Search

Membrane assisted crystallization (MACr) offers an innovative platform for crystallizing Na 2 CO 3 , allowing its reuse after CO 2 capture from flue gases by an alkaline solution ( i.e. , NaOH). In this study, the biomimetic aquaporin Inside™ membrane AIM60 was employed to enhance water removal, facilitating Na 2 CO 3 crystallization. The water channel in the active layer, comprising aquaporin proteins, and the strong wettability of membrane substrate assist a better performance. For instance, the water flux of AIM60 membrane for concentrating a 1.89 mol L −1 Na 2 CO 3 solution (osmotic pressure of 94.8 bar) in forward osmosis (FO) mode was 6.62 L m −2 h −1 and 3.25 L m −2 h −1 in pressure retarded osmosis (PRO) mode when a 5.13 mol L −1 NaCl solution (osmotic pressure of 304.9 bar) was employed as the draw solution. This demonstrates that the AIM60 FO membrane outperformed the previously reported dense reverse osmosis membrane (0.21 L m −2 h −1 in FO mode and 0.16 L m −2 h −1 in PRO mode) and a porous hydrophobic hollow fiber membrane (0.08 L m −2 h −1 ) under the same operating conditions. Crystallization utilizing the AIM60 membrane in an osmotic crystallizer was achieved without noticeable membrane scaling or degradation. Furthermore, a proper control of the supersaturation level induces crystallization of Na 2 CO 3 ·10H 2 O crystals with a purity of 99.94%. Hence, the aquaporin Inside™ FO membrane may be a promising alternative to existing methods for Na 2 CO 3 crystallization for its application in a CO 2 capture scenario. [ABSTRACT FROM AUTHOR]

Membranecontactors have been proposed as an advanced tool for CO2capture from flue gases by absorption in alkaline solutions. However,regeneration of the alkaline reagent and further CO2sequestrationare pending issues. In this paper, membrane-assisted crystallizationis proposed for crystallizing Na2CO3, whichallows its reuse, after CO2absorption from flue gases.Due to the presence of compounds other than CO2in fluegases (i.e., SO2, NOx), othercompounds (Na2SO4and NaNO3) mayinterfere with Na2CO3crystallization. Thiswas evaluated by measuring the flux through the membrane and the morphology,crystallography, and purity of the crystals. Furthermore, the presenceof NaCl possibly transferred from the osmotic solution to the feedsolution was evaluated. The experimental results indicate that thepresence of impurities decreases the flux through the membrane dueto the decrease of water activity, although there is no influenceon the overall mass transfer coefficient. The presence of Na2SO4affected the morphology of the Na2CO3crystals while NaNO3and NaCl had no apparenteffect on the crystalline products. It was confirmed that Na2CO3·10H2O was formed during the crystallization.Moreover, the purity of Na2CO3crystals reachesup to ca. 99.5%. Membrane-assisted crystallization was concluded tobe feasible in recovering CO2as a carbonate salt, whichcan possibly be reused in the industry. [ABSTRACT FROM AUTHOR]

The effect of competing ions in wastewater on the phosphate pre-concentrating efficiency by selectrodialysis was demonstrated in this study. Nitrate, bicarbonate and sulphate are three ions frequently present in wastewater. An inhibition of these ions to the phosphate concentrating efficiency was found to occur initially, but if the system runs for a longer time, the effect disappears. In the presence of nitrate, bicarbonate and sulphate, the phosphate concentrating efficiency in the product was significantly reduced from 188% to 78% after 210 min, but this could be recovered to 161% after 300 min. In addition, when operating selectrodialysis with synthetic municipal wastewater, phosphate was concentrated in the product with a twofold concentration compared to the initial concentration in the wastewater. Scaling on the cation exchange membrane and monovalent selective anion exchange membranes was observed during the selectrodialysis process when carrying out the experiment with synthetic municipal wastewater, but the membranes were almost completely recovered after a simple acid cleaning with 0.1 M HCl solution for 1 h. The present study indicates that selectrodialysis successfully concentrates phosphate from wastewater in the product stream, which makes a subsequent crystallization process viable to recover phosphate from wastewater. [ABSTRACT FROM AUTHOR]

Abstract: A promising and sustainable renewable source of phosphate was obtained through crystallization of calcium phosphate from wastewater. The aim of the present study was to evaluate the feasibility of an integrated selectrodialysis/crystallization process to recover phosphate, in which selectrodialysis was first used to pre-concentrate the phosphate before crystallization in a pellet reactor. The results of selectrodialysis show that an increase in current density, initial pH of the product, and initial feed concentration of phosphate led to an increase in phosphate concentration in the product. The desalination efficiency from wastewater was 87%, the phosphate concentration in the product can reach 16 mM with a purity of 44%, the current efficiency to transport phosphate and chloride was 26.6% for standard anion exchange membrane and 63% for monovalent selective anion exchange membrane. The optimal operational conditions for phosphate recovery with a pellet reactor were examined by changing the initial concentration, the pH and the superficial velocity. A precipitation efficiency of 82.7% of phosphate was achieved at pH 11, an inlet concentration of phosphates of 2.5 mM, a Ca/P molar ratio of 1.5 and a superficial velocity of 61 m/h. From the results, it can be concluded that the pellet reactor combined with selectrodialysis is an appropriate method to recover phosphate from wastewater as calcium phosphate, which is not only technically but also environmentally feasible, reducing water pollution, preventing eutrophication and yielding valuable and sustainable resources. [Copyright &y& Elsevier]