A shortage of safe drinking water is one of the main leading problems in the world. Even, in developed countries where water treatment systems are present, safe drinking water may not be always available due to the limitations of advanced water treatment techniques and high energy costs. On the other hand, many rural communities in Asia and Africa situated in semi-arid to arid regions are without reliable access to clean drinking water. It is, therefore, important to explore how solar energy can be linked to water treatment systems for clean drinking water production. Membrane-based water purification technologies play a major role in water purification by utilization of low-cost heat sources to make the process economically and technically viable for small, medium, and large-scale applications. Solar energy can be a viable source of power for water purification facilities in the coming years. Photovoltaic panels and solar thermal collectors are appropriate solar energy collectors for making a solar-powered water treatment system. Solar-assisted membrane-based water purification techniques could have a viable solution to the existing problems in semi-arid and arid regions. Due to the high quality of potable water demand, studies have been carried out on solar-assisted membrane-based technologies in water purification. This review considers basic concepts, specific energy consumption, water production cost, and applications of solar-driven membrane-based water purification technologies such as reverse osmosis, forward osmosis, electrodialysis, membrane distillation, and hybrid membrane systems. This review will allow the researchers to have a wider overview of the effort made by several investigators in the area of solar-assisted membrane-based water purification technology.
Kaolin (china clay) is a rock material that is very rich in kaolinite. A kaolin ore from Debre Tabor, Ethiopia containing 59.2 wt% SiO2, 24.9 wt% Al2O3, 2.4 wt% Fe2O3, and 8.22 wt% loss on ignition (LOI) was physically beneficiated, chemically leached, and thermally treated for possible industrial use, especially for ceramic membrane fabrication. The leaching experiments were carried out using oxalic acid solutions as leaching reagents for the iron extraction process. The effect of acid concentration, reaction temperature, and contact time on iron leaching was investigated. It was determined that the rate of iron extraction increased with the oxalic acid concentration, leaching temperature, and contact time. A substantial reduction of iron oxide (2.4 to 0.36 wt%) from the raw kaolin was observed at operating conditions of 2.0 M oxalic acid, the temperature of 120 °C, and contact time of 120 min. A maximum kaolin whiteness index of 81.4% was achieved through this leaching process. Finally, the physically beneficiated, chemically leached, and thermally treated kaolin raw material was used to fabricate a low-cost kaolin-based ceramic membrane. After firing at 1100 °C the ceramic membrane was found to have a mass loss of 11.04 ± 0.05%, water absorption of 8.9 ± 0.4%, linear shrinkage of 14.5 ± 0.05%. It was demonstrated to be chemically stable, having less than 3% mass loss in acid solution, and less than 1% mass loss in alkali solution. The newly developed membranes have thus properties comparable to commercial ceramic membranes.
Kaolin (china clay) is a rock material that is very rich in kaolinite. A kaolin ore from Debre Tabor, Ethiopia containing 59.2 wt.% SiO2, 24.9 wt.% Al2O3, 2.4 wt.% Fe2O3, and 8.22 wt.% loss on ignition (LOI) was physically beneficiated, chemically leached, and thermally treated for possible industrial use, especially for ceramic membrane fabrication. The leaching experiments were carried out using oxalic acid solutions as leaching reagents for the iron extraction process. The effect of acid concentration, reaction temperature, and contact time on iron leaching was investigated. It was determined that the rate of iron extraction increased with the oxalic acid concentration, leaching temperature, and contact time. A substantial reduction of iron oxide (2.4 to 0.36 wt. %) from the raw kaolin was observed at operating conditions of 2.0 M oxalic acid, the temperature of 120°C, and contact time of 120 min. A maximum kaolin whiteness index of 81.4 % was achieved through this leaching process. Finally, the physically beneficiated, chemically leached, and thermally treated kaolin raw material was used to fabricate a low-cost kaolin-based ceramic membrane. After firing at 1100°C the ceramic membrane was found to have a mass loss of 11.04 ± 0.05%, water absorption of 8.9 ± 0.4 %, linear shrinkage of 14.5 ± 0.05%. It was demonstrated to be chemically stable, having less than 3 % mass loss in acid solution, and less than 1 % mass loss in alkali solution. The newly developed membranes have thus properties comparable to commercial ceramic membranes.
In this study, the effect of retailing packaging material on tomato quality was investigated. Specifically, non-defective tomato fruits were selected after harvest and packed in four different packaging materials; open market bag, open box, sealed box and Xtend bag. A total of six treatments were prepared by storing the packaged fruits at 4 or 17°C for 10 days. Quality attributes of tomatoes such as calyx freshness, weight loss, fruit firmness, total soluble solids (TSS), colour and physiological damage were assessed. Generally, both packaging material and storage temperature affected the quality of the tomato fruits. The quality of tomato fruits stored at 4oC was generally superior to those stored at 17°C.Calyx of tomato fruits stored in open market bag (stored at 17°C) and open box (stored at 17°C) were very dry after storage compared to the tomato fruits stored at 4°C. Tomato fruits packed in Xtend bag and sealed box were firmer than those packed in open box and open market bag. The carbon dioxide (CO2) concentration in sealed box was substantially higher (8.25%) than that in Xtend bag (2.07%). In contrast, the oxygen (O2) concentration in the Xtend bag was higher (18.90%) than that in the sealed box (14.75%). Tomatoes packed in Xtend bag and sealed box had minimal changes in colour intensity (C*), showed lower TSS values compared to tomato fruits packed in other packaging materials. Xtend bag and sealed box seems to be better packaging material for storing tomato fruits for a period of 10 days.
Hydrophobic metakaolin-based flat sheet membrane was developed via phase inversion and sintering technique and modified through 1H,1H,2H,2H-perfluorooctyltriethoxysilane grafting agents. The prepared membrane was characterized by different techniques such as XRD, FTIR, SEM, contact angle, porosity, and mechanical strength. Their results indicated that the wettability, structural, and mechanical properties of the prepared membrane confirm the suitability of the material for membrane distillation (MD) application. The prepared metakaolin-based flat sheet membrane acquired hydrophobic properties after surface modification with the water contact angle values of 113.2° to 143.3°. Afterward, the membrane performance was tested for different sodium chloride aqueous solutions (synthetic seawater) and various operating parameters (feed temperature, feed flow rate) using direct contact membrane distillation (DCMD). Based on the findings, the prepared membrane at metakaolin loading of 45 wt.% and sintered at 1,300 °C was achieved the best performance with >95% salt rejection and permeate flux of 6.58 ± 0.3 L/m2 · h at feed temperature of 80 °C, feed concentration of 35 g/L, and feed flow rate of 60 L/h. It can be concluded that further optimization of membrane porosity, mechanical, and surface properties is required to maximize the permeate flux and salt rejection.
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