Abstract
Abstract This study investigates the membrane performance and fouling control in bubble-assisted sweeping gas membrane distillation with high concentration saline (333 K saturated solution) as feed. The results show that a longer bubbling interval (3 min) at a fixed bubbling duration of 30 s can most efficiently increase the flux enhancement ratio up to 1.518. Next, the flux increases with the gas flow rate under a relatively lower level, but tends to plateau after the threshold level (1.2 L·min−1). Compared to the non-bubbling case, the permeate flux reaches up to 1.623-fold at a higher bubble relative humidity of 80%. It was also found that greater flux enhancement can be achieved and, meanwhile, dramatic flux decline can be delayed for an intermittent bubbling system with a smaller nozzle size. These results accord well with the observations of fouling deposition in situ on the membrane surface with scanning electron microscope (SEM).
Highlights
Membrane distillation (MD) is an innovative separation technology for desalination, and water and wastewater treatment, due to its merits of mild operation temperature and pressure, with appropriate penetration rate, high rejection rate for nonvolatile components and small footprint when consuming alternative energy sources (Lawson & Lloyd ; Jansen et al )
The temperature/concentration layer at the membrane surface is reduced, and a higher flux is obtained in a bubbling sweeping gas membrane distillation (SGMD) process
It was found that an intermittent gas flow seems to be more effective than a steady one under the same experimental operating conditions, even if it improves the flux in comparison with the one without bubbling
Summary
Membrane distillation (MD) is an innovative separation technology for desalination, and water and wastewater treatment, due to its merits of mild operation temperature and pressure, with appropriate penetration rate, high rejection rate for nonvolatile components and small footprint when consuming alternative energy sources (Lawson & Lloyd ; Jansen et al ). Thereby, MD is an appealing method for extra-high concentration brine treatment owing. The decrease of driving force due to concentration and temperature polarization effects as well as fouling/scaling issues impedes the long-term stability performance of MD (Schofield et al ; Calabro & Drioli ). Many optimization strategies have been adopted to minimize the extent of fouling: (a) pretreatment, (b) membrane flushing, (c) gas bubbling, (d) temperature and flow reversal, (e) surface modification for anti-fouling membrane, (f) effect of magnetic/ultrasonic field, (g) use of antiscalants, and (h) chemical cleaning (Nghiem & Cath ; Hickenbottom & Cath )
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