Comparison of colloidal silica involved fouling behavior in three membrane distillation configurations using PTFE membrane

Abstract

Colloidal silica involved fouling behaviors in direct contact membrane distillation (DCMD), vacuum membrane distillation (VMD) and sweeping gas membrane distillation (SGMD) were studied. Three foulants were used in the experiments, including colloidal silica as representative of particulate foulants, calcium bicarbonate as dissolved inorganic foulant, and NOM (humic acid + alginate + BSA) as the dissolved organic foulant. The three types of fouants were combined to produce four different feed waters: silica alone; silica + calcium bicarbonate; silica + NOM; and silica + calcium bicarbonate + NOM. With 25% feed recovery, it was found that VMD showed the worst performance for most of the foulant combinations due to turbulence dead zones caused by the membrane deformation that increased foulant deposition. For the silica + calcium bicarbonate + NOM feed DCMD had the greatest fouling rate, although DCMD also had the highest flux of all configurations. SGMD showed the best fouling resistance of all configurations, although it was inclined to calcium carbonate fouling because carbon dioxide was removed in the permeate leading to calcium carbonate precipitation and could be alleviated by using air as sweeping gas. For feeds containing high-concentration calcium bicarbonate or carbonate foulants, VMD should be avoided to lower the formation of carbonate precipitants on the membrane surface if scale inhibitors are not used.

Understanding the fouling/scaling resistance of superhydrophobic/omniphobic membranes in membrane distillation

“…[59] with robust resistance to anti-scalants [34,60]. Silica scale was reported to block surface pores without wetting [28], however, this result was challenged by other reports [61][62][63]. [33,38,39]; Inverse solubility to temperature [21] Flux decline by pore blockage; negligible or detrimental effect on the distillate quality [25,33,41,43]; Co-precipitation with CaSO4 [52]; Precipitation inhibited by humic acid [43]; Remove readily by acid [22,26] CaSO4 Industrial, Seawater brine and groundwater…”

Recent Progress in the Membrane Distillation and Impact of Track-Etched Membranes

“…Among the above-listed materials, PTFE ((-C 2 F 4 -) n ) has the lowest surface energy of about 9–20·10 −3 N/m [ 119 ]. It is a highly crystalline polymer with excellent thermal and chemical resistance.…”

“…Authors observed that there is a significant decrease in permeate flux at concentrations up to ~48.9 g/L. The effects of calcium carbonate in the feed solution on the permeate flux were studied by Qin et al [ 119 ]. Decomposition of calcium carbonate in VMD and SGMD was faster than in DCMD.…”

Membrane processes

“…The fouling behavior relationship between colloidal silica and three MD methods (e.g., direct contact, sweeping gas, and vacuum) was studied by Qin, Zongli, et al (2018). Three different foulant mixtures were used: silica, silica plus calcium bicarbonate, silica and NOM, and silica plus calcium bicarbonate plus NOM.…”