Low-pressure Membrane Processes Research Articles

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.

Ammonia Recovery from Hydrolyzed Human Urine by Forward Osmosis with Acidified Draw Solution.

Forward osmosis (FO) is a low-pressure membrane process that can selectively separate low molecular weight neutral compounds such as ammonia from urine. However, an understanding of how un-ionized ammonia transfers is vital for maximizing ammonia recovery. Therefore, this research aimed to determine the transport behavior of low molecular weight neutral nitrogen compounds in order to maximize ammonia recovery from real hydrolyzed human urine by FO. Using urea as a model, batch FO experiments concluded that low molecular weight neutral compound transfer is dependent on concentration equilibrium between the feed and draw solutions due to its ability to freely move across the FO membrane. Therefore, 50% recovery is the theoretical maximum that could be achieved. However, novel strategic pH manipulation between the feed and the draw solution allowed for up to 86% recovery of ammonia by keeping the draw solution pH < 6.5 and the feed solution pH > 11, overcoming the 50% recovery barrier. An economic analysis showed that ammonia recovery by FO has the potential to be more economically favorable compared to ammonia air stripping or ion exchange if the proper draw solute is chosen.

Co-application of energy uncoupling and ultrafiltration in sludge treatment: Evaluations of sludge reduction, supernatant recovery and membrane fouling control

Energy uncoupling is often used for sludge reduction because it is easy to operate and does not require a significant amount of extra equipments (i.e. no additional tank required). However, over time the supernatant extracted using this method can deteriorate, ultimately requiring further treatment. The purpose of this study was to determine the effect of using a low-pressure ultrafiltration membrane process for sludge water recovery after the sludge had undergone an energy uncoupling treatment (using 3,3′,4′,5-tetrachlorosalicylanilide (TCS)). Energy uncoupling was found to break apart sludge floc by reducing extracellular polymeric substances (EPS) and adenosine triphosphate (ATP) content. Analysis of supernatant indicated that when energy uncoupling and membrane filtration were coapplied and the TCS dosage was below 30 mg/L, there was no significant deterioration in organic component removal. However, ammonia and phosphate concentrations were found to increase as the concentration of TCS added increased. Additionally, due to low sludge concentrations and EPS contents, addition of 30-60 mg/LTCS during sludge reduction increased the permeate flux (two times higher than the control) and decreased the hydraulic reversible and cake layer resistances. In contrast, high dosage of TCS aggravated membrane fouling by forming compact fouling layers. In general, this study found that the co-application of energy uncoupling and membrane filtration processes represents an effective alternative method for simultaneous sludge reduction and sludge supernatant recovery.

Application of volume retarded osmosis – Low pressure membrane hybrid process for recovery of heavy metals in acid mine drainage

Recovery of heavy metals in acid mine drainage (AMD) such as Mn, Fe, Cu, Zn, As, Cd and Pb was evaluated using volume retarded osmosis and low-pressure membrane (VRO-LPM) process. In VRO-LPM process, the draw solution (DS) is regenerated by the naturally generated pressure, giving its economic value. Ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) and Poly (sodium-4-styrenesulfonate, PSS-Na) were used and compared to determine more suitable DS in heavy metal recovery from the AMD. Forward osmosis (FO) and nanofiltration (NF) membrane were employed in VRO-LPM process, due to the low EDTA-4Na rejection (about 50%) in ultrafiltration (UF) process. For the FO part in the VRO-LPM process, PSS-Na had flux values of 0.12, 0.11 and 0.05 L m−2 h−1 and at osmotic pressure of 8.9, 12 and 13 bar, respectively. Unlike the flux values, the RSF of PSS remained at 0.01 mmol h−1 at all osmotic pressures. For EDTA-4Na, the flux values were 0.10, 0.06 and 0.04 L m−2 h−1, which are relatively higher than those of PSS-Na; and the RSF values were 0.1, 1.2, 2.2 mmol h−1, which are higher compared to those of PSS-Na. Unlike PSS-Na, RSF for EDTA-4Na increased as the concentration increases. In the NF part of the VRO-LPM process, PSS-Na had higher water flux and rejection than EDTA-4Na, and the flux and rejection both decreased with concentration for both PSS-Na and EDTA-4Na. The overall rejection in VRO-LPM process was over 95% for all heavy metal ions. Therefore, VRO-LPM process has proven its ability to be used in AMD treatment for heavy metal removal.

Ultrafiltration of Aqueous Solutions of Food Dye Using Polymeric Membranes Prepared with Surfactants

The objective of the study is the low-pressure membrane process for treating aqueous solutions containing synthetic food dye (E104 - quinoline yellow). Dye concentration used was 10% (equivalent to 100g/m3). The pressures used in the ultrafiltration process were 0.1, 0.2 and 0.3 MPa. Experiments were performed in dead - end instalations in which the effectiveness of the polysulfone - alkylbenzyldimethylammonium chloride (PSU-ABDMA) and polysulfone - N-dodecylpyridinium chloride (PSU - NDPCl) were tested. The efficiency of these membranes has been proved by calculating the permeate flow and the retention. Analyzing the experimental data, it was found that for the polysulfone-alkylbenzyldimethylammonium chloride composite membrane the degree of retention is completely different, with high values being obtained for low pressures and low values for high pressures used.

New concept of pump-less forward osmosis (FO) and low-pressure membrane (LPM) process

We tested the possibility of energy-saving water treatment methods by using a pump-less forward osmosis (FO) and low-pressure membrane (LPM) hybrid process (FO-LPM). In this pump-less FO-LPM, permeate migrates from the feed solution (FS) to the draw solution (DS) through the FO membrane by use of osmotic pressure differences. At the same time, within the closed DS tank, inner pressure increases as the DS volume increases. By using the DS tank’s internal pressure, the LPM process works to re-concentrate the diluted DS, maintaining the DS concentration and producing clean water. In this study, a polymer - polystyrene sulfonate (PSS) was used as a draw solute. Based on the results of each individual portion of the process, the optimal range of the PSS DS was determined. The performance of the pump-less FO-LPM process was lower than that of a single process; however, we observed that the hybrid process can be operated without a pump for regeneration of a diluted DS. This research highlights the feasibility and applicability of pump-less FO-LPM processes using a polymeric DS for water treatment. Additionally, it is suggested that this novel process offers a breakthrough in FO technology that is often limited by operation and management cost.

Biofiltration of feedwater to control organic fouling of low pressure membranes

ABSTRACTThe application of low pressure membrane (LPM) technology, i.e., ultrafiltration and microfiltration, for drinking water treatment and secondary effluent reclamation has increased rapidly over the past two decades. A major drawback in the use and operation of LPM processes is fouling due to the deposition of organic matter present in the feedwater on the membranes which leads to reduced water productivity necessitating membrane cleaning, process downtime and eventual membrane attrition. Pretreatment of feedwater using biological processes (particularly slow sand filtration and biological activated carbon) has been investigated as a simple and cost-effective means to control organic fouling of the membrane. In this paper, membrane fouling by the organic matter in drinking water and secondary effluent, the mechanisms of biological treatment systems, and the effectiveness of biological processes for fouling reduction are reviewed. It has been demonstrated that biological processes have great potential for controlling the organic fouling of membranes.

Reducing ultrafiltration membrane fouling during potable water reuse using pre-ozonation

Wastewater reclamation has increasingly become popular to secure potable water supply. Low-pressure membrane processes such as microfiltration (MF) and ultrafiltration (UF) play imperative roles as a barrier of macromolecules for such purpose, but are often limited by membrane fouling. Effluent organic matter (EfOM), including biopolymers and particulates, in secondary wastewater effluents have been known to be major foulants in low-pressure membrane processes. Hence, the primary aim of this study was to investigate the effects of pre-ozonation as a pre-treatment for UF on the membrane fouling caused by EfOM in secondary wastewater effluents for hydrophilic regenerated cellulose (RC) and hydrophobic polyethersulfone (PES) UF membranes. It was found that greater fouling reduction was achieved by pre-ozonation for the hydrophilic RC membrane than the hydrophobic PES membrane at increasing ozone doses. In addition, the physicochemical property changes of EfOM, including biopolymer fractions, by pre-ozonation were systemically investigated. The classical pore blocking model and the extended Derjaguin−Landau−Verwey−Overbeek (XDLVO) theories were employed to scrutinize the fouling alleviation mechanism by pre-ozonation. As a result, the overarching mechanisms of fouling reduction were attributed to the following key reasons: (1) Ozone degraded macromolecules such as biopolymers like proteins and polysaccharides into smaller fractions, thereby increasing free energy of cohesion of EfOM and rendering them more hydrophilic and stable; (2) pre-ozonation augmented the interfacial free energy of adhesion between foulants and the RC/PES membranes, leading to the increase of repulsions and/or the decrease of attractions; and (3) pre-ozonation prolonged the transition from pore blocking to cake filtration that was a dominant fouling mechanism, thereby reducing fouling.

Removal of Cu(II) ions from contaminated waters using a conducting microfiltration membrane

Efficient removal of toxic metals using low-pressure membrane processes from contaminated waters is an important but challenging task. In the present work, a conducting microfiltration membrane prepared by embedding a stainless steel mesh in the active layer of a polyvinylidene fluoride membrane is developed to remove Cu(II) ions from contaminated waters. Results showed that the conducting membrane had favorable electrochemical properties and stability as cathode. Batch tests showed that Cu(II) removal efficiency increased with the increase of voltages and leveled off with the further enhancement of electric field. The optimal voltages were determined to be 1.0V and 2.0V for the influent Cu(II) concentrations of 5mg/L and 30mg/L, respectively. X-ray photoelectron spectroscopy and X-ray diffraction results demonstrated the presence of Cu(0) and Cu(OH)2 on the membrane surface. The removal mechanisms involved the intrinsic adsorption of membrane, electrosorption of membrane, adsorption of deposited layer, chemical precipitation of Cu(OH)2 and deposition of Cu(0) which were aided by electrophoresis and electrochemical oxidation-reduction. Long-term tests showed that the major contributors for Cu(II) removal were the deposition of Cu(0) by electrochemical reduction-oxidation (47.3%±8.5%) and chemical precipitation (41.1%±0.2%), followed by electrosorption, adsorption by the fouling layer and membrane intrinsic sorption.

Ultrafiltration of Aqueous Solutions of Food Dye in the Presence of Surfactants

The objective of the study is the low-pressure membrane process for treating aqueous solutions containing food dyes and surfactants. The influence of surfactants (SDS � sodium dedecil sulphate, SO � sodium octanoate) in the separation of synthetic food dyes (E104 � quinoline yellow) was analyzed. Polysulfone and polysulfone-polyaniline membranes were used. Dye and surfactant concentrations used were 10% (equivalent to 100g/m3). The pressures used in the ultrafiltration process were 0.1, 0.2 and 0.3 MPa. When dye containing solutions were passed through the membranes, an increase in their flux was observed. The presence of surfactants in the solutions lead to a decline in flux when pressures of 0.1 and 0.2 MPa were used, but an improvement could be seen as the pressure increased to 0.3 MPa, for both dead-end and cross-flow filtration. Using only dead-end alternative, higher fluxes were achieved for both membranes, but it decreases with time due to accumulation on the membrane surface. The use of cross-flow filtration did not allow accumulation on the membrane surface so that the flux was constant in time.The use of anionic surfactants improved the food dye retention. The interactions between membranes and surfactants can be an important factor supporting the efficiency of the ultrafiltration.

Removal of pharmaceutically active compounds by using low-pressure membrane processes

This is an Accepted Manuscript of an article published by Taylor & Francis in Desalination and water treatment on 2017, available online: http://doi.org/10.5004/dwt.2017.0449

Application of post-consumer recycled high-impact polystyrene in the preparation of phase-inversion membranes for low-pressure membrane processes

In this study, recycled plastic waste was successfully used in preparing low-pressure membranes by phase-inversion method. These membranes are considered as an alternative solution for economical and environmental concerns, namely: water reclamation as well as polymer recycling and reuse. Post-consumer recycled high-impact polystyrene and virgin commercial high-impact polystyrene were separately used to prepare membranes, which were thereafter compared in terms of their respective characteristics and performance. N,N-dimethylacetamide and deionised water were used as a solvent and coagulant, respectively. Membranes were characterised by microscopic observations, contact angle measurements, thermogravimetric analysis, and filtration experiments. The recycled polymeric membranes presented similar thermal properties as the membranes made from commercial high-impact polystyrene, which were used as control membranes. They also obtained similar asymmetric membrane structures, however with slightly higher porosity (from 47.54 ± 5.53% for control membranes to 52.31 ± 4.33% for recycled polymeric membranes). The presence of additives in the recycled polymeric structure was confirmed by EDX results. Such additives made the membranes to become more hydrophilic, reducing the water contact angle value from 81.78 ± 3.42° obtained for control membranes to 79.19 ± 4.15°. Moreover, irreversible fouling was satisfactorily minimised and humic acid rejection was very slightly enhanced (from 95.5 ± 0.2 to 96 ± 0.1%). This indicates that the more hydrophilic the membrane is, the better antifouling properties it possesses. Thus, the results of the post-consumer recycled high-impact polystyrene suggest that they can provide a sustainable and environmental alternative when implemented in low-pressure membrane processes.

Natural Organic Matter Removal and Fouling Control in Low-Pressure Membrane Filtration for Water Treatment

Natural organic matter (NOM) is a primary component of fouling in low-pressure membrane filtration, either solely, or in concert with colloidal particles. Various preventive measures to interfere with NOM fouling have been developed and extensively tested, such as coagulation, oxidation, ion exchange, carbon adsorption, and mineral oxide adsorption. Therefore, this article aims to conduct a literature review covering the topics of low-pressure membrane processes, NOM characteristics and fouling behaviors, and diverse fouling control strategies. In-depth explanations and discussion are made regarding why some treatment options are able to remove NOM from source water, but do not reduce fouling. This review provides insight for hybridized membrane processes with respect to NOM removal and fouling mitigation in water treatment.

Polishing of ceramic ultrafiltration membrane permeates by ion exchange

The growing demand for freshwater and the increasingly stringent regulations concerning drinking water quality are essentially driving the application of membrane processes in the water treatment sector. The removal of natural organic matter (NOM) from the water being treated has become imperative as these pollutants promote the formation of disinfection byproducts. To remove NOM from water intended for human consumption, use is frequently made of a low-pressure membrane process, i.e. ultrafiltration (UF). An inherent limitation to the use of UF membranes for NOM removal is the poor retention of low-molecular-weight s ubstances. It seemed therefore advisable to examine the potential of another polishing process, namely that of ion exchange, for enhancing the final quality of the water being treated. The aim of this work was to assess the efficiency of the ion exchange process as a method for upgrading the quality of the ceramic membrane permeate, with emphasis placed on NOM removal. The process was conducted using two UF ceramic membranes (molecular weight cutoff of 50 and 300 kDa) and four ion-exchange resins (A200, A400, SBW and MIEX®). The study has produced the following findings: the UF membranes provided a sufficiently high extent of NOM removal, and the ion exchange process performed after the process of ultrafiltration significantly improved the quality of the water being treated. Of the ion-exchange resins tested, MIEX® was found to be the most effective.

Short-range forecast of permeate flux in detergent waste water ultrafiltration

Waste water purification is very crucial nowadays and new techniques like low-pressure driven membrane processes are developed to obtain the sufficient productivity and high efficiency of cleaning. However, selection of membrane requires long-lasting tests. The new methods like artificial neural networks (ANN) are essential to avoid time consuming laboratory measurements. In the article the permeate flow rate of detergent waste water was forecasted using ANN. In order to predict the flow rate, the network used short-range time series regression. During two days of continuous measurements (every 5 min) the following parameters were measured: temperature of waste water, recirculation flow rate, inlet pressure and outlet pressure. Those parameters were considered as inputs to the network while permeate flow rate as output value. The best created network (with the highest value of Pearson correlation coefficient and the lowest value of training error) was characterised by the following parameters: hyperbolic tangent and sine function of activation, Quasi-Newton method of learning, 4 input neurons, 8 hidden neurons and 1 output neuron.

A power-law model of electrostatic interactions of colloidal particles in cake layer on membrane surface

The permeability of cake on membrane surface is a crucial factor affecting the efficiency of low pressure membrane process. In this study, a power-law model was suggested for better understanding of the effect of solution chemistry on cake permeability. The model equation was derived from the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and the dimensional analysis of parameters affecting the chemical interactions of colloidal particles. Experimental results from unstirred filtration of submicron latex particles at various ionic strengths were used for model application. The permeate flux as well as specific cake resistance and cake porosity was sensitive to ionic strengths. Different behaviors of cake permeability were observed for non-aggregated and aggregated particles. The proposed model aids to interpret complicated relations of cake permeability in terms of the characteristic ratio, which is defined as the ratio of electrostatic repulsion to van der Waals attraction.

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 2–7.0kDa 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 1.5mgO3/L made membrane flux maximum during 0.5–3.0mgO3/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.

Effect of algal extracellular polymer substances on UF membrane fouling

Low-pressure membrane processes, such as ultrafiltration (UF), are effective for treating algae-laden eutrophic source waters. However, fouling caused by algae excreted organics can be a major obstacle to the smooth operation of membrane processes. In this study, three algae species, with a similar cell size and shape, but a different amount of extracellular polymeric substances (EPS), were selected. The characteristics of the bound EPS, including its amount and constituents, mainly polysaccharide and protein, were analyzed. Cell suspensions were filtered through a dead-end stirred cell with a regenerated cellulose UF membrane. Based on the observations of permeate flux decline at higher transmembrane pressure (TMP) and critical flux values, it can be concluded that algae cell EPS do affect membrane fouling, and the constituents of EPS may also play a role.

The effect of a polyelectrolyte on the efficiency of dye-surfactant solution treatment by ultrafiltration

The effect of a cationic polyelectrolyte (PE) on the dye and surfactant removal from aqueous mixtures by low-pressure membrane process was assessed. Flat ultrafiltration (UF) membranes made of regenerated cellulose and polyethersulfone, and characterized by different cut-off values (5, 10, and 30 kDa) were used in the experiments. The UF process involved a pressure of 0.1 and 0.2 MPa. Permeation measurements were carried out with aqueous solutions of different anionic dyes (methyl orange, indigo carmine, amido black, and direct black) and dye solutions containing an anionic surfactant – sodium dodecyl sulfate (SDS), and/or a cationic PE. Dye, surfactant, and PE concentrations in the experimental solutions amounted to 100, 100, and 0.5 g/m 3, respectively. It was found that when a cationic PE was present in the dye-surfactant mixture, this was concomitant with a decrease in membrane permeability and an increase in dye and surfactant retention. This relationship was more pronounced for polyetersulfone membranes than for membranes made of regenerated cellulose, as well as for membranes of high cut-off values.

Macroscopic and microscopic characterizations of a cellulosic ultrafiltration (UF) membrane fouled by a humic acid cake deposit: First step for intensification of reverse osmosis (RO) pre-treatments

Abstract One of the critical issues for the application of low-pressure membrane processes (microfiltration, MF or ultrafiltration, UF) as pre-treatment processes for freshwater preparation is membrane fouling due to natural organic matter (NOM). The aim of this preliminary study is to contribute to a better understanding of the fouling phenomena occurring on a regenerated cellulose UF membrane fouled with a humic acid cake deposit. The originality of this work is based on a double approach on surface analysis at both macroscopic and microscopic scales. It is presently reported that humic acid fouling is mainly governed by cake formation, which plays a major role in flux decline via the well-known model of resistances in series. We obtained that the adsorbed resistance is 2% of the total resistance while the cake resistance is 52% of the total resistance, which is higher than that of the virgin membrane. From field emission gun scanning electron microscopy (FESEM) it was found for the first time that the humic acid cake is well organized, and particularly in fractal forms. The fractal dimension (FD) of the cake is determined as 2.52, which is in good agreement with the theoretical fractal dimension of particle–cluster aggregation underlying diffusion-limited aggregation (FD = 2.51). This new microscopic fouling index decreases with the presence of cake and can be correlated with the decrease of the hydraulic permeability. The classical silt density index (SDI) and the new modified fouling index (denoted MFI-UF) were obtained and also proved the presence of the cake. To complete this approach transmembrane streaming potential (denoted SP) measurements were conducted with a new homemade apparatus developed in our lab and presented for the first time in the present article, helped us to observe also a penetration of low molecular fractions of humic acid inside the membrane. Indeed the displacement of the isoelectric point (iep) of the membrane from 2.3 to 1.5 for the virgin and fouled membranes, respectively, permitted to illustrate this penetration. This newly designed SP apparatus is a semi-automatic tool assisted by a software denoted as proFluid 1.2. Furthermore, preliminary experiments with seawater were realized in order to estimate the influence of seawater filtration on the hydraulic permeability and SP parameters for the RC 100-kDa membrane.