirements for certain amounts of distillate.
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