A Case Study of Decentralized Off-Grid Water Treatment Using Reverse Osmosis

The present study analyzes the economic viability of an Integrated Energy System (IES) that couples a Reverse Osmosis (RO) water desalination facility with a Nuclear Power Plant (NPP). The case study is conducted in collaboration with Arizona Public Service (APS), the operating owner of the Palo Verde Generating Station (PVGS) NPP. A challenge APS is facing is that their cooling water acquisition contract with the Sub Regional Operating Group (SROG) will expire soon and a renewal can only be done for a significantly higher price of the water. Therefore, APS is seeking alternative sources for their cooling water. One opportunity is to pump brackish water from the regional ground water. Although much less expensive than the water from the new SROG contract, the salinity of the brackish water is so high that a blend of brackish and SROG water will need additional treatment to improve its quality for use in the PVGS cooling towers. A study has been conducted in 2018 at Idaho National Laboratory (INL) to investigate the economics of an PVGS onsite RO desalination plant that would reduce the salinity of a SROG and brackish water blend to an acceptable level. One of the main findings of that study was that the overall economics of water desalination can be greatly improved if, in addition to cooling water for PVGS, potable water could also be produced and sold for profit. In fact, the study concluded that only producing cooling water for PVGS via RO desalination is not economically viable compared to buying all needed cooling water from the SROG. The present report investigates the economic impact of a large, regional RO desalination plant that could provide potable water for the region, considering the conclusions from last year’s scoping study. The study looks in particular at the water-market situation in the West Valley of Phoenix; i.e., in the area of the municipalities of Buckeye, Goodyear, Avondale and Tolleson. In addition to providing potable water for the adjacent municipalities, the concentrate from the regional RO plant would be taken and treated by PVGS to provide some cooling water for a (hopefully) lower cost than that of the SROG water. Furthermore, a cost structure could be put in place for the treatment of the concentrate from the regional RO that would offset some of the water acquisition cost for APS. The analysis used the Nuclear-Renewable Hybrid Energy System (N-R HES) software framework, which was developed at INL in 2016. The framework has reached some level of maturity, such that it can be applied to more than simple demonstration cases; i.e., real industry problems. The analysis in this report considers two cases (for various scenarios): First, the Base Case is the most economic one for APS, as no RO is built, i.e. the case for which cooling water acquisition and treatment cost are lowest. The 2018 INL study showed that some brackish water can be blended with the effluent SROG water without having to build the onsite RO. The Base Case is where APS pumps the maximum volume of less-expensive brackish water (limited by water chemistry in the cooling towers), blends it with the effluent from the SROG, and no RO is built. Second, the proposed RO Case includes two RO plants, one onsite at PVGS and another larger, regional one close to the brackish water wells. The regional RO produces potable water that is sold to the regional municipalities, while the PVGS RO onsite treats (part of) the regional ROs' concentrate and brackish water blend. The desalinated water from the PVGS RO is used in the cooling towers at PVGS. The analysis evaluates the difference in economics, using the Net Present Value (NPV) and Internal Rate of Return (IRR), between the cases. By comparing the two cases, in addition to evaluating the economics of the regional RO, we can also assess the impact of the regional RO on PVGS and consequently APS economics. The study shows that (for the Base Case) to offset the treatment cost for the RO concentrate, the cost of concentrate treatment to be paid by the regional RO to APS would be between 5 – 35 $/m3 of concentrate (depending on the regional RO size envisaged). Correspondingly, the Levelized Cost of Potable Water (LCOPW), which is the average or unit cost, for the regional RO is in the 0.55 – 0.6 $/m3 range of potable water. Or, considering the residential water demand model developed for the Phoenix West Valley, the NPV of the regional RO would be between $20 and 100 billion.

We are continually inundated with news and views about the demand for water outpacing supply. Our unsustainable development along rivers that do not reach the sea, declining ground water levels, damage to wetlands, high costs associated with acquiring new sources of water, and potential shortages related to global climate change are common news items. In most developed economies, there is little or no unallocated fresh water left to exploit. So, the question becomes: Where do we find “new” water for our burgeoning population? The answer may lie in the treatment of both shallow, brackish ground water and postconsumer water. Recent advances in reverse-osmosis membranes have reduced operational costs and established a linear correlation between total dissolved solids and operational cost of desalination; thus, there is increased interest in brackish water as input source. In the Southwest, the El Paso, Texas, Water Utilities Public Service Board recently dedicated a 100 million L/d desalination plant. Surprisingly, Florida with its high rainfall of more than 100 cm a year and many lakes and rivers is commonly thought of as a water-“rich” state; yet it has more water desalination plants than any other state: the city of Tampa Bay has the largest active desalination plant in the United States and uses brackish water from Tampa Bay. It is estimated that the state of New Mexico contains 16,000 billion m3 (13 billion acre-feet) of shallow brackish ground water (total dissolved solids greater than 500 mg/L and less than sea water, which is 35,000 mg/L). I suspect that development of brackish water aquifers would, in general, have less impact on the ecology than development of fresh water aquifers. That being said, we know little about the extent and chemistry of brackish water aquifers and almost nothing about their boundary conditions. Thus, I propose a federal 10-year sunset assessment of 1‰ per 250 gallons on all the ground water that municipalities extract, or about $1.00 each year for the average household using ground water. It is envisioned that this study would quantify the regional hydrology of these aquifers following the USGS’s Regional Aquifer System-Analysis model for fresh water aquifers. It would also identify any potential deeper formations capable of sequestering desalination concentrate. This small investment coupled with reduced consumption from increased rate changes and conservation measures such as low-flush toilets, low-flow showerheads and watering restrictions will prolong our existing resources and give us time to install the necessary infrastructure. We need to wean ourselves from our “once through, throw it out” philosophy that dominates current water resource management. We also need to reframe the linguistic argument away from “sewerage” or “waste water” toward the more societally acceptable “postconsumer” or “surplus municipal water.” (Remember, it is not a “used” car, it is a “previously owned” car!) Cities will soon no longer have the luxury of passing their used municipal water downstream. “Dilution is the solution to pollution” is a dated and unfair concept of passing water quality problems to the aquatic environment and cleanup expenditures to downstream users. Newly engineered membranes in desalination plants are excellent at removing not only salts but also pharmaceuticals, endocrine disruptors, prions, and other undesirable products left untouched by conventional waste treatment facilities. Combining membrane-treated water with aquifer storage and recovery (ASR) offers some interesting water management possibilities. That is, by recharging refreshed water, which is generally of better quality than native ground water, into aquifers, one can control the blending ratio of refreshed to native ground water in producing well fields. Furthermore, the aquifer provides a unique environment to adjust the temperature and chemistry and continue filtering the recharged water, adding insurance against the transport of many undesirable contaminants. Desalination and ASR are, however, energy-intensive processes; thus, greenhouse gas–free energy is likely to be integrated in any future energy scenario. Currently, approximately 28% of all electrical power generated in the United States is greenhouse gas–free (nuclear 19.3%, hydro 6.5%, biofuels 1.6%, wind less than 1%, and solar less than 1%), so these are likely to be the energy sources for desalination. Because both the membrane and the ASR technologies are mature and well established, development of new water from brackish ground water and postconsumer water could be a rapid and straightforward resolution to many of the domestic and industrial demands of our nation’s water resources well into the future.

In recent years, reverse osmosis water desalination has developed rapidly and has become the most competitive and widely used technology in the world. The number of desalination plants is increasing rapidly as freshwater needs increase. Various membrane technologies have been developed and improved, including nanofiltration (NF) and reverse osmosis (RO), whose desalination costs have been relatively reduced. Therefore, this work proposes an experimental study for a small desalination unit based on RO generated by renewable energy, which is mainly suitable for arid regions or desert areas that do not have electricity and water and can be applied for emergency treatment to meet strong freshwater resource needs. In this study, to meet the drinking water demand, a reverse osmosis desalination system is designed and evaluated in order to improve and optimize its operation. This system has a daily capacity of 2 m3. We used brackish groundwater, which has been characterized as reference water, to produce synthetic water for different salinities until seawater. The analysis is based on data obtained from experiments carried out in the standalone RO pilot designed for the production of fresh water. For this purpose, we conducted relevant experiments to examine the influence of applied pressure, salt concentration and temperature on the RO membrane performance. The effects of different factors that affect the energy consumption in the RO desalination process were analyzed, and those with significant influence were explored. The effectiveness of RO desalination coupled with a photovoltaic (PV) energy system is shown. We found the recovery rate for system operation to be 32%. An optimization study is presented for the operation of an autonomous RO desalination system powered by photovoltaic panels. The energy produced by the PV system was used to feed two pumps forthe production of drinking waterwithanRO membrane, under the conditions of the town of Bou-Ismail. As results, a 3 kWp PV system was installed based on the energy demand. The design data have shown that a 3 kWp PV system can power a 1.8 W RO load given the Bou-Ismail climate. Energy consumption in the case study under Bou-Ismail weather conditions were analyzed. The desalination of brackish water at a TDS value of 5 g/L requires an energy of about 1.5 kWh/m3. Using seawater at a TDS value of 35 g/L, this value increases to 5.6 kWh/m3. The results showed that the optimal recovery rate for system operation was determined to be 32% for a feedwater salinity of 35 g/L, and 80% for a feedwater salinity of 1 g/L.

Desalination of brackish water by nanofiltration and reverse osmosis

In recent years, the increasing threat to ground water quality due to human activities has become a matter of great concern. The ground water quality problems present today are caused by contamination and by over exploitation or by combination of both. Reverse osmosis (RO) desalination is one of the main technologies for producing fresh water from sea water and brackish ground water. Algeria is one of the countries which suffer from the water shortage since many years, so desalination technology becomes inevitable solution to this matter. In this study, a comparison is provided of results of reverse osmosis desalination for three different qualities of brackish water from the central-east region of Algeria (Bouira and Setif Prefectures), wherein they cannot use it as human drinking or in irrigation systems. The main objective of our study is to establish a comparison of the reverse osmosis membrane TW30-2540 performances in the term of (permeate flow, recovery rate, permeate total dissolved solids – TDS and salts rejection) under different operation pressures (each one takes a time of 720 second for pilot scaling). In order to make an overview comparison between the experimental and the simulated results we used ROSA (Reverse Osmosis System Analysis) software. At the end of this study we noted that, the simulated results are lower than the pilot scaling values and the most removed salts are the sodium chlorides with 99.05% of rejection rate.

In the past few years, the commercialization of small scale reverse osmosis (RO) plant for low total dissolved solids (TDS) brackish and contaminated groundwater water desalination offered an alternative solution to obtain drinking water with TDS lower than 500 mg/L. Due to rapid development in membrane technology the technical and economical usefulness of RO process has been improved. In the current research work, a prototype Reverse Osmosis (RO) wastewater treatmentplant has been developed and its performance was evaluated to produce the safe and drinkable water at local small community.Salt rejection and ermeatewater flowrate are the key performance parameters. These performance parameters are influenced by other variable parameters such as applied feed pressure, temperature, recovery and feed water salinity.The RO plant performance has been evaluated through testing different water quality parameters; including physical, chemical and biological analysis of the treated sample. The plant was operated by varying feed water pressures and feed water salinity which indicated that the product water has the highest quality and maximum permeateflow rate at 25 bar of applied feed water pressure for feed water salinity upto 4000 mg/L. The water quality results indicate that permeate obtained after treatment has excellent quality free physical and microbial contaminants.

Industrial and brackish water treatment with closed circuit reverse osmosis

With dwindling water supplies and the impacts of climate change, many cities are turning to water sources previously considered unusable. One such source for inland cities is brackish groundwater. With prolonged drought throughout Texas, cities such as El Paso, Lubbock, and San Antonio are desalinating brackish groundwater to supplement existing water sources. Similar projects are under consideration elsewhere in Texas. While brackish groundwater contains fewer total dissolved solids than seawater, desalination of brackish groundwater is still an energy-intensive process. Brackish water desalination using reverse osmosis, the most common desalination membrane treatment process, consumes 20 to 40 times more energy than traditional surface water treatment using local water sources. This additional energy consumption leads to increased carbon emissions when using fossil fuel-generated electricity. As a result of concern over greenhouse gas emissions from additional energy consumption, some desalination plants are powered by wind-generated electricity. West Texas is a prime area for desalination of brackish groundwater using wind power, since both wind and brackish groundwater resources are abundant in the area. Most of the Texas Panhandle and Plains region has wind resource potential classified as Class 3 or higher. Additionally, brackish groundwater is found at depths less than 150 m in most of west Texas. This combination of wind and brackish groundwater resources presents opportunities for the production of alternative drinking water supplies without severe carbon emissions. Additionally, since membrane treatment is not required to operate continuously, desalination matches well with variable wind power. Implementing a brackish groundwater desalination project using wind-generated electricity requires economic feasibility, in addition to the geographic availability of the two resources. Using capital and operating cost data for wind turbines and desalination membranes, we conducted a thermoeconomic analysis for three parameters: 1) transmission and transport, 2) geographic proximity, and 3) aquifer volume. Our first parameter analyzes the cost effectiveness of tradeoffs between building infrastructure to transmit wind-generated electricity to the desalination facility versus pipelines to transport brackish groundwater to the wind turbines. Secondly, we estimate the maximum distance between the wind turbines and brackish groundwater at which desalination using wind power remains economically feasible. Finally, we estimate the minimum available brackish aquifer volume necessary to make such a project profitable. Our analysis illustrates a potential drinking water option for Texas (and other parts of the world with similar conditions) using renewable energy to treat previously unusable water. Harnessing these two resources in an economically efficient manner may help reduce future strain on the energy-water nexus.

Transparent exopolymer particles: Potential agents for organic fouling and biofilm formation in desalination and water treatment plants

As sensitive parts of the water treatment process, reverse osmosis (RO) membranes are the most important for desalination and wastewater treatment. But the performance of RO membranes deteriorates over time due to fouling, necessitating frequent replacements. One of the environmental challenges is the disposal of End-of-Life (EoL) RO membranes, which are made of non-biodegradable polymers. The reuse of EoL membranes as a sustainable approach for waste saving and resource efficiency has recently attracted considerable attention. The present work provides a comprehensive overview of the strategies for reusing EoL RO membranes as sustainable alternatives to conventional disposal methods. Furthermore, the fundamental principles of RO technology, the primary types and impacts of membrane fouling, and advanced cleaning and regeneration techniques are discussed. The conversion of EoL membranes into nanofiltration (NF), ultrafiltration (UF), and forward osmosis (FO) membranes is also covered in this review, as well as their uses in brackish water desalination, dye/salt separation, groundwater treatment, and household wastewater reuse. Environmental and economic benefits, as well as technical, social, and regulatory challenges, are also discussed. Finally, the review highlights innovative approaches and future directions for incorporating EoL membrane reuse into circular economy models, outlining its potential to improve sustainability and reduce operational costs in water treatment systems.

Sea and ocean Reverse Osmosis (RO) desalination plants are often designed to remove more than 90% of dissolved ingredients (organic and inorganic) from feed water, thus creating a permeate water that is potable. Typically 40–60% of the feed water is recovered as permeate water. The water not recovered as permeate becomes concentrated into a stream of RO concentrate (brine) because the salts rejected by RO remain in the unrecovered water. The RO concentrate is usually about 1.67 to 2.5 times the salt concentration of the source water, but can be as high as four times. RO concentrate discharged into a source water body is a major environmental consideration during the planning and design of bay or ocean desalination plants. Co-location of desalination plants with wastewater treatment plants or power plants allows using a shared outfall to dilute the high salt concentration of RO concentrate. Diluting the RO concentrate in a shared effluent outfall mitigates the issue of high salinity around the outfall. This paper compares side by side two main classes of water bodies that receive concentrated brine discharge from Reverse Osmosis (RO) Desalination Plants: oceans (or open seas) and estuarine bays (under the influence of fresh water). These two classes of water bodies have inherent properties which drive not only the operation of RO plants, but also the physical and chemical reactions of outfall discharge. Major differences between oceans and estuarine bays are evident when comparing salinity levels, variability of salinity, and variability of the overall water quality. Furthermore, there are differences in terms of flora and fauna. Using a nuanced approach of comparing and contrasting oceans and estuarine bays as receiving waters for desalination plant concentrate, this paper brings to light the natural processes occurring offshore of potential desalination plant sites, and distinguishes what natural processes may be affected by brine entering the ecosystem.

In this study, we explore the possibility of reusing end-of-life seawater reverse osmosis (RO) membranes to treat brackish water and industrial effluent. Prior to cleaning the end-of-life RO membranes, we conducted several autopsies in order to assess the extent of degradation. Based on these results, three cleaning protocols were tested and Ultrasil10 and/or chlorine solution were selected for further investigation. The cleaning capacity of the chlorine treatment at 4000 ppm.h was tested but proved inefficient as it leads to a denser cake and a significant decrease in hydraulic permeability. Therefore, we recommend commencing chemical cleaning with Ultrasil10 to remove foulants, thereby reconditioning the end-of-life RO membranes to meet nanofiltration membrane specifications. The cleaned end-of-life RO membranes exhibited enhanced hydraulic permeability (1.97 L·h⁻¹·m⁻²·bar⁻¹) and achieved a salt rejection of 85% for brackish water (6 g/L NaCl). With a molecular weight cutoff of 86 Da, these membranes effectively reduced brackish water conductivity to below 1000 µS/cm at 10 bars, complying with Tunisian drinking water standards (300–2500 µS/cm). Additionally, they demonstrated high efficiency in treating industrial effluents, achieving turbidity levels below 2 NTU and conductivity of 180 µS/cm. Operating at lower pressures, these membranes provided cost-effective, sustainable solutions and performed comparably to commercial new NF membranes, validating their potential for reuse in brackish water and wastewater treatment applications.

Biofouling has been referred to as “the Achilles heel” of reverse osmosis (RO) membrane technology; the main cause being polyamide RO membranes lack of chlorine tolerance. Biofouling increases the operating cost of water treatment by increasing RO system feed pressure (i.e., energy demand) and increasing membrane cleaning frequency, which increases downtime and reduces membrane useful life. For waters with known high biofouling potential, plant designs also may require more extensive pretreatment, which increases capital and operating costs as well as the footprint of a desalination plant. It is known from the literature that the three keys to fending off biofouling in RO systems and/or recovering from biofouling once it takes root include (1) understanding site-specific processes governing biofilm formation, (2) implementing effective biofouling pretreatment ahead of RO membranes, and (3) monitoring biofouling to enable more proactive and effective RO membrane cleaning. Herein, we present four case studies of RO membrane biofouling in seawater, municipal wastewater, brackish groundwater and industrial wastewater. Next, we describe what is known about the causes and consequences of bacterial biofilm formation and growth through a process level RO membrane biofouling model. Finally, we review common biofouling control methods including pre-treatment, chemical cleaning and the most common strategies for monitoring biofouling in RO membrane systems.

Copenhagen and the surrounding municipalities face serious water supply challenges due to the combined effects of population growth, urbanization, pollution, and political pressure from the EU Water Framework Directive. The Blue Lagoon has been identified as a possible solution to these challenges that would improve both the self-sufficiency and long term sustainability of the city’s water supply through the utilization of an internal resource that is currently considered as a waste product. In addition, the lagoon would provide an environmental benefit through reduction of the nutrient load that is currently released from wastewater treatment plants during normal flow and overflow events. The Lagoon could also be a valuable component of an improved storm water management system. Presently, water is abstracted from groundwater resources, used, treated, and then pumped to either the Oresund or Koge Bugt. The Blue Lagoon would reuse the waste stream that is currently discharged and recycle the resource back into the urban water cycle [Figure 1]. An artificial lagoon would be used to mix effluent from wastewater treatment plants with seawater, and then used as a source for a Reverse Osmosis (RO) water treatment plant. In addition to improving self-sufficiency and sustainability, this configuration would reduce the salinity (TDS) of the source water for the RO plant and reduce the economic and energy burden when compared to conventional desalination of seawater. Data regarding possible flow sources to the lagoon was compiled and combined with other information in a model to evaluate possible lagoon configurations, resulting water quality and whether or not the lagoon would meet requirements that had been established. In addition, an economic analysis was conducted to further assess lagoon configurations and the economic viability of the lagoon compared to direct desalination of water from Koge Bugt. Results indicate that connection to one or two treatment plants would provide a constant supply and excess lagoon volume for dilution with seawater while still achieving a 35-80% reduction in TDS in the feed stream to a RO plant. No configurations met the water quality standards that had been set for the lagoon. Additional treatment processes are necessary to reduce the average total phosphorus concentration in treatment plant effluent streams from approximately 0.5 mg/l to 0.04 mg/l. Economic evaluation revealed that the operational cost of producing water via the lagoon would be 0.003 to 0.018 DKK/m3 cheaper than direct seawater desalination. Through efficient lagoon configuration, dilution of wastewater effluent is achieved, while still reducing TDS in the feed stream to the RO plant. More investigation is necessary to fully evaluate The Blue Lagoon; however none of the results of this project indicate that this concept is a “pie in the sky”. On the contrary, there is ample evidence to indicate that this is a viable solution that would provide a reliable, high quality, sustainable, and self-sufficient water supply for the city of Copenhagen and the surrounding municipalities.

A nanofibrous composite reverse osmosis (RO) membrane with a polyamide barrier layer containing interfacial water channels was fabricated on an electrospun nanofibrous substrate via an interfacial polymerization process. The RO membrane was employed for desalination of brackish water and exhibited enhanced permeation flux as well as rejection ratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium periodate systems and surface grafting with different alkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl, and octadecanyl groups. The chemical structure of the modified nanocellulose was verified subsequently by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and solid NMR measurements. Two monomers, trimesoyl chloride (TMC) and m-phenylenediamine (MPD), were employed to prepare a cross-linked polyamide matrix, i.e., the barrier layer of the RO membrane, which integrated with the alkyl groups-grafted nanocellulose to build up interfacial water channels via interfacial polymerization. The top and cross-sectional morphologies of the composite barrier layer were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to verify the integration structure of the nanofibrous composite containing water channels. The aggregation and distribution of water molecules in the nanofibrous composite RO membrane verified the existence of water channels, demonstrated by molecular dynamics (MD) simulations. The desalination performance of the nanofibrous composite RO membrane was conducted and compared with that of commercially available RO membranes in the processing of brackish water, where 3 times higher permeation flux and 99.1% rejection ratio against NaCl were accomplished. This indicated that the engineering of interfacial water channels in the barrier layer could substantially increase the permeation flux of the nanofibrous composite membrane while retaining the high rejection ratio as well, i.e., to break through the trade-off between permeation flux and rejection ratio. Antifouling properties, chlorine resistance, and long-term desalination performance were also demonstrated to evaluate the potential applications of the nanofibrous composite RO membrane; remarkable durability and robustness were achieved in addition to 3 times higher permeation flux and a higher rejection ratio against commercial RO membranes in brackish water desalination.