Calcium Alginate Production through Forward Osmosis with Reverse Solute Diffusion and Mechanism Analysis

Abstract

Calcium alginate (Ca-Alg) is a novel target product for recovering alginate from aerobic granular sludge. A novel Ca-Alg production method was proposed herein where Ca-Alg was formed in a sodium alginate (SA) feed solution (FS) and concentrated via forward osmosis (FO) with Ca2+ reverse osmosis using a draw solution of CaCl2. An abnormal reverse solute diffusion was observed, with the average reverse solute flux (RSF) decreasing with increasing CaCl2 concentrations, while the average RSF increased with increasing alginate concentrations. The RSF of Ca2+ in FS decreased continuously as the FO progressed, using 1.0 g/L SA as the FS, while it increased initially and later decreased using 2.0 and 3.0 g/L SA as the FS. These results were attributed to the Ca-Alg recovery production (CARP) formed on the FO membrane surface on the feed side, and the percentage of Ca2+ in CARP to total Ca2+ reverse osmosis reached 36.28%. Scanning electron microscopy and energy dispersive spectroscopy also verified CARP existence and its Ca2+ content. The thin film composite FO membrane with a supporting polysulfone electrospinning nanofiber membrane layer showed high water flux and RSF of Ca2+, which was proposed as a novel FO membrane for Ca-Alg production via the FO process with Ca2+ reverse diffusion. Four mechanisms including molecular sieve role, electrification of colloids, osmotic pressure of ions in CARP, and FO membrane structure were proposed to control the Ca-Alg production. Thus, the results provide further insights into Ca-Alg production via FO along with Ca2+ reverse osmosis.

(3-Aminopropyl)trimethoxysilane-Functionalized Titanium Dioxide Thin-Film Nanocomposite Membrane: Enhanced Rejection Performance for Unary and Binary High-Salt Wastewater

“…The feed solution and the draw solution in the experiment were DI water and 1 M NaCl aqueous solution, respectively. The AL-DS orientation was selected due to the serious concentration polarization when using AL-FS orientation. − As shown in Figure , the water flux of the control TFC group is approximately 5.58 LMH, which is comparable to the commercial FO membranes under the same experimental conditions. − APTMS-TFN0.01 exhibited the highest water flux of up to 18.52 LMH, which is 231.90% higher than that of the TFC FO membrane (5.58 LMH) and 45.25% higher than that of the pristine TFN membrane (12.75 LMH), followed by APTMS-TFN0.05 numbered as high as 18.14 LMH. The enhanced water fluxes can be attributed to the incorporation of modified TiO 2 nanoparticles in the PA active layer, possibly due to the combined effect of increased hydrophilicity (Table ).…”

Separation Techniques and Circular Economy

“…Additionally, the highest possible value added of the separated products is obtained to enhance the economy. This current Special Issue titled “Separation Techniques and Circular Economy” in Membranes presents the novel separation technologies involving the recovery of extracellular polymeric substances (EPSs) [ 1 ], calcium alginate (Ca-Alg) [ 2 ] in wastewater treatment, plasmid DNA in gene therapy [ 3 ], lactose in dairy industry [ 4 ], lactic acid (LA) in the fermented broth of kitchen waste [ 5 , 6 ], phenylalanine losses in neutralization dialysis (ND) [ 7 ], the removal of secondary effluent organic matter (EfOM) [ 8 ], and acetaldehyde (CH 3 CHO) in the atmosphere [ 9 ].…”

“…Ca-Alg is a novel target product for recovering alginate from aerobic granular sludge. A novel production method, where Ca-Alg was formed in a sodium alginate (SA) feed solution (FS) and concentrated via forward osmosis (FO) with Ca 2+ reverse osmosis using a draw solution of CaCl 2 , was proposed [ 2 ]. An abnormal reverse solute diffusion was observed, with the average reverse solute flux (RSF) decreasing with increasing CaCl 2 concentrations, while the average RSF increased with increasing alginate concentrations.…”