Removal of Heavy Metals from Wastewaters and Other Aqueous Streams by Pressure-Driven Membrane Technologies: An Outlook on Reverse Osmosis, Nanofiltration, Ultrafiltration and Microfiltration Potential from a Bibliometric Analysis.

A bibliometric study to analyze the scientific documents released until 2024 in the database Scopus related to the use of pressure-driven membrane technologies (microfiltration, ultrafiltration, nanofiltration and reverse osmosis) for heavy metal removal was conducted. The work aimed to assess the primary quantitative attributes of the research in this field during the specified period. A total of 2205 documents were identified, and the corresponding analysis indicated an exponential growth in the number of publications over time. The contribution of the three most productive countries (China, India and USA) accounts for more than 47.1% of the total number of publications, with Chinese institutions appearing as the most productive ones. Environmental Science was the most frequent knowledge category (51.9% contribution), followed by Chemistry and Chemical Engineering. The relative frequency of the keywords and a complete bibliometric network analysis allowed the conclusion that the low-pressure technologies (microfiltration and ultrafiltration) have been more deeply investigated than the high-pressure technologies (nanofiltration and reverse osmosis). Although porous low-pressure membranes are not adequate for the removal of dissolved heavy metals in ionic forms, the incorporation of embedded adsorbents within the membrane structure and the use of auxiliary chemicals to form metallic complexes or micelles that can be retained by this type of membrane are promising approaches. High-pressure membranes can achieve rejection percentages above 90% (99% in the case of reverse osmosis), but they imply lower permeate productivity and higher costs due to the required pressure gradients.

Green Separation by Using Nanofiltration of Tristerix tetrandus Fruits and Identification of Its Bioactive Molecules through MS/MS Spectrometry.

Membrane technology allows the separation of active compounds, providing an alternative to conventional methods such as column chromatography, liquid-liquid extraction, and solid-liquid extraction. The nanofiltration of a Muérdago (Tristerix tetrandus Mart.) fruit juice was realized to recover valuable metabolites using three different membranes (DL, NFW, and NDX (molecular weight cut-offs (MWCOs): 150~300, 300~500, and 500~700 Da, respectively)). The metabolites were identified by ESI-MS/MS. The results showed that the target compounds were effectively fractionated according to their different molecular weights (MWs). The tested membranes showed retention percentages (RPs) of up to 100% for several phenolics. However, lower RPs appeared in the case of coumaric acid (84.51 ± 6.43% (DL), 2.64 ± 2.21% (NFW), 51.95 ± 1.23% (NDX)) and some other phenolics. The RPs observed for the phenolics cryptochlorogenic acid and chlorogenic acid were 99.74 ± 0.21 and 99.91 ± 0.01% (DL membrane), 96.85 ± 0.83 and 99.20 ± 0.05% (NFW membrane), and 92.98 ± 2.34 and 98.65 ± 0.00% (NDX membrane), respectively. The phenolic quantification was realized by UHPLC-ESI-MS/MS. The DL membrane allowed the permeation of amino acids with the MW range of about 300~100 Da (aspartic acid, proline, tryptophan). This membrane allowed the highest permeate flux (22.10-27.73 L/m2h), followed by the membranes NDX (16.44-20.82 L/m2h) and NFW (12.40-14.45 L/m2h). Moreover, the DL membrane allowed the highest recovery of total compounds in the permeate during the concentration process (19.33%), followed by the membranes NFW (16.28%) and NDX (14.02%). Permeate fractions containing phenolics and amino acids were identified in the membrane permeates DL (10 metabolites identified), NFW (13 metabolites identified), and NDX (10 metabolites identified). Particularly, tryptophan was identified only in the DL permeate fractions obtained. Leucine and isoleucine were identified only in the NFW permeate fractions, whereas methionine and arginine were identified only in the NDX ones. Liquid permeates of great interest to the food and pharmaceutical industries were obtained from plant resources and are suitable for future process optimization and scale-up.

Fractionation of functional oligosaccharides produced from sugarcane straw using serial nanofiltration membranes and their influence on prebiotic potential.

Functional oligosaccharides are non-digestible by human gut enzymes and provide health benefits as fibers and prebiotics. The cello-oligosaccharides (COS) and xylooligosaccharides (XOS) are functional oligosaccharides obtained from xylan and cellulose, respectively, and are present in lignocellulosic material. The serial NF membranes process was performed to investigate the impact of the fractionation process on the prebiotic activity of oligosaccharides from xylan and cellulose. The NP030 (weight cut-off of 500-600 Da) and DK (weight cut-off of 150-300 Da) NF polymeric membranes were employed using defined operational conditions. The diafiltration (DF) was also investigated and it was determined that only a 1-time DF for NP030 was a more suitable strategy and improved the performance indices for short DP oligosaccharides. The short DP fractions obtained favored cell density for probiotic strains, which presented an increase on the optical density of up to 25 % after the fractionating process; enabling the use of short purified fractions in the food and pharmaceutical industry as a prebiotic ingredient.

Ultrafiltration and Nanofiltration for the Removal of Pharmaceutically Active Compounds from Water: The Effect of Operating Pressure on Electrostatic Solute-Membrane Interactions.

The present work investigates nanofiltration (NF) and ultrafiltration (UF) for the removal of three widely used pharmaceutically active compounds (PhACs), namely atenolol, sulfamethoxazole, and rosuvastatin. Four membranes, two polyamide NF membranes (NF90 and NF270) and two polyethersulfone UF membranes (XT and ST), were evaluated in terms of productivity (permeate flux) and selectivity (rejection of PhACs) at pressures from 2 to 8 bar. Although the UF membranes have a much higher molecular weight cut-off (1000 and 10,000 Da), when compared to the molecular weight of the PhACs (253-482 Da), moderate rejections were observed. For UF, rejections were dependent on the molecular weight and charge of the PhACs, membrane molecular weight cut-off (MWCO), and operating pressure, demonstrating that electrostatic interactions play an important role in the removal of PhACs, especially at low operating pressures. On the other hand, both NF membranes displayed high rejections for all PhACs studied (75-98%). Hence, considering the optimal operating conditions, the NF270 membrane (MWCO = 400 Da) presented the best performance, achieving permeate fluxes of about 100 kg h-1 m-2 and rejections above 80% at a pressure of 8 bar, that is, a productivity of about twice that of the NF90 membrane (MWCO = 200 Da). Therefore, NF270 was the most suitable membrane for this application, although the tight UF membranes under low operating pressures displayed satisfactory results.

In-Situ Modification of Nanofiltration Membranes Using Carbon Nanotubes for Water Treatment.

Modification of thin-film composite (TFC) nanofiltration (NF) membranes to increase permeability and improve separation performance remains a significant challenge for water scarcity. This study aimed to enhance the permeability and selectivity of two commercial polyamide (PA) NF membranes, NF90 and NF270, by modifying them with carbon nanotubes (CNTs) using microwave (MW)-assisted in-situ growth. The conducting polymer, polypyrrole (Ppy), and a ferrocene catalyst were used to facilitate the growth process. Chemical and morphological analyses confirmed that the surface of both membranes was modified. The NF270-Ppy-CNT membrane was selected for ion rejection testing due to its superior permeability compared to the NF90-Ppy-CNT. The modified NF270 membrane showed a 14% increase in ion rejection while maintaining constant water permeability. The results demonstrated that it is feasible to attach CNTs to a polymeric surface without compromising its functional properties. The Spliegler-Kedem model was employed to model the rejection and permeate flux of NF270-Ppy-CNT and NF270 membranes, which indicated that diffusive transport contributes to the modification to increase NaCl rejection. The present study provides a promising approach for modifying membranes by in-situ CNT growth to improve their performance in water treatment applications, such as desalination.

A review on membrane concentrate management from landfill leachate treatment plants: The relevance of resource recovery to close the leachate treatment loop.

Membrane filtration processes have been used to treat landfill leachate. On the other hand, closing the leachate treatment loop and finding a final destination for landfill leachate membrane concentrate (LLMC) - residual stream of membrane systems - is challenging for landfill operators. The re-introduction of LLMC into the landfill is typical; however, this approach is critical as concentrate pollutants may accumulate in the leachate treatment facility. From that, leachate concentrate management based on resource recovery rather than conventional treatment and disposal is recommended. This work comprehensively reviews the state-of-the-art of current research on LLMC management from leachate treatment plants towards a resource recovery approach. A general recovery train based on the main LLMC characteristics for implementing the best recovery scheme is presented in this context. LLMCs could be handled by producing clean water and add-value materials. This paper offers critical insights into LLMC management and highlights future research trends.

Technical and economic aspects of a sequential MF + NF + zeolite system treating landfill leachate.

This work explores the techno-economic aspects of landfill leachate treatment by an integrated scheme composed of microfiltration (MF), nanofiltration (NF), and zeolite application for carbon and nitrogen removal. In bench-scale experiments, MF and NF were investigated, and zeolite batch tests were carried out to determine optimum conditions. A preliminary economic analysis is presented for a 200 m3 d-1 full-scale treatment facility based on the data obtained from experimental tests and literature surveys. The maximum removals of 92%, 94%, and 79% for chemical oxygen demand (COD), absorbance at 254 nm, and ammonium nitrogen (NH4+-N) were achieved in bench experiments, respectively. It was possible to reach the local discharge standard for COD (200 mg L-1), but it was not possible to reach the Brazilian disposal requirement for NH4+-N (20 mg L-1). The total cost of the integrated MF + NF + zeolite system was estimated at 19.89 US$m-3. In this study, the costs of the zeolite application account for around 70% of the total costs of the integrated scheme. Membrane process integration was an adequate strategy for removing organic compounds at low operating costs; However, further NH4+-N depuration is needed to meet discharge requirements.

Avaliação de alumina e carvão ativado conjugados com nanopartículas de prata como pré-tratamentos para nanofiltração visando à redução da incrustação / Evaluation of alumina and activated carbon conjugated to silvernanoparticles as nanofiltration pre-treatments aiming at fouling reduction

RESUMO A má distribuição geográfica de águas em território nacional aliada ao seu desperdício, à poluição dos cursos d'água próximos aos centros urbanos e industriais e à eficiência inadequada de processos de tratamento convencionais faz com que o tratamento e o reúso de água sejam tópicos de crescente importância no Brasil. Um dos métodos de tratamento de água são os processos de separação por membranas, como a nanofiltração. No entanto, esses processos estão sujeitos ao fenômeno de incrustação, que provoca diminuição gradativa de sua eficiência. Sendo assim, o presente trabalho visou à avaliação de diferentes métodos de pré-tratamento de água para mitigação da formação de biofilme em membranas de nanofiltração. Os processos de adsorção em partículas de alumina e desinfecção por meio de carvão ativado impregnado com nanopartículas de prata foram aplicados em uma amostra de um corpo d'água superficial. As amostras com e sem pré-tratamento foram nanofiltradas e a propensão à incrustação de cada uma foi avaliada. As eficiências de remoção de compostos orgânicos dos adsorventes empregados separadamente e em conjunto e as análises de absorção UV/Vis, microscópio eletrônico de varredura e espectroscopia de energia dispersiva do carvão ativado impregnado com nanopartículas de prata mostraram que os materiais empregados no pré-tratamento puderam ser apropriadamente sintetizados. Foi possível também identificar os principais grupos funcionais dos biopolímeros presentes nos biofilmes formados ao longo do tempo. Por fim, pôde-se observar que a adsorção da matéria orgânica é mais eficiente para o controle da incrustação rápida, enquanto o efeito bactericida se destaca no controle a longo prazo.

ABSTRACT The poor geographical distribution of water in the national territory combined with its waste, the pollution of watercourses close to urban and industrial centers, and the inadequate efficiency of conventional treatment processes make the treatment and reuse of water topics of increasing importance in Brazil. One of the advanced water treatment methods is membrane separation processes, such as nanofiltration. However, these processes are subject to fouling phenomenon, which causes a gradual decrease in the efficiency of the process. Therefore, the present work aims to evaluate different methods of pretreatment of water to mitigate the formation of biofilm in nanofiltration membranes. The adsorption processes on alumina particles and disinfection through activated carbon impregnated with silver nanoparticles were applied to a sample of a surface water body. Samples with and without pretreatment were nanofiltered and the propensity to fouling was evaluated. The efficiency of the adsorbents, used both separately and together, in removing organic compounds and the UV/Vis, scanning electron microscope, and Energy-dispersive X-ray spectroscopy analyses of the activated carbon impregnated with silver nanoparticles showed that the materials used in the pre-treatment were properly synthesized. It was also possible to identify the main functional groups of the biopolymers present in biofilms formed over time. Finally, it was observed that the adsorption of organic matter is more efficient for the control of rapid fouling while the bactericidal effect stands out in the long-term fouling control.

The Effect of pH on Atenolol/Nanofiltration Membranes Affinity.

Nanofiltration has been shown to be effective in removing pharmaceutical compounds from water and wastewater, so different mechanisms can influence treatment performance. In the present work, we carried out a case study evaluating the performance of two nanofiltration membranes in the removal of Atenolol (ATN)-a pharmaceutical compound widely used for the treatment of arterial hypertension-under different conditions such as operating pressure, ATN concentration, and solution pH. By determining the B parameter, which quantifies the solute/membrane affinity, we verified that the solution pH influenced the performance of the membranes, promoting attraction or repulsion between the ATN and the membranes. At pH 2.5, both membranes and ATN were positively charged, causing electrostatic repulsion, showing lower values of the B parameter and, consequently, higher ATN rejections. At such a pH, the mean ATN rejection for the loose membrane (NF270) was 82%, while for the tight membrane (NF90) it was 88%. On the other hand, at 12 bar pressure, the NF70 membrane (5.1 × 10 -5 m s-1) presented mean permeate fluxes about 2.8 times greater than the NF90 membrane (1.8 × 10-5 m s-1), indicating that NF270 is the most suitable membrane for this application.

Preparation of Thin-Film Composite Nanofiltration Membranes Doped with N- and Cl-Functionalized Graphene Oxide for Water Desalination.

In the present work, chemically modified graphene oxide (GO) was incorporated as a crosslinking agent into thin-film composite (TFC) nanofiltration (NF) membranes for water desalination applications, which were prepared by the interfacial polymerization (IP) method, where the monomers were piperazine (PIP) and trimesoyl chloride (TMC). GO was functionalized with monomer-containing groups to promote covalent interactions with the polymeric film. The composite GO/polyamide (PA) was prepared by incorporating amine and acyl chloride groups into the structure of GO and then adding these chemical modified nanomaterial during IP. The effect of functionalized GO on membrane properties and performance was investigated. Chemical composition and surface morphology of the prepared GO and membranes were analyzed by thermogravimetric analysis (TGA), Raman spectroscopy, FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The fabricated composite membranes exhibited a significant increase in permeance (from 1.12 to 1.93 L m-2 h-1 bar-1) and salt rejection for Na2SO4 (from 95.9 to 98.9%) and NaCl (from 46.2 to 61.7%) at 2000 ppm, when compared to non-modified membranes. The amine- and acyl chloride-functionalized GO showed improved dispersibility in the respective phase.

A Sustainable Recycling Alternative: Electrospun PET-Membranes for Air Nanofiltration.

Currently, the inappropriate disposal of plastic materials, such as polyethylene terephthalate (PET) wastes, is a major environmental problem since it can cause serious damage to the environment and contribute to the proliferation of pathogenic microorganisms. To reduce this accumulation, PET-type bottles have been recycled, and also explored in other applications such as the development of membranes. Thus, this research aims to develop electrospun microfiber membranes from PET wastes and evaluate their use as an air filter media. The solution concentrations varied from 20 to 12% wt% of PET wastes, which caused a reduction of the average fiber diameter by 60% (from 3.25 µm to 1.27 µm). The electrospun filter membranes showed high mechanical resistance (4 MPa), adequate permeability (4.4 × 10-8 m2), high porosity (96%), and provided a high collection efficiency (about 100%) and low-pressure drop (212 Pa, whose face velocity was 4.8 cm/s) for the removal of viable aerosol nanoparticles. It can include bacteria, fungi, and also viruses, mainly SARS-CoV-2 (about 100 nm). Therefore, the developed electrospun membranes can be applied as indoor air filters, where extremely clean air is needed (e.g., hospitals, clean zones of pharmaceutical and food industry, aircraft, among others).

A survey on experiences in leachate treatment: Common practices, differences worldwide and future perspectives.

The necessity for landfill leachate treatment is a requisite to reduce the environmental impact related to municipal solid waste landfills and different aspects must be considered while deciding for an appropriate treatment process. For example, it was demonstrated that the landfill leachate stabilization in tropical regions is achieved right after its first year of operation, requiring technologies capable of treating leachates of a higher recalcitrant character if compared to those leachates from temperate regions and same landfill age. In view of its complexity and variability, stand-alone processes (either biological or physicochemical) are often ineffective in attaining the threshold values for its discharge in receiving bodies. Due to that fact, full-scale facilities have adopted integrated routes, harvesting the benefits of both biological and physicochemical processes. The implementation of membrane bioreactors followed by polishing membrane separation process (nanofiltration and reverse osmosis) seems to be a trend in leachate treatment by full-scale treatment plants. This technology is widely employed in China, European countries, and tropical countries as Brazil, generally with a treatment cost lower than the costs related to its disposal in domestic effluent collection systems. From the technologies already employed by full-scale facilities, four integrated routes were proposed for a sensitive analysis considering the treatment of a landfill leachate of different physicochemical characteristics. From all routes, those employing the membrane separation process as a polishing step had a better efficacy in attaining the threshold values for leachate disposal, being that an interesting alternative for leachate polishing by full-scale facilities.

Recovery of Anthocyanins and Monosaccharides from Grape Marc Extract by Nanofiltration Membranes.

Wastewaters and by-products generated in the winemaking process are important and inexpensive sources of value-added compounds that can be potentially reused for the development of new products of commercial interest (i.e., functional foods). This research was undertaken in order to evaluate the potential of nanofiltration (NF) membranes in the recovery of anthocyanins and monosaccharides from a clarified Carménère grape marc obtained through a combination of ultrasound-assisted extraction and microfiltration. Three different flat-sheet nanofiltration (NF) membranes, covering the range of molecular weight cut-off (MWCO) from 150 to 800 Da, were evaluated for their productivity as well as for their rejection towards anthocyanins (malvidin-3-O-glucoside, malvidin 3-(acetyl)-glucoside, and malvidin 3-(coumaroyl)-glucoside) and sugars (glucose and fructose) in selected operating conditions. The selected membranes showed differences in their performance in terms of permeate flux and rejection of target compounds. The NFX membrane, with the lowest MWCO (150-300 Da), showed a lower flux decay in comparison to the other investigated membranes. All the membranes showed rejection higher than 99.42% for the quantified anthocyanins. Regarding sugars rejection, the NFX membrane showed the highest rejection for glucose and fructose (100 and 92.60%, respectively), whereas the NFW membrane (MWCO 300-500 Da) was the one with the lowest rejection for these compounds (80.57 and 71.62%, respectively). As a general trend, the tested membranes did not show a preferential rejection of anthocyanins over sugars. Therefore, all tested membranes were suitable for concentration purposes.

Bond Strength to Microtraction and Nanofiltration Using Ethanol Wet Bonding Technique in Fresh Extracted Teeth: An Ex Vivo Study.

OBJECTIVE: The objective of this study was to evaluate the bond strength to microtraction and nanofiltration using ethanol wet bonding technique in fresh extracted teeth. MATERIALS AND METHODS: This quasi-experimental ex vivo study evaluated 48 teeth that had an indication of premolar extraction due to orthodontic reasons. The protocol of dental preparation and restorative procedure was carried out to evaluate the adhesion resistance by means of the universal testing machine at a loading speed of 0.5 mm/min and 500MPa. To evaluate the nanofiltration, matches were made that were immersed in ammoniac silver nitrate for 24h, and then the specimens impregnated with silver were washed thoroughly in distilled water and placed in a photo-developer solution for 8h under a fluorescent light. All statistical analyses were statistically evaluated with a level of significance P < 0.05. RESULTS: The ethanol technique without premature failure (PF) group had an average of 31.26 ± 10.26MPa, whereas the lowest value was found in the water technique group with PF, which had 22.59 ± 12.27MPa. When performing inferential statistics, it was evidenced that there were statistically significant differences between both techniques with a value of P < 0.05. CONCLUSION: According to the results in both cases, the adhesive strength showed superiority in the ethanol wash group. It determines that this technique presents greater tolerance to the residual presence of water. Finally, in relation to nanofiltration we found that there were no significant differences between the groups evaluated.

Experimental Design as a Tool for Optimizing and Predicting the Nanofiltration Performance by Treating Antibiotic-Containing Wastewater.

In recent years, there has been an increase in studies regarding nanofiltration-based processes for removing antibiotics and other pharmaceutical compounds from water and wastewater. In this work, a 2k factorial design with five control factors (antibiotic molecular weight and concentration, nanofiltration (NF) membrane, feed flow rate, and transmembrane pressure) was employed to optimize the NF performance on the treatment of antibiotic-containing wastewater. The resulting multiple linear regression model was used to predict the antibiotic rejections and permeate fluxes. Additional experiments, using the same membranes and the same antibiotics, but under different conditions of transmembrane pressure, feed flow rate, and antibiotic concentration regarding the 2k factorial design were carried out to validate the model developed. The model was also evaluated as a tertiary treatment of urban wastewater for removing sulfamethoxazole and norfloxacin. Considering all the conditions investigated, the tightest membrane (NF97) showed higher antibiotics rejection (>97%) and lower permeate fluxes. On the contrary, the loose NF270 membrane presented lower rejections to sulfamethoxazole, the smallest antibiotic, varying from 65% to 97%, and permeate fluxes that were about three-fold higher than the NF97 membrane. The good agreement between predicted and experimental values (R2 > 0.97) makes the model developed in the present work a tool to predict the NF performance when treating antibiotic-containing wastewater.

Nanofiltration applied to the landfill leachate treatment and preliminary cost estimation.

The leachate treatment by nanofiltration (NF) process has received much attention over the last two decades. Previous studies focused on the investigation of the technical feasibility of NF. However, there are a limited number of works that examined leachate treatment costs. On the other hand, in a landfill management system, the economic component is an imperative factor for the decisions of all operations. Thereby, this work aimed to investigate the technical feasibility and economic parameters involved in a full-scale NF plant for the treatment of leachate previously treated by the physicochemical process. The average quality of the pre-treated leachate was 2258 ± 230 mg L-1 chemical oxygen demand (COD) and 821 ± 86 mg L-1 humic substances (HS). NF was performed using a bench-scale filtration module with commercial polymeric membranes SR100 and NP030. At the end of each filtration, a cleaning protocol was applied to recover the initial membrane permeability. The concentration of recalcitrant compounds, expressed as HS, was reduced to 84 ± 8 mg L-1 in the permeate, and COD complies with the wastewater discharge standards imposed by local legislation. The capital costs for a full-scale NF was estimated at MUS$ 0.772, and specific total cost, treated leachate per volume unit, has been estimated at US$ 8.26 m-3.

Separation of microbial oil produced by Mortierella isabellina using polymeric membranes.

The objective of this work was to concentrate, through a membrane separation process, the fatty acids from oil/solvent mixture. The oil was obtained by ultrasound-assisted extraction from freeze-dried cells of Mortierella isabellina. The concentration of the fatty acids was investigated using flat-sheet polymer membranes of ultrafiltration and nanofiltration. The effects of temperature and pressure were evaluated by the retention of the fatty acids. Oil retentions between 45.23 and 58.20% to ultrafiltration membrane and 43.50 and 56.00% to nanofiltration membrane were observed. The best condition for the ultrafiltration membrane was 4 bar and 40 °C and for nanofiltration membrane was 12 bar and 50 °C. The oil contains a high concentration of oleic acid and palmitic acid that is a desirable property for the biodiesel production. The results showed the applicability of this technology in the solvent recovery step whereas the oil recovered contains a high concentration of fatty acids.

Comparative study of nanofiltration and ion exchange for nitrate reduction in the presence of chloride and iron in groundwater.

Public concern on the groundwater contamination by nitrate has grown significantly in recent years. The objective of this study was to determine the appropriate treatment to reduce the nitrate content in the presence of other ions from groundwater, for which nanofiltration and ion exchange were evaluated. In nanofiltration, the effects of pressure, feed flow, initial composition, and performance were studied, in ion exchange the flow rate, initial composition, and resin regeneration process. Nanofiltration tests were carried out on four different commercial membranes: NF97, NF99, NF99H, and NF90. Among these, all membranes removed chloride but only NF97 and NF90 were able to remove nitrate in compliance with Chilean drinking water standard, showing rejections of 97% and 87%, respectively, in an optimum pressure range of 12-20 bar in which the NF90 produced 3.5 times more permeated water than NF97. For ion exchange tests, Purolite A520E resin was used, which decreased nitrate content to <1 mg/L. Results leading to the optimal flow within the exchange column indicated that residence time must be at least 2.1 min. The higher nitrate concentration in water did not lead to changes in the maximum resin capacity, 47.1 mg NO3-/g resin, but it did decrease the resin breakthrough capacity when initial concentration increased. Optimal regeneration was assigned to a 3% w/V NaCl solution and up-flow mode. Due to the ability to remove both nitrate and chloride, and being able to remove iron if necessary, nanofiltration was chosen as the appropriate treatment.

Combinação de processos com membranas para remoção de sulfato da água do mar para injeção em reservatórios de petróleo / Combination of membrane processes for desulfation of seawater used for injection in oilfields

RESUMO Água do mar é comumente utilizada como fluido de injeção em plataformas offshore na recuperação secundária do petróleo. Porém, a presença de sulfato causa diversos inconvenientes, como a formação de precipitados, que podem se depositar em diversas partes da plataforma de produção. Atualmente, a dessulfatação é realizada em unidades removedoras de sulfato (URS) por processo de nanofiltração (NF), cujas amostras precisam ser pré-tratadas, usualmente em filtros cartuchos. Os sólidos suspensos e os microrganismos que não foram retidos pelo sistema de filtração podem depositar sobre a superfície das membranas de NF, diminuindo a produtividade do sistema e reduzindo o tempo de vida das membranas. O processo de microfiltração (MF) pode ser utilizado como pré-tratamento alternativo e possibilitaria a remoção desses elementos. Neste estudo, foi desenvolvido um processo combinado de MF e NF para a dessulfatação da água do mar, visando a sua injeção em reservatórios de petróleo. Módulos de permeação contendo membranas de poli(imida) no formato de fibras ocas foram utilizados na construção de um sistema piloto de MF integrado a um sistema piloto de NF similar aos já atualmente utilizados nas plataformas. O desempenho dos sistemas foi avaliado por meio do acompanhamento da permeabilidade de ambos durante a filtração da água do mar. Parâmetros como grau de recuperação de água, frequência e eficiência de procedimentos de retrolavagem e limpeza química também foram estudados. Os resultados demonstraram que o pré-tratamento da água do mar por MF é uma alternativa eficaz para a dessulfatação por NF.

ABSTRACT Seawater is commonly used in offshore platforms as an injection fluid in secondary oil recovery. However, the sulfate found in seawater has been the cause of many inconveniences, such as the formation of precipitates, which can settle in various parts of the production platform. Nowadays, nanofiltration (NF) is used in sulfate removal units for seawater desulfation, where cartridge filters are commonly used for seawater pretreatment. Suspended solids and microorganisms that have not been retained by the filtration system may deposit on the surface of NF membranes, decreasing system productivity and reducing membrane life. The microfiltration (MF) process can be used as an alternative pretreatment and would allow the removal of these elements. In this study, a combined process of MF and NF for seawater desulfation was developed for injection into oil reservoirs. Permeation modules containing hollow fiber shaped poly (imide) membranes were used in the construction of an MF pilot system, integrated with an NF pilot system similar to those already used on platforms. The performance of the systems was evaluated by monitoring the permeability of both during seawater filtration. Parameters such as degree of water recovery, frequency, and efficiency of backwash procedures and chemical cleaning were also studied. The results showed that MF seawater pretreatment is an effective alternative for NF desulfation.

Bench and pilot scale performance assessment of recycled membrane converted from old nanofiltration membranes.

Recycling of end-of-life polyamide-based thin film composite (TFC) membranes is gaining interest in academic and industrial contexts. The effects of chlorine exposure on the performance of polyamide membranes result in an increase in membrane permeability, whereas the solute rejection decreases. Therefore, the controlled chemical conversion of old reverse osmosis (RO) membranes has been reported by some previous papers. The objectives of this study were to assess recycling of old nanofiltration (NF) membrane, to assess the performance of the recycled membranes for a river water treatment application, and to conduct preliminary cost evaluations. Recycling technique consisted of exposing the membrane to a sodium hypochlorite solution in order to remove its polyamide layer and conversion to a low-pressure membrane. The work conducted bench scale and long-time pilot tests, and the recycled membranes showed a low fouling tendency. The difference between some results in bench- and pilot scale underscores the importance of evaluating design parameters using pilot scale units. Based on the cost analysis, the total cost of chemical recycling end-of-line NF membranes for a river water treatment is approximately 1.1% of the cost of using a new UF membrane. There is a great potential in using recycled membranes for rivers water treatments.