PhD Student, University of Pittsburgh
My research goal is to study the fundamentals of membrane processes by using membrane distillation
Membrane Distillation (MD) is a thermal separation process that is driven by the vapor pressure difference across a hydrophobic membrane. The principle of MD is the same as conventional distillation. However, MD employs hydrophobic membranes for its operation. MD has immense potential in the desalination of highly saline wastewaters where reverse osmosis is not feasible. Recent advances in membrane distillation (MD) have proven that the process can obtain almost pure water from the most challenging wastewaters. MD can also concentrate saline solutions up to saturation and can have very high water recovery. While many studies have been carried out on membrane distillation for recovery of pure water from saline waste waters, there are certain avenues where MD has not been studied in detail. The primary focus of my research is to study the fundamentals and energetics of direct contact membrane distillation when treating high salinity waste waters and apply them on plant-level MD systems.
Abstract: Direct contact membrane distillation (DCMD) supplied with waste heat was demonstrated for water recovery from saline demineralisation regeneration waste. The pilot plant was located at a gas fired power station which provided the < 40 °C waste heat and wastewater to the DCMD system with 0.67 m2 of membrane area. The trial was operated over three months without replacing the membranes or module and achieved 92.8% water recovery. Flux was approximately 3 L/(m2·h) and was dependant mostly on the waste heat temperature being supplied. Membrane fouling affected flux and thermal energy demand only at the very end of the trial. The system produced a high quality distillate product with average 99.9% dissolved solids rejection. Small amounts of ammonia and carbon dioxide however were found in the permeate. Membrane analysis post-trial revealed fouling was principally inorganic scale but organic matter on the membrane was also evident. Permeate side fouling was also observed, attributed to corrosion of the cooling heat exchanger. Based on the available energy for a continuously operating 500 MW (electric) rated power station, the treatment potential was estimated at up to 8000 kL/day, which is practical for supplying water to numerous industrial, residential or agricultural sites.
Pub.: 09 Feb '16, Pinned: 31 Jul '17
Abstract: Authors: Aoyi Luo ; Noam Lior Article URL: http://www.tandfonline.com/doi/full/10.1080/19443994.2016.1152637?ai=10ubn&mi=47tg1r&af=R Citation: Desalination and Water Treatment Publication Date: 2016-02-26T02:29:19Z Journal: Desalination and Water Treatment
Pub.: 26 Feb '16, Pinned: 31 Jul '17
Abstract: Authors: Hyeongrak Cho ; Yongsun Jang ; Jaewuk Koo ; Yongjun Choi ; Sangho Lee ; Jinsik Sohn Article URL: http://www.tandfonline.com/doi/full/10.1080/19443994.2016.1152640?ai=10ubn&mi=47tg1r&af=R Citation: Desalination and Water Treatment Publication Date: 2016-04-15T12:10:59Z Journal: Desalination and Water Treatment
Pub.: 15 Apr '16, Pinned: 31 Jul '17
Abstract: Membrane distillation (MD) and membrane crystallization (MCr) have been applied for treatment of real industrial wastewater to produce high quality sodium sulfate. Simultaneously, MD and MCr minimize waste disposal and generate a fresh water stream. Untreated and wastewater pre-concentrated by nanofiltration have been utilized in MD and MCr under several operative conditions. The untreated wastewater indicated the steadiest performance. The MD and MCr operations have proven their long term stability throughout the concentration of wastewater. The treatment has been continued for more than 90 h for the untreated wastewater. Despite the utilized wastewaters have a high scaling potential in particular for silica, calcium and magnesium, no reduction in flux or wetting of the membrane surface have been observed due to fouling. Moreover, the crystalline product of Na2SO4 recovered as Thenardite (the anhydrous form) exhibits narrow size distribution and low incorporation of impurities.
Pub.: 21 May '16, Pinned: 31 Jul '17
Abstract: Authors: Hyeongrak Cho ; Yongjun Choi ; Sangho Lee ; Jinsik Sohn ; Jaewuk Koo Article URL: http://www.tandfonline.com/doi/full/10.1080/19443994.2016.1190109?ai=10ubn&mi=47tg1r&af=R Citation: Desalination and Water Treatment Publication Date: 2016-06-22T01:17:20Z Journal: Desalination and Water Treatment
Pub.: 22 Jun '16, Pinned: 31 Jul '17
Abstract: Membrane distillation (MD) was evaluated as a treatment option of wastewater reverse osmosis concentrate (WWROC) discharged from wastewater reclamation plants (WRPs). A direct contact MD (DCMD), at obtaining 85% water recovery of WWROC showed only 13–15% flux decline and produced good quality permeate (10–15 µS/cm, 99% ion rejection) at moderate feed temperature of 55 °C. Prevalent calcium carbonate (CaCO3) deposition on the MD membrane occurred in treating WWROC at elevated concentrations. The combination of low salinity and loose CaCO3 adhesion on the membrane did not significantly contribute to DCMD flux decline. Meanwhile, high organic content in WWROC (58–60 mg/L) resulted in a significant membrane hydrophobicity reduction (70% lower water contact angle than virgin membrane) attributed to low molecular weight organic adhesion onto the MD membrane. Granular activated carbon (GAC) pretreatment helped in reducing organic contents of WWROC by 46–50%, and adsorbed a range of hydrophobic and hydrophilic micropollutants. This ensured high quality water production by MD (micropollutants-free) and enhanced its reuse potential. The MD concentrated WWROC was suitable for selective ion precipitation, promising a near zero liquid discharge in WRPs.
Pub.: 29 Nov '16, Pinned: 31 Jul '17
Abstract: In this study, ten different commercially available PTFE, PP and PVDF membranes were tested in desalination of highly saline water by air gap membrane distillation (AGMD). Process performance was investigated under different operating parameters, such as feed temperatures, feed flow velocities and salt concentrations reaching 120 g/L, and different membrane characteristics, such as membrane material, thickness, pore size and support layer, using a locally designed and fabricatd AGMD module and spacer. Results showed that increasing feed temperature increases permeate flux regardless of the feed concentration. However, feed flow velocity does not significantly affect the flux, especially at low feed temperatures. The PP membrane showed a better performance than the PVDF and PTFE membranes. Permeate flux decreases with the increase of salt concentration of feed solution, especially at higher concentrations above 90 g/L. The existence of membrane support layer led to a slight decrease of permeate flux. Membranes with pore sizes of 0.2 and 0.45 μm gave the best performance. Smaller pore size led to lower flux and larger pore size led to pore wetting due to lower LEP values. The effect of concentration polarization and temperature polarization has also been studied and compared.
Pub.: 07 Apr '16, Pinned: 31 Jul '17
Abstract: Advances in membrane distillation are limited by the wetting phenomenon. Wetting is typically determined by examining the permeate water quality. In this work, we apply an electrically conductive membrane to direct contact membrane distillation combined with an electrochemical system. The membrane was fabricated by heat pressing a carbon cloth with electrospun PVDF-HFP mat. The membrane acts not only as a barrier to reject salt with 99.6% rejection, but also as an electrode where in the current through the system is used to detect wetting which allows Na+ and Cl- ions to complete the cell. It was found that the membrane has an LEP of 36 psi and mean pore size of 0.2 µm. A continuous voltage of +1V was applied during the direct contact membrane distillation process process, and a sharp increase in current was observed at the point where wetting was induced.
Pub.: 19 Apr '17, Pinned: 31 Jul '17
Abstract: Hydraulic fracturing used for natural gas extraction from unconventional onshore resources generates large quantities of produced water that needs to be managed efficiently and economically to ensure sustainable development of this industry. Membrane distillation can serve as a cost effective method to treat produced water due to its low energy requirements, especially if waste heat is utilized for its operation. This study evaluated the performance of commercially available hydrophobic microfiltration membranes in a direct contact membrane distillation system for treating very high salinity (i.e., up to 300,000 mg/L total dissolved solids) produced water. Polypropylene and polytetrafluoroethylene membranes yielded the highest permeate flux with membrane distillation coefficient of 5.6 l/m2/hr/kPa (LMH/kPa). All membranes showed excellent rejection of dissolved ions, including naturally occurring radioactive material (NORM), which is a significant environmental concern with this high salinity wastewater. Analysis of membranes after extended testing with actual produced waters revealed unevenly distributed inorganic deposits with significant iron content. A key finding of this study is that the iron oxide fouling layer had negligible effect on membrane performance over extended period of time despite its thickness of up to 12 μm. The results of this study highlight the potential for employing membrane distillation to treat high salinity wastewaters from unconventional gas extraction.
Pub.: 27 Nov '16, Pinned: 31 Jul '17