Low-pressure Membrane Research Articles

Research of phosphate removal from water on reverse osmotic filters

Eutrophication of natural water bodies caused by an excess of biogenic substances is one of the global environmental problems of modern times. Usually, phosphorus is a limiting biogenic element, the concentration of which determines the intensity of eutrophication processes in water bodies. Therefore, it is important to develop methods aimed at preventing excessive amounts of phosphates from entering the environment. To remove phosphates from water, typically used biological degradation technologies, which usually proceed very slowly and depend on the conditions under which the process takes place. Also, Biogenic elements can be removed by using ion exchange, reverse osmosis, and chemical methods. However, the disposal of concentrated solutions becomes an issue with these methods. Baromembrane purification methods, particularly reverse osmosis, are becoming increasingly important in the field of water treatment and purification and are essential in creating efficient and low-waste complex technologies for water purification from biogenic compounds. The study investigated the processes of removing orthophosphates from distilled and artesian water using a low-pressure reverse osmosis membrane Filmtec TW30-1812-50. The dependence of membrane productivity and selectivity on the concentration of phosphates and the degree of permeate rejection was determined. Was found that residual concentrations of phosphates in the permeate increase with the increase in the degree of permeate rejection. The lowest residual concentrations of phosphates were observed at the initial concentration of up to 10 mg/dm3. The highest residual phosphate concentrations were observed at initial concentrations above 900 mg/dm3. At the same time, the membrane productivity constantly decreased with increasing feed concentration and degree of permeate recovery due to the increased osmotic pressure on the membrane. The selectivity of the membrane was highest at an initial concentration of up to 10 mg/dm3 and slightly decreased at a rejection rate of 20-50% for initial phosphate concentrations of 100-900 mg/dm3. At the maximum degree of permeate rejection (90%), the selectivity of the membrane reached 97-99 % and decreased with an increase in phosphate concentrations, which is due to a change in the pH of the medium, hydrolysis of phosphates, hydration of ions, and concentration polarization. The membrane selectivity for phosphates in solutions in artesian water was slightly lower (95-99 %), which was due to the competing influence of chlorides, sulfates, and bicarbonates, as well as a decrease in the pH of the solution to 7.52-7.67, which promotes the hydrolysis of o-phosphates.

Preparation and antifouling performance of low-pressure carbon nanotube membranes based on polydopamine biomimetic modification

In order to investigate the antifouling performance of low-pressure carbon nanotube membranes based on polydopamine (PDA) biomimetic modification, layered multi-walled carbon nanotubes PDA membrane (layered MWCNTs-PDA) and PDA blended MWCNTs membrane (blended PDA/MWCNTs) were prepared. The MWCNTs membranes’ antifouling performance and recoverability was significantly improved in filtrating BSA, HA and SA after PDA biomimetic modification, and the total fouling and irreversible fouling were all decreased. Compared with the blended PDA/MWCNTs membrane, the layered MWCNTs-PDA membrane had higher antifouling property as it further improved the electronegativity and hydrophilicity of membrane surface. In addition, denser surface pore size of the layered MWCNTs-PDA membrane can effectively reduce the fouling by trapping foulants on its surface. The combination of PDA biomimetic modification with MWCNTs membrane had a superior antifouling performance and rejection performance in processing NOM and artificial wastewater, and the majority of humic-like foulants could be excluded by the layered MWCNTs-PDA membrane. PDA biomimetic modification alleviated the adhesion of FITC-BSA on the MWCNTs membrane. The layered MWCNTs-PDA membrane especially alleviated the attachment of bacteria and processed excellent antimicrobial ability for bacteria.

Low-pressure carbon nanotube membrane with different surface properties for the removal of organic dyes and PPCPs

Low-pressure carbon nanotube membranes (CNT membranes) was prepared with multi-walled carbon nanotubes (MWCNTs), carboxyl functionalized MWCNTs (COOH-MWCNTs) and single-walled carbon nanotubes (SWCNTs). Surface properties of MWCNTs and SWCNTs were further altered by their non-covalent functionalization with Humic acid (HA), Sodium dodecyl sulfate (SDS), Sodium alginate (SA) and Polyethylene glycol (PEG). The CNT membranes with different surface properties were then used for the removal of organic dyes and pharmaceuticals and personal care products (PPCPs). The results revealed that HA/SDS/SA non-covalent functionalized MWCNTs membrane significantly promoted the removal of cationic dye MB, while it slightly interfered the removal of anionic dye RB19. During the dynamic filtration process, a 20∼30% increase of MB removal was promoted by HA/SDS/SA-MWCNTs membrane compared with the MWCNTs membrane, while the HA/SDS/SA-MWCNTs membrane significantly deteriorated the removal of PPCPs. The specific surface area of CNTs played a very important role in the dynamic filtration process of CNT membranes. The removal rate of PPCPs by SWCNTs membranes was almost all above 70% after 120 min’s filtration, and a further 10% increase was promoted by SA-SWCNTs membrane. HA and SDS non-covalent functionalization only slightly deteriorate the removal of PPCPs, and the removal rate of majority of PPCPs by HA-SWCNTs membrane and SDS-SWCNTs membrane remained over 60% and 30%. This work present new insight for the effectiveness of low-pressure CNT membranes in actual application, where the impact of competitive background organic materials on the removal of Low-MW organic pollutants were sometimes overestimated.

Feasibility and Environmental Impact of NOM Reduction by Microfiltration at a Finnish Surface Water Treatment Plant

Low-pressure membranes (including microfiltration and ultrafiltration) for natural organic matter removal in drinking water treatment have gained increasing interest in the Nordic countries. Microfiltration can produce stable water quality and requires less space than conventional treatment. Hollow fibre microfiltration coupled with chemical coagulation was tested at a Finnish surface water treatment plant to study its feasibility and environmental impact compared to clarification, rapid sand filtration and ozonation. Microfiltration improved both physical and chemical water quality, while natural organic matter removal was similar to that of conventional treatment. Membrane treatment would increase operational costs by 2.5–3.5 euro cents per m3. Most of the costs derive from chemicals used in membrane cleaning. Membrane treatment is an energy-intensive process, but energy production in the Nordic countries has a low emission factor. Greenhouse gas emissions from operating microfiltration are estimated at 16 g CO2-eq./m3 of permeate. Lowering chemical consumption and using renewable energy in production could decrease total emissions.

Unexpected iron-enhanced water flux and pollutant removal by low-pressure ultrafiltration

A novel mechanism for the effect of ferrous iron (Fe2+) on low-pressure ultrafiltration membrane (LPM) flux is discovered in this study. In previous studies, the Fe2+ concentrations of removing excessive Fe2+ and manganese (Mn2+) by LPM are low (0.4−1.5 mg L−1), and the presence of Fe2+ would reduce the flux, thus not suitable for treating water with high Fe2+ concentrations. In this study, we systematically investigated the performance of down-flow LPM (D-LPM) and opposite-flow LPM (O-LPM) under different Fe2+ concentrations (0−5 mg L−1) with Mn2+ and ammonia (NH4+). The results demonstrate that the flux did decrease at low Fe2+ concentration, while significantly increasing by 95.9% with Fe concentration at 3−5 mg L−1. Furthermore, high Fe2+ enhanced Fe, Mn2+, and NH4+ removal by iron autocatalytic oxidation, enriching the relative abundance of manganese-oxidizing bacteria, and facilitating anammox activities, respectively. A series of characteristic analyses suggest that thin biofilm layer structures in D-LPM and O-LPM, along with the low soluble microbial products-polysaccharide concentrations, resulted in the high steady flux under high Fe2+ concentrations. These findings widen the applicability of LPM in practical applications and provide novel strategies to increase the flux of LPM systems.

Understanding Protein and Polysaccharide Fouling with Silicon Dioxide and Aluminum Oxide in Low-Pressure Membranes.

Humic, protein, and polysaccharide substances have been recognized as significant types of foulants in membrane systems. Despite the remarkable amount of research that has been performed on the interaction of these foulants, particularly humic and polysaccharide substances, with inorganic colloids in RO systems, little attention has been paid to the fouling and cleaning behavior of proteins with inorganic colloids in UF membranes. This research examined the fouling and cleaning behavior of bovine serum albumin (BSA) and sodium alginate (SA) with silicon dioxide (SiO2) and α-aluminum oxide (Al2O3) in individual and combined solutions during dead-end UF filtration. The results showed that the presence of SiO2 or Al2O3 in water alone did not cause significant fouling or a flux decline in the UF system. However, the combination of BSA and SA with inorganics was observed to have a synergistic effect on membrane fouling, in which the combined foulants caused higher irreversibility than individual foulants. Analysis of blocking laws demonstrated that the fouling mechanism shifted from cake filtration to complete pore blocking when the combined organics and inorganics were present in water, which resulted in higher BSA and SA fouling irreversibility. The results suggest that membrane backwash needs to be carefully designed and adjusted for better control of BSA and SA fouling with SiO2 and Al2O3.

Adsorptive membranes for nutrient recovery from wastewater: A novel solution for water purification challenges

The removal of nutrients, like phosphate and ammonium, from wastewater is crucial for controlling eutrophication and water reuse. Traditional methods have limitations and are often supplemented by additional treatment steps, having a large footprint, consuming energy, and incurring added costs. This study presents a solution with the design of highly permeable (>100 LMH/bar) adsorptive polyacrylonitrile membranes embedded with akageneite (PAN/Ak) and zeolite 13X (PAN/Z) with high affinities for phosphate and ammonium uptake, respectively. The chemical compatibility between polymer and inorganic fillers resulted in highly flexible membranes with dispersed particles. Additionally, the membranes were stable, with no leaching of filler particles and complete recovery of uptake capacities after 5 adsorption/desorption cycles. Batch tests demonstrated that the maximum uptake capacities of PAN/Ak and PAN/Z are 0.4 mmol P/g and 1.2 mmol N/g, respectively, with phosphate uptake attributed to ligand exchange and ammonium to ion exchange. Moreover, the membranes’ ability to capture ions under dynamic flow conditions persists despite the presence of other competing ions, resulting in an initial removal of > 84% for ammonium and 100% for phosphate from a synthetic wastewater with initial concentrations of 2.1 mmol N/L and 0.1 mmol P/L. These membranes offer a unique solution for emerging water purification challenges, as they combine the high permeability of low-pressure membranes with high selectivity towards target ions.

Comparing Sedimentation, Flotation, and In-Line Pretreatment for Low-Pressure Membrane Fouling Reduction

Feed water pretreatment commonly is required for low-pressure membrane technologies employed in drinking water treatment applications to reduce membrane fouling and create stable operating conditions. Comparatively few studies have investigated coagulation–flocculation–dissolved air flotation (CF-DAF) pretreatment for drinking water applications, and none have compared CF-DAF, coagulation–flocculation–sedimentation (CF-S), and in-line coagulation (CF-IN) pretreatments using the same water. This study compared these three pretreatments for the filtration of a high dissolved organic carbon (DOC), high hydrophobic (HPO) surface water using a hydrophilic polyvinylidene fluoride (h-PVDF) ultrafiltration (UF) fiber. Multiday filtration tests were carried out using an automated bench-scale testing system operated in an outside-in configuration. CF-S and CF-DAF were found to be equally effective at mitigating membrane fouling, although CF-DAF pretreated water had a lower residual DOC and the greatest removal of UV254 absorbent organics. Compared with CF-DAF and CF-S, CF-IN pretreatment resulted in higher levels of total and irreversible fouling regardless of the applied coagulant dose. For all the pretreatments studied, irreversible membrane fouling was found to be strongly dependent on both the hydrophobicity of the feed water [in terms of specific UV absorbance (SUVA)] and the concentration of the 5–10-kDa DOC fraction, suggesting that the HPO humic organics were the principal foulant for this membrane–water combination. CF-IN pretreatment performance also was strongly impacted by the feed water zeta potential, suggesting that the characteristics of the formed flocculant particles are critical to the fouling behavior of the hybrid CF-IN-UF system.

Low-pressure thin-film composite nanofiltration membranes with enhanced selectivity and antifouling property for effective dye/salt separation

For better sustainable resource recovery and elevating the separation efficiency of dye/salt mixture, it is essential to develop an appropriate nanofiltration membrane for the treatment of textile dyeing wastewater containing relatively smaller molecule dyes. In this work, a novel composite polyamide-polyester nanofiltration membrane was fabricated by tailoring amino functionalized quantum dots (NGQDs) and β-cyclodextrin (CD). An in-situ interfacial polymerization occurred between the synthesized NGQDs-CD and trimesoyl chloride (TMC) on the modified multi-carbon nanotubes (MWCNTs) substrate. The incorporation of NGQDs significantly elevated the rejection (increased by ∼ 45.08%) of the resultant membrane for small molecular dye (Methyl orange, MO) compared to the pristine CD membrane at low pressure (1.5 bar). The newly developed NGQDs-CD-MWCNTs membrane exhibited enhanced water permeability without compromising the dye rejection compared to the pure NGQDs membrane. The improved performance of the membrane was primarily attributed to the synergistic effect of functionalized NGQDs and the special hollow-bowl structure of CD. The optimal NGQDs-CD-MWCNTs-5 membrane expressed pure water permeability of 12.35 L m-2h−1 bar−1 at the pressure of 1.5 bar. Noteworthily, the NGQDs-CD-MWCNTs-5 membrane not only showed high rejection for the larger molecular dye of Congo Red (CR, 99.50%) but also for the smaller molecular dye of MO (96.01%) and Brilliant Green (BG, 95.60%) with the permeability of 8.81, 11.40, and 6.37 L m-2h−1 bar−1, respectively at low pressure (1.5 bar). The rejection of inorganic salts by the NGQDs-CD-MWCNTs-5 membrane was 17.20% for sodium chloride (NaCl), 14.30% for magnesium chloride (MgCl2), 24.63% for magnesium sulfate (MgSO4), and 54.58% for sodium sulfate (Na2SO4), respectively. The great rejection of dyes remained in the dye/salt binary mixed system (higher than 99% for BG and CR, <21% for NaCl). Importantly, the NGQDs-CD-MWCNTs-5 membrane exhibited favorable antifouling performance and potential good operation stability performance. Consequently, the fabricated NGQDs-CD-MWCNTs-5 membrane suggested a prospective application for the reuse of salts and water in textile wastewater treatment owing to the effective selective separation performance.

Brackish water treatment by Ceramic TiO2 Low-Pressure Nanofiltration Membranes

&lt;p&gt;The application of ceramic Nanofiltration (NF) membrane in brackish water treatment is increasing due to strict water quality standards. Ceramic NF is a widely used membrane process and has replaced reverse osmosis (RO) membranes in many applications due to lower energy consumption and higher flux rates. This work aims to study the separation performance of tubular ceramic TiO2 Nanofiltration membrane at low-pressure (2 bar) for single and tertiary salt mixture separation. The results showed that the rejection of ions is ordered as follows: R (Cl1-) ion size &amp;gt; R calcium (Ca2+) ion size &amp;gt; R sodium (Na1+) ion size &amp;gt; R magnesium (Mg2+) ion size. Moreover, the highest Cl1- rejection was about 46%, the highest Ca2+ and Mg2+ rejection was about 44%, and the highest Na1+ rejection was about 37%. The pure water flux through the investigated ceramic NF membrane for distilled water was calculated to be 5.29 x 10-7 m3 s-1 m-2 bar-1, and this flux was dropped down for the salt mixture feed to 2.56 x 10-7 m3 s-1 m-2 bar-1 due to the presence of salt particles in the feed.&lt;/p&gt;&#x0D;

A hybrid ultrafiltration membrane process using a low-cost laterite based adsorbent for efficient arsenic removal

Adsorption has proven to be most effective for arsenic removal. But standalone adsorption cannot cater to the need for large-scale treatment in centralized water supply systems. Combining adsorption with other low-pressure membrane processes may aid in scaling up and intensifying the overall arsenic removal. In the present pilot study, a low-cost laterite-derived adsorbent (LDA) has been used in combination with cross-flow ultrafiltration (Ads-UF) to develop a strategy suitable for remediation of arsenic-contaminated water. Effect of adsorbent particles on permeate flux has been assessed at different transmembrane pressure (0.2–0.6 MPa). Two different hybrid configurations, with and without intermediate sand filtration (SF), i.e. Ads–SF–UF and Ads-UF, were considered. Resistance-in-series and combined complete pore block-cake layer models have been used to understand the flux profiles. In the case of arsenic-spiked groundwater, it was observed that flux decline, at 0.6 MPa, was 28% higher with Ads-UF during a 12 h run compared to Ads–SF–UF. Spent LDA retrieved from the sand column was found to retain the elemental composition as that of the unused LDA (as per FT-IR and EDX) and was considered safe for disposal based on Toxicity Characteristic Leaching Procedure (TCLP). Cost estimation for a facility with 200 m3/day treatment capacity has also been presented.

ВИЗНАЧЕННЯ ЕФЕКТИВНОСТІ ВИЛУЧЕННЯ СУЛЬФАТІВ НА ЗВОРОТНООСМОТИЧНІЙ МЕМБРАНІ НИЗЬКОГО ТИСКУ

The dependence of the efficiency of the low-pressure reverse osmosis membrane Filmtec TW30-1812-50 on the initial concentrations of sodium sulfate in the range of 10-650 mg/dm3 at permeate recovery rates of 1-90 % using a pressure of 4 atm was determined. The effect of increasing the permeate recovery rate on selectivity, membrane performance, and the in-crease in the sulfate content of concentrates was determined. It is shown that the concentration of sulfates in permeate depends on their initial concentration in solutions and increases both with an increase in the initial concentration and with an increase in the degree of permeate extraction. The latter factor is quite significant at initial sulfate concentrations of 650 mg/dm3. The membrane performance increases with decreasing salt content in water and decreases with increasing permeate removal rate, which leads to an increase in salt concentration in the pre-membrane space. The selectivity of the membrane for sulfates is 94.9-99.3 % and increases with increasing concentration of sodium sulfate solutions in solutions, despite a certain increase in salt concentrations in permeates. It is shown that as the degree of permeate selection increases, the selectivity for solutions with low initial sulfate concentrations increases. A FFP-based process modeling was performed to determine the sulfate con-centration in the permeate and concentrate at any initial sulfate concentration in a certain range. It was found that the con-centrate solutions are stable in the entire range of concentrations used with an increase in the degree of permeate recovery from 10 to 90 %. Based on the research results, a method for determining the capacity of the plant and the osmotic and oper-ating pressures based on the salt concentration and the set pressure in the system was proposed. From the data obtained, it can be concluded that the permissible level of mineralization at which the use of low-pressure reverse osmosis membranes is ad-visable.

Reduced Low-Pressure Membrane Fouling by Inline Coagulation Pretreatment for a Colored River Water.

Drinking water treatment (DWT) using low-pressure membranes (LPM) has become increasingly popular due to their many reported advantages compared to conventional technologies. Productivity decline due to fouling has prevented LPMs from becoming the technology of choice in DWT, however, coagulation pretreatment either with or without particle separation mitigates fouling phenomena. The effectiveness of coagulation/flocculation/sedimentation (CF-S), coagulation/flocculation/dissolved air flotation (CF-DAF), and inline coagulation (CF-IN) as technologies for pretreatment of feed water has rarely been investigated using the same water source. In this study, CF-S, CF-DAF, and CF-IN are directly compared as pretreatment of a tubular multi-channeled ultrafiltration (UF) membrane using the same highly colored river water. Three-day long filtration tests were performed using an automated bench-scale filtration apparatus with an inside-out configuration. Although CF-DAF had the greatest removal of dissolved organic matter (DOM) and hydrophobic organics, CF-S pretreatment resulted in a similar level of total fouling. Compared to CF-DAF and CF-S, CF-IN pretreatment resulted in lower fouling. The hydraulic and chemical reversibility of CF-IN fouling was seen to be strongly influenced by the feed water zeta potential, suggesting the importance of floc electrostatic and morphological characteristics on inline coagulation performance.

Research on Autopsy Results of over 10 Year Old Low Pressure Hollow Fiber Membrane from Domestic Water Treatment Plant

Objectives : In this study, membrane autopsy was performed for a parallel arrayed low-pressure membrane (microfiltration) filtration process that is actually applied to water treatment, to check out whether there are differences in the degree of membrane fouling due to the uneven flow rate into each module. Also, membrane foulants were evaluated quantitatively.Methods : In this study, autopsy was performed for over 10 year old membranes used for drinking water purification. In this way, the outer casings of membrane modules at different positions were disassembled and visually observed. In addition, In addition, the size of the pores and the porosity were investigated by taking a SEM (Scanning Electron Microscope) photograph for the new and the used membrane module fiber samples in different positions from the header pipe. The used membrane foulants were classified into organic and inorganic matters and quantitatively analyzed.Results and Discussion : As a result of visually observing inside the membrane module that has produced drinking water for over 10 years, the inside of the No. 1 membrane module close to the inlet was contaminated with black foulants. On the other hand, in the case of No. 10 membrane module located farthest from the header pipe inlet, no foulants were observed with the naked eye. Also, it was observed from SEM photograph results that there were large differences in the surfaces among No. 1, 4, 6, 8 and 10 MF module fibers.Conclusion : Even after periodic physical and chemical cleaning, it was concluded that the fouling levels were different each other in the parallel arrayed low-pressure membrane modules. In addition, the pore size distribution and porosities of the membrane modules may vary depending on the position.

Probing the separation efficiency of sulfur-doped graphitic carbon nitride (g-C3N4)/polysulfone low-pressure ultrafiltration mixed matrix membranes

Probing the separation efficiency of sulfur-doped graphitic carbon nitride (g-C3N4)/polysulfone low-pressure ultrafiltration mixed matrix membranes

Improved performance of an opposite-flow low-pressure ultrafiltration membrane system in the treatment of groundwater containing Fe2+, Mn2+, and NH4.

In remote areas, low-pressure ultrafiltration membrane (LPM) systems can be applied in decentralized water supplies for the treatment of groundwater containing Fe2+, Mn2+, and NH4+. However, improving the performance of the LPM systems, such as the stable flux and removal capacity, presents a challenge. In this study, a novel opposite-flow low-pressure ultrafiltration membrane (O-LPM) system was applied, and its performance was evaluated. Experimental results showed that after 46 days of operation, the steady flux of the O-LPM systems were 1.87-fold and 1.74-fold higher than that of the conventional D-LPM systems under Mn2+ concentration of 0.3mgL-1 and 1.5mgL-1, respectively. With a mixed pollutant system containing Fe2+ (0.5mgL-1), Mn2+ (0.3mgL-1), and NH4+ (1.0mgL-1), the O-LPM-ripening period for Mn2+ removal was shortened from 16 days to 8 days, and the NH4+ removal efficiency was increased from 61.46% to 80.97%. The bio-cake layer in the O-LPM systems was thinner and had a higher uniformity than in the D-LPM systems, resulting in a larger stable flux range. The relative abundance of functional bacteria (MnOB, IOB, and NOB) was generally higher in O-LPM systems than in the D-LPM systems. Overall, these results are of high relevance for groundwater treatment in remote areas, providing guidance for the widespread application of the O-LPM system in decentralized water supplies.

Establishing a dependence of the efficiency of low-pressure reverse osmotic membranes on the level of water mineralization

This paper has established the dependence of the effectiveness of the reverse-osmotic low-pressure membranes Filmtec TW30-1812-50 on the initial concentrations of sulfate and sodium chloride in the range of 20–1000 mg/dm3 at the degrees of permeate selection of 1–90 % with the use of pressure of 3.6–10.0 atm. The dynamics of increasing the content of sulfates and chlorides in concentrates with an increase in the degree of permeate selection, selectivity, productivity, and filtration coefficient of the membrane have been determined. The conditions for calculating the membrane performance depending on the working pressure for sodium sulfate and sodium chloride have been defined. It is shown that the concentrations of sulfates and chlorides in permeates depend on their initial concentration in solutions and increase both with an increase in the initial concentration and with an increase in the degree of permeate selection. The latter factor is quite significant at the initial concentrations of chlorides and sulfates at a concentration of 1000 mg/dm3. The productivity of the membrane increases with a decrease in the salt content in water and decreases as the degree of permeate selection increases, which leads to an increase in the concentration of salts in the premembrane space. The selectivity of the membrane increases with increasing concentration of sodium sulfate and sodium chloride solutions in solutions, despite a certain increase in salt concentrations in permeates. For solutions of Na2SO4 and NaCl (20–1000 mg/dm3) at their reverse-osmotic desalting on the membrane, the filtration coefficients have constant values. For these initial concentrations, the filtration coefficient for Na2SO4 is 3.4–3.8 dm3/(m2∙atm), and for NaCl – 2.6–3.2 dm3/(m2∙atm). The data reported here allow us to conclude about the permissible level of mineralization, at which it is advisable to use reverse-osmotic low-pressure membranes. It is shown that an increase in the concentration of salts in concentrates leads to an increase in osmotic and working pressures

Application of Double Piping Theory to Parallel-Arrayed Low-Pressure Membrane Module Header Pipe and Experimental Verification of Flow Distribution Evenness.

In this study, the improvement effect of flow distribution evenness is evaluated quantitatively by applying the double piping theory to a parallel-arrayed low-pressure membrane module header pipe structure, and its feasibility is discussed. Orifice inner pipes to be inserted into a full-scale membrane module header pipe are designed via the computational fluid dynamics (CFD) technique, and the flow rates into 10 membrane modules are measured in real time using a portable ultrasonic flowmeter during operation to verify the effect. Results of CFD simulation and actual measurements show that the outflow rate from the branch pipe located at the end of the existing header pipe is three times higher than the flow rate from the branch pipe near the inlet. By inserting two inner pipes (with an open end and a closed end into the existing header pipe) and applying the double pipe theory, the flow distribution evenness is improved. The CFD simulation and experimental results show that the flow uniformity can be improved by more than 70% and 50%, respectively.

Transparent exopolymer particles-associated membrane fouling analyses of systems containing sodium alginate, calcium, iron, alum and their combination during dead-end ultrafiltration

In this work, a serious of filtration experiments were designed and implemented to compare the effects of different metal cations (Ca2+, Fe3+, and Al3+) on fouling by sodium alginate. As indicated by the experimental results, these three types of cations all induced biphasic filtration behavior by 50 mg/L sodium alginate, that addition of these cations initially aggravated the fouling but then mitigated it upon further addition. The maximum specific filtration resistance (αav) increased in the following order: Al (34.5 ± 1.2 1014 mg/kg) < Ca (52.4 ± 2.5 1014 mg/kg) ≈Fe (54.1 ± 1.2 1014 mg/kg), but the corresponding critical concentration of the cation was in the order: Al3+ (0.02 mM) = Fe3+ (0.02 mM) < Ca2+ (0.05 mM). Increasing the metal cation concentration induced a higher transparent exopolymer particle concentration with the size being initially decreased but then gradually increased via the cation bridging effect, until the cation concentration reached up to 2 mM with the formation of metal hydroxides. So the fouling resistance mainly resulted from the dynamic equilibrium between concentrations and properties of transparent exopolymer particles with different sizes (0.05–0.1 μm, 0.1–0.2 μm, 0.2–0.4 μm and >0.4 μm). Similar biphasic fouling behavior also observed in the co-existence of Ca2+ and Fe3+/Al3+, but the comparable maximum αav values were obtained at much lower ion concentrations. Besides changes in the transparent exopolymer particle concentration, the hindered back transport of different sodium alginate molecules and steric effect also contributed to the synergistic fouling. Furthermore, there was little competition between the binding sites for divalent and trivalent ions, but the coiling behavior could be limited by changing the cation dosing sequence, leading to a weakened synergistic effect. This study links cation types, transparent exopolymer particle formations and fouling layer structures, with practical relevance for the hydraulic performance of low-pressure membranes, hopefully leading to their wider application in water treatment.

Fouling and chemically enhanced backwashing performance of low-pressure membranes during the treatment of shale gas produced water

The treatment of shale gas produced water (SGPW) for beneficial reuse is currently the most dominant and economical option. Membrane filtration is one preferred method to deal with SGPW, but membrane fouling is an unavoidable problem. In this study, two types of ultrafiltration (UF) membranes and one type of microfiltration (MF) membrane were investigated to treat SGPW from Sichuan basin. Results showed that increased total dissolved solid (31–40 g/L) and UV254 (10–42.9 m−1) were observed for the same shale gas plays, and the primary fluorescent organic substances were humic acid-like components. Compared to UF membranes with the flux decline by 2% to 60%, MF membranes with larger pore size were more likely to be fouled with the flux decline by 43% to 95%. Cake layer filtration was verified to be the primary membrane fouling mechanism. Statistical analysis showed that UV254 played the most significant role in membrane fouling which had the highest correlation (0.76 to 0.93). Compared to permeate backwashing (13%), deionized water backwashing and chemically enhanced backwashing (CEB) using NaClO, H2O2 and citric acid improved the cleaning efficiencies (31%–95%). CEB using NaOH prepared by deionized water aggravated membrane fouling, while excellent cleaning efficiencies (39%–79%) were observed for CEB using NaOH prepared by permeate. The difference in cleaning behaviors for fouled membranes by SGPW was verified by morphology observation and element composition analysis.