Reverse Osmosis Water Treatment Research Articles

Molecular Dynamics Insights into Water Transport Mechanisms in Polyamide Membranes: Influence of Cross-Linking Degree.

Polyamide (PA) membranes are widely utilized in desalination and water treatment applications, yet the mechanisms underlying water transport within these amorphous polymer materials remain insufficiently understood. To gain more insight into these problems on a microscopic scale, we employ molecular dynamics (MD) simulations to analyze the relationship between the structural properties and the water permeation behavior of PA membranes. Two distinct atomistic models of PA membranes are developed by controlling their degrees of cross-linking (DC). We then conducted a comparative analysis on their microscopic structural properties and configurations of water inside the membranes and investigated how these differences lead to different water diffusion coefficients. Our results reveal that the membrane with a lower DC exhibits higher polymer mobility and a more orderly microscopic structure, allowing the formation of pores that can hold larger water clusters as well as more transient passages between pores, both contributing to an increased water diffusion coefficient. From these observations, we can conclude that water permeability within PA membranes is governed by both the morphology of semirigid pores and the oscillatory movements of the polymer chains. Overall, these findings contribute to a deeper understanding of the intricate mechanisms governing water permeation in PA membranes and may inform the design of more efficient membranes for reverse osmosis and other water treatment technologies.

Interfacial Polymerization of Aromatic Polyamide Reverse Osmosis Membranes.

Polyamide membranes are widely used in reverse osmosis (RO) water treatment, yet the mechanism of interfacial polymerization during membrane formation is not fully understood. In this work, we perform atomistic molecular dynamics simulations to explore the cross-linking of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) monomers at the aqueous-organic interface. Our studies show that the solution interface provides a function of "concentration and dispersion" of monomers for cross-linking. The process starts with rapid cross-linking, followed by slower kinetics. Initially, amphiphilic MPD monomers diffuse in water and accumulate at the solution interface to interact with TMC monomers from the organic phase. As cross-linking progresses, a precross-linked thin film forms, reducing monomer diffusion and reaction rates. However, the structural flexibility of the amphiphilic film, influenced by interfacial fluctuations and mixed interactions with water and the organic solvent at the solution interface, promotes further cross-linking. The solubility of MPD and TMC monomers in different organic solvents (cyclohexane versus n-hexane) affects the cross-linking rate and surface homogeneity, leading to slight variations in the structure and size distribution of subnanopores. Our study of the interfacial polymerization process in explicit solvents is essential for understanding membrane formation in various solvents, which will be crucial for optimal polyamide membrane design.

Graphene Oxide Surface Modification of Reverse Osmosis (RO) Membrane via Langmuir-Blodgett Technique: Balancing Performance and Antifouling Properties.

The reverse osmosis water treatment process is prone to fouling issues, prompting the exploration of various membrane modification techniques to address this challenge. The primary objective of this study was to develop a precise method for modifying the surface of reverse osmosis membranes to enhance their antifouling properties. The Langmuir-Blodgett technique was employed to transfer aminated graphene oxide films assembled at the air-liquid interface, under specific surface pressure conditions, to the polyamide surface with pre-activated carboxylic groups. The microstructure and distribution of graphene oxide along the modified membrane were characterized using SEM, AFM, and Raman mapping techniques. Modification carried out at the optimal surface pressure value improved the membrane hydrophilicity and reduced the surface roughness, thereby enhancing the antifouling properties against colloidal fouling. The flux recovery ratio after modification increased from 65% to 87%, maintaining high permeability. The modified membranes exhibited superior performance compared to the unmodified membranes during long-term fouling tests. This membrane modification technique can be easily scaled using the roll-to-roll approach and requires minimal consumption of the modifier used.

Development of Sustainable Dust Compression System for Coal Yard Safety

A sustainable water mist spray system for a closed coal yard. The project aims to address the need for dust suppression in the coal yard to mitigate environmental and health risks. The design specifications will be determined by considering the coal yard's size, layout, and specific requirements. The system will utilize a pneumatic air vane motor powered by residual dry steam from the plant's operation and, coupled with a fan for effective mist dispersion. Ro Reject water, a byproduct of reverse osmosis water treatment, will be used as the water source. The project will involve collaboration with mechanical engineering, fluid dynamics, and environmental studies to develop an optimized system design. Field tests will be conducted to validate the system's functionality, mist spray effectiveness, and coverage area. Safety features will be installed to ensure operator protection, and training programs will be developed to educate operators on safe system operation. The effectiveness of the mist spray system will be evaluated and monitored through regular assessments and data collection. Maintenance activities will be conducted to ensure system functionality, and safety features will be updated as necessary. The successful implementation of this sustainable water mist spray system will contribute to dust suppression, environmental sustainability, and safety in the coal yard.

Economic Feasibility of Reverse Osmosis (RO) Water Treatment Plants: A Case Study from Dimbulagala, Polonnaruwa, Sri Lanka

Social wellbeing is strongly linked with economic feasibility when it needs to attain with the technological advancements. Installation of Reverse Osmosis (RO) water treatment plants have been considered as a promising solution to provide clean water for human consumption, especially in the areas where the CKDu (chronic kidney disease of unknown etiology) prevails. At present, over 2,000 RO treatment plants were installed in the dry zone of Sri Lanka, yet economic feasibility for operation and maintenance of RO plants has not been assessed so far. The present study was intended to identify economic feasibility of operation and maintenance of RO plants. Investigations were carried out in six community RO plants which provided drinking water for over 17,000 people which accounts for 20% of total population in Dimbulagala Divisional Secretariat over a period of 12 months. Six in-depth interviews and questionnaire survey were caried out with RO plant operators. The operational cost per production of cubic meter of filtered water was computed by considering electricity consumption bills. The maintenance costs and service charges were also obtained from the records available with RO plant operators. The results found that the average electricity consumption to produce 1 cube of filtered water is approximately 9kWh and cost is LKR 734 (based on 2021 rates). The average water selling price ranged between LKR 1.00-2.50 per liter. The average monthly income generation from one RO plant is approximately between LKR 561- 875 per cube of filtered water and it largely depended on the type of water source, climatic conditions. It was found that the income generated from RO plants was sufficient enough to cover the operation cost (monthly electricity bill) and for the subsequent maintenance and service charges whenever required. It can be concluded that the use of RO treated water is an economically viable option to provide portable drinking water. 
 Keywords: CKDu, Economic sustainability, Drinking water, Purification cost

Assessment of the quality of freshwater based on the use/non of reverse osmosis water treatment technology in commercial plants in Egypt

Assessment of the quality of freshwater based on the use/non of reverse osmosis water treatment technology in commercial plants in Egypt

Discussion on the Application of Reverse Osmosis Water Treatment Equipment in Industrial Sewage Treatment

Discussion on the Application of Reverse Osmosis Water Treatment Equipment in Industrial Sewage Treatment

Groundwater Quality in the Endemic Areas of Chronic Kidney Disease of Unknown Etiology in Sri Lanka and Its Treatment by Community-Based Reverse Osmosis Water Treatment Plants

Groundwater Quality in the Endemic Areas of Chronic Kidney Disease of Unknown Etiology in Sri Lanka and Its Treatment by Community-Based Reverse Osmosis Water Treatment Plants

New approach of recycling end-of-life reverse osmosis membranes via sonication for microfiltration process

Due to the continuing growth of reverse osmosis (RO) water treatment plants worldwide, the amount of discarded end-of-life (EoL) RO membrane modules is expected to increase drastically in coming years. One of the approaches to address this problem is to transform the EoL membranes for other purposes. In this study, a new approach based on sonication was studied to convert the EoL RO membrane from RO properties into microfiltration (MF) properties, offering a transformation process that was much faster (15 min) than that of typical chemical treatment process (ranging from hours to days) using oxidizing agent solution. Our results indicated that with only 15-min ultrasonication, the properties of EoL RO membrane could be significantly altered, reaching pure water permeability of 172.6 L/m2.h.bar (70-fold increment) with NaCl rejection reduced from ~80% to less than 2%. This is attributed to the deterioration of the polyamide thin selective layer atop the EoL RO membrane. As a comparison, the chemical treatment using 5000-ppm potassium permanganate (KMnO4) solution requires at least 168 h to achieve similar membrane properties. It was also found that the presence of KMnO4 during ultrasonication process could accelerate the rate of polymeric degradation, resulting in even higher pure water permeation. As a conclusion, our work demonstrated a rapid and new approach that is capable of transforming the EoL RO membrane for the filtration process of macromolecules, thus offering a practical solution to address the disposal issues of EoL RO membrane modules.

Assessment of a wastewater stabilization pond system for removal of arsenic, iron, and ammonia from reverse osmosis water treatment plant residual wastewater

Drinking water treatment plants (DWTPs) produce wastewaters with elevated concentrations of heavy metals, metalloids, ammonia, and other contaminants. These wastewaters require treatment via processes including wastewater stabilization ponds (WSPs). This study assessed the arsenic (As), iron (Fe), and ammonia (NH3) concentrations in a Saskatchewan DWTP WSP system of five sequential ponds. Drone imaging combined with flow and depth data was used to estimate retention times which increased from 7–9 to 8–10 days after the DWTP upgrade. Concentration trends showed Fe decreased from Pond 1 to 3 and increased in Ponds 3 and 5, while As decreased from Pond 1 to 5. Average effluent As concentrations of 10.6 µg/L were above the 5.0 µg/L guideline, while concentration guidelines for both Fe and NH3 were easily met post-upgrade in 2020. Several actions are recommended to ensure adequate WSP operation including dredging, aeration, and installing macrophytes capable of As uptake.

Investigating reverse osmosis membrane fouling and scaling by membrane autopsy of a bench scale device

ABSTRACT In response to the escalating world water demand and aiming to promote equal opportunities, reverse osmosis desalination has been widely implemented. Desalination is however constantly subjected to fouling and scaling which increase the cost of desalination by increasing the differential pressure of the membrane and reducing the permeate flux. A bench-scale desalination equipment has been used in this research to investigate the mitigation of fouling and scaling. This study involved the performance of membrane autopsy for fouling characterisation with special attention to flux decline due to sulphate precipitation and biofouling. Visual inspection, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and microbiology tests (API) were performed. Results obtained showed the presence of diatoms, pseudomonas and polysaccharides as the main foulants causing biofouling. Analysis revealed sulphate deposits as well as aluminium, calcium and silica as the main elements contributing to inorganic scaling. Findings pointed out that the pre-treatment system of the small-scale reverse osmosis water treatment was inefficient and that selection of pre-treatment chemicals should be based on its compatibility with the membrane structure. The importance of characterisation for the verification of fouling mechanisms is emphasised.

Design and application of purified water preparation device for chemical analysis

Qualified purified water is essential for all chemical analysis. Spectral analysis, trace analysis and general chemical analysis require different purity of water. This paper introduces a kind of purified water preparation device which can be widely used in all chemical analysis work. The purified water preparation device consists of two-stage reverse osmosis device and water treatment device of ion exchange system. The two-stage reverse osmosis water treatment unit can be operated in two modes: program-controlled and manual mode, and the water production rate is about 80%. The ion exchange water treatment unit consists of two cation exchangers, two cation exchangers and one mixed ion exchanger, which can prepare silicon free water and sodium free water and meet the requirements of trace analysis. The ion exchange water treatment unit is equipped with independent purified water pipeline system and regenerated liquid pipeline system to avoid the pollution of purified water. The regeneration operation of ion exchange resin is simple, and the discontinuous water production can be easily realized. This set of purified water preparation device can adapt to various water sources to complete purification treatment, and produce purified water meeting various chemical analysis.

Groundwater quality change impacts on a brackish-water reverse osmosis water treatment plant design: the City of Clearwater, Florida

Groundwater quality change impacts on a brackish-water reverse osmosis water treatment plant design: the City of Clearwater, Florida

НОВЫЙ ИМПОРТОЗАМЕЩАЮЩИЙ АНТИСКАЛАНТ ДЛЯ МЕМБРАННЫХ СИСТЕМ ОПРЕСНЕНИЯ ВОДЫ

The paper deals with a new import-substituting antiscalant to protect reverse osmosis membranes of water desalination systems in Uzbekistan. The studies show that during the purification of natural brackish waters typical for Uzbekistan, the reverse osmosis membrane is contaminated by mineral salts and colloidal particles, which leads to the reduction of the membrane capacity and service life of expensive reverse osmosis water treatment systems. The developed import-substituting antiscalant has proved to prevent the sedimentation process on membranes, and to have technical specifications almost identical to its more expensive foreign analogues. Since 2020 water desalination systems using the new antiscalant have been widely used in Uzbekistan to provide the population of the Republic with high-quality drinking water.

Development of a quorum quenching-column to control biofouling in reverse osmosis water treatment processes

Biofouling is recognized as one of the most problematic fouling types in reverse osmosis (RO) processes and lead to high energy requirements and operating costs. Over the past decade, many studies on membrane bioreactor (MBR) systems for wastewater applications demonstrated that disrupting cell-cell communications among bacteria, called quorum quenching (QQ), is a promising approach to inhibit biofouling of membranes. Here, we developed the QQ-column as a novel strategy to control biofouling in RO systems. The QQ-column was prepared by incorporating a recombinant bacterial QQ strain into hydrogel beads and embedding these beads inside a column. The QQ-column was installed upstream of the RO module to degrade N-acyl homoserine lactone, a quorum sensing (QS) signal, from the feed in a laboratory-scale RO system operating in total recycle mode. The QQ-column reduced the concentrations of signal molecules by ∼29% in an RO system and mitigated biofilm formation (38.6% reduction of cell number) on the membrane, consequently reducing the transmembrane pressure by 50.1%. These results demonstrate that integrating QQ bacteria into columns is a practical method to control biofouling in RO systems.

Repurposing Reverse Osmosis Concentrate as a Low-Cost Thermal Energy Storage Medium

The reject of the reverse osmosis water treatment process (aka brine, concentrate, ROC) is a mixture of salts that are dissolved in high salinity water. The ROC is classified as an industrial waste by the U.S. Environmental Protection Agency and can face regulatory limitations on disposal. State-of-the-art of ROC disposal includes deep-well injection, surface discharge to rivers, discharge to the ocean, and evaporation ponds. In this study, the feasibility of using Reverse Osmosis Concentrate as a low-cost Thermal Energy Storage (TES) medium is explored by a techno-economic analysis. The normalized cost of TES (cost per unit volume of stored thermal energy) is estimated through a series of cost analyses and is compared to the cost targets of the U.S. Department of Energy for low-cost thermal energy storage. It was shown that the normalized cost of TES using ROC salt content is in the range of $6.11 to $8.73 depending on ROC processing methods.

Evaluation of groundwater quality and reverse osmosis water treatment plants in the endemic areas of Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka

Community-based reverse osmosis (RO) water treatment plants are employed as an interim solution for producing safe drinking water for the endemic areas of Chronic Kidney Disease of Unknown Etiology (CKDu) in the rural dry zone of Sri Lanka. It is recognized that RO-treated groundwater diminishes the progression of CKDu; thus, proper maintenance of these RO plants would be indispensable to protect public health. The present study broadly investigated the quality of groundwater in CKDu-endemic areas, and the performance, operations, and maintenance of the RO plants which purified this groundwater. The feedwater (i.e., groundwater) and treated water from 32 RO plants in Anuradhapura District, comprising 27 in the CKDu high-risk (HR) region and 5 in the low-risk (LR) region, were analyzed for major chemical and biological water quality parameters. Alkalinity, hardness, and microbiological parameters in groundwaters exceeded the maximum allowable levels (MALs) for drinking in all study areas. Additionally, TDS and magnesium exceeded the MALs, exclusively in the HR areas. Elevated occurrence of magnesium-predominant hardness and ionicity in groundwater showed significant relations with the incidence of CKDu. All RO plants achieved high removal rates (>95%) for excessive chemical constituents in groundwater, but the recovery rates were fairly low (~46%). The current disinfection practices in RO plants were insufficient to ensure the microbial safety of the product water. Low demand for product water, scarcity of groundwater, lack of technical capacity of the local communities, poor maintenance practices and unplanned brine removal were the key issues related to RO plant O&M. Unless properly handled, the lack of rules and regulations for RO water treatment in the CKDu-endemic region could lead to numerous environmental and public health issues in the future.

Evaluating the Efficacy of Point-of-Use Water Treatment Systems Using the Water Quality Index in Rural Southwest China

Rural China faces a shortage of safe drinking water. There are significant challenges associated with small centralized water supply systems and decentralized water supply systems. Many rural residents use point-of-use water treatment systems to ensure the safety of their drinking water. The actual water purification effect and applicability of these water treatment systems in small centralized and decentralized water supply systems need to be determined urgently. In this study, the water quality index (WQI) method was applied for the first time in rural areas to evaluate the effectiveness of point-of-use water treatment systems. A total of 67 reverse osmosis water treatment systems were tested. The rate of compliance with drinking water standards of the decentralized water supply was low (37%). Compared with untreated water, the use of a reverse osmosis water treatment system improved the rate of compliance with drinking water standards, but this effect was not satisfactory (8%). Among the factors potentially affecting the purified water quality of point-of-use water treatment systems (e.g., service time of the water treatment system, service time of the filter element, and type of water source), the service time of the filter element had the most significant influence on the water quality. If the filter element had not been replaced for a long period, the removal effect of the water treatment system on the total hardness, sulfide, copper, and ammonia nitrogen was significantly affected, reducing the quality of the purified water. To ensure the safety of drinking water, it is recommended to replace the filter element of a reverse osmosis water treatment system at least once a year.

Morphology of Thin Film Composite Membranes Explored by Small-Angle Neutron Scattering and Positron-Annihilation Lifetime Spectroscopy.

The morphology of thin film composite (TFC) membranes used in reverse osmosis (RO) and nanofiltration (NF) water treatment was explored with small-angle neutron scattering (SANS) and positron-annihilation lifetime spectroscopy (PALS). The combination of both methods allowed the characterization of the bulk porous structure from a few Å to µm in radius. PALS shows pores of ~4.5 Å average radius in a surface layer of about 4 μm thickness, which become ~40% smaller at the free surface of the membranes. This observation may correlate with the glass state of the involved polymer. Pores of similar size appear in SANS as closely packed pores of ~6 Å radius distributed with an average distance of ~30 Å. The main effort of SANS was the characterization of the morphology of the porous polysulfone support layer as well as the fibers of the nonwoven fabric layer. Contrast variation using the media H2O/D2O and supercritical CO2 and CD4 identified the polymers of the support layers as well as internal heterogeneities.

DuPont buys another water treatment firm

DuPont has signed an agreement to acquire Desalitech, a Massachusetts-based company that sells closed-circuit reverse osmosis water treatment systems. Desalitech says its approach allows 90–98% water recovery, versus the 75% typical with conventional reverse osmosis systems. DuPont is a major producer of reverse osmosis membranes and ion exchange resins. It struck deals earlier this year to acquire water filtration–membrane businesses from BASF and Evoqua Water Technologies.