Application of ultrafiltration membranes for removal of humic acid from drinking water

Humic acids are primarily a result of the microbiological degradation of surrounding vegetation and animal decay and enter surface waters through rain water run-off from the surrounding land. This often gives rise to large seasonal variations, high concentrations in the wet season and lower concentrations in the dry season. Alone humic acid is just a colour problem but when present in conventional treatment processes like chlorination, carcinogenic by-products like trihalomethane and haloacetic acid are formed. This, in addition to the demand for clean potable drinking water, has sparked extensive research into alternative processes for the production of drinking water from various natural/industrial sources. One of the major areas of focus in these studies is the use of membranes in microfiltration, ultrafiltration and nanofiltration. In this report the humic acid removal efficiency of ultrafiltration membranes with 3 kDa, 5 kDa and 10 kDa MWCO is examined. The membranes were made of regenerated cellulose and were in the form of cassette providing a 0.1 m² surface area. At first distilled and deionised water, known as milliQ water, was used as the background feed solution to which humic acid powder was added. It was found that all three membranes removed humic acid with an efficiency of approx. 90% and were capable of reducing initial concentrations of 15mg/L to below the New Zealand regulatory limit of 1.17 mg/L. The permeate flux at a transmembrane pressure of 2.1 bar was approx. 20 l/m²/h (LMH) and 40 LMH, respectively through the membranes with MWCO 3 kDa and 5 kDa. These membranes experienced significant surface fouling resulting in retentate flow rates as low as 11 litres per hour after just four runs compared to the recommended 60–90 l/h. Cleaning with 0.1 M NaOH slightly improved the retentate flow rate, but well below those obtained with fresh membranes. The 10 kDa membrane provided high retentate flow rates which evidently minimised fouling by providing a good sweeping action across the membrane surface while maintaining humic acid removal below the regulatory 1.17 mg/L level. The permeate flux through this membrane was initially high (140–180 LMH) and reduced to approx. 100 LMH after 10–12 min of operation. Increasing the initial humic acid feed concentration from 10 mg/L to 50 mg/L did not significantly decrease humic acid removal efficiency although the retentate flow rate was lower at higher concentrations. Finally the tap water was tested as the background solution and treated for the removal of humic acid. The presence of ions and other impurities in the tap water had little effect on humic acid removal. However, the permeate flux through 10 kDa membrane decreased from 100 LMH for milliQ water to 60 LMH for tap water after 20 min of operation.     

A Two-Step Nanofiltration Process for the Production of Phenolic-Rich Fractions from Artichoke Aqueous Extracts

Commercial nanofiltration (NF) membranes in spiral-wound configuration (NP030 from Microdyn Nadir and Desal DK from GE Water & Process Technologies) were used in a sequential design in order to produce a separated fraction of phenolic and sugar compounds from an aqueous artichoke extract. For both membranes, the effect of transmembrane pressure (TMP) on the permeation flux was evaluated. In optimized conditions of TMP, the NP030 membrane exhibited high rejections of apigenin, cynarin and chlorogenic acid (higher than 85%); on the other hand, very low rejections of fructose, glucose and sucrose (lower than 4%) were measured. Starting from an extract with a total antioxidant activity (TAA) of 5.28 mM trolox a retentate fraction with a TAA of 47.75 mM trolox was obtained. The NF permeate from the NP030 membrane was processed with the Desal DK membrane in optimized conditions of TMP producing a permeate stream free of phenolic and sugar compounds. Accordingly, as most part of phenolic compounds was removed in the first NF step, the concentration of sugar compounds in the NF retentate had much higher results than that of phenolic compounds.     

Study of drinking water treatment by ultrafiltration of surface water and its application to China

In China, many water supplies depend on conventional water treatment. Due to unfit soil and water conservationin some regions of China, conventional water treatment has showed some defects for the poor quality of water resource. In addition, advances in membrane technology and increasing requirements on water quality have stimulated ultrafiltration (UF) for water treatment. In this research, OF test apparatus was set up to produce drinking water from raw water of the Binxian Reservoir (China). The performance of UF membranes was investigated. There was a linear relationship between membrane resistance and accumulated permeate water. Using coagulation before OF increased permeate flux and retarded membrane flux decline. Surprisingly, membrane permeate flux in a coagulation/UF process was higher than that in coagulation-sand filtration-UF process with raw water of medium turbidity. OF treatment provided effective turbidity removal. Iron, manganese and aluminum were removed completely. The UF membrane also perfectly removed all coliform bacteria. The reduction of total organic carbon was satisfactory. The treated water quality complied with China's drinking water guidelines. The Ames test showed that the mutagenic activities of membrane permeate water was negative.     

Effects of acceleration on spiral-wound membrane performance in reverse osmosis

Experimental data show that acceleration, applied to spiral-wound reverse osmosis membranes by centrifugation, increases membrane performance. The effects of acceleration on concentration polarization were determined by testing spiral-wound membranes under accelerations up to 500 × g with 0.5% sodium chloride. The data indicate a reduction in salt concentration at the membrane surface from 2.2 to 1.0% from a nonaccelerated state when 500 × g acceleration is applied to a properly oriented membrane. This reduces the osmotic pressure at the membrane and increases permeate recovery by 21%.     

Application on to nanofiltration to water management options for oil sands operation

A membrane separation process, nanofiltration (NF), has been applied successfully for treatment of oil sandswaters, particularly to water softening and removal of toxic components. This study focused on the selection of appropriate membranes and the assessment of their performance for the removal of polyvalent ions (hardness) and naphthenic acids (NA) (the main acute toxicant in oil sands process-affected imported waters) from both imported and potential discharge waters. Experiments were carried out using a bench-scale flat sheet membrane system with several commercially available NF membranes. It was found that after membrane filtration, both water hardness and the NA concentrations were reduced significantly (>95%). A permeate flux was maintained at 15 L/m²/h or higher, with a retentate volume of about 10% of the feed volume.     

Direct filtration of Procion dye bath wastewaters by nanofiltration membranes: flux and removal characteristics

The treatment and reuse of industrial wastewaters by membrane processes has become more attractive in the last few years due to constraints on water usage. The aim of this study was to investigate the direct filtration of reactive dye house wastewaters by nanofiltration membranes based on permeate flux, and sodium chloride and colour removal. Experiments were performed using both synthetic and industrial dye bath wastewaters with the fluxes of the industrial dye bath wastewaters lower than those of the synthetic solutions. The effects of operating conditions such as pressure and pH were assessed. Studies with DS5 DK type (polysulfone–polyamide) membranes showed that nanofiltration membranes are suitable for direct treatment of wastewaters and the permeate quality was appropriate for reuse in the dyeing process. Pre‐treatment and neutralisation were important for recovery of large amounts of salt and water from the permeate stream. Neutralisation of the solution with HCl rather than H₂SO₄ gave a better permeate from the point of view of the reuse. The highest permeate flux and colour removal and the lowest salt removal were achieved with the HCl neutralisation. Copyright © 2003 Society of Chemical Industry     

Pilot plant studies on the removal of trihalomethanes by composite reverse osmosis membranes

The effect of single trihalomethane (THM) (CHCl₃) content in various types of water on the performance of two types of reverse osmosis composite membranes (the AFC99 membrane in tubular module B1, PCI, and the FT30 membrane in a spiral-wound element BW3040, FilmTec) have been investigated. The performance of these membranes in RO tests carried out using distilled water, tap water and brackish water (1000–5000 ppm NaCl) with the addition of THM have been evaluated in terms of permeate flux and the rejection of dissolved solids and THM. The FT30 membrane provided THM rejection better than 99.5% during the reverse osmosis treatment of tap water and brackish water. The AFC99 membrane exhibited only 80% retention of THM, obtained for the transmembrane pressures in the range of 10 to 30 bars. It was found that the presence of CHCl₃ slightly affects the transport and separation properties of the composite membranes used.     

Pilot-scale spiral wound membrane assessment for THM precursor rejection from upland waters

The outcomes of a pilot-scale study of the rejection of trihalomethanes (THMs) precursors by commercial ultrafiltration/nanofiltration (UF/NF) spiral-wound membrane elements are presented based on a single surface water source in Scotland. The study revealed the expected trend of increased flux and permeability with increasing pore size for the UF membranes; the NF membranes provided similar fluxes despite the lower nominal pore size. The dissolved organic carbon (DOC) passage decreased with decreasing molecular weight cut-off, with a less than one-third the passage recorded for the NF membranes than for the UF ones.

The yield (weight % total THMs per DOC) varied between 2.5% and 8% across all membranes tested, in reasonable agreement with the literature, with the aromatic polyamide membrane providing both the lowest yield and lowest DOC passage. The proportion of the hydrophobic (HPO) fraction removed was found to increase with decreasing membrane selectivity (increasing pore size), and THM generation correlated closely (R² = 0.98) with the permeate HPO fractional concentration.     

Nanofiltration Membrane Process for the Removal of Arsenic from Drinking Water

The removal of arsenic from drinking water by nanofiltration membranes was investigated. Experiments were conducted with tap water to which arsenate and arsenite were added. Two types of nanofiltration membranes, i.e., NF‐90 and NF‐200, have been tested. The effect of various operating conditions, e.g., applied pressure, feed concentration, pH and temperature, were also investigated. The pH and arsenic concentration in the feed and the operating temperature are found to be decisive factors in determining the arsenic concentration remaining in the permeate. The level of removal of As(V) was higher than 98 % for both membranes, but that of As(III) was much lower. It can be concluded that by controlling the operating parameters, source water containing As(V) may be recovered as drinking water to EPA maximum contaminant level quality standards, but that water containing As(III) must undergo a pre‐oxidation treatment before passing through the nanofiltration membrane in order to maintain drinking water quality.     

Electrolytic removal of 17α‐ethinylestradiol (EE2) in water streams

The electrolytic removal of ethinylestradiol (EE2), the most potent synthetic estrogen, in effluent of a membrane bioreactor (MBR) treating hospital sewage and in drinking water, was studied at dosed concentrations of about 1 mg EE2 L^?1. Removal efficiencies of up to 98% were obtained with supplemental efficient eradications of bacteria (up to 3.4 log units). Residual effects were observed when a treated flow was mixed with an untreated flow. An increasing concentration of NaCl resulted in an enhanced EE2 removal. This effect was more pronounced in MBR effluent than in drinking water. To approach more environmentally realistic concentrations, an experiment with initial concentration of 10 µg EE2 L^?1 drinking water was set up, still resulting in an EE2 removal of 85%. Copyright © 2006 Society of Chemical Industry     

Study on the cleaning of new ultrafiltration spiral-woundmodules to prevent membrane fouling (including biological fouling)

A study of cleaning a Bulgarian OF 60 PAN spiral-wound module was carried out on an ultrafiltration unit(Millipore, USA). Chemical cleaning of the membrane with a 0.25% solution of sodium metabisulfite did not prevent biological fouling. When treated with a 1% solution of formaldehyde, membrane fouling was diminished and the ultrafiltrate obtained contained a significantly lower number of microorganisms and colloid formations including iron and humic acids. After treatment with the two cleaning agents, the membrane maintained its flux for the water studied within a range of 1.58 to 1.64 m³/m²/d. The effect on the contaminants to be removed was also found to be comparatively constant. Membrane selectivity remained constant at different permeate yields.     

Relation between salt rejection and electrokinetic properties on Shirasu porous glass (SPG) membranes with nano-order uniform pores

The salt rejection by Shirasu porous glass (SPG) membranes having nano-order uniform pores was investigated for understanding the electrokinetic mechanism resulting from the surface charge developed on the membrane when in contact with salt solutions. Due to the dissociation of the hydroxyl groups such as silanol groups on the membrane surface, the membrane was negatively charged over a pH range of 3–10 from electrophoretic measurements. Cross-flow filtration experiments showed that up to 63% of NaCl was rejected by an SPG membrane having a mean pore diameters of 33 nm in a 1 mol m⁻³ NaCl solution at pH 7 under a transmembrane pressure of 74 kPa, even though the pore diameter is much larger than the ion diameter. This is a consequence of the electrostatic repulsive interaction between the co-ions (Cl⁻ ions) and the membrane surface. At the same pH, the rejection factor of NaCl decreased with increasing salt concentration due to an increase in the ionic strength. More negative charge on the membrane surface at higher pH resulted in higher rejection factors of NaCl for a fixed salt concentration. Higher rejection factors of NaCl by SPG membranes with smaller pore sizes for a fixed concentration are due to the higher ratio of the thickness of the electric double layer (Debye length) to the pore radius. The SPG membrane showed a salt rejection sequence: Na₂SO₄, NaCl and CaCl₂ at the same pH. This is because divalent anions (SO₄²⁻) are more strongly repelled by the negatively charged membrane, while divalent cations (Ca²⁺) adsorb specifically onto the membrane surface than monovalent cations (Na⁺). The salt rejection factor increased with increasing permeate volume flux. Due to the stronger acidity of the membrane materials, SPG membranes had a higher rejection factor and a lower isoelectric point (IEP < 3) than ceramic membranes.     

Pilot study for reclamation of secondary treated sewage effluent

A pilot study for reclamation of secondary treated sewage effluent in Singapore was conducted using a MF/RO system with the capacity of 20 m³/d. A 0.1 μm MF membrane from Asahi and RE-4040-FL RO membrane from Saehan were used in this study. The pilot plant consists of six spiral-wound RO elements. The RO train was configured in single stage. The pilot plant was designed with automatic control system and it was operated continuously (24 h) during the study. Trial runs on various flux rates of the RO membrane at different operating pressures were conducted over 3 months. The pilot results showed that the optimal operation flux rate of the RO membrane ranged from 10 to 15 gal/f²/d (GFD) for this application. The normalized flux after CIP was 97% of the initial one. At a flux rate of 10 GFD and water recovery of 50%, the average operating pressure of 57 psi was noted corresponding to a high normalized flux of 38 L m⁻² h⁻¹ MPa⁻¹ at 25°C. Rejections of the RO membrane in terms of conductivity, TOC, ammonium and nitrate were higher than 96%,97%,90% and 85%, respectively. It was concluded that the RO permeate quality in terms of conductivity, turbidity, TOC, ammonium, nitrate, hardness, total bacteria and total coliform matched the quality of high-grade water (NEWater) for use in the electronics industry.     

Membrane application for recovery and reuse of water from treated tannery wastewater

Secondary treated tannery wastewater contains high concentrations of Total Dissolved Solids (TDS) and other residual organic impurities, which cannot be removed by conventional treatment method. A pilot plant membrane system with a designed processing capacity of 1 m³/h, comprising of nano and reverse osmosis (RO) membrane units, accompanied by several pre-treatment operations, was evaluated in order to further treat and reuse the tannery wastewater. The maximum TD S removal efficiency of the polyamide RO membrane was more than 98%. The permeate recovery of about 78% was achieved. The water recovered from the membrane system, which had very low TDS concentration, was reused for wet finishing process in the tanneries. The reject concentrate obtained from the operation was sent to solar evaporation pans. It was evident from the study that the membrane system can successfully be applied for recovery of water from secondary treated tannery effluent, provided a suitable and effective pretreatment system prior to membrane system is employed. Combining nano and RO membranes improved the life of the membranes and permeate recovery rate.     

Unsupported electrospun membrane for water desalination using direct contact membrane distillation

In this project, an unsupported electrospun poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) membrane was used for water desalination using direct contact membrane distillation (DCMD). The membrane was electrospun using a laboratory-scale machine with multiple nozzles that was developed in-house. Critical process parameters, including the applied voltage and polymer concentration, were optimized to obtain bead-free electrospun membranes with fiber diameters less than 300 nm. To improve the membrane thermal stability and performance, the selected electrospun membrane was heat-pressed at 160°C. The untreated and heat-pressed membranes were tested in a DCMD setup at different feed temperatures (60, 70, and 80°C) and feed flow rates (0.4, 0.6, and 0.8 L/min), while maintaining the permeate temperature and flow rate at 20°C and 0.2 L/min, respectively. The modified electrospun membrane exhibited a very high permeate flux (>37.5 kg/m²/h) and a salt rejection rate of 99.99% at a feed temperature of 70°C. The performance of the heat-pressed unsupported PVDF-HFP electrospun membrane was nearly identical to a commercially available polytetrafluoroethylene (PTFE) supported membrane. These promising results demonstrate that relatively low-cost electrospun membranes can be easily produced and successfully used in DCMD to minimize the capital cost and increase the energy efficiency of the process.     

Membrane separation of low volatile organic compounds by pervaporation and vapor permeation

Pervaporation of dilute benzyl alcohol solutions was studied using polydimethylsiloxane (PDMS) membranes. The membrane performance was investigated under various temperatures, downstream pressures and feed concentrations. The benzyl alcohol concentration in the permeate decreased dramatically by increasing the downstream pressure, but increased by increasing the operating temperature. The separation and recovery of benzaldehyde from nitrogen was also investigated. Polyetherimide flat sheet membranes were prepared and then coated with silicone material. The performance of membranes in both coupon form and spiral-wound configuration was studied. When the experimental results from both configurations were compared, it was found that for the same material the membrane coupons had higher separation efficiency than the spiral-wound prototype modules. The ratio of benzaldehyde mole fraction in the permeate to the feed reached 500 for a small membrane coupon of effective surface area 10.2 cm². This ratio was only 26 for the prototype modules, which can be attributed to some limitations of the membrane system design. These limitations are discussed and some recommendations to improve the performance are given.     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

Flat-plate submerged membrane bioreactor for the treatment of higher-load graywater

Graywater treatment has been the focus when topics of decentralized treatment systems are discussed. In this paper, the treatment of higher-load graywater, a mixture of washing machine and kitchen sink wastewater, was investigated. A 10 L lab-scale submerged membrane bioreactor (subMBR) was operated with a flat-plate membrane for 87 days. Permeate was intermittently withdrawn at constant transmembrane pressure (TMP) induced by water level difference and without pump requirement. The pollutants' removal and membrane behavior were monitored. The COD removal was around 96% and a permeate COD of about 26 mg L^− 1 was obtained. The total linear alkylbenzene sulfonate (LAS) removal achieved was > 99%, indicative of its non-inhibited degradation even at influent concentration of 30.8 mg L^− 1. The subMBR was operated at almost stable and constant flux of 0.22 m³ m^− 2 d^− 1 at a mean HRT of 13.6 h.     

An advanced treatment of high-strength opium alkaloid processing industry wastewaters with membrane technology: pretreatment, fouling and retention characteristics of membranes

This paper presents the results of the laboratory and pilot-scale membrane experiments of opium alkaloid processing industry effluents. Different types of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for membrane fouling, permeate flux and their suitability in separating COD, color and conductivity. Experiments demonstrated that membrane treatment is a very promising advanced treatment option for pollution control for opium alkaloid processing industry effluents. Almost complete color removal was achieved with NF and RO membranes. COD and conductivity removals were also greater than 95% and met the current local standards. Nevertheless, pretreatment was an important factor for the NF and RO membrane applications. Membrane fouling occurred with direct NF membrane applications without UF pretreatment. The total estimated cost of the UF and NF treatment system was calculated as $0.96/m³, excluding the concentrate disposal cost.     

Application of hybrid coagulation–microfiltration process for treatment of membrane backwash water from waterworks

A coagulation–microfiltration (MF) system was studied to treat the discharged membrane backwash water (MBW) to meet the drinking water quality requirements. The values of dissolved organic carbon (DOC) and trihalomethanes formation potential (THMFP) in MBW were higher than those in Luan River water (LRW, the raw water for a pilot-scale membrane plant, which produced MBW used in this study), and organic matter enriched in MBW distributed mainly in molecular weight (MW) > 10k Da. When 15 mg FeCl₃/L and 15 mg/L powdered activated carbon (PAC) were added into the system, the average concentration of DOC was reduced from 5.731 mg/L in MBW to 3.377 mg/L in the treated water, and the average UV₂₅₄ was reduced from 0.047 to 0.030 cm⁻¹. The removal of organic matter was main in the range of MW > 30k Da. Efficient organic removal by the hybrid coagulation–MF system resulted in significant reduction of THMFP in the treated water. Concentrations of trihalomethanes, turbidity, bacteria and coliforms in the treated water were below the limit value of the drinking water standards. The results show that the treated water from MBW is with satisfactory organic and microbiological quality.