NF membrane fouling by aluminum and iron coagulant residuals after coagulation–MF pretreatment

Abstract

The effects of coagulant residuals on fouling of a nanofiltration (NF) membrane were investigated. Experiments were carried out with a laboratory-scale microfiltration (MF)-NF setup and a pilot MF-NF plant. In the laboratory-scale experiments, NF feed water was pretreated with poly-aluminum chloride (PACl) or alum followed by MF. NF membrane permeability declined when the feed water contained residual aluminum at 18 µg/L or more, but not when it was lower than 9 µg/L. When pretreated with ferric chloride, no substantial decline of NF membrane permeability was observed; residual iron did not affect the permeability. When SiO2 was added to the water before the pretreatment with PACl, the NF membrane permeability declined at about double the speed. Thermodynamic calculations and elemental analysis of foulants recovered from the membranes indicated that the majority of inorganic foulants were compounds composed of aluminum, silicate, and possibly potassium. In the pilot plant, NF feed was pretreated by PACl. Transmembrane pressure for NF doubled over 4.5 months of operation. Although the aluminum concentration in the NF feed was not high (30 µg/L), analysis of membrane foulants revealed excessive accumulation of aluminum and silicate, also suggesting that aluminum residuals caused the membrane fouling by alumino-silicates or aluminum hydroxide.2

Non-enveloped virus reduction with quaternized chitosan nanofibers containing graphene

“…3,4 Advanced systems of purification include ozone treatment, coagulation, activated carbon filtration, and ultra-and nano-filtration are currently employed in select municipal water systems. 2,5 These methods have many of the same difficulties, including high backpressures of small pore-sized membranes, the ability of small viruses and heavy metals to escape the system, high cost, and the requirement for a large, multistep municipal system. Smaller systems can use photo and catalytic reduction of pathogens, often termed SODIS (solar disinfection), but require long disinfection times and the results can be variable.…”

Coagulation/flocculation as a pretreatment of landfill leachate for minimizing fouling in membrane processes

“…The MFI for the leachate pretreated in the best conditions with aluminum sulfate coagulation (pH 6.0 and 4,500 mgAl 2 (SO 4 ) 3 /L) was about 10 times greater than the value obtained for the one pretreated in the best conditions for ferric chloride coagulation (pH 6.0 and 4,200 mg FeCl 3 /L). Residual aluminum can cause great decline of NF membrane permeability when aluminum coagulants are used in the water pretreatment process; on the contrary, there is no substantial decline in NF membrane permeability when ferric chloride is used as a coagulant [34,35].…”

Optimization of air sparging and in-line coagulation for ultrafiltration fouling control

“…Emission Scanning Electron Microscope analysis (Wray et al, 2016) and contribute to increased cake resistance (Jang et al, 2005;Ohno et al, 2010;Wray et al, 2016). Furthermore, sweep flocculation promotes the formation of a more compressible and less porous layer when compared to the foulant layer under charge neutralization conditions (Lee et al, 2000).…”