Suppression Of Fouling Research Articles

An overview of analytical techniques for heavy metal ion detection and removal from industrial sewage

Removal of heavy metal ions from wastewater is of paramount importance for a clean environment and human health. Various reported processes have addressed the removal of heavy metal ions from various wastewater sources. These processes can be divided into adsorption, membrane, chemical, electrical, and photo catalytic processes. This article provides a comprehensive and critical overview of these methods, discussing the media/sorbents used, removal efficiency, operating conditions, and advantages and disadvantages of each method. We also summarize the main results of previous studies reported in the literature. It should be noted that recent research has generally focused on adsorption techniques. The main obstacles to the adsorption process are the ability to simultaneously remove different types of ions, the long retention time of the adsorbent and cycle stability. Although chemical and membrane processes are practical, high levels of sludge formation and post-treatment requirements are key issues that must be addressed in chemical processes. Suppression of fouling and scaling can further improve membrane separation. However, pretreatment and regular cleaning of the membrane incurs additional costs. Electrical methods have also been reported to be efficient. However, in addition to overcoming the problem of massive sludge formation, industrial scale separation is required. Electrical and photo catalytic-based methods are not yet mature. Future research should focus on environmentally friendly, inexpensive, and sustainable materials and methods.

Ultrahigh efficient emulsification with drag-reducing liquid gating interfacial behavior

Emulsification is a crucial technique for mixing immiscible liquids into droplets in numerous areas ranging from food to medicine to chemical synthesis. Commercial emulsification methods are promising for high production, but suffer from high energy input. Here, we report a very simple and scalable emulsification method that employs the drag-reducing liquid gating structure to create a smooth liquid-liquid interface for the reduction of resistance and tunable generation of droplets with good uniformity. Theoretical modeling and experimental results demonstrate that our method exhibits ultrahigh efficiency, which can reach up to more than 4 orders of magnitude greater energy-saving compared to commercial methods. For temperature-sensitive biological components, such as enzymes, proteins, and bacteria, it can offer a comfortable environment to avoid exposure to high temperatures during emulsifying, and the interface also enables the suppression of fouling. This unique drag-reducing liquid gating interfacial emulsification mechanism promotes the efficiency of droplet generation and provides fresh insight into the innovation of emulsifications that can be applied in many fields, including the food industry, the daily chemical industry, biomedicine, material fabrication, the petrochemical industry, and beyond.

Fouling mechanism in airblast atomizers and its suppression for water desalination

A detailed experimental study is presented on fouling behavior of the anti-clogging perforated plate atomizer designed for high salinity applications, and compared with a conventional (plain-jet) airblast atomizer. Low-pressure regions around fast moving air in the outer layer of spray (as in conventional atomizers: plain-jet and prefilming) due to Venturi suction were identified as the root cause of atomizer clogging, as they facilitate salt accumulation on the atomizer surface from spray. Accordingly, severe atomizer fouling, and fluctuations in spray cone angle were observed in the conventional airblast atomizer over 2 h at 100°C air and 50°C saline (44° to 76° at 35,000 ppm, and 44° to 91° at 100,000 ppm). In this regard, the perforated plate atomizer provides a novel liquid-film airblast atomization by maintaining a liquid-annulus film (around the air outlet) as the outer layer of spray. Doing so we achieved nearly complete suppression of fouling, and spray cone angle fluctuations (28° ± 1° at 35,000 ppm, and 30° ± 1° at 100,000 ppm). Later, novel liquid-film atomization was adopted in the conventional airblast atomizer. While, the conventional airblast atomization needed atomizer cleaning/maintenance after 35 min for 175°C air and 65°C saline at 100,000 ppm, the liquid-film atomization showed no sign of fouling over 14 h. Hence, current work establishes a benchmark liquid-film airblast atomization mechanism in the anti-clogging perforated plate atomizer for complete suppression of fouling in airblast atomization. This extends the application of airblast atomizers from high evaporation jet engines to ZLD-HDH desalination systems, spraying, powder metallurgy, pharmaceuticals and hospitals, and spray drying and cooling.

A model-based analysis of electrodialysis fouling during pulsed electric field operation

When electrodialysis (ED) is applied to process streams that are known to foul and scale the system, it can be operated with an oscillating electric field. This procedure is known as pulsed electric fields (PEF) and has been proven to reduce the fouling susceptibility of the system. In literature, the suppression of fouling is attributed to a combination of three effects: the reduction of concentration polarisation, the promotion of electroconvection and the suppression of water splitting. However, these effects have yet to be substantiated quantitatively. Here we study how much of the fouling suppression during PEF can be attributed to the reduction of concentration polarisation. A Nernst–Planck and Kedem–Katchalsky modelling approach is adopted to simulate the evolution of concentration profiles of a ternary solution of sodium, chloride and dodecyl sulfate (DS) during PEF. The effect of the pulse parameters on the boundary layer concentration of sodium dodecyl sulfate (SDS) is studied along with an evaluation of the current efficiency and energy consumption. Our results illustrate the counterproductivity of low-frequency pulses and the trade-off between the current efficiency and fouling suppression but fail to explain the improvement when compared to the constant current operation. Fouling layer relaxation is put forth to complement to previously mentioned fouling suppression effects and is relevant for future research.

Plasma Graft Polymerization and Surface-Initiated Atom Transfer Radical Polymerization: Characteristics of Low-Fouling Membranes Obtained by Surface Modification with Poly(2-methoxyethyl Acrylate)

This study investigated the characteristics of membranes modified by grafting poly(2-methoxyethyl acrylate) (PMEA) onto their surfaces and pore walls via plasma graft polymerization (PGP) and surface-initiated atom transfer radical polymerization (SI-ATRP) to render the membrane surfaces fouling-free. The grafting of PMEA was successfully achieved using both methods. Although no remarkable differences were observed in the modified membranes through structural analyses such as FT-IR and FE-SEM, pure water permeability was higher in the membranes modified by SI-ATRP than in those modified by PGP, particularly at the same grafting amount. This was probably because the length of the grafted PMEA was shorter with a higher PMEA density per surface area when SI-ATRP was employed for the modification with PMEA, compared to those obtained when PGP was used. The modified membranes exhibited excellent low-fouling properties against bovine serum albumin (BSA), regardless of the modification method used. In addition, it was demonstrated that the low-fouling properties resulted from the suppression of BSA adsorption by the grafted PMEA. Finally, no flux decline was demonstrated through a 10 h filtration test of raw water for water supply with the modified membranes, which clearly indicated the effective fouling suppression performance of the modified membranes.

Flow and Drop Transport Along Liquid-Infused Surfaces

Liquid-infused surfaces (LISs) are composite solid–liquid surfaces with remarkable features such as liquid repellency, self-healing, and the suppression of fouling. This review focuses on the fluid mechanics on LISs, that is, the interaction of surfaces with a flow field and the behavior of drops on such surfaces. LISs can be characterized by an effective slip length that is closely related to their drag reduction property, which makes them suitable for several applications, especially for turbulent flows. Drag reduction, however, is compromised by failure mechanisms such as the drainage of lubricant from surface textures. The flow field can also sculpt the lubricant layer in a coupled self-organization process. For drops, the lubricant reduces drop pinning and increases drop mobility, but also results in a wetting ridge and the associated concept of an apparent contact angle. Design of LIS wettability and topography can induce low-friction drop motion, and drops can dynamically shape the lubricant ridges and film thickness.

Understanding the mechanism of membrane fouling suppression in electro-anaerobic membrane bioreactor

Anaerobic membrane bioreactor (AnMBR) is a promising technology for wastewater treatment. However, membrane fouling as an inevitable challenge restricts its application. Recently novel membrane fouling control technology by applying electric field in AnMBR showed its economics and effectiveness. Nevertheless, the mechanism of fouling suppression is still unclear, limiting the development of this technology. In this study, electro-AnMBR was constructed. Long-term running showed that applying electric field of 0.5 V suppressed the membrane fouling evolution rate by nearly 23% and reduced the organic foulants on membrane by nearly 10%. To clarify the mechanism of fouling suppression, the contribution of electrophoresis to membrane fouling suppression was quantified by theoretical calculation for the first time. Results showed that electrophoresis was approximately equivalent to backwash with a flux of 0.56 L/(m2·h). Besides, impact of electric field on mixed liquor filterability of AnMBR was first investigated by dead-end filtration. Results presented that electric field reduced the filtration resistance of mixed liquor by nearly 77%. Then mixed liquor properties analysis, electrochemical oxidation simulation tests and metagenomic analysis revealed that electric field might improve mixed liquor filterability by bioelectrochemical oxidation. Finally, novel mechanism of electric field suppressed membrane fouling was elucidated, including electrophoresis to drive off the foulants and mixed liquor filterability improvement. This study might contribute to better understanding for membrane fouling control by applying electric field in AnMBR, and was meaningful for technical development.

A review of dielectrophoretic separation and classification of non-biological particles.

Dielectrophoresis (DEP) is a selective electrokinetic particle manipulation technology that is applied for almost 100 years and currently finds most applications in biomedical research using microfluidic devices operating at moderate to low throughput. This paper reviews DEP separators capable of high-throughput operation and research addressing separation and analysis of non-biological particle systems. Apart from discussing particle polarization mechanisms, this review summarizes the early applications of DEP for dielectric sorting of minerals and lists contemporary applications in solid/liquid, liquid/liquid, and solid/air separation, for example, DEP filtration or airborne fiber length classification; the review also summarizes developments in DEP fouling suppression, gives a brief overview of electrocoalescence and addresses current problems in high-throughput DEP separation. We aim to provide inspiration for DEP application schemes outside of the biomedical sector, for example, for the recovery of precious metal from scrap or for extraction of metal from low-grade ore.

Membrane fouling suppression using intermittent electric current with low exposure time in a sequencing batch membrane bioreactor

Abstract This study assessed for the first time the use of intermittent electric current with low exposure time in a sequential batch membrane bioreactor (SB-MBR) aiming at reducing the membrane fouling and improving the treatment performance. The SB-MBR was initially operated without electric current application (control period) and, subsequently, using the electric current density of 10 A m−2 and intermittent exposure mode of 6 min ON/30 min OFF (1.2 h d−1). Compared to the control period, the mixed liquor filterability improved substantially when the electrocoagulation was applied, resulting in a membrane fouling rate 65% lower. This better filterability condition was attributed to the improvement of the floc formation process, which resulted in larger floc size and lower sludge volume index. The biomass growth was positively impacted by the electrochemical process, resulting in a higher sludge yield coefficient. The reactor performance regarding COD and NH4+-N removal was not influenced by the electric current application, exhibiting efficiencies above 99% in both experimental periods. On the other hand, the phosphorus concentration in the reactor effluent decreased as the electrocoagulation was applied, increasing its average removal efficiency from 62% (control period) to 89%. The anodic dissolution rate was estimated at 1.28 g d−1, considerably lower than the values reported in other studies regarding EBRM running in continuous mode. Thus, it can be inferred that the integration of the electrochemical process with SB-MBR using low exposure mode is an interesting alterative to reduce the membrane fouling, extend the anode lifespan and improve the reactor performance.

Nano and traditional copper and zinc antifouling coatings: metal release and impact on marine sessile invertebrate communities

Artificial surfaces in coastal waters and offshore oceans, including boat hulls, docks, and offshore structures, are invariably colonized, or fouled, by a host of sessile species known collectively as fouling communities. Fouling has great economic impacts on shipping and other marine industries and plays an important role in the spread of marine invasive species across the globe. The main strategy to prevent fouling of artificial surfaces is application of antifouling coatings containing varying concentrations and mixtures of biocides. Presently, copper and zinc are popular antifouling biocides, and the latter is gaining in usage due to the known toxic characteristics of copper in the marine environment and consequent regulation and consumer opinion. Nanomaterials, including Cu and ZnO nanoparticles, have been explored as a way to efficiently deliver biocides from coating matrices. Here, we examine the efficacy and biocide release characteristics of several copper- and zinc-based antifouling coatings, including formulations containing traditional micron-sized Cu and ZnO particles and two containing copper and ZnO nanoparticles, respectively. Most of the antifouling coatings tested significantly reduced the abundance and biodiversity of the fouling community in the three study locations across California. Invasive species were suppressed by most coatings at similar levels to natives, suggesting that in general, antifouling coatings do not favor invasive species. We found that zinc-based antifouling coatings were similar and in some cases better performing than copper, despite the generally lower toxicity of zinc to aquatic organisms compared with copper. The performance of zinc-based coatings, moreover, was not directly related to the amount of zinc released into the water or their zinc content. Nano-based coatings did not offer any clear advantages over non-nano coatings, either in the degree of Zn leaching or fouling suppression. Coating matrix properties clearly are an important factor affecting the efficacy and biocide leaching rate of antifouling coatings.

Versatile zero valent iron applied in anaerobic membrane reactor for treating municipal wastewater: Performances and mechanisms

Comprehensive insight into the long-term impact of applying zero valent iron (ZVI) in anaerobic membrane reactor (AnMBR) was conducted here. ZVI showed its versatility for enhancing the performances of AnMBR including COD and TP removal, H2S removal and membrane fouling suppression in this study, and the iron ions releasing rate of ZVI had great influence on the enhancing performances. Two iron ions releasing states were used including “with electric field” and “without electric field”. Applying electric field could boost iron ions releasing rate by 12 times here. COD removal rate increased by 3% via coagulation effect with and without electric field. H2S in biogas was decreased from >500 ppm to <60 ppm via the formation of FeS precipitation with and without electric field. Applying ZVI with electric field increased the removal rate of TP by 50% via the formation of Fe3(PO4)2, but applying ZVI without electric field did not change the TP removal due to the insufficient iron ions. Utilizing ZVI without electric field suppressed the membrane fouling rate by 20% via the improvement of mixed liquor filterability, however utilizing ZVI with electric field accelerated the membrane fouling rate by 17 times due to the formation of dense Fe-enriched fouling layer with server inorganic and organic fouling. This study provided a novel approach to improve the performances of AnMBR by utilizing versatile ZVI. Meanwhile, this study enclosed that the iron ions releasing rate of ZVI is vital technical parameter for its application.

Impact of aeration rate and dielectrophoretic force on fouling suppression in submerged membrane bioreactors

Membrane bioreactors (MBRs) present a unique opportunity in waste water treatment by combining the activated sludge process with membrane filtration. Although MBRs require less area, produce less volume of sludge and have high purification efficiency, they suffer from high membrane fouling. Membrane fouling can be reduced by applying aeration and Dep voltage. However, application of these two anti-fouling mechanisms would make the process expensive. Thus, a new aeration and DEP scheme of 5 min on – 5 min off is being suggested in this study. With this scheme, it was found that through application of DEP at 100 V and 0.3 L/min.m2 aeration flowrate and reduced lumen size of 6 mm, the membrane permeate flux can be increased by 58% compared to MBR without DEP and aeration. However, through energy analysis the optimum operating parameters were found to be at 0.3 L/min.m2 aeration flowrate and 50 V DEP using the suggested 5 min on-5 min off scheme. At the optimum operating condition, the permeability flux is 54% higher than MBR without DEP and aeration.

Insulator-based dielectrophoresis for fouling suppression in submerged membranes bioreactors: Impact of insulators shape and dimensions

The application of insulator-based dielectrophoresis (iDEP) has the potential to enhance membrane fouling suppression in submerged membrane bioreactors without extra energy consumption. In this study, the effect of the insulators shapes and sizes within the interidigitated electrodes (IDE) configuration was investigated for a better dielectrophoresis (DEP) force with a better membrane fouling suppression. Three circular insulators CS 1, CS 1.5 and CS 2 with diameters of 1 mm, 1.5 mm and 2 mm, respectively, were tested. A 2 mm side square section insulator SS 2 was also examined. The numerical simulation results show that the DEP force extension is greater with a similar diameter as the excited electrodes (2 mm in this study) when using circular insulators. The use of square section insulator (SS 2) increases the overall electric field gradient squared (∇|E|2) by 16% compared to the 2 mm circular insulator (CS 2). The square section insulator also extends the dielectrophoresis (DEP) force field more uniformly across the membrane surface while generating sufficient force to move the suspended solids away from the membrane. The experimental investigation verified the theoretical simulation prediction and demonstrated that SS 2 membrane modules provide longer membrane service time by maintaining a normalized permeate flux of 55% more than the circular section membrane modules, with a maximum intensification factor of 14 at a 220 V voltage and 50 Hz with a transmembrane pressure of 0.1 bar.

Investigation on suppression of fouling by magnetically responsive nanofiltration membranes

Abstract Magnetically responsive nanofiltration membranes have been developed by attaching a superparamagnetic nanoparticle to the end of polymer chains grafted from the surface of commercially available nanofiltration membranes. In an oscillating magnetic field, movement of these magnetically responsive polymer chains leads to break up of the concentration polarization at boundary layer. Experiments using feed streams consisting of an organic salt, an inorganic salt, as well as a synthetic oily wastewater have been conducted for periods of up to 6 h in order to determine the effect on long term membrane fouling. The results indicate suppression of long term fouling in the presence of an oscillating magnetic field.

Fouling suppression in submerged membrane bioreactors by obstacle dielectrophoresis

Submerged membrane bioreactor (MBR) is currently believed to be an efficient biological treatment for reusing and recovering wastewater to extenuate the ever increasing water scarcity crisis. To mitigate the main problem, membrane fouling, in MBR systems, we propose a solution that avoids usage of chemicals, and allows uninterrupted operation using a novel concept of obstacle dielectrophoresis (oDEP). The utilization of obstacles, insulator or metal (floating) electrodes, between electrically excited electrodes, can extend the DEP force field to move suspended particles away from membranes without having to increase voltage, for suppressing fouling with low energy consumption. Experimental investigation verified our theoretical simulation prediction and demonstrated that insulator membrane modules provide longer membrane service time for maintaining normalized permeate flux of 55% than those by floating electrode membrane modules, with a maximum intensification factor of 7.8 when applied 220V voltage and 50Hz as well as the transmembrane pressure of 0.1bar. Although stronger DEP force and hence better performance of fouling suppression can be generated by higher voltage, 50V insulator membrane module demonstrated to be the most energy efficient process with a specific energy consumption of 0.295kWh/m3 product and 13 times higher efficient factor than the 220V.

Intensification of cross-flow membrane filtration using dielectrophoresis with a novel electrode configuration

Fouling can be a serious problem in membrane filtration processes. Here we present a solution that avoids addition of chemicals and allows for uninterrupted operation of cross-flow micro-filtration process. A novel electrode configuration is suggested for generating an inhomogeneous electric (ac) field for repelling particles from the membrane by means of dielectrophoresis (DEP). Undesired electrochemical reactions are avoided even in case of aqueous suspensions due to a sufficiently high frequency of the applied field (200kHz). The inhomogeneous electric field generated by interdigitatedly installed cylindrical electrodes (IDE) could move clay particles (size 100–3000nm) away from membrane (pore size 0.2µm), thereby reducing fouling in membrane filtration process. A specific cosine-wave like DEP force distribution induced by the IDE along the feed flow was observed to allow for enhancing the DEP fouling suppression by removing the particles agglomerate adhered to the membrane at lower electric field regions. The fouling suppression performance of this new DEP filtration process was revealed comparing experimentally the permeate flux using same membrane with and without electrical field. With continuous DEP operation period with more than 69% of initial permeate flux was 9 times higher. In this lab-scale process with feed flow rate of 12mL/min, Joule heating was observed elevating permeate temperature with rate of 3K/h indicating a demand for electrical power (dissipated as heat) of about 2.5W.

Continuous membrane-based screening system for biocatalysis.

The use of membrane reactors for enzymatic and co-factor regenerating reactions offers versatile advantages such as higher conversion rates and space-time-yields and is therefore often applied in industry. However, currently available screening and kinetics characterization systems are based on batch and fed-batch operated reactors and were developed for whole cell biotransformations rather than for enzymatic catalysis. Therefore, the data obtained from such systems has only limited transferability for continuous membrane reactors. The aim of this study is to evaluate and to improve a novel screening and characterization system based on the membrane reactor concept using the enzymatic hydrolysis of cellulose as a model reaction. Important aspects for the applicability of the developed system such as long-term stability and reproducibility of continuous experiments were very high. The concept used for flow control and fouling suppression allowed control of the residence time with a high degree of precision (±1% accuracy) in a long-term study (>100 h).

Development of a novel fouling suppression system in membrane bioreactors using an intermittent electric field

A novel membrane bioreactor system that uses an intermittent electric field was successfully developed to suppress membrane fouling, caused mainly by activated sludge. We found that the surface of the activated sludge is negatively charged, and propose the utilization of an electric repulsive force to move the sludge away from the membrane by applying an electric field only when the permeate flux has drastically declined because of membrane fouling. The experimental results showed that a field of 6 V cm −1, switched on and off every 90 s, significantly improved the removal of the activated sludge from the membrane and accordingly improved the average permeate flux.

Structure and Electrochemical Properties of Carbon Films Prepared by a Electron Cyclotron Resonance Sputtering Method

This paper describes the characterization, electrochemical properties, and applications of carbon films prepared by the electron cyclotron resonance (ECR) sputtering method. The ECR-sputtered carbon film was deposited within several minutes at room temperature. The optimized sputtering conditions significantly change the film structure, which includes many more sp3 bonds (sp3/sp2 = 0.702) than previously reported film (sp3/sp2 = 0.274)1 with an extremely flat surface (0.7 A). The ECR-sputtered carbon films exhibit excellent electrochemical properties. For example, they have nearly the same potential window in the positive direction as that of high-quality, boron-doped diamond (moderately doped, 10(19)-10(20) boron atoms/cm3)2 and an even wider potential window in the negative direction with a low background current, high stability, and suppression of fouling by electroactive species without pretreatment. The electron-transfer rates at ECR-sputtered carbon films are similar to those of glassy carbon (GC) for Ru(NH3)(6)(2+)/(3+) and Fe(CN)(6)(3-)/(4-), whereas they are much slower than those of GC for Fe2+/3+, dopamine oxidation, and O2 reduction due to weak interactions between electroactive species and the ECR-sputtered carbon film surface. Such a response can be attributed to the ultraflat surface and low surface O/C ratios of ECR-sputtered carbon films. ECR-sputtered carbon film is advantageous for measuring biochemicals with high oxidation potentials because of its wide potential window and high stability. Highly reproducible and well-defined cyclic voltammograms were obtained for histamine and azide ions with a peak potential at 1.25 and 1.12 V vs Ag/AgCl, respectively. The film is very stable for continuous voltammetry measurements in 10 microM bisphenol A, which usually fouls the electrode surface with oxidation products.