Physical Cleaning Research Articles

Novel insights into the interaction reactive components and synergistic fouling mechanisms of ultrafiltration by natural organic matter fractions and kaolin

The mechanisms governing interactions among various natural organic matter (NOM) fractions and the subsequently impact on ultrafiltration process have not been systematically studied. In this work, bovine serum albumin (BSA), humic acid (HA), sodium alginate (SA) were applied as model NOM to explore the influence of the interactions among NOM on ultrafiltration process. Results indicated that tryptophan-like fluorescence fraction was the dominant reaction fraction of HA to react with SA and BSA. Different interactions among model NOM not only changed the interception order of fluorescence fractions by ultrafiltration from fulvic acid-like, humic-like and tryptophan-like in BSA/HA mixture to tryptophan-like, humic-like and fulvic acid-like in BSA/HA/SA/kaolin mixture, but also remarkably influence the membrane fouling behavior. In BSA/HA mixture, new-generated aggregates with molecular weight (MW) of 10 kDa could not pass though ultrafiltration membrane and mainly contributed to chemical reversible fouling. In BSA/HA/SA mixture, SA simultaneously reacted with BSA and HA to generate aggregates with larger MW which could be washed down by physical cleaning. In BSA/HA/SA/kaolin mixture, the aggregates with MW of 10 kDa and chemical reversible fouling were disappeared due to the adsorption role of kaolin. These findings could further improve our understanding regarding membrane fouling mechanisms of raw water with different components.

Control strategies against algal fouling in membrane processes applied for microalgae biomass harvesting

Microalgae biomass is increasingly applied in a variety of high-end applications, such as biofuel production, CO2 fixation, food, and cosmetics. As the demand for microalgae increases, improvements in biomass harvesting techniques are required since dewatering represents a significant fraction of the total algae production cost. While membrane technology is growing as a means to achieve effective biomass harvesting, fouling from microalgae suspensions is a major drawback, since these streams are rich in organic compounds, nutrients, and biological materials. The aim of this paper is to present the state-of-the-art of the control strategies to manage algal fouling. The control strategies are divided into: (i) mitigation strategies, including pre-treatment options, modified membrane surfaces, and hydrodynamic approaches; and (ii) adaptation strategies, which include physical, mechanical, and chemical cleaning. Fouling mitigation strategies are implemented in membrane separation processes seeking to maintain high productivity without compromising biomass quality, while minimizing the energy cost related to fouling control. Adaptation techniques include optimization of the cleaning time and effective removal of the irreversible foulants. Further, minimization in the use of chemicals and of the backflush permeate must be achieved to ensure an efficient performance in chemical cleaning and backwash approaches, respectively. Finally, the article discusses future research perspectives in membrane-based microalgae harvesting with a focus on zero liquid discharge and effective fouling control strategies within the water-energy nexus.

Loose nanofiltration membranes functionalized with in situ-synthesized metal organic framework for water treatment

In this study, modified loose nanofiltration membranes were prepared by in-situ decoration with Zeolitic Imidazolate Framework-7 (ZIF-7) on the surface of porous polyethersulfone substrates functionalized with co-deposited sulfobetaine methacrylate (SBMA) zwitterion (ZW) and polydopamine (PDA). With the aid of ZW/PDA active layer co-deposition under mild conditions, ZIF-7 metal organic framework (MOF) nanocrystals were successfully formed and anchored onto the membrane surface via both non-covalent and covalent bonds to simultaneously achieve the desired selectivity and productivity of the loose nanofiltration membranes. The characterization results confirmed the successful deposition of the ZW/PDA active layer and the consequent decoration with ZIF-7 nanocrystals. The average water contact angle decreased notably from 81.4 to 51.43° upon the formation of ZIF-7. This membrane showed high rejection (∼99.9%) of methyl blue and Congo red dyes and high water flux with dye solutions (around 40 L m−2h−1) at a very low applied pressure of 1.5 bar. Moreover, the filtration experiments revealed that functionalized membranes exhibited a significant reduction in fouling and biofouling propensity. Notably, the MOF-SBMA/PDA membrane displayed favorable antifouling behavior associated with a significant ability to recover flux upon simple physical cleaning. The combination of these two properties is possibly the most promising feature of the membrane proposed in this study.

Biocarriers facilitated gravity-driven membrane filtration of domestic wastewater in cold climate: Combined effect of temperature and periodic cleaning

In this study, two lava stone biocarrier facilitated gravity-driven membrane (GDM) reactors were operated at ~8 °C and ~22 °C in parallel for treating primary wastewater effluent. Although the biocarrier reactor at 8 °C displayed less efficient removals of biodegradable organics than that at 22 °C, both GDM systems (without cleaning) showed comparable fouling resistance distribution patterns, accompanying with similar cake filtration constants and pore constriction constants by modelling simulation. Compared to the GDM at 8 °C, more foulants were accumulated on the GDM at 22 °C, but they presented similar soluble organics/inorganics contents and specific cake resistances. This indicated the cake layers at 22 °C may contain greater-sized foulants due to proliferation of both prokaryotes and eukaryotes, leading to a relatively less-porous nature. In the presence of periodic cleaning (at 50 °C), the cleaning effectiveness followed a sequence as ultrasonication-enhanced physical cleaning > two-phase flow cleaning > chemical-enhanced physical cleaning > physical cleaning, regardless of GDM operation temperature. However, significantly higher cake resistances were observed in the GDM system at 22 °C than those at 8 °C, because shear force tended to remove loosely-attached foulant layers and may compress the residual dense cake layer. The presence of periodic cleaning led to dissimilar dominant prokaryotic and eukaryotic communities in the cake layers as those without cleaning and in the lava stone biocarriers. Nevertheless, operation temperature did not influence GDM permeate quality, which met EU discharge standards.

Gypsum scaling mechanisms on hydrophobic membranes and its mitigation strategies in membrane distillation

Mineral scaling is one of the significant obstacles in hypersaline wastewater treatment using membrane distillation (MD) technology. A deeper understanding of the scaling mechanism can help to solve mineral scaling problems. This work investigated three porous membranes with different surface pore sizes and hydrophobic properties, i.e., PTFE-0.22, PTFE-0.10, and PVDF-0.22, used in the direct-contact membrane distillation (DCMD) process. We selected gypsum as a model contaminant in the scaling experiment and focused on its homogeneous and heterogeneous nucleation effects on membrane scaling. The morphology analysis of the scaled membrane revealed that homogeneous nucleation might be the main reason for scaling. In addition, gypsum crystallization in the membrane pores was the main reason for the significant flux decline and low physical cleaning efficiency (PTFE-0.22). When the surface pore size of the membrane (PTFE-0.10 and PVDF-0.22) was reduced, gypsum crystalization in the pores could be alleviated. Such phenomenon was mainly initiated by homogeneous nucleation. Nonetheless, the surface scaling was still severe for PVDF-0.22 because its hydrophobicity was too low to inhibit the heterogeneous nucleation on the membrane. However, PTFE-0.10 with a small surface pore size and high hydrophobicity could simultaneously alleviate the effect of two nucleations. We could easily remove the gypsum crystals deposited on the membrane surface by physical cleaning and achieve more than 90% flux recovery efficiency. Therefore, reducing the surface pore size and increasing the surface hydrophobicity should be two main strategies in preparing the anti-scaling hydrophobic membrane used in MD.

Argan oil as a pretreatment of human hair before exposure to oxidative damage: Attenuated total reflectance and protein loss studies.

In recent years, argan oil has gained increasing interest in hair care products. In this study, attenuated total reflectance technique was utilized as a fast method and the results were compared to protein loss measurements in order to show the preventive effect of argan oil pre-treatment on excised human hair after oxidative hair damage. Hair tresses were divided into three groups: in group-1; they were damaged using oxidant agent solely, in group-2 and 3; hair were pre-treated with argan oil before undergoing the oxidative damage. In group-2, the oil was removed by physical cleaning but in group-3 the oil was removed with a washing procedure. ATR (attenuated total reflectance) spectrum was recorded for different samples. Quantitative studies of protein loss in hair samples were performed by Lowry method. The antioxidant properties of argan oil were also measured in vitro using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) protocol, which determined the ability of the oil to scavenge the DPPH free radicals. The amount of protein loss with oil pre-treated groups was reduced significantly. The ATR spectrum showed oil deposition on hair even after washing. Four distinctive ATR peaks were changed during oxidation. The changes in peak height values were linear. The antioxidant property measured with DPPH method led to a IC50 value of 59µg/ml. Argan oil pre-treatment was effective in protecting hair against oxidative damage. ATR outcomes were in accordance with protein loss results. In this study, the ATR testing method as a fast technique was used efficiently in quantification of hair damage.

Oil-in-water emulsion separation: Fouling of alumina membranes with and without a silicon carbide deposition in constant flux filtration mode

Ceramic membranes have drawn increasing attention in oily wastewater treatment as an alternative to their traditional polymeric counterparts, yet persistent membrane fouling is still one of the largest challenges. Particularly, little is known about ceramic membrane fouling by oil-in-water (O/W) emulsions in constant flux filtration modes. In this study, the effects of emulsion chemistry (surfactant concentration, pH, salinity and Ca2+) and operation parameters (permeate flux and filtration time) were comparatively evaluated for alumina and silicon carbide (SiC) deposited ceramic membranes, with different physicochemical surface properties. The original membranes were made of 100% alumina, while the same membranes were also deposited with a SiC layer to change the surface charge and hydrophilicity. The SiC-deposited membrane showed a lower reversible and irreversible fouling when permeate flux was below 110 L m−2 h−1. In addition, it exhibited a higher permeance recovery after physical and chemical cleaning, as compared to the alumina membranes. Increasing sodium dodecyl sulfate (SDS) concentration in the feed decreased the fouling of both membranes, but to a higher extent in the alumina membranes. The fouling of both membranes could be reduced with increasing the pH of the emulsion due to the enhanced electrostatic repulsion between oil droplets and membrane surface. Because of the screening of surface charge in a high salinity solution (100 mM NaCl), only a small difference in irreversible fouling was observed for alumina and SiC-deposited membranes under these conditions. The presence of Ca2+ in the emulsion led to high irreversible fouling of both membranes, because of the compression of diffusion double layer and the interactions between Ca2+ and SDS. The low fouling tendency and/or high cleaning efficiency of the SiC-deposited membranes indicated their potential for oily wastewater treatment.

Effect of Aeration Intensity on Performance of Lab-Scale Quorum-Quenching Membrane Bioreactor.

Biofouling is one of the main drawbacks of membrane bioreactors (MBRs). Among the different methods, the quorum-quenching (QQ) technique is a novel method as it delays biofilm formation on the membrane surface through disruption of bacterial cell-to-cell communication and thus effectively mitigates membrane biofouling. QQ bacteria require a certain concentration of dissolved oxygen to show their best activities. Despite the importance of the amount of aeration, there have not been enough studies on aeration condition utilizing the separate determination of pure QQ effect and physical cleaning effect. This research aimed to find the optimum aeration intensity by separation of the two effects from QQ and physical cleaning. Three bead type conditions (no bead, vacant bead, and QQ beads) at three aeration intensities (1.5, 2.5, and 3.5 L/min representing low, medium, and high aeration intensity) were applied. From the results, no QQ effect and small QQ effect were observed at low and high aeration, while the greatest QQ effect (48.2% of 737 h improvement) was observed at medium aeration. The best performance was observed at high aeration with QQ beads having a 1536 h operational duration (303% improvement compared to the no bead condition); however, this excellent performance was attributed more to the physical cleaning effect than to the QQ effect.

Treatment of Hydrothermal-Liquefaction Wastewater with Crossflow UF for Oil and Particle Removal.

This study aims to evaluate the application of ceramic ultrafiltration membranes in the crossflow mode for the separation of particles and oil in water emulsions (free oil droplets and micelles) from hydrothermal-liquefaction wastewater (HTL-WW) from the hydrothermal liquefaction of municipal sewage sludge. The experiments were carried out using one-channel TiO2 membranes with pore sizes of 30, 10 and 5 nm. The results showed that the highest stable permeability could be achieved with a membrane-pore size of 10 nm, which experienced less fouling, especially through pore blockage, in comparison to the two other pore sizes. Instead of observing an increase in the permeability, the application of a higher feed temperature as well as backwash cycles led to a clear increase in irreversible fouling due to the presence of surfactants in the HTL-WW. Among several physical and chemical cleaning methods, alkaline cleaning at pH 12 proved to be the most efficient in removing fouling and maintaining stable performance on a long-term basis. Ceramic-membrane ultrafiltration can be considered as an adequate first-stage treatment of real HTL wastewater.

Accelerated spraying-assisted layer by layer assembly of polyethyleneimine/titania nanosheet on thin film composite membrane for reverse osmosis desalination

Layer by layer (LbL) is a simple and versatile technique for the preparation of an ultrathin layer of composite membrane but the conventional dip-assisted LbL deposition is time consuming. In this study, an accelerated LbL assembly based on spray-on technique was successfully adopted to modify the surface of reverse osmosis (RO) thin film composite (TFC) membrane. The alternate layers of titania nanosheets (TNS) and polyethyleneimine (PEI) were formed on TFC membrane via electrostatic interaction using both spray and dip-assisted LbL deposition techniques. The membrane was investigated in terms of the changes of surface charge, hydrophilicity, roughness, ionic crosslinking and morphology. The spray-coated TFC membrane with 1 bilayer of PEI/TNS (1PEI/TNSSC-TFC) achieved the highest water permeability of 1.39 L.m−2.h−1.bar−1 compared to that of TFC membrane. It also achieved 19.42% increment in the water permeability compared to the dip-coated membrane with the same bilayer of PEI/TNS (1PEI/TNSDC-TFC) with salt rejection of 97%. 1PEI/TNSSC-TFC membrane exhibited excellent anti fouling property towards bovine serum albumin (BSA) and sodium alginate (NaAlg) with 100% of permeate recovery upon physical cleaning. This work demonstrates the feasibility of spray-coated technique in terms of the time effectiveness and the precise control of nanoparticles deposition during the surface membrane modification.

Fouling control strategies for direct membrane ultrafiltration: Physical cleanings assisted by membrane rotational movement

Recently, interest in the application of direct membrane filtration (DMF) in wastewater treatment has increased as an alternative to conventional activated sludge technologies. However, membrane fouling remains the main limitation for its application on an industrial scale. Dynamic shear-enhanced membrane systems, such rotating hollow fibre membranes (R-HFM), have shown to be effective in fouling control and mitigation with complex suspensions (e.g. anaerobic membrane bioreactors). In fact, previous works with DMF demonstrated the capability of membrane rotation to prevent matter deposition during the filtration cycles. Nevertheless, physical cleanings aided by membrane rotation in systems where there is no biological organic matter degradation has not been previously explored.Therefore, the current study addresses a physical cleaning strategy based on membrane module rotation for DMF. The effect of rotational speed (0 – 340 rpm) and relaxation time (0 – 270 s) on filtration performance was studied at dead-end lab scale trials. Pre-treatment effectiveness by in-situ and ex-situ sewage coagulation on fouling mitigation has been also assessed. DMF improved with pre-coagulation, reducing significantly membrane fouling. Ex-situ coagulation was identified as the best pre-treatment mode since flocs breakage and foulants releasing are avoided. In addition, the rotational speed increase during the backwashing stage enhanced erosion and dispersion of detached foulants. Besides, the addition of a relaxation stage (tR ≥ 180 s) enhanced the effectiveness in fouling re-dispersion. The physical cleanings demonstrated their effectiveness during long term trials, allowing operation at high permeate fluxes (24 L·h−1·m−2) with moderate organics up-concentration.

Characterization of scalants and strategies for scaling mitigation in membrane distillation of alkaline concentrated circulating cooling water

Treatment of circulating cooling water via reverse osmosis for water reuse is attractive. However, the discharge of the concentrated circulating cooling water (CCCW) is still an issue to environment. In this paper, direct contact membrane distillation (DCMD) was exploited to treat alkaline CCCW for water reclamation and volume reduction. Results suggested that the alkaline CCCW can be concentrated to achieve high volume concentration factor. DCMD performance decline was primarily due to calcium carbonate (CaCO3) scaling. The CaCO3 deposited on the membrane surface was identified as calcite. Various strategies were adopted to mitigate membrane scaling. Acidization of the CCCW can effectively improve system performance. Additionally, the main scalant transformed from CaCO3 to calcium sulfate (CaSO4) with initial pH decrease. Physical cleaning using deionized water can effectively remove CaSO4 and restore DCMD performance. Compared with commercial antiscalants (sodium polyaspartic acid and amino trimethylene phosphonic acid), EDTA showed excellent scale-inhibition performance. The calcium and magnesium in the CCCW were efficiently pre-removed by chemical softening and ion exchange methods, resulting in improvement of DCMD performance. Given scale inhibition and chemical agent costs, chemical softening was the best strategy to alleviate membrane scaling. Our work suggested that DCMD can be selected as a promising approach for treating the high alkaline CCCW combined with proper strategies to control membrane scaling.

Study on Treatment of Low Concentration Oily Wastewater Using Alumina Ceramic Membranes

In this study, alumina ceramic plate microfiltration membranes (ACMs) were used for the treatment of oily wastewater with different concentrations. The permeate oil concentration of the system was basically less than 5 mg·L−1, and the oil rejection rate was up to 97.6%. The effects of raw oil concentration on permeation flux and oil rejection rate of oily wastewater were studied. The results showed that with the increase of raw oil concentration, the oil rejection rate increased slightly due to the existence of oil film on the surface of filtered ACMs. Moreover, the existence of oil film had little effect on the flux change of ceramic membranes. The results showed that the permeability of ACMs mainly depended on their own oleophobic properties. In this system, physical cleaning technology is used to remove oil droplets and particles blocked in membrane pores. The results showed that physical cleaning could significantly recover the permeation flux as well as improve the oil rejection rate. On this basis, a system is proposed as a potential technique for oily wastewater treatment.

The Use of Verbascum Thapsus L as a Biomembrane for Activated Sludge Filtration

Membrane technology is a green technology, but it still faces a pressing problem related to the effect of fabrication materials on the environment. The plant Verbascum thapsus L (VTL) was utilized as a biomembrane to reduce chemicals. In this study, VTL was successfully utilized as a membrane for activated sludge separation. The membrane was characterized via scanning electron microscopy (SEM)-EDX, Fourier transform infrared (FTIR), and contact angle measurement. Additionally, the effects of pressures on the fluxes and the rejection ability were studied. The permeability of the bio-based membrane reached 581 L/m2 .h.bar. The VTL membrane was examined for the removal of chemical oxygen demand (COD), protein, and carbohydrate. Accordingly, the maximum COD removal was obtained at a transmembrane pressure of 2.5 bar and reached up to 57%. The protein and carbohydrates rejections raised from 80% and 84% at 0.5 bar to 90% and 98% at 2.5 bar, respectively. The total resistance increased from 87% at a pressure of 0.5 bar to 96% at 2.5 bar. The flux recovery ratio (FRR) for the membrane at working pressures (0.5-2.5 bar) was 96% for 0.5 bar and 70% for 2.5 bar. The physical cleaning showed a flux recovery after three operation cycles. At the end of the filtration experiments, the pressure variation along streamlines over the membrane cross-section was simulated. As a result of this study, the use of a naturally-derived membrane is considered a green technology. The plant-based membrane reduces the use of non-green chemicals. Moreover, VTL has no commercial value and is recognized as an invasive plant species. All of the previous issues made the study worthwhile.

Insights into the fouling layer of flat-sheet membrane and its development in an integrated oxidation ditch-membrane bioreactor

This work revealed the characteristics of fouling layer on the flat-sheet membranes and its development in an integrated oxidation-ditch membrane bioreactor. During the operation period (130 days), the reactor performed very well in removing pollutants. As the operation proceeded, membrane fouling occurred on the flat-sheet membranes and trans-membrane pressure showed a cyclical variation. The experimental results showed that the process of membrane fouling appeared successively in two different structures: biofilm (BF) and sludge fouling (SF). The substances causing membrane fouling were mainly organic foulants and a small amount of inorganic metal compounds, especially the protein-like and fulvic acid-like substances in loosely bound extracellular polymeric substances (LB-EPS). The analysis of microbial communities revealed that SF and BF had very different microbial properties. Although most membrane foulants could be removed by physical and chemical cleaning methods, the protein-like and fulvic acid-like substances in BF were contribute much to causing irreversible membrane fouling.

Interfacial polymerization nanofiltration membrane with visible light photocatalytic self-cleaning performance by incorporation of CQD/TiO2

• Photocatalytic CQD/TiO 2 -mediated nanofiltration membrane was prepared via interfacial polymerization. • The prepared membrane has excellent separation performance for dye wastewater treatment. • The membrane exhibits efficient and stable visible light-driven self cleaning ability. Integration photocatalysis with membrane technology offers a potential solution to combat fouling dilemma. Herein, an interfacial polymerization polyamide nanofiltration (NF) membrane with self-cleaning ability was prepared by incorporation of carbon quantum dots /titanium dioxide (CQD/TiO 2 ) nanoparticles (NPs). The addition of hydrophilic CQD/TiO 2 NPs promoted membrane hydrophilicity and endowed the NF membrane with high water flux (67.22 L m −2 h −1 ), which was 1.8 times compared with that of the pristine membrane, and salt rejection of Na 2 SO 4 (96.7%). Simultaneously, the prepared NF membranes maintained high dye rejection to methyl blue (MYB, 99.1%) and congo red (99.8%). Moreover, visible light-driven photocatalytic ability of CQD/TiO 2 allowed the membranes to efficiently degrade MYB dyes absorbed on the membrane surface. In stark contrast to the results of cyclic physical water cleaning, the flux recovery ratios were maintained 97–98% without sacrificing MYB rejections during the cyclic fouling-irradiation process, demonstrating stable and efficient self-cleaning performance. Even after continuous membrane fouling for 72 h, the water flux only decreased by 6.7% after visible light irradiation, surpassing the performance of pristine polyamide NF membrane (decreased by 23.4%). The hydrophilicity and visible light-driven self-cleaning ability make the prepared NF membrane via interfacial polymerization highly suitable for efficient dye wastewater treatment.

Phosphorus Concentration in Water Affects the Biofilm Community and the Produced Amount of Extracellular Polymeric Substances in Reverse Osmosis Membrane Systems.

Biofouling is a problem that hinders sustainable membrane-based desalination and the stratification of bacterial populations over the biofilm’s height is suggested to compromise the efficiency of cleaning strategies. Some studies reported a base biofilm layer attached to the membrane that is harder to remove. Previous research suggested limiting the concentration of phosphorus in the feed water as a biofouling control strategy. However, the existence of bacterial communities growing under phosphorus-limiting conditions and communities remaining after cleaning is unknown. This study analyzes the bacterial communities developed in biofilms grown in membrane fouling simulators (MFSs) supplied with water with three dosed phosphorus conditions at a constant biodegradable carbon concentration. After biofilm development, biofilm was removed using forward flushing (an easy-to-implement and environmentally friendly method) by increasing the crossflow velocity for one hour. We demonstrate that small changes in phosphorus concentration in the feed water led to (i) different microbial compositions and (ii) different bacterial-cells-to-EPS ratios, while (iii) similar bacterial biofilm populations remained after forward flushing, suggesting a homogenous bacterial community composition along the biofilm height. This study represents an exciting advance towards greener desalination by applying non-expensive physical cleaning methods while manipulating feed water nutrient conditions to prolong membrane system performance and enhance membrane cleanability.

Influences of different modification methods on surface activation of waste tire rubber powder applied in cement-based materials

This study aimed to investigate the effects of different modification methods on the surface activation of waste tire rubber powder. The improvement of surface activation and hydrophilicity is necessary when considering the use of waste tire rubber powder in cement-based materials. Physical cleaning and chemical reaction methods were applied to activate the 20-mesh waste tire rubber powder. Specifically, deionized water, 5 wt% NaOH solution, and CCl4 solution were used in the physical cleaning method, whereas silane coupling agents (KH-550, KH-560, and KH-570) and NaClO solution were used in the chemical reaction method. The activation index and contact angle were selected to characterize the activation effects on waste tire rubber powder. The microscopic morphology and modification mechanism of waste tire rubber powder were explored using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and testing of particle size distribution. Moreover, the mechanical performance of cement mortar containing modified rubber powder was tested, which confirmed the practical application value of the proposed modification method in this study. Test results showed that both physical cleaning and chemical reaction methods improved the surface activation and hydrophilicity of rubber powder. The physical cleaning method results revealed that 5 wt% NaOH solution removed hydrophobic impurities and increased the number of pores on the surface of rubber powder. Consequently, 5 wt% NaOH solution was considered more appropriate to improve the hydrophilicity and activity of rubber powder compared with deionized water and CCl4 solution. After the chemical reaction method, results showed that KH-550 had the highest activation effect on rubber powder since activated substances were generated and agglomerated on the surface of rubber powder. Moreover, the modification increased the mechanical strength and toughness of cement mortar containing rubber powder, and the modification effect was more prominent while using KH-550.

Improved separation performance of SS fiber nonwoven felt by the coating of a non-isotropic porous SS membrane layer

With excellent mechanical properties, large porosity, and permeability, stainless steel (SS) fiber nonwoven felt has outstanding application advantages in high-temperature filtration and purification. However, the pore size of the SS nonwoven felt, which is directly determined by the diameter of the produced fiber stacked inside, usually varies from tens of microns to several microns. Low filtration accuracy greatly limits its application in the fields of fine separation and purification. In this study, the separation performance of SS fiber nonwoven felt was improved by the coating of a non-isotropic porous SS membrane layer via the immersion precipitation phase inversion-sintering method. The effects of sintering temperature on pore structure, surface wettability, separation performance, and mechanical properties of the coated SS nonwoven felt were characterized by scanning electron microscope (SEM), water contact angle (WCA), water permeability, and tensile test, respectively. The results suggest that with the increase of sintering temperature from 1000°C to 1200°C, both porosity and pore size reduce gradually. The WCA value shows an increase from 31.4 to 62.3° and pure water flux shows a corresponding decrease from 2562 to 889 L . m−2 . h−1. The sintering temperature has a negative effect on the mechanical strength of the coated SS fiber nonwoven felt, which is mainly determined by the mechanical properties of the sintered SS fiber nonwoven felt substrate. The coated SS fiber nonwoven felt exhibits a long-term durable separation performance even after frequent combined physical washing and chemical cleaning when applied in the treatment of potato starch wastewater.

Twelve and LanzaTech partner to transform CO2 into polypropylene

The impact of sludge discharge on membrane fouling during ultrafiltration of surface water was investigated in this study. Discharge sludge and without discharge during UF were compared by measuring the increase of transmembrane pressure (TMP) and the accumulation of foulants with running time was studied. It was found that turbidity and dissolved organic carbon of retentate solution apparently increased as UF proceeded. Three-dimensional excitation/emission matrix fluorescence spectroscopy analyses of raw water and retentate solution demonstrated that UF could lead to the accumulation of humic and protein-like substances. Filtration experiments showed that membrane fouling could be alleviated by discharging the retentate solution after physical cleaning due to the reduced cake layer formation and concentration polarization. In addition, effects of sludge discharge intervals on the TMP and fouling characteristics were further investigated. Results indicated that short SDI would benefit control of both reversible and irreversible fouling. However, frequent discharge of retentate solution may increase the self-use water and decrease the water production rate of the UF system, leading to an expansion of running cost. In general, SDI was a critically important factor for both membrane fouling and water production rate.