Microfiltration of bovine and ovine milk for the reduction of microbial content in a tubular membrane: a preliminary investigation

In the present work a preliminary study on bovine and ovine milk microfiltration is reported. The study was aimed at the reduction of milk microbial content through a “cold technology” (i.e. at temperatures not higher than 40°C), with the obvious advantages for the preservation of essential elements. Considering the system's fouling characteristics, membrane washing was firstly optimised: Ultrasil 25 resulted to be more effective than NaOH, which was suggested by the membrane producer. Then, some preliminary tests with skimmed bovine milk evidenced the importance of the back-pulse device used in order to reduce fouling. In fact, no permeate flux was observed in the absence of back-pulse, while penneate fluxes of about 350 and 410 L h⁻¹ m⁻² were observed with back-pulse activated every 4 and 1 min, respectively. After this preliminary study on fouling, some tests with ovine milk were performed. It was previously centrifuged in order to remove fats, and a filtration step prior to microfiltration was demonstrated to be necessary for satisfactory performances. An average permeate flux of about 200 L h⁻¹ m⁻² was obtained in the same conditions of bovine milk (back-pulse activated every 1 min) and an effective microbial removal was realised in the permeated ovine milk.     

Numerical and experimental methodology for the development of a new membrane prototype intended to microfiltration bioprocesses. Application to milk filtration

In tangential flow filtration, the non-uniform TransMembrane Pressure (TMP) on the membrane length produces a non homogeneous filtration cake, initiates process selectivity changes and modifies the permeate quality. The purpose of this study is to create a tubular ceramic membrane prototype with a more uniform TMP, intended to filtration of fouling fluids. The principle of this membrane structure is to waterproof the external membrane surface to limit flow circulation in the porous support of the membrane. The production was controlled by sizing «permeation vents». This development was achieved using a CFD modelling tool interacting with experiments. A preliminary modelling study was made with water. This work was afterwards applied to the industrial process of casein micelle separation from skim milk. The influence of operating conditions on the membrane hydrodynamics was highlighted. The modelling results were experimentally confirmed, with a discrepancy smaller than 3% and a reproducible water permeability of 2.3 L h⁻¹ bar⁻¹ for 1 mm-wide vent (TMP = 1 bar, T = 20 °C). Then, milk filtration experiments showed a production ratio milk/water equal to 1/2. The permeate quality parameters were studied and the fouling phenomena were taken into account. A parametric study led to the sizing of a final prototype. Its efficiency was experimentally evaluated.     

Effect of operational parameters on sludge accumulation on membrane surfaces in a submerged membrane bioreactor

In the present study, an orthogonal array design was adopted to investigate effects of operational parameters including aeration intensity, membrane flux, suction time and non-suction time on sludge accumulation on membrane surfaces respectively at a high SS concentration of 10 g l⁻¹ and a low SS concentration of 1 g l⁻¹ in a submerged membrane bioreactor. Average transmembrane pressure (TMP) increase rate over the operation time was used to evaluate sludge accumulation. Among the four factors, membrane flux was found to influence TMP the most obviously. The effect of aeration intensity became significant only at a high SS concentration of 10 g l⁻¹. TMP increased with suction time and decreased with non-suction time. There was a critical membrane flux over which sludge particles were deposited, and accordingly, TMP increased sharply. Two zones, predicting whether sludge particles are deposited or not, could be comprehensively determined by the critical flux, correspondent aeration intensity and SS concentration. For long-term stable operation, it is suggested that a membrane bioreactor be operated in the zone with prediction of no obvious sludge deposit on membrane surfaces.     

Microfiltration of Milk with Third Generation Ceramic Membranes

The objective of this study was to compare the behavior of different ceramic membranes during skimmed milk microfiltration. Permeate flow rates, protein rejection, and decimal reduction of bacteria were compared for three different 1.4-µm pore size ceramic membranes, one of which was considered traditional (ceramic multichannel membrane) while the other two had a modified structure (on either the macroporous support or the filtering layer). Permeate flux ranged from 400 to 530 Lm^?2h^?1 at 0.5 bar of transmembrane pressure. Protein rejection values between 0.8 and 2.9% were obtained. Temperature (21–45°C) did not have a significant effect. Membranes showed decimal reduction in total bacterial count between 3.5 and 5.2, with Isoflux® membranes showing higher values. The lifespan of microfiltered milk was extended to 10 days in the absence of heat treatment.     

Effects of hypochlorite exposure on flux through polyethersulphone ultrafiltration membranes

Polyethersulphone ultrafiltration membranes with a nominal molecular weight cut off of 10 kDa were degraded in solutions of sodium hypochlorite over a range of pH values at 55 °C to achieve exposure measured in ppm-days of chlorine exposure. The degraded membranes were tested, using an ÄKTAcrossflow? system, for clean water flux, demineralised whey flux and protein rejection. The water fluxes for three membranes (new, 10,000 ppm-day pH 12, and 10,000 ppm-day pH 9) were found to be about 100, 200 and 400 L m^?2 h^?1, respectively with cross flow at 1 bar transmembrane pressure. However whey fluxes were about 23, 5, and 6 L m^?2 h^?1 for the same three membranes. Size exclusion chromatography of the permeates showed significant permeation of α-lactalbumin and β-lactoglobulin through membranes degraded at pH 9 for 20,000 ppm-days, while almost no permeation was found for degradation at pH 12.These results show that hypochlorite degradation affected fluxes by at least two mechanisms. It was likely that membrane pitting increased the pore size causing increased water flux and reduced protein rejection. However hypochlorite also seemed to alter the membrane surface properties, causing the protein to form a less permeable layer that reduced the flux of whey.     

Separation of casein from whey proteins by dynamic filtration

It has been proven that functional properties of milk proteins can improve the quality and nutritional value of foods. This paper investigates the separation of whey proteins from casein micelles using a Multi Shaft Disk (MSD) module and a rotating disk dynamic filtration module. The MSD module was equipped with 6 ceramic membranes of 0.2 µm pores. PVDF and Nylon membranes of 0.2 µm pores were tested in the rotating disk module. Permeate flux with the MSD module increased with TMP and rotation speed, reaching a maximum of 132 L h^− 1 m^− 2 at 1931 rpm. α-Lactalbumin (α-La) and β-Lactoglobulin (β-Lg) transmissions also increased with rotation speed, ranging from 25% at 1044 rpm to 40% at 1931 rpm . With a Nylon membrane, the rotating disk module yielded lower permeate fluxes than the MSD module, while when equipped with a PVDF membrane it provided higher permeate fluxes than the MSD, but casein micelles rejection was lower. α-La and β-Lg transmissions were higher with the rotating disk module, using Nylon and PVDF membranes, than for the MSD. From this comparison, it can be concluded that the MSD module gave the best compromise between high permeate flux, high α-La and β-Lg transmissions and high casein micelles rejection.     

CRITICAL FLUX DETERMINATION IN ULTRAFILTRATION OF WASTEWATER FROM A FOOD INDUSTRY BY OPTIMIZATION METHOD

Two ultrafiltration membranes with different geometries (spiral polymeric and tubular ceramic) but similar cutoffs were used to treat wastewater from a food industry. Hydrodynamic conditions were optimized by statistical methods as a strategy to get more accurate values of the critical parameters and then to produce higher water flux and minimization of membrane fouling. The validation of the optimization method was obtained by experimental critical flux determination at critical parameters. Membrane fluxes revealed significant differences during filtration. The polymeric membrane showed an optimal flux of 45.60 Lh^?1 m^?2 at 3.21 bar while operating at a stable time of 11.61 h, whereas optimal flux of the ceramic membrane was 32.43 Lh^?1 m^?2 at 3.98 bar for 16.03 h. Experimental critical flux values were only slightly lower than optimal fluxes for both membranes, showing the validity of the statistics models applied. Negligible osmotic pressure was found on the two membranes at critical flux parameters, indicating irreversible fouling for both cases. The polymeric membrane revealed strong fouling behavior and the ceramic membrane showed a weak form; the flux decline occurred first in the polymeric membrane, whereas the ceramic membrane exhibited high stability during the filtration operations. A high degree of purification of wastewater was obtained by this membrane at critical flux conditions.     

Preparation and characterization of new tubular kaolino-illitic ceramic membrane used for dairy wastewater treatment

Low cost asymmetric tubular ceramic membrane was developed from kaolino-illitic clay collected from the region of Medenin (Tunisia). The obtained membrane was designed to be used for ultrafiltration. The effect of pore forming agent on the plasticity, porosity, pore size distribution, mechanical strength, and permeability was evaluated. The support was performed by extrusion using the raw clay and olive pomace (OP) as pore forming agent. The effect of the use of OP was noticeable; it improved the plasticity of the paste. Also it helped to ameliorate both permeability and porosity of the obtained supports. Top layer was prepared using acid activated clay suspension. The obtained membrane had gas permeability of about 13 cm³.s⁻¹.cm⁻².bar⁻¹ at a pressure of 1.5 bar and water flux of 1700 L.h⁻¹.m⁻² at a pressure of 1 bar. The final membrane was successfully used to eliminate the fat present in a solution containing 10% of milk. Regeneration of the used membrane was carried out by calcination at 550°C. The performances of the used membrane were recovered by 97% after regeneration.     

Protein Extraction and Membrane Recovery in Enzyme-Assisted Aqueous Extraction Processing of Soybeans

Enzyme-assisted aqueous extraction processing (EAEP) is an environmentally friendly process in which oil and protein can be simultaneously recovered from soybeans by using water and enzymes. The significant amount of protein-rich effluent (skim) constitutes a challenge to protein recovery. Countercurrent two-stage EAEP at a 1:6 solids-to-liquid ratio, 50 °C, pH 9.0, and 120 rpm for 1 h was used to extract oil and protein from dehulled, flaked and extruded soybeans. Different enzyme use strategies were used to produce different skim fractions: 0.5% protease (wt/wt extruded flakes) in both extraction stages; 0.5% protease only in the 2nd extraction stage; and no enzyme in either stage. Dead-end, stirred-cell membrane filtration was evaluated with each skim. About 96, 89, and 66% of the protein were extracted with the three enzyme treatments, respectively. Protein retentate yields of 91, 96, and 99% were obtained for the three enzyme treatments, respectively, by using double membrane filtration (30 kDa/500 Da) of the skims, achieving permeate fluxes up to 1.24 kg/m² h at 3.9–4.8 concentration factors (CF) and 0.56 kg/m² h at 1.9–2.9 CF for 30 kDa ultrafiltration and 500 Da nanofiltration, respectively. For cross-flow ultrafiltration with the 3-kDa membrane, pH and presence of insoluble protein aggregates significantly affected permeate flux. Maximum permeate flux occurred at high pH and in the presence of protein aggregates, achieving a mean value of 4.1 kg/m² h at 1.7 bar transmembrane pressure.     

Dye removal from colored textile wastewater using acrylic grafted nanomembrane

In this paper, the dye removal ability of the acrylic grafted polysulfone nanomembrane using ultraviolet radiation was studied to remove dyes from colored textile wastewater. Acrylic acid was used to modify polysulfone ultrafiltration membrane. The effect of different operating parameters such as pressure, salt concentration and chemical structure of dyes was evaluated. Data indicated that the photografted membrane has acceptable performance both in terms of flux and rejection. The dye rejection and hydraulic permeability were 86–99.9% and 7.6 L m^{− 2} h^{− 1} bar^{− 1}, respectively. It was found that the rejection of dyes decreased with salt concentration due to a decrease of the Donnan effect. Also, the low molecular weight dyes and highly charged dyes were more sensitive in the presence of salts. Addition of 80 mM Na₂SO₄ in dye solution decreased the dye rejection more than 15%. The rejection enhancement for all cases was negligible by increasing driving pressure from 1 to 4 bar. Dyes with low charger were more sensitive to operating pressure than that of dyes with higher charges. All findings supported that acrylic grafted nanomembrane is potentially capable to separate dyes from colored textile effluent.     

Designing block copolymer architectures for targeted membrane performance

Using a combination of block copolymer self-assembly and non-solvent induced phase separation, isoporous ultrafiltration membranes were fabricated from four poly(isoprene-b-styrene-b-4-vinylpyridine) triblock terpolymers with similar block volume fractions but varying in total molar mass from 43 kg/mol to 115 kg/mol to systematically study the effect of polymer size on membrane structure. Small-angle X-ray scattering was used to probe terpolymer solution structure in the dope. All four triblocks displayed solution scattering patterns consistent with a body-centered cubic morphology. After membrane formation, structures were characterized using a combination of scanning electron microscopy and filtration performance tests. Membrane pore densities that ranged from 4.53 × 10¹⁴ to 1.48 × 10¹⁵ pores/m² were observed, which are the highest pore densities yet reported for membranes using self-assembly and non-solvent induced phase separation. Hydraulic permeabilities ranging from 24 to 850 L m⁻² h⁻¹ bar⁻¹ and pore diameters ranging from 7 to 36 nm were determined from permeation and rejection experiments. Both the hydraulic permeability and pore size increased with increasing molar mass of the parent terpolymer. The combination of polymer characterization and membrane transport tests described here demonstrates the ability to rationally design macromolecular structures to target specific performance characteristics in block copolymer derived ultrafiltration membranes.     

Application of gas/liquid two-phase flows during crossflow microfiltration of skimmed milk under constant flux conditions

This work constitutes a first approach to determine the critical zone of stability during gas-sparged crossflow microfiltration () of skimmed ultra-high temperature (UHT) and reconstituted milks for the separation of casein micelles from soluble proteins. Conditions for stable operation were investigated with and without air sparging by imposing, at a constant wall shear stress, different levels of permeate flux while monitoring the variation in the transmembrane pressure (TMP). The determination of the critical fluxes allowed to assume a common domain of stability for single- and two-phase flows conditions, thus confirming the relevance of the wall shear stress value during microfiltration of skimmed milk whichever way it is generated (standard crossflow filtration or unsteady gas/liquid flow). Whatever the filtration conditions (single-phase flows/two-phase flows), during the phase of increasing flux, a significant decrease in soluble protein transmission was observed: for reconstituted milk, under two-phase flow conditions, the transmission decreased from 80% to 60% for α-lactalbumin (α-LA) and from 50% to 30% for β-lactoglobulin (β-LG). This was due to the sharp increase in TMP when the flux was close to the limiting flux. During the phase of decreasing J, separation performance was strongly altered: for the same J, the TMP was significantly higher and lower soluble protein transmissions were observed, especially for the β-LG. These results showed the transition to an irreversible fouling, which led to a more tightly packed, thus less porous, cake structure. Unsteady filtration conditions, as well as standard ones, failed to disrupt it.     

A pilot scale study of reverse osmosis for the purification of condensate arising from distillery stillage concentration plant

Reverse osmosis (RO) is an interesting process to eliminate small organic solutes (carboxylic acids and alcohols) from distillery condensates before recycling them into the fermentation step. This work investigates the influence of transmembrane pressure, pH and volume reduction factor (VRF) on the efficiency of reverse osmosis treatment of condensate from distillery stillage concentration at pilot scale using three pre-selected membranes (CPA2 and ESPA2 from Hydranautics, BW30 from DOW). Performances were assessed according to permeate flux, solutes rejection and abatement of fermentation inhibition. Transmembrane pressure increase leads to an increase of these three parameters with a plateau for rejections and abatement at 20 bar; however, in order to comply with membranes manufacturer's recommendations and to limit or delay polarization and fouling, it was decided to keep the permeate flux below a value of 30 L h⁻¹ m⁻². This corresponded to a maximum pressure of 10 bar for CPA2 and ESPA2 membranes and 25 bar for BW30 membrane. pH increase leads to a diminution of permeate flux and an increase of carboxylic acids rejection whatever the membrane; nevertheless, no abatement of fermentation inhibition is observed. Increasing VRF provokes a decrease of the permeate flux. Although local rejections are stable, the mean rejection assessed with the raw condensate (feed) and the mean permeate decreases. However, the fermentation inhibition remains under 10% up to a VRF of 8. BW30 membrane exhibits the highest rejections and inhibition abatement. On the basis of the pilot scale results with the BW30 membrane, a preliminary estimation of the membrane area is proposed for an industrial plant with 100 m³ h⁻¹ of condensate flow rate and the optimized parameters (pressure 25 bar, no pH modification, VRF 4 and 8).     

Calculation of reversible electrode heats in the proton exchange membrane fuel cell from calorimetric measurements

A calorimeter was used to measure the heat production in polymer electrolyte membrane (PEM) fuel cells operated on hydrogen and oxygen at 50 °C and 1 bar. Two cells were examined, one using a 35 μm thick Nafion membrane and a catalyst loading of 0.6/0.4 mg Pt cm⁻², for the cathode and anode layer, respectively, the other using a 180 μm thick Nafion membrane and loading of 0.4/0.4 mg Pt cm⁻². The cells investigated thus had different membranes and catalyst layers, but identical porous transport layers and micro-porous layers. The calorimeter is unique in that it provides the heat fluxes out of the cell, separately for the anode and the cathode sides. The corresponding cell potential differences, ohmic cell resistance and current densities are also reported. The heat fluxes through the current collector plates were decomposed by a thermal model to give the contributions from the ohmic and the Tafel heats to the total heat fluxes. Thus, the contributions from the reversible heat (the Peltier heats) to the current collectors were determined. The analysis suggests that the Peltier heat of the anode of these fuel cell materials is small, and that it is the cathode reaction which generates the main fraction of the total heat in a PEM fuel cell. The entropy change of the anode reaction appears to be close to zero, while the corresponding value for the cathode is near −80 J K⁻¹ mol⁻¹.     

Customization of ZrO2 loose/tight bilayer ultrafiltration membranes by reverse micelles-mediated aqueous sol-gel process for wastewater treatment

Two types of spherical zirconyl oxalate aqueous sols were successfully customized by a reverse micelles-mediated aqueous sol-gel process, and the sols were sequentially spin-coated on porous supports to prepare ZrO₂ loose/tight bilayer ultrafiltration membranes. After three times of spin-coating process, a defect-free ZrO₂ loose ultrafiltration membrane with pure water permeability of 110.5 ± 2.25 L m^?2 h^-1 bar^-1, molecular weight cut-off (MWCO) of 16.5 kDa and excellent rejection of up to 97.5 % for bovine serum albumin was fabricated. Then, the loose ultrafiltration membrane was used as a substrate to prepare ZrO₂ tight ultrafiltration membrane. Performances of tight ultrafiltration membrane regarding to permeability, retention of polyethylene glycol and treatment of dyes wastewater were evaluated. The tight ultrafiltration membrane with a thickness of 200 nm exhibited a pure water permeability of 22.5 ± 0.3 L m^-2 h^-1 bar^-1 and MWCO of 1150 Da. Additionally, the rejections of methyl red and methyl orange by the tight ultrafiltration membrane were both <65 %, while of alizarin red, direct red, bromocresol green and methyl blue achieved maximum values of 98.5 %, 99.2 %, 99.5 % and 99.6 %, respectively. The fouled membranes could restore the virgin performance for reuse by cleaning and low-temperature calcination.     

Application of Vibratory System to Improve the Critical Flux in Submerged Hollow Fiber MF Process

Submerged hollow fiber membrane system is widely used in water and wastewater treatment plants. One of the major problems of the microfiltration/ultrafiltration (MF/UF) process is membrane fouling. Few techniques have been developed to reduce membrane fouling and increase critical flux of the filtration process. In this study, membrane vibration was applied to improve the critical flux in a submerged hollow fiber MF system. A bench scale unit was especially built for this purpose and different vibrating speed was tested. The effect of the feed concentration and vibrating speed on the critical flux measurement were investigated. The critical flux was measured at different vibrating speeds varied from 0–500 oscillation per minute (opm) (5.83 Hz). The lowest critical flux was 15 L·m^?2·h^?1 when no membrane vibration was used and then increased gradually from 27 to 56 L·m^?2·h^?1 when the vibrating speed increased from 100 to 500 opm (8.35 Hz). A sharp drop in the critical flux was noticed when the concentration of feed suspension doubled from 5 g/L to 10 g/L. However, the increase in the critical flux was insignificant at higher feed concentration even when a high membrane vibrating speed was applied. This signifies that there is a limit for flux improvement in a vibratory system which is strongly dependent on the feed concentration.     

Critical flux determination by flux‐stepping

In membrane filtration related scientific literature, often step‐by‐step determined critical fluxes are reported. Using a dynamic microfiltration device, it is shown that critical fluxes determined from two different flux‐stepping methods are dependent upon operational parameters such as step length, step height, and flux start level. Filtrating 8 kg/m³ yeast cell suspensions by a vibrating 0.45 × 10^?6 m pore size microfiltration hollow fiber module, critical fluxes from 5.6 × 10^?6 to 1.2 × 10^?5 m/s have been measured using various step lengths from 300 to 1200 seconds. Thus, such values are more or less useless in itself as critical flux predictors, and constant flux verification experiments have to be conducted to check if the determined critical fluxes can predict sustainable flux regimes. However, it is shown that using the step‐by‐step predicted critical fluxes as start guesses, in our case, in constant flux verification experiments for 5 and 1/2 hours, a sustainable flux was identifiable. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Preparation and application of zinc oxide/poly(m-phenylene isophthalamide) hybrid ultrafiltration membranes

A small molecular-weight cut-off (MWCO) of 6000 Da poly(m-phenylene isophthalamide) (PMIA) embedded zinc oxide (ZnO) hybrid ultrafiltration (UF) membrane was synthesized via nonsolvent-induced phase separation (NIPS). Tests of field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), thermal gravimetric analyzer (TGA), Fourier transform infrared (FTIR), capillary flow porometer (CPF), mechanical test, and pure water flux (PWF) for characterization of membranes were carried out. The EDX, FTIR, and TGA indicated the presence of ZnO in the polymer matrix. The hybrid membranes showed enhanced pore density, PWF by the presence of the particles. The contact angle and water flux of modified membrane with 0.03 wt % of nano-ZnO were 47.7° and 52.58 L·m⁻²·h⁻¹ compared to 71.6° and 36.27 L·m⁻²·h⁻¹ respectively; Compared with the hydrophobic membrane, the PMIA membrane, with hydrophilicity, is supposed to exhibit good antifouling properties. Furthermore, the thermal stability and mechanical properties of the modified membranes were increased. Finally, the hybrid membrane was used in treating papermaking white wastewater and exhibited good separation and high water flux. The great properties of the ultrafiltration PMIA membranes indicate their potential for excellent performance in industrial applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47583.     

Permeation of binuclear, sulphur containing aromatic compounds

Removal of sulphur containing aromatics from fuel is strictly regulated and thus interesting for research as well as for industrial application. Especially difficult is the removal of complex dinuclear thiophenes and their methylated derivatives with conventional hydrotreating technology. Pervaporation could be an alternative separation technology. In order to find out if the separation of the more complex aromatics is possible, especially in low concentrations, variation of separation conditions and development of suitable membrane materials is necessary. The synthesized membrane materials based on 6FDA-4MPD/DABA copolyimides were analyzed by size exclusion chromatography (SEC) and differential thermal analysis (DTA) in combination with thermogravimetric analysis (TGA). In this work temperature-dependent pervaporation experiments were carried out with benzothiophene (about 0.25 wt.%) and n-dodecane as components of a binary feed mixture. The temperature has been varied between 80 °C and 140 °C. Thereby fluxes between 4.1 kg μm m^− 2 h ^− 1 and 32 kg μm m^− 2 h ^− 1 were found. Enrichment factors up to β = 3.3 were reached. In summary, the pervaporation experiments have shown that a significant enrichment of dinuclear aromatic sulphur compounds in combination to an adequate flux is possible.     

Electrocoagulation pretreatment of seawater prior to ultrafiltration: Bench-scale applications for military water purification systems

The objectives of this research were to investigate the use of in-line electrocoagulation (EC) as a pretreatment for seawater prior to ultrafiltration (UF) at the bench-scale and to compare EC with equivalent doses of ferric chloride. UF membrane performance was evaluated by transmembrane pressure (TMP) and hydraulic resistances at sub- and super-critical fluxes, and by flux recovery after hydraulic and chemical cleanings. Modified Atlantic Ocean seawater was used. Constant flux UF operation (50 to about 350 lmh) was used to evaluate short-term performance at sub- and super-critical fluxes, and constant feed-pressure (15 psi) experiments were used to investigate filter cake stability under high TMP conditions. In-line EC improved UF membrane performance for all coagulation and flux conditions. Compared to no coagulant pretreatment, ferric chloride improved UF membrane performance under short-term, constant flux conditions that resulted in TMP < 8 psi, but produced increased TMP and resistance to filtration at 15 psi. EC always resulted in lower resistance and improved flux recovery after cleaning compared to an equivalent dose of ferric chloride. Overall, EC is a feasible and competitive pretreatment strategy at the bench-scale, but scale-up issues, electrode cleaning requirements, and sustainability during long-term operation need further study.