Membrane System Performance Research Articles

Enhancing gravity-driven membrane system performance in shale gas wastewater treatment: Effect and mechanism of sodium acetate solution backwashing

The low-carbon gravity-driven membrane (GDM) filtration technology has great potential for treating highly decentralized shale gas wastewater (SGW), but its performance requires further enhancement. This study explores the effects and underlying mechanisms of sodium acetate (NaAc) solution backwashing on enhancing GDM system performance in SGW treatment. Results indicated that NaAc solution backwashing for 30 min per day significantly improved the stable flux, organic matter removal rate, and total organic nitrogen removal rate by 64%, 176%, and 1085%, respectively. Structural and compositional analysis of the biofouling layer revealed that NaAc solution backwashing effectively reduced its thickness and coverage, thereby diminishing filtration resistance and enhancing stable flux. Furthermore, comparative analysis with pure water backwashing and evaluations of microbial community structures demonstrated that NaAc solution, as a carbon source, substantially stimulated microbial activity and growth, and optimized the microbial community within the biofouling layer. Specifically, NaAc solution backwashing selectively enriched functional microbes with denitrification and organic degradation abilities, such as Roseovarius, Marinobacter, Bacillus, and Citreitalea, thereby augmenting the GDM system’s nitrogen and carbon removal capabilities. Overall, the performance improvements observed were primarily attributed to the physical cleaning effects and bioaugmentation function provided by NaAc solution. This study offered valuable insights for designing and optimizing backwashing strategies in the GDM system.

Insights of membrane fouling under scale inhibitor synergistic condition monitored by ultrasonic phased array: Fouling spatial and density characteristics

Achieving accurate dosing of scale inhibitors in full reverse osmosis (RO) membrane systems for industrial applications is a critical challenge due to a lack of understanding of membrane fouling characteristics. To address this, this study investigated membrane performance at different inhibitor concentrations and proposed a method using ultrasonic phased arrays (UPA) to evaluate the fouling layer's spatial and density characteristics. The study also examined the relationship between fouling reversibility and compaction, and the results showed a clear conversion process from inhibition to exacerbation of membrane fouling by scale inhibitors. Additionally, the fouling layer distribution characteristics were opposite at different concentrations. At insufficient concentrations, the scaling layer forms near the outlet and spreads to the far-end with a continuously decreasing thickness. Conversely, at surplus concentrations, the opposite effect was observed. At sufficient concentrations, the fouling layer thickness and range exhibited a discontinuous distribution. The high-density layer was dominant on the membrane surface and showed low fouling reversibility. However, scale inhibitors were found to minimize fouling density by interfering with ion deposition, reducing the ion content and significantly increasing its reversibility. These findings have significant implications for scale inhibitor efficiency evaluation and scientific application, which can improve industrial membrane system performance.

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.

A Critical Review on Electric Field-Assisted Membrane Processes: Implications for Fouling Control, Water Recovery, and Future Prospects

Electrofiltration, an electric field-assisted membrane process, has been a research topic of growing popularity due to its ability to improve membrane performance by providing in situ antifouling conditions in a membrane system. The number of reports on electrofiltration have increased exponentially over the past two decades. These reports explored many innovations, such as novel configurations of an electric field, engineered membrane materials, and interesting designs of foulant compositions and membrane modules. Recent electrofiltration literature focused mainly on compiling results without a comprehensive comparative analysis across different works. The main objective of this critical review is to, first, organize, compare and contrast the results across various electrofiltration studies; second, discuss various types of mechanisms that could be incorporated into electrofiltration and their effect on membrane system performance; third, characterize electrofiltration phenomenon; fourth, interpret the effects of various operational conditions on the performance of electrofiltration; fifth, evaluate the state-of-the-art knowledge associated with modeling efforts in electrofiltration; sixth, discuss the energy costs related to the implementation of electrofiltration; and finally, identify the current knowledge gaps that hinder the transition of the lab-scale observations to industry-scale electrofiltration as well as the future prospects of electrofiltration.

Assessment of an Integrated and Sustainable Multistage System for the Treatment of Poultry Slaughterhouse Wastewater.

This paper assesses the performance of an integrated multistage laboratory-scale plant, for the treatment of poultry slaughterhouse wastewater (PSW). The system was comprised of an eco-flush dosed bio-physico pre-treatment unit for fats, oil, and grease (FOG) hydrolysis prior to the PSW being fed to a down-flow expanded granular bed reactor (DEGBR), coupled to a membrane bioreactor (DEGBR-MBR). The system’s configuration strategy was developed to achieve optimal PSW treatment by introducing the enzymatic pre-treatment unit for the lipid-rich influent (PSW) in order to treat FOG including odour causing constituents such as H2S known to sour anaerobic digestion (AD) such that the PSW pollutant load is alleviated prior to AD treatment. This was conducted to aid the reduction in clogging and sludge washout in the DEGBR-MBR systems and to achieve the optimum reactor and membrane system performance. A performance for the treatment of PSW after lipid reduction was conducted through a qualitative analysis by assessing the pre- and post-pre-treatment units’ chemical oxygen demand (COD), total suspended solids (TSS), and FOG concentrations across all other units and, in particular, the membrane units. Furthermore, a similar set-up and operating conditions in a comparative study was also performed. The pre-treatment unit’s biodelipidation abilities were characterised by a mean FOG removal of 80% and the TSS and COD removal reached 38 and 56%, respectively. The final acquired removal results on the DEGBR, at an OLR of ~18–45 g COD/L.d, was 87, 93, and 90% for COD, TSS, and FOG, respectively. The total removal efficiency across the pre-treatment-DEGBR-MBR units was 99% for COD, TSS, and FOG. Even at a high OLR, the pre-treatment-DEGBR-MBR train seemed a robust treatment strategy and achieved the effluent quality set requirements for effluent discharge in most countries.

Combining chlor(am)ine-UV oxidation to ultrafiltration for potable water reuse: Promoted efficiency, membrane fouling control and mechanism

Wastewater reuse has been progressively popular as a practical method for protecting aquatic environment and water sources. In this work, the chlor(am)ine-UV oxidation was employed to enhance membrane system performance during potable water reuse. The achievements were comprehensively evaluated from the aspects of membrane fouling mitigation and organic matter removal. The various dosages of chlorine and UV irradiation were applied and the effects of typical inorganic species in wastewater effluent were considered as well. It was suggested that the chlor(am)ine-UV oxidation could significantly promote the normalized flux by 94.9% under the condition of 10 mg L-1/960 mW cm-2 (chlorine dose and UV irradiation density). And the certain lower concentration of inorganic pollutant in wastewater effluent could further prevent the membrane fouling accumulation, especially for the reversible and total fouling resistances. The model fitting of filtration flux revealed that the combination of pore blockage and cake filtration was responsible for the mechanisms of fouling formation, and the transition moment was adjusted by the oxidation process. The characteristics of dissolved organic matter were modified as well, which were positive for the improvement of membrane effluent quality and security. The results demonstrated that the combination of the chlor(am)ine-UV oxidation and ultrafiltration could be a promising alternative for efficient wastewater recycle and reuse.

Enhancement of membrane system performance using artificial intelligence technologies for sustainable water and wastewater treatment: A critical review

In recent years, membrane technologies are widely utilized in water and wastewater treatment processes. However, controlling and improving these systems still need to be investigated and, therefore, are attracting increasing amounts of attention from researchers worldwide. Industry 4.0 has increased in importance over the past few years, and artificial intelligence (AI) technology has demonstrated its strength in supporting decision-making in various fields, including environmental systems and especially membrane processes. AI allows for cost-effective operation of systems, including better planning and tracking as well as comprehensive understanding of resource-loss in real-time, then maximizing revenue capture and water quality satisfaction. This study therefore aims to provide a comprehensive review of the current application of AI-based tools in simulating membrane processes as well as the feasibility of applying these models to other fields in which membranes are to be used in the future. The existing conventional mathematical models are illustrated along with their advantages and shortcomings. The definition and classification of state-of-the-art AI models, as well as the benefits of these over conventional models, are also discussed. Furthermore, the basic principle of membrane processes and current application of AI-based technologies in simulating the performance of these membrane systems are systematically reviewed. Finally, the implications and recommendations for future studies are discussed.

Enhanced hydraulic cleanability of biofilms developed under a low phosphorus concentration in reverse osmosis membrane systems

A critical problem in seawater reverse osmosis (RO) filtration processes is biofilm accumulation, which reduces system performance and increases energy requirements. As a result, membrane systems need to be periodically cleaned by combining chemical and physical protocols. Nutrient limitation in the feed water is a strategy to control biofilm formation, lengthening stable membrane system performance. However, the cleanability of biofilms developed under various feed water nutrient conditions is not well understood.This study analyzes the removal efficiency of biofilms grown in membrane fouling simulators (MFSs) supplied with water varying in phosphorus concentrations (3 and 6 μg P·L-1 and with constant biodegradable carbon concentration) by applying hydraulic cleaning after a defined 140% increase in the feed channel pressure drop, through increasing the cross-flow velocity from 0.18 m s-1 to 0.35 m s-1 for 1 h. The two phosphorus concentrations (3 and 6 μg P·L-1) simulate the RO feed water without and with the addition of a phosphorus-based antiscalant, respectively, and were chosen based on measurements at a full-scale seawater RO desalination plant. Biomass quantification parameters performed after membrane autopsies such as total cell count, adenosine triphosphate, total organic carbon, and extracellular polymeric substances were used along with feed channel pressure drop measurements to evaluate biofilm removal efficiency. The outlet water during hydraulic cleaning (1 h) was collected and characterized as well. Optical coherence tomography images were taken before and after hydraulic cleaning for visualization of biofilm morphology.Biofilms grown at 3 μg P·L-1 had an enhanced hydraulic cleanability compared to biofilms grown at 6 μg P·L-1. The higher detachment for biofilms grown at a lower phosphorus concentration was explained by more soluble polymers in the EPS, resulting in a lower biofilm cohesive and adhesive strength. This study confirms that manipulating the feed water nutrient composition can engineer a biofilm that is easier to remove, shifting research focus towards biofilm engineering and more sustainable cleaning strategies.

A Performance analysis of the Claridge-Culp-Liu dehumidification process: A novel approach for drying moist air based on membrane separation, vacuum compression and sub-atmospheric condensation

Abstract This paper covers a basic model for analyzing the performance of the Claridge-Culp-Liu dehumidification process. The fundamental process efficiency limit for dehumidification is close to COPCarnot, but for the eight dehumidification cases examined, the limiting or ideal energy use required is 26% to 56% that of a Carnot condensing system as shown in an earlier paper. The model presented in this paper is used to show the membrane system performance reduction caused by finite membrane area, finite water vapor permeance, non-zero air permeance, non-zero system air pressure drop, non-ideal compressors, vacuum pumps, and condensers. The performance of a “conservative” membrane system based on the use of existing components is computed for eight specific conditions along with that of a “target” system that assumes expected component performance after additional future component development. The “conservative” membrane system would use 36% to 66% as much energy as a system with a COP=7 chiller to produce the same dehumidification for the eight cases examined while the “target” system would use 15% to 40% the energy of a system with a COP=7 chiller. In addition to the significant energy reduction over conventional technology, the membrane system offers the advantages of: 1) no HFC refrigerant use; 2) direct isothermal control over humidity ratio setpoint; 3) maximum capacity occurs at design conditions; and 4) system generates pure water extracted from air as a by-product.

Biofouling control by phosphorus limitation strongly depends on the assimilable organic carbon concentration

Nutrient limitation is a biofouling control strategy in reverse osmosis (RO) membrane systems. In seawater, the assimilable organic carbon content available for bacterial growth ranges from about 50 to 400 μg C·L−1, while the phosphorus concentration ranges from 3 to 11 μg P·L−1. Several studies monitored biofouling development, limiting either carbon or phosphorus. The effect of carbon to phosphorus ratio and the restriction of both nutrients on membrane system performance have not yet been investigated.This study examines the impact of reduced phosphorus concentration (from 25 μg P·L−1 and 3 μg P·L−1, to a low concentration of ≤0.3 μg P·L−1), combined with two different carbon concentrations (250 C L−1 and 30 μg C·L−1), on biofilm development in an RO system. Feed channel pressure drop was measured to determine the effect of the developed biofilm on system performance. The morphology of the accumulated biomass for both carbon concentrations was characterized by optical coherence tomography (OCT) and the biomass amount and composition was quantified by measuring total organic carbon (TOC), adenosine triphosphate (ATP), total cell counts (TCC), and extracellular polymeric substances (EPS) concentration for the developed biofilms under phosphorus restricted (P-restricted) and dosed (P-dosed) conditions.For both carbon concentrations, P-restricted conditions (≤0.3 μg P·L−1) limited bacterial growth (lower values of ATP, TCC). A faster pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 250 μg C·L−1 was dosed. This faster pressure drop increase can be explained by a higher area covered by biofilm in the flow channel and a higher amount of produced EPS. Conversely, a slower pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 30 μg C·L−1 was dosed. Results of this study demonstrate that P-limitation delayed biofilm formation effectively when combined with low assimilable organic carbon concentration and thereby, lengthening the overall membrane system performance.

Improve Membrane System Performance and Reduce Costs

Although a relatively new technology, membrane systems are widely used for water filtration. To save money and increase reliability, take a proactive approach to membrane system operations by understanding the basics, following recommendations, and using updated design concepts

Engineering evaluation of CO2 separation by membrane gas separation systems

The possible application of membranes for CO2 separation in the treatment of non-valuable streams (e.g., flue gas of a power plant or cement industry) or valuable streams (e.g., biogas) has been analyzed. Some selection criteria useful in the choice of membrane gas separation for CO2 capture are discussed to evaluate the advantages potentially offered by membrane systems. Membrane selectivity ranging from 30–50 (values of commercial membranes) to 100–500 (values of most promising laboratory membranes) and different feed/permeate pressure ratios were considered for the various cases. The composition and recovery of carbon dioxide in the membrane-treated stream were the target parameters taken into account as guidelines in the evaluation of the separation technology performance. General “maps” of CO2 permeate concentration versus CO2 recovery have been developed by means of a simple tool that takes into account the influence of the most important parameters affecting the membrane system performance (that is, membrane selectivity and permeation driving force). The analyses indicated that the separation depends on various interrelated factors: the membrane material (selectivity and flux), the operating conditions (pressure ratio), and the final requirements (CO2 recovery and composition). Also, the operational limit and the potentialities of the membrane gas separation technology were analyzed under these conditions. The “maps” proposed and utilized for CO2 separation are valid and can be utilized for other gas separations in which the membrane shows selectivities similar to those taken into account here.

A parametric study of the impact of membrane materials and process operating conditions on carbon capture from humidified flue gas

Membranes are among a suite of technologies being considered for post-combustion carbon capture. Recent studies have shown the importance of process design in optimizing membrane system performance and setting guidelines for membrane materials development. In this study, the simulated performance of membranes based on a rubbery poly(ethylene oxide) block copolymer, a polyvinylamine/polyvinyl alcohol blend that shows facilitated CO2 transport, and a glassy thermally-rearranged polybenzimidazole is compared for a single-stage membrane operation treating humidified flue gas. Parametric studies were conducted to investigate the impact of different operating modes and conditions. For all cases, high membrane CO2 permeance minimizes membrane area requirements, while high CO2/N2 selectivity improves the CO2 purity and reduces the energy needed for CO2 purification. The benefits of higher selectivity are accentuated at higher feed-to-permeate pressure ratios, at the expense of increased energy cost. The advantages of higher permeance are most pronounced at a lower pressure ratio. The effects of water vapor in flue gas on CO2 capture with membranes can be complex depending on possible interactions of sorbed water with the membrane. From a process standpoint, a slight positive sweep effect is generated from the co-permeation of water vapor which increases the CO2 separation degree at a fixed membrane area.

산화철 나노입자 표면개질 분말활성탄 유동층에 의한 MF 막 분리 공정의 운전 및 NOM 제거 효율 향상

Effects of powdered activated carbon impregnated by iron oxide nano particle (Impregnated PAC) on the microfiltration (MF) membrane system performance in NOM removal from water were investigated in this study. A fluidized bed column was employed as a pretreatment of MF membrane process. The Impregnated PAC bed was stably maintained at an upflow rate of 63 m/d without leakage of the Impregnated PAC particles, which provided a contact time of 29 minutes. A magnetic ring at the upper part of the column could effectively hold the overflowing discrete particles. The Impregnated PAC column demonstrated a significant enhancement in the MF membrane performance in terms of fouling prevention and natural organic matter (NOM) removal. Trans-membrane pressure of the MF membrane increased to 41 kPa in 98 hours of operation, while it could be maintained at 12 kPa with the Impregnated PAC pretreatment. Removal of NOM determined by dissolved organic carbon and UV254 was also enhanced from 46% and 51% to 75% and 84%, respectively, by the pretreatment. It was found that the Impregnated PAC effectively removed a wide range of different molecular-sized organic compounds from size exclusion analysis.

Membrane technology for sustainable treated wastewater reuse: agricultural, environmental and hydrological considerations

Field experiments were conducted in agricultural fields in which secondary wastewater of the City of Arad (Israel) is reused for irrigation. For sustainable agricultural production and safe groundwater recharge the secondary effluent is further polished by a combined two-stage membrane pilot system. The pilot membrane system consists of two main in row stages: Ultrafiltration (UF) and Reverse Osmosis (RO). The UF stage is efficient in the removal of the pathogens and suspended organic matter while the successive RO stage provides safe removal of the dissolved solids (salinity). Effluents of various qualities were applied for agricultural irrigation along with continuous monitoring of the membrane system performance. Best agricultural yields were obtained when applying effluent having minimal content of dissolved solids (after the RO stage) as compared with secondary effluent without any further treatment and extended storage. In regions with shallow groundwater reduced soil salinity in the upper productive layers, maintained by extra membrane treatment, will guarantee minimal dissolved solids migration to the aquifers and minimize salinisation processes.

Pilot Study Steers Membrane System Research

This article discusses a field‐scale pilot test by the Seoul Metropolitan Government's (SMG's) Waterworks Research Institute to determine the feasibility of using microfiltration (MF) and ultrafiltration (UF) as treatment technologies for achieving the required level of Cryptosporidium treatment, and protecting public health from waterborne pathogens. Five types of membrane systems, three pressure‐driven and two vacuum‐driven, were installed at SMG's Gu‐ui water treatment plant in eastern Seoul. Details of pilot tests are provided, along with water quality analysis, membrane system performance, energy consumption analysis, and a comparison of direct filtration. Test results are discussed, indicating that the submerged membrane process was more sustainable than the pressure‐driven process for high turbidity.

A statistical approach to the optimisation of membrane operation

AbstractA bench‐scale analysis has been conducted on the ultrafiltration of synthetic and real domestic wastewaters post‐biotreatment by a biological aerated filter. This paper presents a rigorous analytical technique to identify the process parameters that have a significant influence on a membrane system performance. By applying statistical techniques, the influence of each parameter and the level of uncertainty were quantified within a highly complex, interrelated and variable process. The results showed that the fouling propensity for real greywater was significantly variable, both during the trial and from one trial to the next. The variability was primarily due to the inherent variability of greywater quality and the extent of settling within the storage facility. However, the fouling propensity for real greywater was generally lower than for settled sewage. The results of the analysis were extended to produce a predictive model that can be used as a guide in the design of membrane systems and their operation. The methodology is readily transferable and adaptable to other membrane systems.

Bench‐scale evaluation of critical flux and TMP in low‐pressure membrane filtration

Critical flux has been defined as the permeate flux of a membrane system under which little or no fouling is observed. Exceeding critical flux results in rapidly increasing transmembrane pressure and fouling. This article describes bench‐scale techniques that can be used to measure critical flux and determine the effects of changing water quality on membrane performance. The bench‐scale technique also demonstrates the effectiveness of coagulation on low‐pressure membrane system performance. The critical flux test for low‐pressure filters could be considered the operational equivalent of jar testing in conventional water treatment plants. It is proposed that utilities and consultants should use similar bench‐scale critical flux measurements to assist in low‐pressure membrane system design, to modify operation during periods of changing water quality, and to determine the effects of coagulation or other treatments on low‐pressure membrane system performance.

Early discovery of RO membrane fouling and real-time monitoring of plant performance for optimizing cost of water

RO plant operators, end-users, membrane manufacturers and system suppliers have been facing two major problems since the advent of commercial membrane technology applications for water desalination utilizing reverse osmosis (RO) and other membrane processes: how to reliably monitor their membrane system performance and how to detect membrane fouling and scaling development in real time and before significant or irreversible loss of performance efficiency occurs, resulting in lower plant availability and significantly higher OM costs. The current industry-standard performance analysis and evaluation technique is based on trending RO flux decline characteristics of membranes via normalizing system operating data in accordance with ASTM D-4516 standard method. This paper discusses the shortfalls of this technique, and introduces a practical new technology for measuring and monitoring membrane fouling and flux performance in real-time. The new Silent Alarm™ technology, designed as an early-warning system, allows the discovery of any fouling or scaling development on the RO membranes in the very early stages, thus providing a valuable tool for the plant operator to take immediate corrective measures before it is too late. Two major brackish and seawater Arabian Gulf RO plant case studies with and without a fouling history are discussed. This proven capability to monitor RO plant performance in real-time and measure the actual development of any membrane fouling or scaling very early on has a direct and dramatic positive impact on optimizing the total cost of desalinated water.

Early discovery of RO membrane fouling and real-time monitoring of plant performance for optimizing cost of water

RO plant operators, end-users, membrane manufacturers and system suppliers have been facing two major problems since the advent of commercial membrane technology applications for water desalination utilizing reverse osmosis (RO) and other membrane processes: how to reliably monitor their membrane system performance and how to detect membrane fouling and scaling development in real time and before significant or irreversible loss of performance efficiency occurs, resulting in lower plant availability and significantly higher OM costs. The current industry-standard performance analysis and evaluation technique is based on trending RO flux decline characteristics of membranes via normalizing system operating data in accordance with ASTM D-4516 standard method. This paper discusses the shortfalls of this technique, and introduces a practical new technology for measuring and monitoring membrane fouling and flux performance in real-time. The new Silent Alarm™ technology, designed as an early-warning system, allows the discovery of any fouling or scaling development on the RO membranes in the very early stages, thus providing a valuable tool for the plant operator to take immediate corrective measures before it is too late. Two major brackish and seawater Arabian Gulf RO plant case studies with and without a fouling history are discussed. This proven capability to monitor RO plant performance in real-time and measure the actual development of any membrane fouling or scaling very early on has a direct and dramatic positive impact on optimizing the total cost of desalinated water.