Techno-economic assessment of electrodialysis and reverse osmosis desalination plants

Process for Producing Lithium Iodide Cleanly through Electrodialysis Metathesis

Lithium iodide is commonly used in the production of batteries and drugs. Currently, the neutralization method is the primary means of producing lithium iodide. This method involves using hydriodic acid as a raw material, adding lithium carbonate or lithium hydroxide, and obtaining lithium iodide through evaporation and concentration. However, hydriodic acid is chemically unstable. Its preparation can lead to explosive accidents and encountering high temperatures generates toxic iodine vapors. These limitations restrict its industrial production. The study evaluates the impact of membrane stack configuration, operating voltage, and initial concentrations and volume ratios of reactants on the production process. Electrodialysis metathesis, characterized by a simpler process flow, lower energy consumption, and environmental benefits, emerges as an effective technique for electrically driven membrane separation in lithium salt production and purification. Under the specific conditions of a C-C-A-C-A-C membrane stack configuration, operating voltage at 25 V, initial potassium iodide concentration at 0.4 mol/L, initial lithium sulfate concentration at 0.2 mol/L, and a 1:1 volume ratio of product liquid to raw material liquid, the method achieves a lithium iodide purity of 98.9% with a production cost of approximately 0.502 $/kg LiI.

The potential of electrodialysis as a cost-effective alternative to reverse osmosis for brackish water desalination

While electrodialysis (ED) demonstrates lower energy consumption than reverse osmosis (RO) in the desalination of low salinity waters, RO continues to be the predominant technology for brackish water desalination. In this study, we probe this skewed market share and project the potential for future disruption by ED through systematic assessment of the levelized cost of water (LCOW). Using rigorous process- and economic-models, we minimize the LCOW of RO and ED systems, highlighting important tradeoffs between capital and operating expenditure for each technology. With optimized current state-of-the-art systems, we find that ED is more economical than RO for feed salinities ≤ 3 g L-1, albeit to a minor extent. Considering that RO is a highly mature technology, we focus on predicting the future potential of ED by evaluating plausible avenues for capital and operating cost reduction. Specifically, we find that reduction in the price of ion-exchange membranes (i.e., < 60 USD m-2) can ensure competitiveness with RO for feed salinities up to 5 g L-1. For higher feed salinities (≥ 5 g L-1) we reveal that the LCOW of ED may effectively be reduced by decreasing ion-exchange membrane resistance, while preserving high current efficiency. Through extensive assessment of structure-property-performance relationships, we precisely identify target membrane charge densities and diffusion coefficients which optimize the LCOW of ED, thus providing novel guidance for future membrane material development. Overall, we emphasize that with a unified approach - whereby ion-exchange membrane price is reduced and performance is enhanced - ED can become the economically preferable technology compared to RO across the entire brackish water salinity range.

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.

Techno-economic assessment of a novel algal-membrane system versus conventional wastewater treatment and advanced potable reuse processes: Part II

This study developed a comprehensive techno-economic assessment (TEA) framework to evaluate an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) in comparison with a conventional potable water reuse system (i.e., the benchmark system). The TEA study aims to estimate the levelized costs of water of individual units and integrated processes including secondary wastewater treatment, advanced water purification for potable reuse, and sludge treatment. This would provide decision-makers valuable information regarding the capital and operational costs of the innovative main system versus a typical potable water reuse treatment train, along with possible routes of cost optimization and improvements for the design of full-scale facilities. The main system consists of (i) a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water reuse and hydrothermal liquefaction (HTL) to produce bioenergy and subsequent nutrients extraction from the harvested algal biomass. The benchmark system includes (ii) an advanced water purification facility (AWPF) that consists of a conventional activated sludge biological treatment (CAS), microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), with anaerobic digestion for sludge treatment. Capital expenditures (CAPEX) and operational expenditures (OPEX) were calculated for each unit of both systems (i.e., sub-systems). Based on a 76% overall water recovery designed for the benchmark system, the water cost was estimated at $2.03/m³. The highest costs in the benchmark system were found on the CAS and the anaerobic digester, with the UV-AOP combined with GAC for hydrogen peroxide (H₂O₂) quenching as the driving factor in the increased costs of the system. The cost of the main system, based on an overall 88% water recovery, was estimated to be $1.97/m³, with costs mostly driven by the FO and SWRO membranes. With further cost reduction and optimization for FO membranes such as membrane cost, water recovery, and flux, the main system can provide a much more economically viable alternative in its application than a typical benchmark system.

A membrane-based seawater electrolyser for hydrogen generation

Electrochemical saline water electrolysis using renewable energy as input is a highly desirable and sustainable method for the mass production of green hydrogen^1-7; however, its practical viability is seriously challenged by insufficient durability because of the electrode side reactions and corrosion issues arising from the complex components of seawater. Although catalyst engineering using polyanion coatings to suppress corrosion by chloride ions or creating highly selective electrocatalysts has been extensively exploited with modest success, it is still far from satisfactory for practical applications^8-14. Indirect seawater splitting by using a pre-desalination process can avoid side-reaction and corrosion problems^15-21, but it requires additional energy input, making it economically less attractive. In addition, the independent bulky desalination system makes seawater electrolysis systems less flexible in terms of size. Here we propose a direct seawater electrolysis method for hydrogen production that radically addresses the side-reaction and corrosion problems. A demonstration system was stably operated at a current density of 250 milliamperes per square centimetre for over 3,200 hours under practical application conditions without failure. This strategy realizes efficient, size-flexible and scalable direct seawater electrolysis in a way similar to freshwater splitting without a notable increase in operation cost, and has high potential for practical application. Importantly, this configuration and mechanism promises further applications in simultaneous water-based effluent treatment and resource recovery and hydrogen generation in one step.

Integrated energy system optimal scheduling considering the comprehensive and flexible operation mode of pumping storage

The integrated energy system (IES) optimal scheduling under the comprehensive flexible operation mode of pumping storage is considered. This system is conducive to the promotion of the accommodation of wind and solar energy and can meet the water, electricity and heat needs of coastal areas far away from the energy center. In this study, the joint dispatch between double pumped storage power stations is used to accommodate wind and solar energy better and smooth their fluctuations on the grid. Through the scheduling of water between the high and low reservoirs of double pumped storage power stations and the reservoir of the seawater desalination plant, the impact of storage capacity constraints on pumped storage power plants is reduced. Moreover, the objective function to build the IES optimization scheduling model is to achieve minimum economic cost. The results reveal that the integrated energy system accommodates all wind energy and solar energy. As such, the system increases the average working time of the pumped storage unit by 1.9 hours and reduces the economic cost by 31.50%. Based on the simulation results, the model can enhance the accommodation capability of wind energy and solar energy and improve the system economy.

Reverse Osmosis Membrane Zero Liquid Discharge for Agriculture Drainage Water Desalination: Technical, Economic, and Environmental Assessment

Agricultural drainage water (ADW) represents a potential source for fresh water after receiving appropriate treatments to satisfy the water quality requirements. Desalination of ADW with medium salinity and moderate contamination with organic and inorganic chemical pollutants could provide a techno-economically feasible approach for facing water scarcity in arid areas. The current work presents a conceptual zero liquid discharge ADW desalination system proposed to treat 300,000 m³/d. The system is based on pretreatment to remove impurities harmful to desalination by staged reverse osmosis (RO) membrane. The brine from the last RO stage is treated via thermal vapor compression followed by evaporation in solar ponds to recover more fresh water and salts of economic value. The essential technical features of the proposed system components are formulated. The proposed system components and its technical and economic indicators are deduced using available software for water pretreatment, RO membrane, desalination, thermal desalination, and solar evaporation ponds. The system provides total distilled water recovery of about 98% viz. 294,000 m³/d in addition to recovered salts of 245,000 t/y. The net cost of water production amounts to USD 0.46 /m³. The environmental considerations of the system are addressed and advantages of applying zero liquid discharge system are elucidated.

The noteworthy chloride ions in reclaimed water: Harmful effects, concentration levels and control strategies

Chloride ions (Cl^-), which are omnipresent in reclaimed water, can cause various problems in water reuse systems, especially during water transmission and at end use sites. Although reverse osmosis (RO) is considered as an effective technology to reduce chloride, its high investment and complex maintenance requirements hinder its application in many water reclamation plants (WRPs). Recently, several technologies bringing new options to better deal with chloride have gained increased attention. This review provides detailed information on the harmful effects, concentration levels, and sources of chloride in reclaimed water and summarizes and discusses various chloride removal technologies, including non-selective methods (e.g., membrane filtration, adsorption and ion exchange, oxidation, and electrochemical methods) and selective methods (e.g. precipitation and specially designed electrochemical methods). Among these, Friedel's salt precipitation and capacitive deionization showed attractive development potential. This review also proposes a holistic framework for chloride control from aspects of "Fit-for-Purpose" planning, technical system development, and whole process optimization, which could facilitate the planning and operation of long-term sustainable water reuse practices.

Assessment of Graphical Methods for Determination of the Limiting Current Density in Complex Electrodialysis-Feed Solutions

Electrodialysis (ED) is a promising technology suitable for nutrient recovery from a wide variety of liquid waste streams. For optimal operating conditions, the limiting current density (LCD) has to be determined separately for each treated feed and ED equipment. LCD is most frequently assessed in the NaCl solutions. In this paper, five graphical methods available in literature were reviewed for LCD determination in a series of five feed solutions with different levels of complexity in ion and matrix composition. Wastewater from microbial fermentation was included among the feed solutions, containing charged and uncharged particles. The experiments, running in the batch ED with an online conductivity, temperature, and pH monitoring, were conducted to obtain data for the comparison of various LCD determination methods. The results revealed complements and divergences between the applied LCD methods with increasing feed concentrations and composition complexity. The Cowan and Brown method had the most consistent results for all of the feed solutions. Online conductivity monitoring was linearly correlated with the decreasing ion concentration in the feed solution and corresponding LCD. Therefore, the results obtained in this study can be applied as a base for the automatized dynamic control of the operating current density–voltage in the batch ED. Conductivity alone should not be used for the ED control since LCD depends on the ion exchange membranes, feed flow, temperature and concentration, ionic species, their concentration ratios, and uncharged particles of the feed solution.