[Influence of magnetic field on membrane flux and CaCO3 crystallization in the unstirred dead-end NF process].
With reference to a control system operating under same conditions, unstirred dead-end NF processes of magnetic pretreated solution containing Ca2+ were conducted with NF and NF270 nanofiltration membranes to study the influence of magnetic field on the membrane flux and the crystallization of CaCO3 on membrane surface. Ca2+ in the solution was 3.6 mmol/L, and the hardness was equal to the alkalinity. When experimental solution with initial volume of 300 mL was concentrated 2 times, the flux of membranes treating general solution presents a monotonously falling trend, while the flux of membranes treating magnetic solution decreased firstly and then increased, and then failed again. The average flux in treating magnetic solution was higher than that of the general solution, which indicated that magnetic pretreatment could ameliorate parts of membrane performance. More crystals were formed on membranes treating magnetic solution according to the SEM observation and the chemical analysis. It was assumed that magnetization could speed crystallization on membrane surface, which resulted in concentration falling in the polarization layer and flux increasing accordingly. The formed crystals that may decrease effective membrane areas were all deposited on the membrane surface, so the flux decreased finally. Average flux was higher while more crystals were formed on membranes, which conflicted to the conventional concept of membrane fouling and could not be explained by the serial-resistance model, implied the crystallization on membrane surface unnecessarily detered membrane performance.
Zhu
An-na
AN
Department of Environmental Science & Engineering, Tsinghua University, Beijing 100084, China.
Zhu
Wan-peng
WP
Wang
Xiao-lin
XL
D002119:Calcium Carbonate / Q000737:chemistry*; D003460:Crystallization; D004574:Electromagnetic Fields; D004868:Equipment Failure; D005374:Filtration; D008567:Membranes, Artificial; D036103:Nanotechnology; D014865:Waste Disposal, Fluid / Q000379:methods*; D018508:Water Purification / Q000379:methods*
D008567:Membranes, Artificial; D002119:Calcium Carbonate