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Application of membrane filtration to sugarcane juice refining is appealing because it can eliminate the usage of chemicals, achieve continuous and automated production, as well as produce superior quality of juice. However, some technical problems, such as low permeate flux, high sucrose loss in membrane retentate and serious membrane fouling, are impeding this technological upgrading in sugar industry. In this work, an integrated membrane process consisting of a tubular loose ultrafiltration (UF), a spiral-wound tight UF and a spiral-wound NF was developed to refine the raw sugarcane juice at pilot-plant scale. With a super high volume reduction ratio (VRR) of 20, the loose UF was able to be operated at a flux from 30 to 70 L m −2 h −1 , and the tight UF could run at a flux from 10 to 40 L m −2 h −1 ; at the same time, the color removal kept more than 95%. Moreover, diafiltration operation could recover most of sugar in the UF concentrates, leading to a high sucrose recovery of up to 98% in two-stage UF. A novel cascade diafiltration mode was proposed to save water by 25% compared with the separated diafiltration. Mathematical models could well predict the diafiltration efficiency for the loose UF but not for the tight UF. Permeate flux of the loose UF was dominated by membrane fouling while for the tight UF, osmotic pressure played a more important role in the flux decline. With a suitable cleaning strategy, the performance of this integrated membrane process can be nearly regenerated although the temperature jump between filtration and cleaning (60–30 °C) might result in some foulants accumulating in the membrane system. These results would serve as a valuable guide for process design and practical operation in subsequent industrial application. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs), as a group of micropollutants with high toxicity, are commonly detected in the environment and difficult to remove. In this work, five commercial polyamide (PA) nanofiltration (NF) membranes were used to treat three PAHs in the synthetic solution or coking wastewater and their removal mechanisms were discussed. By comparing water permeability and PAHs rejections of the NF membranes before and after PAHs adsorption, we found that the PAHs adsorption into the membrane was the dominant rejection mechanism at the initial filtration stage. Due to the limited adsorption capacity and increasing diffusion of PAHs in the membrane, the PAHs rejections would drop rapidly and then reach steady. Size exclusion mechanism was also important to PAHs removal by NF, especially for PAHs with weaker polarity and higher molecular weight. Although the polysulfone intermediate layer could adsorb substantial PAHs resulting in an increase of filtration resistance, the pore blocking and narrowing effects on the PA separation layer were still the main reasons for the permeability loss of NF membranes. However, the glucose rejection did not change obviously after the PAHs adsorption in the membrane. Through analyzing porosity and pore size distribution of the NF membranes before and after PAHs adsorption, we found that for the NF membrane with small pore size and narrow pore size distribution (e.g. NF270), PAHs adsorption produced indiscriminate pore blocking effect, and thus the average pore size and its distribution as well as glucose rejection did not change obviously after fouling formation; while for the NF membrane with large pore size and wide pore size distribution (e.g. NF10), PAHs adsorption occurred more seriously in the larger pores leading to a pore narrowing effect, but the reduced pore size was still too large to affect glucose rejections. The outcomes of this work suggested that the PAHs adsorption in both separation and intermediate layers of NF membranes should be avoided, and the NF membrane with narrow pore size distribution was preferred for PAHs removal. Image 1 • PAHs adsorption and size exclusion are the main mechanisms of PAHs removal by NF. • PAHs adsorb in both polyamide separation layer and polysulfone intermediate layer. • Membrane permeability loss is mainly attributed to the porosity decrease by PAHs adsorption. • PAHs adsorption produces pore blocking and narrowing effects on NF270 and NF10, respectively. • PAHs adsorbed in the membrane are eluted by chemical cleaning and release to the environment. [ABSTRACT FROM AUTHOR]

Interrelationship between physicochemical properties and separation performance of nine commercial nanofiltration (NF) membranes was systematically investigated. Seven NF membranes, NT103 and NT102 from Microdyn-Nadir, DF90 and DF30 from OriginWater, NF70, NF40-I and NF40-II from Hangzhou Development Center of Water Treatment Technology, were reported for the first time. FTIR spectra demonstrated that the skin layer of NF90, NT103 and DF90 was made from fully aromatic polyamide, while other membranes were the semi-aromatic ones. The fully aromatic membranes had rougher, thicker and less hydrophilic polyamide layer as well as lower permeability than the semi-aromatic ones. When applying these membranes to concentrate the pretreated dairy wastewater, NF270, DF30 and NF40-I with high lactose rejection, low salt rentention low transmembrane pressure (TMP) and negligible irreversible fouling (IF) are preferable. Furthermore, it was found that the pore size and skin thickness dominated the membrane permeability. Meanwhile, the pore size and TMP produced a negligible effect on the IF, while the higher roughness and contact angle resulted in the higher IF, implying that the main fouling mechanism in this case is the foulants adsorption at membrane surface rather than pore blocking (affected by pore size) or cake formation (its compressibility was influenced by TMP). Moreover, the retentions of both lactose and salts by the tight NF membranes appeared to be governed by steric hindrance. Thus, this work provides a new method to study membrane separation and fouling mechanisms by correlating the physiochemical properties and separation performance of different membranes. [ABSTRACT FROM AUTHOR]

The development of high-performance nanofiltration (NF) membranes with extreme chemical stability is urgently needed for the recovery of spent lithium. In this study, a series of polyurea membranes with high lithium recovery efficiency and pH stability were fabricated by zone-regulated interfacial polymerization (IP). The reaction inhibitor Cu2+ in the bulk aqueous phase reduces IP intensity by reversibly binding to the amino groups of polyethyleneimine monomers through chelate bonds. Meanwhile, surfactant promote the uniform diffusion of macromolecular aqueous monomers at the phase interface. The milder polymerization reaction and the more stable phase interface endow the polyurea membrane (NF 10k PEI-SDS-Cu 2+) with higher water permeance (2.1 L m−2 h−1 bar−1), desirable MgCl 2 rejection (94.7 %), and excellent fabrication repeatability. Moreover, the membrane demonstrates stable separation selectivity for Co2+/Li+ and SO 4 2−/Li+ under conditions of 0.05 mol L−1 H 2 SO 4 and 2 mol L−1 LiOH, respectively. Our study provides a facile method for constructing NF membranes with extreme pH stability and confirms the feasibility of membrane-based lithium recovery. [Display omitted] • The diffusion behavior of aqueous monomers is zone-regulated by adding Cu2+ and SDS. • PEI monomer chelated by Cu2+ reduces its diffusion in bulk phase and the intensity of IP reaction. • SDS improves distribution and diffusion of macromolecular monomers at the phase interface. • Milder IP reaction endows the membrane with better fabrication repeatability, especially for larger PEI. • The PU NF membrane is used for purification of Li + at extreme pH in spent lithium-ion battery recycling. [ABSTRACT FROM AUTHOR]

Clarification operations are vital to extract high-quality products from cane molasses. Ultrafiltration (UF) is very efficient for this purpose, although membrane fouling limits its large-scale application. In this work, five commercially available polyethersulfone UF membranes were evaluated for the clarification of molasses, whereby 30–100 kDa membranes were found to be the most suitable for this purpose. In order to minimise fouling formation during molasses clarification, the threshold flux concept was for the first time applied to dilution–concentration membrane processes. The threshold flux in concentration mode could be determined by correlating the average transmembrane pressure, average fouling rate, and specific energy consumption with the permeate flux at the same feed. An optimal dilution factor of eight was found based on such threshold flux concept and, only above the threshold flux, higher retentate concentrations and longer concentration times resulted in obvious fouling aggravation. Moreover, polydopamine coating and subsequent polymer (polyethyleneimine, chitosan oligosaccharide, alginate dialdehyde) grafting were used to tune the membrane surface properties to further control the membrane fouling. It was found that membranes modified with positive charges were more prone to molasses fouling, where the effect of the membrane surface properties on fouling was significant only above the threshold flux. However, pore narrowing after surface modification may increase the foulant retention and accumulation on the membrane, thus exerting certain influence on the threshold flux. The threshold flux value for the clarification of molasses with 50 and 100 kDa UF membranes was found to be 27–32 L m−2 h−1. The outcome of this work not only provides a guide to study threshold fluxes for industrial fluids at high concentrations, but also clarifies the effect of surface modification on the concentration polarisation/fouling formation during the clarification of cane molasses. Image 1 • The threshold flux was determined in dilution–concentration mode for the first time. • Correlation of the pump energy consumption with the permeate flux allows threshold flux determination. • This threshold flux concept can help find the optimal molasses dilution factor. • The negatively charged modified membrane exhibits the greatest antifouling performance. • Above the threshold flux, fouling is more sensitive to the feed and membrane properties. [ABSTRACT FROM AUTHOR]

Abstract: Furfural, found in the lignocellulosic prehydrolyzates at high concentration, is a strong inhibitor of growth and ethanol fermentation of Saccharomyces cerevisiae. Removal of furfural and concentration of monosaccharides were investigated by using two commercial nanofiltraton (NF) membranes with synthetic glucose–xylose–furfural solution as model. The effects of main operating parameters such as feed pH, permeation flux, temperature and feed concentration on the rejections of the three solutes, were studied. Results showed that rejections of the three solutes decreased with increasing feed pH and temperature, and increased with increasing permeation flux for both membranes. The concentrations of the three solutes had interaction effect on the rejection of furfural by NF90 membrane and rejections of the three solutes by NF270 membrane. Furthermore, the effects of two filtration modes, concentration and diafiltration, on the separation of furfural from monosaccharides were also investigated. With the two commercial NF membranes, concentration and purification of monosaccharides in the model solution can be accomplished. [Copyright &y& Elsevier]