MBR suppliers are largely recommending NaOCl as the cleaning agent. Despite the popularity of this chemical for membrane cleaning, there is a lack of publications regarding NaOCl optimum cleaning conditions. To properly conduct this optimization study (i.e. obtain the required level of reproducibility and confidence), a rigorous methodology is still required. The potential effect of NaOCl on polymeric materials ageing has drawn attention and recent studies have been dedicated to assess the impact of its exposure on numerous membrane materials (except polyvinylidene fluoride (PVDF)). PVDF and polypropylene (PP) hollow fibers were investigated using unwashed yeast as model fouling solution, while mixture of sodium alginate and bovine serum albumin (BSA) acted as feed solution for PVDF flat sheet. The cleaning efficiency and optimum NaOCl concentration were found to vary between the different membrane materials and between single and cyclical cleanings. During cyclical cleaning, foulant was more difficult to remove. When 2% NaOCl was used, Fourier Transform Infra Red (FTIR) Spectroscopy showed a change in membrane function groups on PVDF flat sheet, indicating ageing occurrence. NaOCl agemg caused changes in membrane properties. PP hollow fibers became more brittle with 60 % elongation decrease after 13 weeks. PVDF flat sheet membrane exhibited two-steps-degradation mechanism; firstly, the removal of its surface modification substance, and secondly, the increase of its hydrophilicity. These results were confirmed by X-ray Photoelectron Spectroscopy (XPS), FTIR Spectroscopy, contact angle and hydraulic measurement. Enzyme is an alternative option for membrane cleaning. However, the enzymatic cleaning study did not present encouraging results. Optimum cleaning efficiency for protease (68%) and amylase (73%) were found to be lower compared to NaOCl cleaning (95%). Lowry and Dubois methods found that residual foulants were present on the membrane after the cleaning process, which caused fouling to occur faster when membrane was re-used.

Membrane distillation (MD) is an emerging thermal separation technology which proved its efficiency in desalination of highly saline waters, including seawater, brines and impaired process waters. In a long-term prospective, MD can reinforce sustainability of the clean water production and mitigate the water-energy stress caused by lacking suitable freshwater recourses. However, just like in any other membrane separation process, MD membrane is susceptible to biofouling which presents a significant challenge by substantially reducing its performance and deteriorating permeate quality. This study evaluated different cleaning methods aimed at controlling biofilm development on a surface of hydrophobic MD membrane in a direct contact MD (DCMD) process fed by the Red Sea water. This was achieved by applying physical (hydraulic) cleaning and chemical cleanings with a range of chemicals utilized in membrane separation processes including citric acid (mineral acid), ethylenediaminetetraacetic acid (EDTA, metal-chelating agent) and sodium hypochlorite (NaOCl, oxidant). Flux recovery and changes in biofilm morphology, including its thickness and structure as well as microbial and extracellular polymeric substances (EPS) contents before and after cleanings have been analyzed to elucidate cleaning mechanisms and suggest effective strategies of biofilm removal. The results showed that 0.3% EDTA exhibited the best cleaning performance resulting in the highest permeate flux recovery (93%), followed by 0.3% NaOCl (89%), 3% citric acid (76%), and hydraulic (66%) cleanings. Application of EDTA and NaOCl has also resulted in the lowest number of bacterial cells and substantial reduction of the peak intensities caused by protein-like compounds and tyrosine-containing proteins present on the membrane surface after its treamtent. The observed trends are in a good correlation with the optical coherence tomography (OCT) observations which revealed substation changes in biofilm morphology leading to a significant reduction of biofilm thickness which followed the order of hydraulic cleaning < citric acid cleaning < NaOCl cleaning < EDTA cleaning. This study suggests that selection of an appropriate cleaning type and formulation is critical for achieving sustainable MD plant operations, both technically and economically.

Produced water is a major waste produced from oil and natural gas wells in the state of Texas. This water could be a possible source of new fresh water to meet the growing demands of the state after treatment and purification. This thesis describes a research project that evaluated the treatment of brine generated in oil fields (produced water) with ultrafiltration membranes. The characteristics of various ultrafiltration membranes for oil and suspended solids removal from produced water were studied to test whether they could be used in a pretreatment method. The research measured the effect of pressure and flow rate on performance of three commercially available membranes for treatment of oily produced water. Oil and suspended solids removal were measured by using turbidity and oil in water measurements taken periodically. The study also analyzed the flux through the membrane and any effect it had on membrane performance. The research showed that an ultrafiltration membrane provided turbidity removal of over 99% and oil removal of 78% for the produced water samples. The results indicated that the ultrafiltration membranes would be useful as one of the first steps in purifying the water. Membrane cleaning of produced water-fouled membranes by micellar solutions was investigated. A neutral pH and ambient temperature micelle solution for effective cleaning of oily water-fouled membranes was developed and studied. The performance of cleaning solutions on ultrafiltration membranes was investigated on laboratory size membrane testing equipment. Different micro emulsion solutions were studied to evaluate the effect of solution properties on cleaning performance. Three types of multiple membranes were studied, each having the same polyvinylidene fluoride (PVDF) material but with different nominal separation or flux characteristics. The data showed that the use of a micelle solution to clean the produced water-fouled membranes was a feasible and effective method. The study showed with further adjustment of the micelle solution the cleaning effectiveness could be optimized to provide double the effectiveness of current industry methods for membranes fouled by produced water.

Produced water is a major waste produced from oil and natural gas wells in the state of Texas. This water could be a possible source of new fresh water to meet the growing demands of the state after treatment and purification. This thesis describes a research project that evaluated the treatment of brine generated in oil fields (produced water) with ultrafiltration membranes. The characteristics of various ultrafiltration membranes for oil and suspended solids removal from produced water were studied to test whether they could be used in a pretreatment method. The research measured the effect of pressure and flow rate on performance of three commercially available membranes for treatment of oily produced water. Oil and suspended solids removal were measured by using turbidity and oil in water measurements taken periodically. The study also analyzed the flux through the membrane and any effect it had on membrane performance. The research showed that an ultrafiltration membrane provided turbidity removal of over 99% and oil removal of 78% for the produced water samples. The results indicated that the ultrafiltration membranes would be useful as one of the first steps in purifying the water. Membrane cleaning of produced water-fouled membranes by micellar solutions was investigated. A neutral pH and ambient temperature micelle solution for effective cleaning of oily water-fouled membranes was developed and studied. The performance of cleaning solutions on ultrafiltration membranes was investigated on laboratory size membrane testing equipment. Different micro emulsion solutions were studied to evaluate the effect of solution properties on cleaning performance. Three types of multiple membranes were studied, each having the same polyvinylidene fluoride (PVDF) material but with different nominal separation or flux characteristics. The data showed that the use of a micelle solution to clean the produced water-fouled membranes was a feasible and effective method. The study showed with further adjustment of the micelle solution the cleaning effectiveness could be optimized to provide double the effectiveness of current industry methods for membranes fouled by produced water.

Water desalination has the potential to alleviate a significant part of the world’s thirst, with a majority of desalinated water capacity coming from seawater reverse osmosis (SWRO). However, SWRO membrane systems suffer from the loss of performance due to biofouling leading to economic costs. There is no control or preventive strategy for SWRO biofouling and current industry practices recommend chemical treatments to restore membrane performance. Chemical cleaning results in high economic costs due to chemical acquisition, storage, transportation, long plant downtimes and ultimately shorter membrane lifetime and early replacement; in addition to the environmental impact associated with disposing of chemicals. Therefore, there is a need for novel effective green cleaning strategies for SWRO to meet the increasing demand for desalinated water while taking care of the environment. Micronanobubbles (MNBs) consist of small gas cavities formed in aqueous solutions. This study evaluates the efficiency of both air-filled micronanobubbles (AMNBs) and CO2 nucleated MNBs as: i) curative cleaning-in-place (CIP) treatments and ii) preventive daily treatments for biofouling over long-term studies. Experiments were performed using the membrane fouling simulator (MFS) under conditions that are representative of SWRO membrane systems. Pressure drop was implemented as the main biofilm growth monitoring parameter as used by standard industry practices. Curative studies showed that both MNBs CIP treatments had high cleaning efficiencies of 49-56% pressure drop recovery. MNBs pressure drop recovery values were close to the conventional chemical cleaning (NaOH/HCl) at 51% and were significantly higher than the hydraulic flush (HF) physical cleaning control at 24%. The pressure drop recovery results were supported by the optical coherence tomography (OCT) images before and after CIP and biomass autopsy results. Similarly, preventive MNBs daily treatments showed a significant delay in the system’s performance decline. This delay was 5.1 days for the CO2 MNBs experiments, 4 days for the AMNBs, and only 0.6 days for the hydraulic flushing treatments compared to the control. Compared to the control the duration of the operation was doubled in time before the cleaning criteria was met. OCT images confirmed biofilm growth delay with lower biomass occurrence.

Membrane biofouling is a common occurrence in water treatment plants that utilize reverse osmosis (RO). As bacteria and biofilm material build up on the membrane surface, it becomes more difficult for clean water to permeate through the membrane, and more pressure is required to produce the same amount of water. When pressures become critically high, membranes must be cleaned. This process is expensive in terms of chemical cost, labor, and downtime. Even after membranes have been cleaned, they can re-foul quickly if the cleaning did not effectively remove the biofilm. The water treatment plant in Dunedin, FL, which uses RO for treating groundwater, has experienced membrane biofouling since it began operation in 1992. Without the means to systematically evaluate a multitude of cleaning strategies on the bench scale, cleaning optimization must be conducted on the production skid level, which restricts the evaluation of alternative protocols. This problem is typical for many RO plants. The objectives of this project are: (1) using a multi-level and systematic approach, develop cleaning strategies for biofouled membranes that will lead to improved cleaning and decreased operational costs; (2) develop other cleaning strategies that will add to the scientific knowledge base; (3) quantify the effects of improved protocols; and (4) determine the policy implications of developed protocols in terms of cost suitability to Dunedin and elsewhere in Florida. This project consists of three phases, with phases progressively more similar to the water production environment. In the first phase, a series of bench tests were performed in the laboratory. Fouled membrane swatches were soaked and agitated in different cleaning solutions for different lengths of time, at different temperatures and pH. Protein and carbohydrate assays were then performed on both the cleaning solution and the membrane swatch to determine which conditions yield most complete removal of protein and carbohydrate from the membrane surface. Results indicate that carbohydrate removal does not appear to depend strongly on pH or temperature. Protein removal increases with increasing pH and is slightly greater at higher temperatures. The second phase of testing employed a 4"x6" stainless steel flat-sheet module in which cleanings were performed under different conditions to document corresponding changes in water flux and salt rejection. Operational parameters were based on pertinent literature and optimization results from Phase 1. Results indicate that water flux increases in response to cleaning at increasing pHs and increasing temperatures with best performances occuring after 30 minutes of cleaning. Salt rejection appears to decrease with pH. The most effective cleaning protocols, determined through trials in Phases 1 and 2, were put to the test again in Phase 3 where cleanings were performed on a specially constructed single-element cleaning system (for 8.5" x 40" elements), designed to clean a membrane element in isolation. This phase also served as final verification of new cleaning protocols before implementation on the production scale. Results from this phase were inconclusive due to mechanical problems. A multi-level, systematic cleaning evaluation leads to better understanding of the dependence of biofilm material removal and membrane performance on critical factors such as temperature, pH, time of cleaning, and chemical dose, which results in improved cleaning protocols and ultimately cost savings to RO water utilities such as Dunedin.

The use of Reverse osmosis (RO) membranes have been significantly increasing in water desalination, and the main operational obstacle in RO desalination plants is membrane fouling. Among other solutes, dissolved biopolymers, such as polysaccharides can lead to severe membrane fouling especially with the addition of calcium ions because of the complexation formation between the surface of membrane and foulants materials. However, this complexation can also take place in the feed bulk, resulting in foulants aggregates formation. Although there are some physical techniques that can maintain the membrane performance without reducing its lifetime, only chemical cleanings are still commonly used in RO plants. In this study, a novel cleaning method is proposed to restore the membrane performance by removing the deposited foulants without reducing the membrane lifetime. The cleaning method is based on using water saturated with dissolved CO2 gas, and its principle is based on producing spontaneous CO2 bubbles due to local pressure difference leading to nucleation of bubbles throughout the membrane surface, especially at nucleation sites, which improve the cleaning efficiency. Alginic acid sodium salt was used as a model of polysaccharides foulants in presence of different concentrations of NaCl and calcium ions aiming to enhance membrane fouling, and then CO2 cleaning solution efficiency, in terms flux recovery (FR), was tested under different operating conditions and compared to other cleaning methods. Average FR of 20%±3, 25%±3 and 80%±3 for MilliQ water, a cleaning solution at pH4, and CO2 solution at 6 bar, 0.17 m/s, and 23 ̊C ±0.2 for 6 minutes were obtained, respectively. The efficiency of this novel cleaning method was also compared to direct osmosis overnight, and the average flux was comparable (about 60%±3), though that the cleaning time was significantly different. Various calcium concentrations (0-10 mM) were added in the alginate solution to study the fouling behavior in terms of the potential for bulk complexation to form cake alginate layer on the membrane surface rather than a gel layer, and the role of CO2 bubbles nucleation to remove foulants was investigated. This cleaning method can be considered as an alternative more environmentally friendly technique in RO application.

Forward osmosis (FO) as a novel membrane separation technology has recently been investigated in various water treatment applications. The natural mass transfer process between two solutions driven by the osmotic pressure difference leads to many operational advantages in the FO process, such as low energy consumption and minimal fouling problems. It makes FO a feasible technology for the treatment of produced water (PW). Although previously, the treatment of PW using FO has been investigated, osmotic backwashing (OB) is not systematically examined for water flux recovery of the PW fouled FO membranes. Moreover, the cleaning of FO membranes used for the simultaneous treatment of different PW streams was never previously attempted. In this study, OB was thoroughly investigated for the cleaning of PW-fouled FO membranes. Also, FO membrane chemical cleaning using SDS and NaOH solutions was examined too. To investigate OB, the cleaning efficiency of a 60 min OB cleaning protocol was examined under different FO operating modes in (5 x 20 h) experiments using synthetic desalter effluent as FO feed solution (FS) and 1.2 M NaCl solution or water-oil separator outlet (WO) as draw solutions (DS). The AL-FS (active layer facing FS) mode outcompeted the AL-DS (active layer facing DS) mode, achieving a flux of 12.9 LMH and 80.1% water reclamation when using WO as a DS. Therefore, this FO configuration 5 was selected when evaluating the cleaning protocols. Moreover, after evaluating different OB methods, the 30 min OB protocol achieved the highest system efficiency rate of 95% and was studied for the treatment of real PW streams. The SDS and NaOH chemical cleaning methods achieved flux recovery rates of 99% and 98% by the end of the third treatment cycle, respectively, outperforming the 89% flux recovery rate of the optimized OB protocol. Although the investigated cleaning methods were able to restore the system performance, a substantial increase in RSF was observed due to mainly irreversible colloidal fouling. This study demonstrates the feasibility of OB and chemical cleaning in restoring FO system performance for the simultaneous treatment of PW streams

L’électrodialyse (ED) est principalement basée sur l’action spécifique des membranes échangeuses d’ions (MEIs) et est largement répandue en industrie agroalimentaire pour la stabilisation tartrique des vins, la désacidification et le traitement des jus de fruits, la déminéralisation du lactosérum ou l’élimination et le fractionnement des protéines du lait. Le colmatage organique, accentué par la complexité de composition des effluents alimentaires et leur richesse en composés phénoliques, représente un facteur majeur de limitation de l’efficacité des procédés et des performances des MEIs. Ce phénomène provoque une diminution de la sélectivité de membranes, une augmentation de leur résistance électrique et réduit le rendement énergétique du procédé conduisant à des pertes économiques en industrie. Cette étude consiste principalement à étudier le décolmatage de MEIs par procédés chimiques et biologiques. Des lots de membranes échangeuses de cations (MECs) et d’anions (MEAs) neuves (1 lot de MEC et 1 lot de MEA) et usées (3 lots de MECs et 2 lots de MEAs) à différentes durées d’utilisation en ED dans l’industrie agroalimentaire –application confidentielle- ont été étudiés. L’ensemble des échantillons ont préalablement été caractérisés pour détermination des paramètres physicochimiques (capacité d’échange (CE), épaisseur (Tm), conductivité électrique (km), angle de contact (θ), teneur en eau (WC) ainsi que la fraction volumique de la solution inter-gel (f2) résultant de l’exploitation du modèle microhétérogène), de structure et morphologiques par spectroscopie IR-TF, microscopie optique, microscopie électronique à balayage et mécaniques par essais de traction. Les effets directs et indirects (causés par les opérations de lavage régulières en industrie) du colmatage ainsi que l’anisotropie des propriétés mécaniques de membrane ont été mis en évidence. Des méthodes de nettoyage non agressives et respectueuses de l’environnement ont été expérimentées en mode statique en ex-situ : Solutions salines (NaCl à 35 g.L-1 et eau de mer reconstituée), solution hydro-alcoolique (mélange eau-éthanol 12%, pH=3,5) et solutions biologique utilisant 3 catégories d’agents enzymatiques (Rohalase BX-BXL, β-glucanase / Corolase 7089, endo-peptidase / Tyrosinase, polyphenol-oxydase) dont les conditions opératoires d’activité enzymatiques optimale ont été déterminées. L’évolution de CE, km, θ et f2 ont été suivis en fonction de la durée de nettoyage. Les solutions salines ont un effet négligeable sur le nettoyage en profondeur mais restent efficaces pour le nettoyage de surface. Cependant, l’application de la solution hydro-alcoolique et des solutions d’enzymes se sont avérées être efficaces pour le décolmatage interne et externe et parviennent à rétablir significativement les paramètres suivis. Il a été démontré que les composés phénoliques, principaux constituants des effluents traités, sont en majeure partie responsables du colmatage des MEIs. Ceux-ci forment des nanoparticules colloïdales denses, non perméables aux ions dans les méso- et macropores des MEIs et ne pénètrent pas dans ses micropores. Une modification du modèle microhétérogène selon cette hypothèse a permis de fournir une interprétation adéquate du km et de modéliser la modification structurale de la phase inter-gel engendrée par les mécanismes de colmatages de polyphénols et expliquer les raisons de diminution du facteur f2app. Une méthode d’extraction utilisant un mélange de solvants (25%V/V, acétone/méthanol/isopropanol/eau) a été mise au point et a permis d’extraire certains composés phénoliques de différents lots de MECs et MEAs usées et ont été identifiés par chromatographie liquide à haute performance. Il a été démontré que les interactions entre les composés phénoliques et la matrice polymère étaient principalement régies par l’empilement des cycles aromatiques et des interactions électrostatiques du type CH-pi et pi-pi ainsi que les liaisons hydrogènes / Conventional electrodialysis (ED) is mainly based on the specific action of ion exchange membranes (IEMs) and is widely used in food industry for tartaric stabilization of wines, deacidification and treatment of fruit juices, demineralization of whey or elimination and fractionation of milk proteins. The organic fouling, accentuated by the complex composition of the food effluents and their richness in phenolic compounds, represents a major limitative factor of the process efficiency and the IEMs performance. This phenomenon causes a decrease in the selectivity of membranes, an increase in their electrical resistance and reduces the energy efficiency of the process leading to economic losses in industry. This study mainly consists in studying the IEMs cleaning by chemical and biological methods. Two batches of new membranes (cation- (CEMs) and anion-exchange membranes (AEMs)) and five batches of used ones (3 CEMs and 2 AEM) with different durations of use in ED units in food industry -confidential application- have been studied. All the samples have been previously characterized to determine their physicochemical parameters (ion-exchange capacity (IEC), thickness (Tm), electrical conductivity (km), contact angle (θ), water content (WC) and the volume fraction of the inter-gel solution (f2) resulting from the study of the micro heterogeneous model), structure and morphology by FTIR spectroscopy, optical microscopy, scanning electron microscopy and mechanical by tensile strength tests. The direct and indirect effects (caused by the regular cleaning operations in industry) of fouling as well as the anisotropy of the membranes mechanical properties have been highlighted. Non-aggressive and environmentally friendly cleaning methods have been experimentally tested in ex-situ static mode: Saline solutions (35 g.L-1 NaCl and reconstituted seawater), hydro-alcoholic solution (12% water-ethanol mixture, pH = 3,5) and biological solutions using 3 categories of enzymatic agents (Rohalase BX-BXL, β-glucanase / Corolase 7089, endo-peptidase / Tyrosinase, polyphenol oxidase) whose operating conditions of optimal enzymatic activity have been determined. The evolution of IEC, km, θ and f2 were followed in function of the cleaning duration. Saline solutions have a negligible effect on intern cleaning but remain efficient for extern cleaning. However, the application of the hydro-alcoholic solution and enzyme solutions have been found to be efficient for both intern and extern cleaning and led to significant recoveries of the studied parameters. It has been shown that phenolic compounds, the principal constituents of treated effluents, are mainly responsible for MEIs fouling. Apparently, they form dense colloidal nanoparticles not permeable for ions within membrane meso- and macropores, not penetrating into micropores. A modification of the micro heterogeneous model under this assumption allowed an adequate interpretation of km and the modelization of structural modifications of the inter-gel phase generated by the fouling mechanisms by polyphenols and explained the reasons why the f2app decreases. An extraction method using a mixture of solvents (25% V/V, acetone/methanol/ isopropanol/water) was developed and made it possible to extract certain phenolic compounds from different batches of used CEMs and AEMs that were identified by high performance liquid chromatography. It has also been demonstrated that the interactions between the phenolic compounds and the polymer matrix are mainly governed by the stacking of aromatic rings and electrostatic interactions of the CH-pi and pi-pi type as well as the hydrogen bonds

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