Fouling Parameters Research Articles

Investigation of ash problems potential for a blend of high-sulfur coal and bamboo pellet biomass

Abstract Biomass bamboo can be utilized as co-firing fuel in power plants in order to provide more green energy. However, the characteristics of biomass bamboo with high potassium and chlorine that probably increase ash problem aspects need to be investigated before the implementation. This study aims to obtain an initial prediction of slagging, fouling, abrasion, and corrosion for bamboo pellets and high-sulfur coal blends using empirical indices. This study used seven slagging parameters, four fouling parameters, one abrasion parameter, and two corrosion parameters. The result shows that a composition of 10-30 wt.% bamboo pellets is more recommended than others. Despite the composition of 50 wt.% and above being predicted to reduce the slagging risk of high-sulfur coal, the composition of 40 wt.% and above is predicted to increase the fouling risk. At higher compositions, 80 wt.% and above are predicted to increase the corrosion risk. Further test using a drop tube furnace is necessary to obtain comprehensive results. Moreover, the calorific value aspect needs to be considered depending on the need of the power plant for the efficiency aspect.

Optimizing sustainability in hybrid cooling towers: Investigating fouling resistance, water quality correlations, modeling, and cleaning strategies for thermal power plants

This research explored the intricacies of water consumption and energy requirements within cooling systems designed for concentrated solar power plants. In the present work, an innovative hybrid cooling tower was presented and studied, aiming at reducing water consumption and preserving power generation efficiency. Experimental cooling towers were studied with four different cooling water qualities, elucidating that, compared to kaolinite, calcium carbonate has a substantial influence on fouling behavior as an additive to the cooling water. Through the establishment of correlations between water quality and critical fouling parameters such as fouling resistance Rf, deposition rates mf, and fouling thickness εf, the study provided valuable insights for predicting fouling behavior in similar operating conditions. Furthermore, the development and validation of a numerical code with both literature and experimental work was helpful in predicting the thermal performance of hybrid cooling along one-year operation. The assessment of three cleaning methods; water jet, air jet, and chemical cleaning, revealed distinct impacts on heat transfer and associated costs. Particularly noteworthy were the substantial improvements in heat transfer efficiency, especially with air jet cleaning, which enhanced heat transfer of the polymer bundles by 6.1% with no water consumption. These findings not only portend cost-effective maintenance practices but also endorse environmentally friendly approaches by significantly curtailing water usage, a pivotal progression in the sustainability of hybrids cooling systems.

Investigation of slagging-fouling tendency for high-sulfur coal and solid recovered fuel (SRF)

SRF can be utilized as co-firing fuel in power plants in order to provide more green energy and decrease the waste landfill. However, the characteristics of SRF with high potassium and chlorine need to be investigated first to avoid ash problem aspects in the future. This study aims to obtain initial prediction of slagging, fouling, abrasion, and corrosion for SRF and high-sulfur coal blend using empirical indices. This study used five slagging parameters, four fouling parameters, one abrasion parameter, and two corrosion parameters. The result shows that SRF contains high ash content, chlorine, Fe2O3, CaO, and K2O, that affects ash deposit formation like slagging, fouling, abrasion, and corrosion. Therefore, composition of 0-15 wt% SRF is more suitable than other compositions.

CoFe2O4 modified bentonite-based mixed matrix loose nanofiltration membranes for effective wastewater treatment

Mixed-matrix membranes (MMMs) with an ideal polymer/hydrophilic flux enhancer interface considerably recuperates the separation and purification performance of membrane. In this direction, a novel CoFe2O4 functionalized natural clay-bentonite (CoFe2O4@BT) material as a compatible flux enhancer was synthesized for preparation of mixed matrix based in polyethersulfone (PES) matrix. Here, the influences of CoFe2O4@BT on the morphology and performance of the MMMs membranes were systematically investigated using various analytical techniques. Meanwhile, the water flux and sepration eficiency of the CoFe2O4@BT-PES membranes significantly enhanced due to the incorporation of CoFe2O4@BT that altered hydrophilicity, pore and surface characteristic features. The water flux as well as separation efficiency range up to 95%, 94.69%, 94.16% of Congo red (CR), Crystal violet (CV), and humic acid (HA) respectively. Meanwhile, the fouling parameters demonstrated that the CoFe2O4@BT-PES membranes exhibited better antifouling property in the long term experiment comparing with commercial polyamide membrane. CoFe2O4@BT material incorporated membranes showed less decline ratio and a better recovery ratio. The high rejection of dyes with a high permeation flux of the newly designed membranes indicated an amazing possibility for dye purification. In this study, a potential dye mechanism for composite membranes impacted by synthetic CoFe2O4@BT was also put forth. Within the context of application considerations for environmental protection, new materials stock in membranes show good potential for the separation of different organic contaminants.

A Comparative Study of the Self-Cleaning and Filtration Performance of Suspension Plasma-Sprayed TiO2 Ultrafiltration and Microfiltration Membranes.

This study investigated the performance of photocatalytic titanium dioxide microfiltration membranes with an average pore size of approximately 180 nm and ultrafiltration membranes with an average pore size of around 40 nm fabricated with the suspension plasma spray process. The membranes were evaluated for their filtration performance using SiO2 particles of different sizes and polyethylene oxide with molecular weights of 20 kDa to 1000 kDa, and the fouling parameters were characterized. The rejection rate was enhanced by increasing the thickness of the membranes. This effect was more pronounced with the ultrafiltration membranes. The rejection rate of the ultrafiltration membrane was improved significantly after filling the larger pores on the surface with agglomerates of titanium dioxide nanoparticles. The self-cleaning performance of the membranes was assessed under visible light. Both ultrafiltration and microfiltration membranes showed a flux recovery under visible light illumination due to the photocatalytic activity of titanium dioxide. The membranes also show a flux recovery of more than 90%.

Novel positively charged PVDF/SPES membranes surface grafted by hyperbranched polyethyleneimine (HBPEI): Fabrication, characterization, antifouling properties, and performance on the removal of cationic E-coat paint

Surface modification of ultrafiltration membranes has shown a significant potential to reduce fouling and increase flux and lifetime, which are the most important factors in membrane filtration. In this study, the surface-modified membranes were prepared by grafting hyperbranched polyethyleneimine (HBPEI) onto polyvinylidene fluoride (PVDF)-sulfonated polyethersulphone (SPES) blending membranes. Electrostatic interactions between HBPEI and SPES result in a well-attached positive-charged HBPEI grafting layer on the PVDF membrane surface. Surface-modified membranes were examined for the removal of cationic E-coat paint and their performance was measured in terms of total permeation flux, paint rejection, and fouling resistance parameters. In addition, the physicochemical properties and morphology of the membranes were examined by field emission scanning electron microscopy (FESEM), Fourier-transformed infrared spectroscopy (FTIR), atomic force microscopy (AFM), and water contact angle (CA). The optimum membrane shows a total permeation flux of 35.5 L per square meter per hour (LMH) and paint rejection of 99.9%. Additionally, the fouling parameter of the optimized membrane shows a flux recovery ratio of 90%. As a result of its considerable properties, such as the high flux and separation performance as well as its antifouling properties, the surface modified membrane is an excellent candidate for the removal of E-coat paint at industrial scale.

Influence of magnetic casting on the permeability and anti‐fouling properties of a novel iron oxide/alumina/polysulfone mixed matrix membrane

AbstractNovel mixed matrix membranes (MMMs) were fabricated using Fe3O4, and Al2O3nanoparticles (NPs) were added to the polysulfone (PSf) and N‐methylpyrrolidone (NMP) solution. The nanocomposite membranes were fabricated using the NIPS (non‐solvent induced phase separation) method. In order to create preferential permeation pathways for water across the MMMs, membrane formation is accomplished with an external magnetic field. Using magnetic casting cause the targeted placement of NPs in the best location and orientation. The performance of the prepared membranes was examined in terms of pure water flux and fouling parameters. Magnetic casting considerably increased pure water flux and decreased the total resistance of the optimum mixed matrix membrane, which contains 0.2% wt. of Fe3O4NPs to 1175 L/m2h and 13.4 * 1011(m−1), respectively. This is explained by the ordering of magnetic nanoparticles on the membrane sub‐layer cast under the magnetic field of 500 mT, which changed the sub‐layer structure. Less rough membrane surface of the mixed matrix membranes offered preferable anti‐fouling properties against fouling by BSA proteins. The characterization of fabricated membranes was carried out using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energy dispersive X‐ray (EDX), and water contact angle measurement methods.

Development of a dynamic model for effective mitigation of membrane fouling through biogas sparging in submerged anaerobic membrane bioreactors (SAnMBRs)

The deterministic mechanistic model derived from the fundamental of the dynamical fouling system was investigated to estimate fouling parameters, with theoretical biogas sparging performance evaluated of a Submerged Anaerobic Membrane Bioreactor treating trade wastewater. The result showed that the sparging effectiveness of EPSc removal was average, 35% higher than the sparging effectiveness of EPSp, with the coefficient of fouling removal characterizing the dynamic time behaviour increasing with the organic loading rate. The dynamic system analysis predicted that the process gain for SAnMBR-1 was more than 30% compared with SAnMBR-2, which supported a widely known theory of fouling dependence of organic loading rate.

Membrane fouling mechanisms by BSA in aqueous-organic solvent mixtures

To exploit the benefits of membrane-based separation for the pharmaceutical and chemical industries, the understanding of membrane fouling in organic solvents is crucial. Specifically for the separation of biocatalysts in the manufacture of pharmaceuticals, this study investigated membrane fouling by bovine serum albumin (BSA) in 10% v/v isopropanol (IPA), 10% v/v dimethyl sulfoxide (DMSO), 30% v/v IPA, and 30% v/v DMSO, benchmarked against that in water. The presence of either IPA or DMSO worsened fouling, with the latter comparatively worse. To understand the fouling mechanisms, Field Emission Scanning Electron Microscopy (FESEM) images were taken to assess external fouling, Evapoporometry (EP) was used to measure the pore-size distributions of the fouled membranes to examine internal fouling, a fouling model was applied to extract the fouling parameters, and the interfacial interaction energies were derived. Results indicate that the worst fouling in 30% v/v DMSO was due to both significant external fouling and internal fouling, whereas the second-worst fouling by 30% v/v IPA was caused predominantly by internal fouling. The magnitudes of the total DLVO- and XDLVO-based interaction energies were found to be poorly related to the relative flux declines. This study provides valuable insights into membrane fouling in different solvent environments.

Exposure to stressful conditions alters the properties and fouling behavior of suspended microparticles in anaerobic processes

Microparticles, a type of suspended particles in anaerobic membrane bioreactors (AnMBRs) with a size ranging from 0.45 to 10 µm, play a vital role in fouling. Here, the occurrence, composition, and fouling behavior of microparticles were determined during the cultivation of anaerobic sludge under stressful conditions that included high sulfate (3 g/L), high ammonium (3 g/L), high temperature (55 °C), and high salinity (28 g NaCl/L) tests. The results showed that the total organics in the supernatant of anaerobic sludge liquor increased after exposure to high temperature and high salinity, and the proportion of microparticles decreased significantly compared with that of the control, which could be due to the decreasing ratios of live/dead cells in the microparticles, thereby producing more soluble organics (< 0.45 µm). Accordingly, dead-end filtration tests showed that the supernatants with the same organic concentration in high temperature and high salinity groups had a decreasing fouling potential. Based on Hermia’s model, the cake filtration model fitted the supernatant filtration data under all stressful conditions. Moreover, the high-temperature group also fitted well with the pore-blocking model. The correlation between fouling parameters and the microbial species of microparticles suggested the potential contributions of Bacteroidales, Aminicenantales, Anaerolineales, and Caldisericales to cake/gel fouling, and the positive effects of Ignavibacteriales and Syntrophobacterales on pore blocking. Overall, exposure to stressful conditions considerably altered the production and characteristics of microparticles during the anaerobic digestion, thus leading to different fouling mechanisms in AnMBRs.

Survival of the fittest: Prokaryotic communities within a SWRO desalination plant

Water scarcity is known to affect 40% of the global population. By 2030, it is estimated that 700 million people will potentially become displaced due to drought. Seawater reverse osmosis (SWRO) desalination is recognised as one of the most cost effective and efficient methods to produce freshwater. However, biofouling of the SWRO membranes is detrimental to the efficacy of the desalination plants. In this study, the bacterial community composition within the pre-treatment system at Penneshaw SWRO desalination plant (Kangaroo Island, Australia) and the biological fouling parameters on the SWRO membranes were characterised. Membrane autopsies were undertaken on stages 1 and 2 positioned membranes that were operational for two and four years. Results showed that the pre-treatment system allowed for the removal of microorganisms from the water, however niche communities were able to establish and proliferate within the plant due to environmental adaption. The communities associated with the SWRO membranes were stable and had the ability to flourish on the membranes within biofilms. This study provides insights into the community structure within the pre-treatment system of the desalination plant, as well as on the SWRO membranes and examines how they impact on the performance of the plant.

Synthesis and characterization of novel PES/GO-g-PSS mixed matrix membranes with outstanding antifouling and dye rejection properties

In this study, a novel mixed matrix ultrafiltration membrane based on polyethersulfone (PES) was prepared by embedding graphene oxide-g-polystyrene sulfonate (GO-g-PSS) nanoplates into the polymer matrix by using the phase inversion method. The GO-g-PSS nanoplates were synthesized by using the ATRP method, based on which the ATRP initiator was first grafted onto pre-modified graphene oxide (GO-NH2), and subsequently, the polymerization process was carried out in the presence of monomers. Water contact angle and porosity measurements were both employed for characterization of the prepared membranes. Additionally, the structure and morphology of all the prepared membranes were evaluated by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was also found that, using these nanoparticles, water flux, porosity and hydrophilicity of membranes remarkably increased. Moreover, the more the modified GO loading amount increased, the more the roughness of the prepared membranes increased. The performance of all the prepared membranes was also investigated in terms of rejection, flux recovery and fouling parameters. Accordingly, the retention of two dyes and bovine serum albumin (BSA) molecules was tested, by which the effects of mean pore size, dimensions of permeated molecules and hydrophilicity of the membrane surface were analyzed. It was demonstrated by the fouling test that the 0.75wt% GO-g-PSS/PES membrane sample could provide the highest FRR value (89.9%) and the lowest irreversible fouling resistance (Rir) value (10.1%).

Fouling Behavior during Sterile Filtration of Different Glycoconjugate Serotypes Used in Conjugate Vaccines.

Sterile filtration can be a particular challenge when processing very large glycoconjugate vaccines. The objective of this study was to examine the sterile filtration performance of a series of glycoconjugate vaccines produced by coupling different polysaccharide serotypes to an immunogenic protein. Sterile filtration was performed at constant filtrate flux using 0.22μm pore size Durapore® polyvinylidene fluoride membranes. Glycoconjugates were characterized by dynamic light scattering, rheological measurements, and nanoparticle tracking analysis (NTA). Confocal microscopy was used to examine glycoconjugate capture profiles within the membrane. Transmembrane pressure data were analyzed using a recently developed fouling model. All glycoconjugates deposited in a narrow band near the entrance of the Durapore® membranes. The rate of fouling varied significantly for the different serotypes, with the fouling parameter correlated with the fraction of glycoconjugates larger than 200nm in size. The fouling behavior and sterile filter capacity of the different glycoconjugate serotypes are determined primarily by the presence of large species (>200nm in size) as determined by nanoparticle tracking analysis. The modified intermediate pore blockage model provides a framework for predicting the sterile filtration performance for these glycoconjugate vaccines.

Dual ionic liquid-based crosslinked chitosan for fine-tuning of antifouling, water throughput, and denitrification performance of polysulfone membrane

This study aimed to design a facile and efficient protocol for upgrading the performance indices of polysulfone (PS) membrane (porosity, hydrophilicity, pure water flux (PWF), surface charge, and fouling-resistance) by blending with newly synthesized poly(ionic) crosslinked chitosan Schiff bases (PICCSBs). The PS-PICCSBs mixed-matrix membranes (MMMs) have successfully fabricated and characterized based on spectral and microscopic analyses, porosity, zeta potential, water contact angle, and water uptake (wettability) measurements. The PWF, fouling-resistance against bovine serum albumin (BSA), as well as ion exchange capacity (IEC) against nitrate anion were studied. The wettability, hydrophilicity and overall porosity of new MMMs have greatly increased, in comparison to a pristine PS membrane (M0). In addition, blending of PS with PICCSBs resulted in switching its surface from negatively- to positively-charged. The PWF of MMMs has increased to reach a maximum value of 238.6 L/m2 h for MMM1 (9.3-fold higher than M0). Meanwhile, BSA rejection has declined from 96.62% for M0 to 41.9% for MMM1. The fouling parameters results of MMMs indicated their low fouling propensity. The IEC of nitrate anions revealed that the nitrate uptake by MMM1 is higher than that for M0 and MMM2 by 34% and 14%, respectively.

Fouling characterization during initial stage of cross-flow ultrafiltration

Ultrafiltration (UF) membrane is an attractive pretreatment technology used in desalination water system. However, the unavoidable membrane fouling over time is the key problem in the development of this technology. Fouling evaluation in the initial stage may provide relevant information about the fouling tendencies. In this work, the extent of fouling was investigated through a new method allows evaluating the fouling in cross-flow UF in the initial filtration stage. An empirical adjustment of flux decline data based on a bi-exponential equation with 4 coefficients is proposed for determining the Rcfi and RV − CF parameters. The first parameter Rcfi is defined as the initial cross-flow resistance. The second parameter RV − CF is defined as increasing resistance per specific volume of permeate in cross-flow. The measurement of the fouling parameters is evaluated in a laboratory facility with the following established conditions: (1) operation in cross-flow mode and (2) a flow measurement period limited to roughly 1 h. The procedure is intended to detect two different flow decline zones with different fouling processes at the initial stage of cross-flow filtration. The method applicability was tested with two cellulosic membranes of 10 kDa and 20 kDa and solutions of 4 kDa and 35 kDa polyethylene glycol (PEG) and alginate at different concentrations. In the case of the Rcfi parameter, the results show measurable values with high colloidal concentration of PEG. The RV − CF results shows a sensitive increase with foulant concentration, in different degree, depending on the type of solution and membrane used.

Development of an embossed nanofiber hemodialysis membrane for improving capacity and efficiency via 3D printing and electrospinning technology

A three-dimensional (3D) pattern was fabricated using a 3D printer to develop a hemodialysis nanofiber membrane with an embossed structure for portable or wearable hemodialyzers. The membrane of the embossed structure had a much larger surface area than that of the planar membrane structure. The high-flux hemodialysis membrane was prepared using a poly(methyl methacrylate)-graft-poly(dimethylsiloxane) (PMMA-g-PDMS) copolymer and polyamide 6 (PA6). The PMMA-g-PDMS copolymer is an organic-inorganic hybrid material in which the nanofiber diameter was controlled under 0.437 μm with a surface layer thickness of 50 (±20) μm. The polyamide 6 (PA6) nanofiber membranes were made with fibers 0.072 μm in diameter with a 0.14 μm pore size. This PMMA-g-PDMS/PA6 nanofiber hemodialysis membrane was modified for enhanced dialysis efficacy, and the modified membranes were evaluated based on clearance of saline and small molecules. Esterification and crosslinking reactions resulted in anionic hydrophilic hemodialysis membranes, and the fouling resistance is due to esterification of carboxylic acid groups (COOH) of sodium alginate with hydroxyl groups (OH) of polyethylene glycol, which generated a negatively charge surface. Thereby, repulsive electrostatic forces might be generated between the negatively charged blood cells and negative surface membrane. The water contact angle showed that the membrane hydrophilicity increased from 129 and 90° to 50°, and the total fouling parameter decreased to 0.112. The fouling resistance was enhanced due to the negatively charged membrane surface. Membrane contamination was measured by protein adhesion using a surface potential difference based on fluorescent whitening with zeta potential analysis, and the efficiency of creatinine removal was increased using a beta (β-cage) zeolite.

Fouling behavior of colloidal particles in organic solvent ultrafiltration

Membrane technology is increasingly becoming a promising alternative in the chemical and pharmaceutical industries, wherein organic solvents may form the continuous phase. Regarding the inevitable membrane fouling phenomenon, although the knowledge base is rich for feeds involving water, an analogous understanding for feeds involving organic solvents is limited. Accordingly, in this study, we systematically investigated the fouling behaviors of a model colloidal foulant (namely, silica) dispersed in water and five organic solvents (namely, methanol, ethanol, acetone, toluene and hexane) during ultrafiltration. The flux decline trends were clearly different. The XDLVO model and a fouling model were employed to extract mechanistic insights. Firstly, zeta potential alone was a poor indicator of the fouling extent. Secondly, solvents with high polarity (i.e., methanol, ethanol) had repulsive foulant-foulant and foulant-membrane interfacial interactions, which were beneficial in mitigating membrane fouling, leading to lesser flux decline and lower cake resistance. Thirdly, solvents with no or low polarity (i.e., n-hexane, toluene and acetone) had attractive interfacial interactions, which worsened membrane fouling. However, attractive foulant-foulant interaction was beneficial in augmenting shear-induced diffusion, which mitigated fouling. Fourthly, the fouling parameters extracted from the fouling model generally were lesser and greater respectively for the high-polarity and lower-polarity solvents, which agree with the interfacial interaction values and flux decline trends. The insights emanating from this study on membrane fouling in organic solvents are expected to be valuable in the design and operation of such emerging membrane-filtration systems.

Synthesis and characterization of nanocomposite ultrafiltration membrane (PSF/PVP/SiO2) and performance evaluation for the removal of amoxicillin from aqueous solutions

Abstract The presence of antibiotics in drinking water sources indicates the inefficiency of their removal using common water treatment process. Removal of these micro-pollutants from water requires more advanced and efficient processes. The purpose of this study was to synthesize a nanocomposite ultrafiltration membrane (Polysulfone/Polyvinylpyrrolidone/SiO2) and to evaluate for removal of amoxicillin from aqueous media. Ultrafiltration membranes were synthesized using phase inversion method. SiO2 nanoparticles ( ∼ 10-20 nm) were used in the range of 0 to 4 wt% as a hydrophilic agent for membrane modification. The characterizations of the membranes were determined using FTIR, water contact angle, AFM and SEM techniques. Also, the performance of synthesized membranes was evaluated in terms of pure water flux, amoxicillin separation efficiency and fouling parameters analysis. The results of FTIR analysis and contact angle measurement indicated that the hydrophilicity of nanocomposite membranes has increased significantly due to the presence of hydroxyl group in SiO 2 structure. The results of AFM images also showed that with increasing the addition of nanoparticles, the average surface roughness of the synthesized membranes increased negligibly. Also, FE-SEM micrographs showed that with increasing SiO2 concentration, the porous structure of the membranes changes from a spongiform and tear-like to a canal-shaped, finger-shaped and macro-void structures. This change in the structure increased the porosity and then the membrane flux, so that the pure water flux was 6.6 L/m2.h for the unmodified membrane to 42.28 L/m2.h for the membrane with 3 wt% of nanoparticles. The evaluation of membrane performance showed that with increasing SiO2 nanoparticles from 0 to 4 wt%, the amoxicillin separation performance increased from 66.52% to 89.81%. In addition, the analysis of the membrane fouling parameters showed that the addition of SiO2 nanoparticles also improved the membrane resistance against fouling, so that the relative flux reduction ratio (RFR) from 57.03% ( R r e v e r s i b l e r = 9 . 9 and R i r r e v e r s i b l e = 47 . 13 ) for the unmodified membrane reduce to 22.89% ( R r e v e r s i b l e r = 16 . 10 and R i r r e v e r s i b l e = 6 . 79 ) for the modified membrane with 3 wt% of nanoparticles. The results of this study showed that the use of nanocomposite membranes is promising for the removal of biodegradable resistant pollutants such as amoxicillin antibiotics from water resources.

Biopolymer extracted from Moringa oleifera Lam. in conjunction with graphene oxide to modify membrane surfaces

ABSTRACT A novel modification through pressurized filtration technique of commercial polyethersulfone membranes was proposed using a biopolymer extracted from Moringa oleifera Lam. (MO) along with graphene oxide (GO), in order to decrease fouling and improve the membrane selectivity for the removal of methylene blue dye. The effect of these agents over the morphology and performance of the membranes were studied through the evaluation of permeability, dye removal and fouling parameters. The characterization of the membrane indicates a significant decrease in pore size, as confirmed by the filtration experiments. Also, according to FTIR and SEM analysis the modification was effectively accomplished. All modified membranes presented low fouling rates (<10.55%) and high dye removal rates (from 2.85% to 96.73%). Furthermore, it is the first time that MO has been used as a natural polymer to improve and confer new characteristics on membranes, creating new possibilities for further study of this promising environment-friendly biopolymer in membrane separation processes.

In-situ monitoring and quantification of fouling development in membrane distillation by means of optical coherence tomography

Fouling formation in membrane distillation limits process stability and could cause besides wetting a rapid flux decrease making the process inefficient. Process performance is conventionally assessed by flux monitoring. Optical Coherence Tomography (OCT) enables in-situ visualization and quantification of fouling layers dominated by scaling in a fully operated direct contact membrane distillation system (DCMD). This study presents an innovative methodology for 3D dataset analysis allowing for the detection and quantification of predominant scaling on the membrane surface. Defined fouling parameters permit a correlation between process performance indicators, especially flux decrease and quantified fouling layer coverage. Additionally, structural information about the fouling layer was derived from the fouling parameters calculated from OCT C-scans across the feed channel within the flat sheet membrane unit. The method was successfully applied in DCMD of hot spring water, showing a critical fouling ratio between RS = 50–60 µm3/µm2, resulting in an overall flux decrease of 80%. The consideration of covered membrane area in RC proved the correlation of increasing fouling layer coverage (up to 90%) inducing a flux decline (by 80%) verifying the hypothesis, that the share of covered membrane area is the limiting step for MD performance. The presented method was able to link scalable fouling parameters with macroscopic process parameters. Hence making performance monitoring possible while enabling an adapted process control.