Feed Water Salinity Research Articles

Techno-economic investigation of an entirely solar-powered hybrid HDH/RO desalination plant for moderate water demand under various operating conditions

The study presented a scalable, entirely solar-powered hybrid desalination system suitable for moderate demand and valid for various water salinities. The system merged two desalination techniques: HDH (humidification-dehumidification) and RO (reverse osmosis) units. The required power for all components was obtained from a photovoltaic system. The experiments were conducted to evaluate the separate units and hybrid system performances under different conditions, including various sprayed hot water (to the HDH) temperatures, RO feed water temperatures, air velocities, and water salinities. Based on the recorded data, the techno-economic analyses were conducted to assess the gain output ratio (GOR), recovery ratio (RR), specific energy consumption (SEC), the total amount of dissolved solids (TDS), and product cost. As a result, the RO unit's productivity increased almost linearly with feed temperature, showing a maximum hourly yield of 60 L/m2. In contrast, HDH productivity showed exponential growth with feed temperature, achieving a maximum hourly yield of 18 L/m2. The SEC of the RO unit decreased from 1.1 kWh/m³ to 0.63 kWh/m³ when using the rejected HDH's hot brine. The hybrid system's accumulated productivity reached 535 L/m2, significantly higher than the standalone HDH (58.5 L/m2) and standalone RO (368 L/m2). Additionally, the hybrid system demonstrated substantial improvements in GOR and RR, with daily values of 11.15 and 55.73%, respectively. Economically, the distillate water cost was significantly lower, at 0.63 $/m³ for the HDH/RO system compared to 3.51 $/m³ for the standalone HDH.

Insights on CDI parametric controls and dependencies using gloabal sensitivity analysis

Capacitive deionization (CDI) emerges as a promising desalination technology due to its high energy efficiency and potential for energy recovery. Its performance improvement and application extension highly require understanding how variations in multiple input parameters, as well as their interactions, lead to variations in output, which is not straightforward in the complex system of CDI. In this work we use the extended Fourier amplitude sensitivity test (eFAST) method to conduct a global sensitivity analysis (GSA) in order to examine the effects of several parameters, including material properties, operating conditions, and ionic properties, on the energy consumption and salt removal efficiency of CDIs. The research reveals that high capacitance and efficient mass transfer are crucial for CDI advancement, with a trade-off between desalination rate and energy efficiency. The interplay between input parameters is revealed by factorial design and GSA, which show that no single parameter alone determines salt adsorption capacity but that feedwater salt concentration and current density are important when considering both individual and coupled effects. The study suggests that the specific application and feedwater characteristics should be taken into consideration when deciding between the CC and CV modes of desalination. While CC mode excels in water production and energy efficiency for high salinity feedwater pretreatment, CV mode is better at treating low salinity waterr. The comprehensive parametric analysis provides valuable insights into optimizing CDI design and operating conditions to balance desalination capacity and energy efficiency.

Screening the Performance of a Reverse Osmosis Pilot-Scale Process That Treats Blended Feedwater Containing a Nanofiltration Concentrate and Brackish Groundwater.

A two-stage pilot plant study has been completed that evaluated the performance of a reverse osmosis (RO) membrane process for the treatment of feedwater that consisted of a blend of a nanofiltration (NF) concentrate and brackish groundwater. Membrane performance was assessed by monitoring the process operation, collecting water quality data, and documenting the blended feedwater's impact on fouling due to microbiological or organic means, plugging, and scaling, or their combination. Fluorescence and biological activity reaction tests were used to identify the types of organics and microorganisms present in the blended feedwater. Additionally, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to analyze suspended matter that collected on the surfaces of cartridge filters used in the pilot's pretreatment system. SEM and EDS were also used to evaluate solids collected on the surfaces of 0.45 µm silver filter pads after filtering known volumes of NF concentrate and RO feedwater blends. Water quality analyses confirmed that the blended feedwater contained little to no dissolved oxygen, and a significant amount of particulate matter was absent from the blended feedwater as defined by silt density index and turbidity measurements. However, water quality results suggested that the presence of sulfate, sulfide, iron, anaerobic bacteria, and humic acid organics likely contributed to the formation of pyrite observed on some of the membrane surfaces autopsied at the conclusion of pilot operations. It was determined that first-stage membrane productivity was impacted by the location of cartridge filter pretreatment; however, second-stage productivity was maintained with no observed flux decline during the entire pilot operation's timeline. Study results indicated that the operation of an RO process treating a blend of an NF concentrate and brackish groundwater could maintain a sustainable and productive operation that provided a practical minimum liquid discharge process operation for the NF concentrate, while the dilution of RO feedwater salinity would lower overall production costs.

Capacitive deionization: Capacitor and battery materials, applications and future prospects

Water scarcity all over the world attracts alternative methods to purify saline water and supplement the available dwindling freshwater resources. Capacitive deionization (CDI) is hopeful to supply water to the population due to operation at low potential along with low energy expenditure when low salinity (5 mM NaCl) feed water solutions are desalinated. Electrode material is the main controlling factor in CDI system and a lot of efforts are devoted to develop excellent materials for better CDI performance. So far, carbon materials are widely used as the electrode for CDI, though limitations such as co-ion expulsion and faradaic reactions hinder their full utilization. Alternatively, battery materials are used since their performance is great due to mitigation of co-ions ejection as well as faradaic reactions. In 2019 our group reviewed factors affecting the performance of activated carbon electrode materials and revealed lack of selectivity, co-ion expulsion, low electrical conductivity and inappropriate pore size distribution to largely contribute to its low salt removal capacity [1]. Therefore, herein, we extend the discussion beyond AC to include other carbons such as aerogels, nanotubes, graphenes etc., and battery materials such as MXenes, sodium super ionic conductors, and BiOCl to mention the few. This article also discusses the extent CDI is applied in the laboratory scale as well as in the field for desalination of real water, wastewater remediation and removal of harmful contaminants to substantiate what it can offer beyond the laboratory experiments. The work is expected to save as a complete reference for the progress of CDI electrode materials and its applications in water purification.

Component innovations for lower cost mechanical vapor compression

Despite significant capital and operating costs, mechanical vapor compression (MVC) remains the preferred technology for challenging brine concentration applications. This work seeks to assess the dependence of MVC costs on feedwater salinity and desired water recovery and to quantify the value of improved component performance or reduced component costs for reducing the levelized cost of water (LCOW) of MVC. We built a cost optimization model coupling thermophysical, heat and mass transfer, and technoeconomic models to optimize and identify low cost MVC system designs as a function of feedwater salinity and water recovery. The LCOW ranges over 3.6 to 6.1 $/m3 for seawater feed salinities of 25–150 g/kg and water recoveries of 40–80 %. We then perform sensitivity analysis on parameter inputs to isolate irreducible costs and determine high value component innovation targets. The LCOW was most sensitive to evaporator material costs and performance, including the overall heat transfer coefficient in the evaporator. Process and material innovations such as polymer-composite evaporator tubes that reduce evaporator costs by 25 % without reducing heat transfer performance by more than 10 % would result in MVC cost reductions of 8 %.

Experimental investigation of a sun tracking concentrated solar still with economic analysis

The current paper evaluated experimentally an innovative sun tracking concentrated solar still under Egyptian climatic conditions during the summer of 2022. The proposed system consists of a 120-cm-diameter parabolic reflector mirror that tracks the sun using a dual axis tracking system, a cylindrical solar still with a volume of 3.7 L positioned in its focal point, and a concentration ratio of 12.5. The performance of the concentrated solar still was investigated in the context of two critical parameters. First, three feed water salinity (17, 27, 37) ppt samples were evaluated, followed by four percentages of saline water filling ratio (26.5, 39.8, 53.1, 66.3)%. Increasing the salinity of the feed water had no effect on solar still productivity, but increasing the saline water filling ratio did. The daily cumulative productivity of the system was 6 kg/m2 with an optimal filling ratio of 53.1%, a daily efficiency of 42.88%, and an average cost of freshwater production of 0.0489 $/L. The proposed system also had the highest instantaneous efficiency of 61.77% and the highest distilled water productivity rate of 0.941 kg/h m2.

Optimizing energy efficiency in brackish water reverse osmosis (BWRO): A comprehensive study on prioritizing critical operating parameters for specific energy consumption minimization

Reverse osmosis (RO) systems offer a viable solution for treating brackish water (BW), a common but underutilized water resource. However, the energy-intensive nature of brackish water reverse osmosis (BWRO) systems poses affordability challenges to water supply, necessitating a focus on minimizing their energy consumption to support SDG6's goal of providing safe and affordable drinking water for all. This study addresses the critical need to minimize the specific energy consumption (SEC) of a typical BWRO system, defined as the energy consumed per unit of water recovered, mathematically and experimentally. Empirical models were developed proving there is a global minimum SEC while adjusting the operating conditions. Furthermore, we identified the key operating factors influencing SEC and their priority levels, along with their interactive effects. Notably, no prior study has discussed the significance and interaction of these operating factors (e.g., feed water salinity, temperature, pressure, flowrate and membrane permeability) on SEC of a BWRO system. Employing a full factorial experimental design with mixed levels of operating parameters, the study developed regression models that elucidate the mechanistic interaction between these parameters and system performance. Moreover, the models were validated experimentally, with a new dataset demonstrating their accuracy and reliability. ANOVA statistical analysis identified feed salinity, pressure, flow rate, feed flow rate×pressure, salinity×pressure, and temperature as influential operating parameters in reducing SEC, in descending order of importance. Operating within the determined optimum range resulted in a 36 % decrease in SEC and a more than fourfold increase in water recovery. The study's systematic approach and findings can be extrapolated to optimize the performance of other desalination technologies and diverse feed water types, contributing significantly to global water sustainability efforts.

Innovative pilot plant capacitive deionization for desalination brackish water

A semi-industrial demineralization facility was used in six CDI cells to desalinate in two steps. A desalination cycle lowered the feedwater salinity from 1 to 0.5 g/L and produced 200 l/h of demineralized water. This process may be repeated to increase efficiency. Initially, feedwater commenced at 1 g/L. Monitoring both voltage and current during the salt ion removal indicated that CDI cells may recover 30% of the energy utilized. Furthermore, V–Q curves using charge and voltage measurements increased energy recovery by 30%. By cutting off the CDI cells' power source, the electrodes' operating voltage was recorded between 0.85 and 0.9 V, much lower than the external contacts' 1.2 V. The desalination system's efficiency could rise if the electrode voltage was measured and adjusted. In conclusion, storage tanks can provide desalinated water while minimizing water waste; hence, they should be installed. This study examined the physical–technical parameters of a CDI desalination system through experiments and several operational modes. Moreover, it revealed CDI desalination system improvements.

Thin-Film Composite Membranes for Hydrogen Evolution with a Saline Catholyte Water Feed.

Hydrogen gas evolution using an impure or saline water feed is a promising strategy to reduce overall energy consumption and investment costs for on-site, large-scale production using renewable energy sources. The chlorine evolution reaction is one of the biggest concerns in hydrogen evolution with impure water feeds. The "alkaline design criterion" in impure water electrolysis was examined here because water oxidation catalysts can exhibit a larger kinetic overpotential without interfering chlorine chemistry under alkaline conditions. Here, we demonstrated that relatively inexpensive thin-film composite (TFC) membranes, currently used for high-pressure reverse osmosis (RO) desalination applications, can have much higher rejection of Cl- (total crossover of 2.9 ± 0.9 mmol) than an anion-exchange membrane (AEM) (51.8 ± 2.3 mmol) with electrolytes of 0.5 M KOH for the anolyte and 0.5 M NaCl for the catholyte with a constant current (100 mA/cm2 for 20 h). The membrane resistances, which were similar for the TFC membrane and the AEM based on electrochemical impedance spectroscopy (EIS) and Ohm's law methods, could be further reduced by increasing the electrolyte concentration or removal of the structural polyester supporting layer (TFC-no PET). TFC membranes could enable pressurized gas production, as this membrane was demonstrated to be mechanically stable with no change in permeate flux at 35 bar. These results show that TFC membranes provide a novel pathway for producing green hydrogen with a saline water feed at elevated pressures compared to systems using AEMs or porous diaphragms.

Towards long-term operation of flow-electrode capacitive deionization (FCDI): Optimization of operating parameters and regeneration of flow-electrode

This study systematically optimized the key operating parameters and interpreted their effecting mechanisms in a flow-electrode capacitive deionization (FCDI) system. The optimal voltage, activated carbon electrode content, electrolyte concentration, feedwater flowrate, and electrode flowrate for desalinating low salinity feedwater (1.0 g L−1 NaCl) were determined to be 1.8 V, 2.0 wt%, 10.0 g L−1, 80 mL min−1, and 60 mL min−1, respectively. The variations of the above parameters can affect the system conductivity, the thickness and stability of the electric double layers, and/or the degree of concentration polarization, thereby influencing the desalination performance. Moreover, a sensitivity analysis identified the operating voltage as the dominant parameter with the most significant influence on the FCDI system. Subsequently, a long-term operation was carried out under single-pass mode. The results showed that the lab-scale FCDI system was able to constantly maintain the desalination efficiency of 1.0 g L−1 feedwater (NaCl) at 40–60 % for multiple operating cycles. Over 99.8 % of electrode material regeneration and desalination efficiency recovery was able to be obtained during a 60-h operation, demonstrating that the FCDI system showed strong stability and long-term operation potential.

A Novel Configuration of Hybrid Reverse Osmosis, Humidification–Dehumidification, and Solar Photovoltaic Systems: Modeling and Exergy Analysis

The pressing demand for clean water worldwide has increased attention to developing innovative desalination processes. In this work, the second law of thermodynamics is used to examine and assess two coupled desalination systems: a separation-based reverse osmosis (RO) system and a thermal desalination-based humidification–dehumidification (HDH) system. The HDH unit configuration used here is based on the working principle of the heat pump, where the process is open-air, open-water, and air-heated. The RO system is equipped with a pressure exchanger (PX) and has been examined under various operating circumstances, such as different feed water pressures, salinities, and flow rates. To improve the system’s sustainability, a solar photovoltaic system (PV) was integrated. An exergy model was used to precisely evaluate the system components and the hybrid systems by employing a proper exergy efficiency definition. The evaluation of the second law of thermodynamics for the RO–HDH–PX and RO–HDH–PX–PV systems indicated maximum efficiencies of 23% and 23.25%, respectively. A cost analysis was also performed on the hybrid RO–HDH–PX–PV desalination system using two approaches: the first included a battery storage system, whereas, in the second, the battery was not considered. When a battery storage system is included, the cost per cubic meter varies from USD 3.22 to USD 5.10. In contrast, it varies from USD 3.96 to USD 7.12 without a battery storage system.

Nitrogen compounds removal from brackish water by electrodialysis at fixed electric potential and dynamic current density operations

Nitrogen (N) compounds can occur in water resources from natural and anthropogenic activities. It is ideal that these contaminants be removed before water consumption. As water quality has been affected by increased salinity and pH variation, more advanced and robust technologies such as electrodialysis (ED) can be considered for simultaneous desalination and pollutant removal. In this context, the removal of N-species (NO3−, NO2−, NH4+, and CH4N2O) from brackish water by ED was investigated for different feed water quality, considering increased salinity (0 – 10g/L NaCl) and pH variation (3 – 11), under limit current density (LCD) at fixed electric potential condition. The applied electric potential (5 – 25V) under, at, and over the LCD at fixed electric potential and dynamic current density (DCD), as a percentage of LCD (0.4 - 1.2), were analyzed to improve the process. In addition, energy efficiency in the form of specific energy consumption (SEC) and current efficiency (CE) were assessed for ED at fixed electric potential and DCD. The results showed that, at extreme pH of the feed water, the removal of NO2− and NH4+ can be affected, while NO3−was the most stable compound with pH variation. An increase in feed water salinity just slightly impacted the removal of N-compounds, due to the similar characteristics of the ions in the water. The increase in electric potential at fixed electric potential or DCD increased the removal and molar flux of N-compounds. However, operating over the LCD increased the SEC of the ED process while changes in removal were not significant. DCD procedures resulted in higher CE and shorter run time of the experiments. Therefore, ED proved to be a suitable treatment technique to produce fresh water due to the selective removal of the studied ions, especially at 15V (fixed electrical potential) and 0.8 LCD (DCD) related to removal, molar flux, and run time to achieve guidelines.

Direct wind-powered vertical axis brackish water desalination system

The supply of freshwater based on wind-powered desalination is technically feasible, but energetic losses associated with conventional systems necessitate new approaches. This study explores a direct wind-powered desalination (D-WPD) system using a small-scale vertical axis wind turbine (VAWT) for reverse osmosis via a high-pressure pump without electricity generation or a system controller. A comprehensive parametric study examined the effects of feed water salinity, loading, and wind speed on the system's performance, demonstrating high efficiency under various operating conditions. A stand-alone system demonstrated operation at effectively constant system efficiency, approximately 13.5 %, and low specific energy consumption for a wide range of wind speeds and salinities. Despite the turbine's small projected area of 0.8 m2, the D-WPD system yielded a daily permeate production of up to 0.6 m3/day at an average wind speed of 6 m/s. The D-WPD system surpassed previous wind-powered desalination studies in terms of specific energy consumption, relative efficiency, and relative desalination capacity. Leveraging the environmental benefits of the slow-spinning VAWT, this D-WPD offers a cost-effective off-grid solution for small-scale desalination.

Feasibility Study of a Reverse Osmosis Desalination Unit Powered by Photovoltaic Panels for a Sustainable Water Supply in Algeria

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.

Performance and control of a reverse osmosis unit integrated with Pelton Wheel to supply emergency electric loads under various operating conditions

Nowadays, the whole world is moving very quickly into the field of seawater desalination. This is because the world suffers from a lack of potable water. Water and energy are adjoining linked fields. The present work aims at investigating the performance of a reverse osmosis (RO) plant integrated with Pelton Wheel under various operating conditions. The main reason for using Pelton turbine instead of the pressure exchanger (PX) is the low cost of Pelton compared to that of PX. The RO system integrated with the Pelton Wheel was tested under various operating pressures of 650, 700, 750, 800, and 850 kPa. Changing the feed water pressure affects the pressure of the reject entering the Pelton wheel and this, in turn, affects the velocity of the water jet. Also, the impact of varying the feed water salinity (total dissolved solids (TDS) = 400, 500, 600, 700, and 850 ppm) and temperature (20–39 °C) on the permeate and reject of RO was tested. In addition, a theoretical modeling was built to predict the performance of the RO system. The permeate flow rate was increased by raising the RO operating pressures. The permeate flow rate was augmented from 2.5 to 4.3 L min−1 when increasing the operating pressure from 650 to 850 kPa, respectively. Therefore, the permeate flow rate is enhanced by around 72% when increasing the operating pressure by only 30%. Besides, increasing the pressure by 30% (from 650 to 860 kPa) decreased the generated power of the Pelton Wheel by approximately 72% (from 960 to 270 W, respectively). Also, increasing the feed water salinity leads to raise the salinity of RO permeate, and vice versa. The RO permeate salinity is raised from 165 to 285 ppm when increasing the operating pressure from 650 to 850 kPa, respectively. As well, the more the increase in feed water temperature, the more improve in the permeate flux and salinity. The permeate TDS was decreased from 140 ppm at feed-water temperature 20 °C to 56 ppm at feed water temperature 39 °C. In this study, the Arduino program circuit was used to supply the required emergency loads by controlling the pressure values of high-pressure pump due to easy and open code program. Finally, the theoretical modelling results are in good correspondence with the experimental results. The average deviation among the theoretical and experimental results was 3.5%.

Triple-layer nanofiber membrane with improved energy efficiency for treatment of hypersaline solution via membrane distillation

A new triple-layer, electrospun nanofiber membrane was fabricated in sequential electrospinning steps for enhancing the thermal efficiency of the membrane for desalination of high-salinity solution in a membrane distillation process. The membrane structure is designed to form a Janus structure comprised of two hydrophobic layers made of polyvinylidene fluoride and polystyrene at the top and middle, respectively, and one hydrophilic layer made of polyacrylonitrile at the bottom layer (support). The low thermal conductivity of the polystyrene layer and the Janus structure of the membrane could considerably enhance the flux and thermal performance of the membrane for desalination of hypersaline solution. The experimental results demonstrated that the designed membrane achieved high permeate flux and high energy efficiency compared with single and dual-layer membranes when used for treatment of high salinity solution. The results further showed that increasing feedwater salinity dropped the permeate flux of the single-layer membrane by over 50 % and reached 10 L/m2h, while for the triple-layer membrane, it just dropped 20 % for the feed salinity of 200 g/l. Moreover, the triple-layer membrane showed 20 % higher energy efficiency at the same operation conditions. Furthermore, a simulation model was developed and validated via the experimental results to understand the effect of various parameters.

Design and optimization of a novel flash-binary-based hybrid system to produce power, cooling, freshwater, and liquid hydrogen

The current work aims to design and analyze a novel hybrid system that can produce power, cooling, freshwater, and liquid hydrogen from a single energy source. The system consists of a flash-binary system, a double-effect absorption refrigeration cycle, a multi-effect desalination unit, and a hydrogen liquefaction unit. The steam turbine provides the power input for the hydrogen liquefaction unit. The system's performance is evaluated by thermodynamic and economic analyses, and a sensitivity analysis is conducted to investigate the effects of some key parameters on the operation mode. Moreover, the optimal state is determined based on three multi-objective optimization scenarios. The results show that the system consumes 33.93 kW of power and generates 2.106 kg/h of liquid hydrogen. The net present value is mainly influenced by the temperature of the saline feed water, while the fixed capital investment is highly dependent on the cooling load production rate. The optimal state of the system achieves an exergetic efficiency of 25.71% with a payback period of 4.48 years, producing 447.2 kW of cooling load, 1.804 kg/s of freshwater, and 2.107 kg/h of liquid hydrogen.

Renewable Energy Powered Membrane Technology: Energy Buffering Control to Reduce Shut‐Down Events and Enhance System Resilience under Different Solar Days

AbstractFluctuating and intermittent solar energy cause shut‐down and reduce resilience of photovoltaic powered membrane (PV‐membrane) systems. A charge controller based on pre‐set voltage thresholds for supercapacitors (SC) is designed and employed on varied solar days to cope with these issues. Several parameters—number of shut‐down events (#SD), shut‐down duration (tSD) and resilience factor in flux (RFflux)—are quantified. The controller reduces tSD by 37% (partly cloudy) and 12% (very cloudy), and #SD by 2 and 13 events, respectively. During the 90 min fluctuations, tSD is shortened to 1–4.5 min and #SD is reduced by 1–4 events for feed water salinities of ≤7.5 g L−1. Increasing the PV power capacity to 600–1000 W, zero #SD occurs and RFflux rises from 0.3 to 0.8, indicating enhanced system resilience.

Combination of H2O2-producing microbial desalination cells and UV/H2O2 advanced oxidation process: Water salinity reduction and microbial inactivation

Microbial desalination cells (MDCs) are bioelectrochemical devices that can recover usable energy and chemicals from organic wastes and concurrently desalinate saltwater. MDCs can also produce the green oxidant, H2O2, through a two-electron oxygen reduction reaction occurring on the cathode electrode. If MDCs producing H2O2 are used in the pretreatment of brackish water or seawater for reverse osmosis (RO) processes, the salinity of feed water can be reduced in MDCs and the MDC-produced H2O2 can be utilized onsite to oxidize organic contaminants or disinfect microorganisms in the feed water. This strategy of using MDC pretreatment may substantially alleviate the energy requirements and biofouling tendency of downstream RO units. Herein, we assessed the applicability of a combination of H2O2-producing MDCs and ultraviolet (UV) or UV254nn -based advanced oxidation process (AOP) (i.e., UV/H2O2) as pretreatment for RO processes. We first examined the effect of catholyte conditions, which is one of the most crucial factors directly affecting the H2O2 composition and decomposition, on the performance of MDCs. Then, we evaluated the microorganism disinfection efficiencies of advanced photo-oxidation processes using H2O2 obtained from MDCs. The MDC investigated herein achieved 93.1% desalination efficiency and > 5.0 mM H2O2 concentration. In addition, UV-based AOP with the produced H2O2 demonstrated up to 15-fold higher inactivation kinetics than that by UV254 nm disinfection alone.

An experimental investigation on a crushing and washing-free freezing desalination system based on brine extraction during melting

Freezing desalination has regained attention due to its potential to lower energy usage compared to other methods. However, the freezing technology faces major challenges that hinder its commercialization. One is the significant mass loss due to washing the product's ice. Also, most freezing systems require a crushing stage to obtain the desired ice, limiting mass production. This work proposes a freezing desalination system based on brine extraction during melting. The proposed system can use multiple stages of a brine extraction and can be implemented using multiple cycles of the full process. The experiments were carried out at different feed water salinities. The results have shown that the system has the potential to produce low-salinity water with a relatively low number of stages and without the need for washing or crushing. To get product water at 90 ppm from 45000 ppm feed water, the system requires 3, 4, and 7 cycles (of the full process) for three, two, and single stages of brine extraction, respectively. When considering recovery rates between 60 and 90%, specific energy consumption is reduced to a range of 15–89 kWhr/m3 with COP from 4 to 6, respectively.