Fouling Removal Research Articles

Flexible electro-responsive in-situ polymer acid doped polyaniline membranes for permeation enhancement and membrane fouling removal

This study investigates the performance of a new electrically tuneable polyaniline (PANI) membrane, and shows that this synthesis method has the potential to address key challenges of small-acid doped PANI membranes, including: acid dopants leaching out during filtration and low mechanical strength. The novel in-situ polymerisation used poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), as polymer acid template leads to the formation of inter-polymer complexes of PANI and polymer acid. The developed membranes were comprehensibly evaluated through visual, chemical, mechanical and filtration studies and compared to small-acid doped membranes (PANI-HCl membranes). The PANI-PAMPSA membranes were smooth, acid leach resistant, had higher tensile strength and showed conductivity three magnitudes higher compared to PANI membrane with post cast doping. The developed membrane showed in-filtration performance stability, electrical tuneability (in-situ control of flux and rejection) and fouling removal characteristics under applied electrical potential. Data obtained by SEM, IR spectroscopy, electrical analysis and cross-flow filtration confirm these results. The overall results showed that the proposed membrane fabrication procedure resulted in a significant improvement in performance across a range of critical parameters, including conductivity, stability, flexibility, permeance and fouling removal with additional advantage of being electrically tuneable.

Real-time optimization of the key filtration parameters in an AnMBR: Urban wastewater mono-digestion vs. co-digestion with domestic food waste

This study describes a model-based method for real-time optimization of the key filtration parameters in a submerged anaerobic membrane bioreactor (AnMBR) treating urban wastewater (UWW) and UWW mixed with domestic food waste (FW). The method consists of an initial screening to find out adequate filtration conditions and a real-time optimizer applied to a periodically calibrated filtration model for minimizing the operating costs. The initial screening consists of two statistical analyses: (1) Morris screening method to identify the key filtration parameters; (2) Monte Carlo method to establish suitable initial control inputs values. The operating filtration cost after implementing the control methodology was €0.047 per m3 (59.6% corresponding to energy costs) when treating UWW and €0.067 per m3 when adding FW due to higher fouling rates. However, FW increased the biogas productivities, reducing the total costs to €0.035 per m3. Average downtimes for reversible fouling removal of 0.4% and 1.6% were obtained, respectively. The results confirm the capability of the proposed control system for optimizing the AnMBR performance when treating both substrates.

Characterization of the Use of Low Frequency Ultrasonic Guided Waves to Detect Fouling Deposition in Pipelines.

The accumulation of fouling within a structure is a well-known and costly problem across many industries. The build-up is dependent on the environmental conditions surrounding the fouled structure. Many attempts have been made to detect fouling accumulation in critical engineering structures and to optimize the application of power ultrasonic fouling removal procedures, i.e., flow monitoring, ultrasonic guided waves and thermal imaging. In recent years, the use of ultrasonic guided waves has been identified as a promising technology to detect fouling deposition/growth. This technology also has the capability to assess structural health; an added value to the industry. The use of ultrasonic guided waves for structural health monitoring is established but fouling detection using ultrasonic guided waves is still in its infancy. The present study focuses on the characterization of fouling detection using ultrasonic guided waves. A 6.2-m long 6-inch schedule 40 carbon steel pipe has been used to study the effect of (Calcite) fouling on ultrasonic guided wave propagation within the structure. Parameters considered include frequency selection, number of cycles and dispersion at incremental fouling thickness. According to the studied conditions, a 0.5 dB/m drop in signal amplitude occurs for a fouling deposition of 1 mm. The findings demonstrate the potential to detect fouling build-up in lengthy pipes and to quantify its thickness by the reduction in amplitude found from further numerical investigation. This variable can be exploited to optimize the power ultrasonic fouling removal procedure.

Biofouling of polysulfone and polysulfone-graphene oxide nanocomposite membrane and foulant removal

The present paper evaluates the performance decline of Polyulfone and Polysulfone-Graphene oxide nanocomposite membranes by biofouling. The membranes were exposed to two different bacteria, - Klebsiella and Pseudomonas for 3 days at a constant temperature of 30 °C and 40 °C. Upto 96.66% decline in water-flux was observed when the polysulfone membrane was exposed to Pseudomonas strain at 30 °C; however the percent decline for nanocomposite membrane was significantly lower. The fouled membranes were treated with sodium hypochlorite to remove the biofouling and it was found that % increase in water-flux after the treatment was more pronounced in case of nanocomposite as compared to polysulfone membrane for Klebsiella strain. The absolute water-flux was higher in nanocomposite membrane as compared to polysulfone membrane for both cases. The fouling was quite evident in scanning electron micrographs and atomic force microscope analysis, which got removed significantly by the treatment.

Fouling Release Coatings Based on Polydimethylsiloxane with the Incorporation of Phenylmethylsilicone Oil

In this study, phenylmethylsilicone oil (PSO) with different viscosity was used for research in fouling release coatings based on polydimethylsiloxane (PDMS). The surface properties and mechanical properties of the coatings were investigated, while the leaching behavior of PSO from the coatings was studied. Subsequently, the antifouling performance of the coatings was investigated by the benthic diatom adhesion test. The results showed that the coatings with high-viscosity PSO exhibited high levels of hydrophobicity and PSO leaching, while the high PSO content significantly decreased the elastic modulus of the coatings and prolonged the release time of PSO. The antifouling results indicated that the incorporation of PSO into coatings enhanced the antifouling performance of the coating by improving the coating hydrophobicity and decreasing the coating elastic modulus, while the leaching of PSO from the coatings improved the fouling removal rate of the coating. This suggests a double enhancement effect on the antifouling performance of fouling release coatings based on PDMS with PSO incorporated.

Modeling approach to describe fouling removal during relaxation

Abstract Filtration tests were designed with fixed filtration durations and varying relaxation lengths to study the influence of relaxation time on flux recovery and fouling removal. A mathematical model was used to estimate the development and removal of fouling during the filtration and relaxation phases. During the relaxation phases, a relaxation-time dependent back transport constant was introduced to properly simulate removal of the cake layer. It was found that the rate of removal of cake was highest in the beginning of relaxation period and decreased during relaxation. This shows that the rate of removal depends on the amount of cake to be removed, but can also be explained by cake not being removed as single flocs or colloids, but as fragments of flocs released in the beginning or relaxation, followed by release of colloids more strongly adhered to the surface or due to an initial swelling of the cake layer during the relaxation. Based on this, a model was proposed to simulate the development in amount of cake during filtration and removed during relaxation. With this, the development in amount of cake and permeability could be simulated for different filtration and relaxation times to identify the setting with the highest net flux.

Numerical modelling of acoustic pressure fields to optimize the ultrasonic cleaning technique for cylinders

Fouling build up is a well-known problem in the offshore industry. Accumulation of fouling occurs in different structures, e.g. offshore pipes, ship hulls, floating production platforms. The type of fouling that accumulates is dependent on environmental conditions surrounding the structure itself. Current methods deployed for fouling removal span across hydraulic, chemical and manual, all sharing the common disadvantage of necessitating halting production for the cleaning process to commence. Conventionally, ultrasound is used in ultrasonic baths to clean a submerged component by the generation and implosion of cavitation bubbles on the fouled surface; this method is particularly used in Reverse Osmosis applications. However, this requires the submersion of the fouled structure and thus may require a halt to production. Large fouled structures such as pipelines may not be accommodated. The application of high power ultrasonics is proposed in this work as a means to remove fouling on a structure whilst in operation. The work presented in this paper consists of the development of a finite element analysis model based on successful cleaning results from a pipe fouled with calcite on the inner pipe wall. A Polytec 3D Laser Doppler Vibrometer was used in this investigation to study the fouling removal process. Results show the potential of high power ultrasonics for fouling removal in pipe structures from the wave propagation across the structure under excitation, and are used to validate a COMSOL model to determine cleaning patterns based on pressure and displacement distributions for future transducer array design and optimization.

Integrated aerobic granular sludge and membrane process for enabling municipal wastewater treatment and reuse water production

Aerobic granular sludge (AGS), as an aggregate of numerous self-immobilized functional microorganisms, has been recognized as an increasingly viable option for wastewater treatment and reuse water production. This study aimed at evaluating the application of AGS reactor as primary, ultrafiltration (UF) as secondary and nanofiltration (NF) as tertiary treatment for the treatment of municipal wastewater, focusing on determining the membrane fouling mechanism and reuse water production. AGS reactor, UF and NF exhibit high removal efficiency for COD (51.33%, 90.48% and 99.26%) and nutrients (53.63%, 94.84% and 98.06% total nitrogen, and 49.8%, 97.07% and 98.73% phosphorus), indicating that the integrated aerobic granular sludge and UF/NF process could provide high pollution removal and quality reuse water. As for filtration behavior of UF and NF, shear stress produced by agitation speed could significantly improve flux, due to the dispersion of pollutants. Besides, for AGS, improved simultaneous nitrification and denitrification by the internal anaerobic, anoxic, and aerobic structure and the richer biological community increased foulant removal, while the larger pore size and mature structure also reduced foulant deposition. Moreover, shear stress also diminished the total fouling resistance, reversible fouling and irreversible fouling, as well membrane cleaning efficiency was promoted, by controlling AGS deposition on membrane. In addition, the fouling mechanism of conventional floc sludge and that of AGS were deeply analyzed and respectively compared, from three aspects, namely, Scanning Electron Microscope (SEM), Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscope (AFM). Overall, the results demonstrated an alternative option for water treatment and reuse water production in an integrated AGS and membrane process.

Fouling indicators for field monitoring the effectiveness of operational strategies of ultrafiltration as pretreatment for seawater desalination

The applicability of fouling indicators for real time performance assessment of UF feed pretreatment in RO seawater desalination was explored in a field study using an integrated seawater UF-RO desalination pilot plant. Fouling indictors were evaluated with respect to quantification of UF backwashability, unbackwashed fouling resistance and UF fouling rate. Feed water quality and coagulant dose demonstrated measurable impact on both UF fouling rate and effectiveness of foulant removal via UF backwash. Increased coagulant dose promoted higher rate of cake formation and in turn improved backwash efficiency. However, there was a maximum coagulant dose beyond which there was no further backwash improvement. Backwash effectiveness increased with higher backwash flux and duration, up to threshold upper limits, but declined as the filtration period increased above a threshold limit. Field tests during periods of temporally varying feed quality demonstrated that higher fouling rate (promoted by inline coagulation) resulted in more effective backwash and correspondingly lower progressive rise in post-backwash UF resistance. The study results suggest that real-time UF fouling indicators, based on UF filtration resistance metrics and backwash effectiveness, should be potentially useful for tracking UF performance and thus for deployment of UF feed-back control for optimal performance of UF feed pretreatment.

Non-woven PET fabric reinforced and enhanced the performance of ultrafiltration membranes composed of PVDF blended with PVDF-g-PEGMA for industrial applications

Ultrafiltration (UF) membranes composed of poly(vinylidene fluoride) (PVDF) blended with poly(vinylidene fluoride)-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA) can present high flux and excellent foulant removal efficiencies under suitable preparation conditions. However, these PVDF/PVDF-g-PEGMA blended membranes cannot be applied industrially because of the insufficient mechanical strength (strength-to-break value of 8.4 ± 0.6 MPa). We incorporated two types of non-woven polyethylene terephthalate (PET) fabrics (thin hydrophobic and thick hydrophilic fabrics) as support layers to improve the mechanical properties of the blended membranes. The thin and thick PET fabrics were able to significantly improve the tensile strength to 23.3 ± 3.7 MPa and 30.1 ± 1.4 MPa, respectively. The PET fabrics had a limited impact on the separation-related membrane performance such as hydrophilicity, foulant rejection, whereas the mechanical strength and pure water flux was improved several folds. The enhanced flux was attributed to the higher surface porosity and wider finger-like voids in the cross-section. The thin PET fabric with larger porosity was able to maintain a consistent toughness simultaneously; thus it is recommended as a support material for this blended membrane.

Experimental study of calcium sulfate fouling in a heat exchanger during liquid-solid fluidized bed with cylindrical particles

Calcium sulfate fouling was determined experimentally in a heat exchanger during liquid-solid fluidized bed with cylindrical particles and forced convective (without particles) heat transfer. The effects of bed voidage, wall temperature and foulant concentration on fouling resistance were studied during fluidized bed heating and compared with corresponding cases in forced convective (without particles) heating. The results show that fouling resistance was considerably decreased during fluidized bed heat transfer compared with forced convective heat transfer (without particles). Maximum fouling removal as heat transfer occurred at bed voidages ranging from 0.6 to 0.8; under these conditions, fouling resistance was lowered to at least one-seventh that of similar cases in forced convective heat transfer.

The effect of aeration types on foulant removal in ex-situ chemical cleaning in place (CIP) with membranes fouled by secondary effluents

In wastewater treatment, filtration membranes that are used for extended periods of time must inevitably be cleaned with chemical agents that can influence the membrane properties. In addition, the use of secondary effluents in reclamation readily contaminates membranes with irreversible fouling. In this study, to investigate the phenomenon of fouling control by ex-situ CIP, different types of aeration (coarse bubble, microbubble) and various concentrations (100–3000 mg/L) of NaOCl were employed to fouled membranes by secondary effluents from wastewater treatment. The cleaning efficiencies of each cleaned membrane were evaluated after ex-situ CIP, and the selected membranes, including the fouled membrane before ex-situ CIP, were examined through comparative changes in the physicochemical properties. Microbubbles were more effective in retaining the membrane permeability in ex-situ CIP with a low concentration (100 and 500 mg/L) of NaOCl. Additionally, the ex-situ CIP with microbubbles showed the greatest cleaning efficiency at a cleaning time of more than 2 h.

Unpacking compaction: Effect of hydraulic pressure on alginate fouling

High pressure is often considered to be the cause of the high fouling propensity of reverse osmosis (RO) relative to forward osmosis (FO). Several experimental studies have shown that alginate fouling is more susceptible to cleaning in FO than in RO, but the theory that foulant compaction causes this disparity seems to be contradicted by the incompressibility of alginate hydrogels. In addition, the effect of hydraulic pressure on fouling in osmotic membrane desalination has never been experimentally isolated, because fixed-flux comparisons at different hydraulic pressures require different draw solution osmotic pressures. In this study, a new approach to isolating the effect of hydraulic pressure on alginate fouling and cleaning is introduced: operating FO with elevated but equal feed and draw hydraulic pressures. The same concentration of sodium chloride is used as the draw solution in all trials to eliminate possible effects of draw solution osmotic pressure on membrane fouling or cleaning. Theoretical modeling of the effect of alginate foulant compaction on flux reveals that foulant compaction should accelerate flux decline with low salinity feeds but retard flux decline at high salinity. However, in low-salinity alginate fouling trials, for which foulant compaction should accelerate flux decline, the measured flux decline rate was not affected by hydraulic pressure. Furthermore, when fouled membranes were cleaned by increasing the feed velocity and reducing the draw osmotic pressure, there was no apparent relationship between hydraulic pressure and cleaning effectiveness. Finally, in situ visualization of foulant removal during the cleaning process revealed no difference in foulant removal mechanisms between different hydraulic pressures. These findings demonstrate that alginate gel compaction by high feed hydraulic pressure does not occur and suggest that other explanations should be sought for FO's high fouling resistance relative to RO.

Impact of Powdered Activated Carbon Structural Properties on Removal of Organic Foulants in Combined Adsorption-Ultrafiltration

The impact of structural properties of three commercial PACs as well as two mechanically ground PACs on their efficiency in NOM removal and fouling reduction in combined adsorption-ultrafiltration (PAC-UF) of northern German groundwater was investigated. All PACs showed highest adsorption affinity for medium molecular weight NOM fractions. The meso-pore surface area rather than the total surface area (B.E.T.) mainly governed the extent of NOM removal. However, adsorption of macromolecular NOM fractions, which were found to be the main contributor to total and irreversible fouling, was limited by tested commercial carbons, and no significant mitigation of fouling was achieved by any tested PAC concentration. Lowering the particle size by grinding of the PAC, however, enhanced removal of macromolecular NOM fractions considerably, and fouling mitigation occurred at substantially lower PAC concentrations compared to raw carbons. A larger external surface area probably let to more shell adsorption, a more homogeneous particle distribution on the membrane surface and a better mass transport. In addition, comparison of the adsorption isotherms of raw and milled PACs showed that, due to the grinding of PAC particles, additional inner pores structures became available for NOM adsorption. Results of this study point out that structural properties of PAC dramatically influence the efficiency of combined PAC-UF, which needs to be considered during PAC selection and process design.

Ozone Cleaning of Fouled Poly(Vinylidene) Fluoride/Carbon Nanotube Membranes

ABSTRACTThis research demonstrates for the first time that ozone is an effective cleaning agent for polyvinylidene fluoride (PVDF) membranes fouled by natural organic matter (NOM). Bare PVDF membranes as well as PVDF impregnated with CNTs (pristine (CNTs–P) and oxidized (CNTs–O)) at 0.3% mass membranes were used. Three different methods were investigated for cleaning the fouled membranes including; A: 10-min cleaning by pure water, B: 5-min water followed by 5-min ozonated water, and C: 10-min fully ozonated water. It was found that the application of fully ozonated water for 10 min was very effective to reinstate the flux to almost its original value of unfouled membrane. The CNTs–P/PVDF membrane exhibited the highest fouling with a total fouling ratio of 81%, while for the bare PVDF and the CNTs–O/PVDF membranes, the fouling ratios were 76% and 74%, respectively. The full ozonated water cleaning method gave the highest removal of fouling leaving the lowest irreversible fouling on the membrane as compared to the other cleaning methods. On the other hand, the highest removal of NOM fouling was obtained for CNTs–O/PVDF membranes indicating that fouling on CNTs–O/PVDF membrane was less bound than the other membranes. Contact angle measurements of the fouled membranes showed that all membranes exhibited increased contact angles due to the NOM deposition but after cleaning, particularly with ozonated water, the membrane contact angles returned to almost their original values. FTIR analysis of the membranes corroborated the results obtained.

Influence of an external electric field on removal of protein fouling on a stainless steel surface by proteolytic enzymes

Enzymatic cleaning is a potentially useful method for removing proteinaceous fouling from solid surfaces under mild conditions. Herein, the influence of an external electric field on the enzymatic cleaning of a metal surface fouled with a protein was investigated. The model fouling protein (BSA; lysozyme) was prepared on a stainless steel (St) surface, and the resulting surface subjected to enzymatic cleaning with an electric potential being applied to the St plate. Trypsin, α-chymotrypsin, and thermolysin were used as model proteases. The amounts of protein remaining on the plate before and during the cleaning process were measured by means of a reflection absorption technique using Fourier transform infrared spectroscopy. In the case for BSA fouling, the cleaning efficiency of the protease tended to increase at more negative applied potentials. Whereas, there was an optimum applied potential for removing the lysozyme fouling. Atomic force microscopy analyses indicated that applying an adequate range of electric potential enhanced the enzymatic removal of protein fouling inside scratches on the St plate surface. These findings suggest the existence of two modes of electrostatic interactions for the external electric field, one with protease molecules and the other with digested fragments of the fouling protein.

Effect of cycle run time of backwash and relaxation on membrane fouling removal in submerged membrane bioreactor treating sewage at higher flux.

Intermittent backwashing and relaxation are mandatory in the membrane bioreactor (MBR) for its effective operation. The objective of the current study was to evaluate the effects of run-relaxation and run-backwash cycle time on fouling rates. Furthermore, comparison of the effects of backwashing and relaxation on the fouling behavior of membrane in high rate submerged MBR. The study was carried out on a laboratory scale MBR at high flux (30 L/m2·h), treating sewage. The MBR was operated at three relaxation operational scenarios by keeping the run time to relaxation time ratio constant. Similarly, the MBR was operated at three backwashing operational scenarios by keeping the run time to backwashing time ratio constant. The results revealed that the provision of relaxation or backwashing at small intervals prolonged the MBR operation by reducing fouling rates. The cake and pores fouling rates in backwashing scenarios were far less as compared to the relaxation scenarios, which proved backwashing a better option as compared to relaxation. The operation time of backwashing scenario (lowest cycle time) was 64.6% and 21.1% more as compared to continuous scenario and relaxation scenario (lowest cycle time), respectively. Increase in cycle time increased removal efficiencies insignificantly, in both scenarios of relaxation and backwashing.

Numerical and experimental investigation for cleaning process of submerged outside-in hollow fiber membrane.

Membrane fouling has limited extensive applications for hollow fiber membranes in water treatment. Backwashing and air scouring can effectively solve this problem in the submerged outside-in hollow fiber membrane system. In this study, variation of the fouling layer on the membrane surface during backwashing and the impact of shear stress caused by air scouring on fouling removal were investigated through computational fluid dynamics (CFD) simulation. The backwashing and air scouring process were simulated using CFD and the results were verified by experimental studies. The results of experimental studies are in accordance with the simulation results. During the backwashing process, the velocity profile inside the reactor was presented, and visualization of the particle movement to illustrate the dynamic peeling process of the fouling layer on the membrane surface was also shown. The formation of uneven cleaning reveals that the upper region of the fibers has an excellent cleaning effect during backwashing. After that, the supporting role of air scouring was investigated in the study. It is concluded that the lower part and the middle region of the fibers suffer greater shear stress by analyzing the velocity contours and vectors, and the analysis results indicated that air scouring can further remove membrane fouling.

Effects of chemical cleaning on RO membrane inorganic, organic and microbial foulant removal in a full-scale plant for municipal wastewater reclamation

Of all of the strategies for controlling reverse osmosis (RO) membrane fouling, chemical cleaning is indispensable. To study the effects of chemical cleaning on membrane foulant removal, a comparative analysis of RO membranes before and after common alkaline and acid cleaning was conducted by dissecting lead and terminal RO membranes in a full-scale municipal wastewater reclamation plant. Most foulants on the membranes were removed by chemical cleaning processes. Calcium was the major inorganic component of the foulants because of its highest concentration in the feed water. Aluminum and iron were also abundant elements on the membranes due to their high deposition ratios and low removal efficiencies. Hydrophilic neutrals (HIN) and hydrophobic neutrals (HON) were the two largest dissolved organic matter (DOM) fractions on the membranes before cleaning. HIN and hydrophilic acids (HIA) were not effectively removed. Chemical cleaning removed 94% and 90% of the total bacteria on the lead and tail membranes and considerably changed the structure of the microbial communities. Bacteria excessively producing extracellular polymeric substance (EPS), such as Pseudomonas and Zoogloea, were much more resistant to the chemical cleaning process. After cleaning, the membrane microbial community structures were more similar to those in the feed water than the structures on the membranes before cleaning. These results shed light on the effects of cleaning in a full-scale RO plant, improves our understanding of the removal of foulants and provides potential research directions for cleaning methods and RO pretreatment processes.

Evaluation of a novel physical cleaning strategy based on HF membrane rotation during the backwashing/relaxation phases for anaerobic submerged MBR

A novel physical cleaning strategy based on membrane rotation was investigated in an anaerobic membrane bioreactor treating wastewater. This strategy was proposed to improve the fouling removal effectiveness of the traditional physical cleaning techniques (such as backwashing and relaxation) by the shear-enhanced conditions associated with the rotation. The effectiveness of this strategy has been investigated in a bench filtration unit during short-term tests and also compared to the conventional mode with gas scouring. Based on the resistances-in-series approach, the external residual fouling has been identified as the main factor determining the process productivity. The contribution of this type of fouling obtained with the rotating membrane was lower than with the gas scouring application (56–18% versus 60–53%, respectively). Other operational parameters such as the transmembrane pressure set-point for cleaning initiation and the backwashing time have also showed a significant influence on external fouling re-dispersion. A long-term test revealed the sustainability of the operation during more than 400h, achieving a stable net permeate flux of 6.7L/hm2 when the rotating speed was fixed in 340rpm.