Search

Hypophosphorous acid (H3PO2) is an important chemical product with wide applications in pharmaceuticals and electroless plating. In this study, bipolar membrane electrodialysis (BMED) was used to p...

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.

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.

Cane molasses is mainly used for ethanolic fermentation but a large amount of wastewater with refractory pigments and highly concentrated salts limited its application. For the first time, we attempt to directly extract pigments from molasses, and an integrated process consisting of ceramic membrane clarification, nonpolar resin adsorption and loose nanofiltration purification was proposed for recovery and fractionation of the molasses pigments. A 300 KDa ultrafiltration membrane was preferred for clarification of the pretreated molasses due to high permeate flux and low irreversible fouling, which could improve the quality of the extracted pigments. The nonpolar macroporous resin was chosen for only extracting the hydrophobic caramel pigments in order to reduce the resin regeneration frequency and improve the pigment purity, where ethanol was used for resin regeneration as it was easy to separate and reuse. The resin adsorption could reduce hydrophobic fouling formation and reappear the “salt-induced pore swelling” effect on the nanofiltration membrane, thus decreasing operating pressure by 50% at 60 °C and increasing the sucrose/salt transmission during diafiltration (save diafiltration water by 27%). The polyphenol pigments were obtained in the nanofiltration retentate after removing sugar and salts by diafiltration, and the permeate could be further desalted to produce syrup drinking. This novel integrated process could not only recover two natural pigments in a clean way, but also save energy and water consumption during the nanofiltration separation, which provided a sustainable strategy to utilize cane molasses.

Additional file 1: Table S1. Primer sequences used for qPCR assays. Table S2. RNA probes for FISH.

Coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been declared a pandemic. We herein report four COVID-19 cases with long-term positive viral ribonucleic acid (RNA) for about 61 days. Despite treatment with recombinant human interferon, convalescent plasma from COVID-19 patients, arbidol, etc., nucleic acid results were still positive for SARS-CoV-2. After treatment with ritonavir-boosted danoprevir (DNVr, 100/100 mg, once daily), all four patients showed two to three consecutive negative SARS-CoV-2 RNA and were thus discharged from hospital. Therefore, DNVr may be a potentially effective antiviral for COVID-19 patients with long-term positive SARS-CoV-2 RNA.

Interrelationship between physicochemical properties and separation performance of nine commercial nano-filtration (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.

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.

A novel integrated isoelectric precipitation-nanofiltration (NF)-anaerobic fermentation process was proposed for fully recycling model dairy wastewater (MDW). Isoelectric precipitation at pH 4.80 and subsequent centrifugation could remove most proteins. Acetic and butyric acids from anaerobic fermentation were available for acidic precipitation, and the performance was comparable to that of hydrochloric acid. The pretreatment of MDW by precipitation could greatly retard NF membrane fouling, especially at pH 7.09 owing to the electrostatic repulsion between solutes and membrane. NF270 membrane was preferred for MDW concentration due to its high antifouling performance, high permeability and acceptable permeate quality. Anaerobic fermentation fed with model NF retentate without caseins produced higher proportion of acetate, butyrate and hydrogen, and this effluent with shorter-chain volatile fatty acids (VFAs) and lower pH was more suitable for casein precipitation in dairy wastewater. (C) 2015 Elsevier B.V. All rights reserved.

Recovery of water and soluble substances from soybean soaking water (SSW) was carried out using an integrated membrane system consisting of ultrafiltration (UF) and reverse osmosis (RO). It was found that even using the four-stage UF-UF-RO-RO process with pH adjustment, the quality of RO permeate did not satisfy the emission standard, while the RO permeate from the two-stage UF-RO treatment could be reused for soybean soaking. The chemical oxygen demand (COD) of RO permeate from this process was 1700–2800 mg/L including acetic acid, γ-aminobutyric acid, lactic acid, alcohol, and other unidentified soybean extract with –C═O or –N–H groups, which had negligible effect on the subsequent soybean soaking. The RO permeate was reused for five cycles with addition of tap water (RO permeate/tap water = 1:1.5), and the soaked soybeans were used for Koji making, which showed the similar properties with Koji made from soybeans soaked by tap water. Furthermore, the concentrates in the integrated UF-RO system provided a raw material for culturing algae or preparing animal feed. This work demonstrated that through UF-RO treatment, the wastewater pollution from food industry could be eliminated by resource recovery and utilization.

Perfluorooctanoate (PFOA) is a persistent chemical that has been detected globally in the natural aquatic environment, while the waste discharge of fluoropolymer industry is one of the major sources of PFOA pollution. In this study, the removal and recovery of PFOA by nanofiltration (NF) were investigated with ammonium perfluorooctanoate model solutions under a wide range of PFOA concentrations. Performances of two commercially available NF membranes, namely NF270, NF90, were evaluated. The results show that the NF90 membrane offered a higher PFOA rejection (almost 100% at a PFOA concentration below 800 mg L-1). Using NF90 membrane, a model solution with a higher initial PFOA concentration of 1000 mg L-1 was used to further test the membrane performance. Both stable osmotic pressure at membrane surface and high PFOA rejection (99.3%) were obtained when the PFOA concentration was larger than a certain value due to the formation of micelles. Furthermore, membrane operation parameters (i.e. stirring speed, pH, temperature, and permeate flux) on the TMP and the PFOA concentration in permeate were investigated under a much higher initial PFOA concentration (10,000 mg L-1). The experimental results clearly confirm that recovery of highly concentrated PFOA of more than 117073.7 mg L-1 could be achieved by one-step NF treatment, while the permeate could be further treated by multi-stage NF to fully recover the PFOA. It was also found that the permeability of membrane could be recovered completely by simple water rinse, suggesting that NF is highly applicable for recovery of PFOA from wastewater in fluoropolymer production. (C) 2015 Elsevier B.V. All rights reserved.

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. (C) 2011 Elsevier Ltd. All rights reserved.