Levelized Cost Of Water Research Articles

Performance Enhancement in Air Gap Membrane Distillation Using Heat Recovery Configurations

Experimental investigations were conducted on an air gap membrane distillation (AGMD) unit to evaluate the impact of heat recovery on system performance. The study utilized a steady-state heat source in conjunction with a spiral air gap membrane module for water desalination. The process was implemented using two configurations aimed to minimize heat loss enhancing productivity, gain output ratio (GOR), and thermal efficiency. The experiments involved feedwater with salt concentrations ranging from 10,000 to 30,000 ppm. The measurements were recorded for inlet and outlet temperatures of the heat source, water productivity, and thermal efficiency at various coolant and water feed flow rates. These configurations effectively addressed critical technical challenges in thermal AGMD systems by optimizing heat recovery. The incorporation of heat recovery resulted in a significant increase in water productivity by 37.07% compared to systems without heat recovery while maintaining the same initial heat input. The heat recovery in series (HRSS) and parallel (HRPS) configurations resulted in power consumption reductions of approximately 29.7% and 23.1%, respectively compared to the conventional configuration (CC) at a flow rate of 12 L/min. The levelized cost of water (LCOW) for the AGMD system was comprehensively evaluated and found to be $ 7.71 per cubic meter. This figure reflected the total cost of water production over the system's operational lifespan including capital expenditures, operating and maintenance costs, and energy consumption. The calculated LCOW provides a clear indicator of the system's economic viability, demonstrating the cost required to produce each cubic meter of water through the AGMD.

The apparatus for atmospheric water harvesting in an arid climate - Prototype design and testing in laboratory conditions

The paper describes the development of a prototype system for water extraction from the air. The aim was to develop a device that allows one to autonomously obtain, without the need for external energy, an annual average of 100 L of water per day during extreme desert conditions. In this paper, a mathematical model simulating the operation of the unit for extracting water from the air in any climatic conditions is presented. Psychrometric calculations for different climatic conditions were carried out for two basic principles: condensation and sorption. The analyses confirmed that devices based on the condensation of water vapour from the air can only be used to a limited extent in extreme desert conditions. The average water production of a condensation-based system is only 20 l/day in Riyadh, with an air flow rate of 2000 m3/h. A unit with a desiccant wheel and an integrated heat pump was designed for water harvesting from the air. The prototype of the unit was tested in a climate chamber with the possibility of adjusting the climatic conditions and the presented mathematical model was experimentally verified. The final prototype designed for a nominal outdoor air flow rate of 2000 m3/h will produce 168 l of water per day under dry desert conditions (Riyadh) with continuous operation. The verification of the computational model allows one to determine the real water production and the required unit performance. An analyses of energy requirements and evaluation of levelized cost of water (LCOW) have been performed. Sorption unit has lower LCOW in target arid desert climate and electricity prices under 0.1 EUR/kWh compared to direct condensation technology.

Solar-enhanced DCMD: Dual-tank system for superior efficiency and viability

ABSTRACT This study investigates a novel solar-powered direct contact membrane distillation (DCMD) system designed to significantly enhance desalination efficiency and economic feasibility. The system features a dual-tank configuration integrated with a solar collector, which optimizes thermal energy storage and ensures consistent feedwater temperatures. Therefore, continuous operation is possible despite fluctuations in solar radiation. An assessment of the system's performance under various solar radiation conditions predicted an average daily permeate flux of 14.4 kg/m2 and a specific energy consumption of 1810 kJ/kg, indicating superior thermal efficiency. The economic analysis revealed a competitive levelized water cost of $25.75 per cubic meter, highlighting the system's potential as a viable alternative to conventional desalination technologies. These findings suggest that the proposed DCMD system is a leading technology in the pursuit of sustainable desalination. Considering its thermal management and cost-effectiveness, the system presents a transformative solution for sustainable freshwater production in regions with abundant solar resources.

Synergistic cotreatment of cooling tower blowdown and produced waters: Techno-economic, sustainability, and optimization systems analyses

A blowdown and produced water cotreatment train design was preliminarily simulated to explore water-energy nexus synergy. This process model was able to provide results concerning water compositions, chemical demand, and energy intensity. The computational expense associated with this simulation made it intractable to use within optimization algorithms for further informative, comprehensive systems analyses. This work details the efforts of developing a framework suitable for the optimization of computationally demanding wastewater treatment train simulations, specifically demonstrated for the cotreatment train’s process, economic, and sustainability models. The unique challenges of the cotreatment train model motivated a modified surrogate optimization methodology to be developed. Using this framework, worst and best case economic scenarios were optimized to minimize the levelized cost of water (LCOW) employed in a reduced-order model-based simulation. Applying the optimal designs obtained from the surrogate optimization into the original comprehensive simulation resulted in an expected range of LCOW from $2.01 to $4.43m-3. Other established techno-economic and sustainability indicators further inform on process implications. The process was compared to current management practices of blowdown water treatment and produced water injection to discuss the advantages and disadvantages of the proposed cotreatment train designed for water reuse. The cotreatment process was estimated to have lower levelized treatment costs but require more chemicals and energy to manage a higher salinity wastewater than pure blowdown water alone. If sustainable management goals motivate produced water remediation, the cotreatment process can be beneficial for the broader scope of water management.

Techno-economic assessment of vertical axis wind turbine driven RO desalination with compressed air energy storage for remote communities

Renewable energy desalination is gaining much attention in remote off-grid communities facing challenges in accessing clean water. Typically, batteries ensure the continuous operation of small-scale renewable reverse osmosis (RO) desalination systems; however, they are expensive and have relatively shorter lifespans. This study investigates the implementation of a compressed air energy storage (CAES) system coupled with a vertical axis wind turbine (VAWT) to directly drive small-scale RO desalination, potentially replacing batteries and reducing energy conversions. A Simulink model was developed to simulate the performance of a VAWT-driven CAES operating RO units, adaptable for both technical and economic assessments. Parametric studies have identified the optimal configuration. The most cost-effective configuration, utilising eleven VAWTs and a pressure exchanger (PX), achieves a levelised cost of water (LCOW) of 1.63 US$/m3 and an annual water production of 9400 m3. The normalised daily water production per square metre of turbine swept area at the study site is 0.19 m3/m2/day at an average wind speed of 5 m/s. While this configuration has a higher initial capital cost, it yields the lowest LCOW. The CAES system effectively addresses the intermittency challenges of wind energy. This study presents a novel, battery-free VAWT-CAES-RO system as a sustainable desalination solution for remote communities, offering a promising approach to address water scarcity in an environmentally friendly manner.

Performance modeling and cost optimization of a solar desalination system using forward osmosis with energy storage

This study presents the design and performance evaluation of a solar-driven water desalination system based on forward osmosis (FO) with thermally responsive ionic liquids (ILs). FO is a two-step process involving dilution of the ILs with water, followed by heating above a critical temperature to induce phase separation of liquid water from the IL. This regeneration step can be achieved by integrating FO with low-grade solar energy, which is abundant in regions that face severe water scarcity. A system design is presented that couples an FO membrane module with a compound parabolic concentrator solar collector and thermal energy storage to minimize solar intermittency and produce clean water at a distributed scale of 10 m3/day. To determine the optimal sizing of components in the system, a technoeconomic analysis using the TRNSYS software is performed with the goal of minimizing the levelized cost of water (LCOW). Notably, over 96 % of the energy required for regeneration comes from solar energy and/or the thermal energy storage (TES) in all cases, with auxiliary heat from electricity being used to maintain a continuous process. To evaluate the potential of solar-FO in three different locations within the United States, a case study is presented for Phoenix, AZ; San Diego, CA; and Atlanta, GA. The simulation results reveal that for a small-scale desalination system, LCOW values as low as $1.31/m3 can be attained, with the potential to approach $1/m3 by lowering the costs of the solar collector and FO module based on a sensitivity analysis.

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 %.

Brine concentration using air gap diffusion distillation: A performance model and cost comparison with membrane distillation for high salinity desalination

Zero liquid discharge (ZLD) has emerged as a treatment process to address the challenges with brine disposal from desalination plants. To achieve ZLD, a brine concentrator is commonly used to extract water up to a high salinity approaching saturation. However, state-of-the-art brine concentrators are energy-intensive thermal evaporators comprising expensive metal alloys and complex maintenance. This study presents the design of a new brine concentrator referred to as air gap diffusion distillation (AGDD) that operates without a membrane up to a high salinity. A holistic analytical model is developed to evaluate the system performance in terms of its energy efficiency (gain output ratio, GOR) and water flux (represented as the recovery ratio, RR), as these metrics directly impact the levelized cost of water (LCOW). A multi-pass AGDD system achieves an overall water recovery of ~70 % and GOR of 7 (88 % latent heat recovery) with an initial feed salinity of 70 g/kg. A comparison is made to its thermodynamically similar counterpart, air gap membrane distillation (AGMD), which reveals that AGDD outperforms AGMD by eliminating heat and mass transport resistances associated with the membrane. The corresponding LCOW is 1.6× lower than AGMD, making it promising as a brine concentrator to achieve salinities >200 g/kg for minimal liquid discharge.

Optimize and analyze a large-scale grid-tied solar PV-powered SWRO system for sustainable water-energy nexus

The lack of clean water and access to energy are two major obstacles to global sustainable systems. The development of solar photovoltaic (PV) technology gained the attention of water desalination projects due to its cost decline, carbon-free emission, and the on-site energy production. However, studies on in-depth analysis of the performance of these systems remain rare. This study performs a comprehensive a design optimization and seven-factor analysis (energy, exergy, economic, environmental, energoeconomic, exergoeconomic, enviroeconomic - 7E) of a grid-tied PV system powering a large-scale seawater reverse osmosis (SWRO) plant. First, an optimal design model is developed based on real hourly measured data for the SWRO load demand and renewable resources, while considering net energy metering mechanism. The objective function is delineated to diminish the energy cost of the system, concomitant with the imposition of operational constraints. Second, an analytical model is established to perform exergetic calculations for the optimal design. Third, a sensitivity analysis is conducted to show how the model parameters affect the system design and costs. The results show that the optimal system relies on a 4.25 MW solar PV array and a 3.125 MW grid-tied inverter. This configuration reduces the levelized cost of energy by 48.3 % and carbon emissions by 50 % compared to a grid-only system. The implementation of net-metering has also maximized the designed system's revenues to 263,834 $/year. Further, the optimally designed system achieves a lower levelized cost of water (0.2217 $/m3), minimal capacity shortage, and negligible unmet load ratios (0.048 %) despite grid outages. From the exergetic assessment, the proposed system has a high exergy efficiency (9.3 %) which can be achieved despite the high value of the exergy loss. Moreover, the energoeconomic and exergoeconomic indicators have recorded tiny values (3.35E-5 kWh/$ and 0.0311 kWh/$, respectively), which are considered a desired outcome. Notably, a profit of 4285.4$ is achieved through the sale of carbon emissions reduction. The sensitivity analysis revealed an increase in the system's total cost of 4.91 % and 9.36 % and the system's energy cost of 4.91 % and 8.7 % if the energy purchase price raised by 10 % and 20 %, respectively. Also, it indicates that a fall in the electricity sellback rate of 10 % would remarkably raise the system's energy cost by 47.3 %. Finally, reducing the PV-Inverter costs by 15 % would drop the system's net present and energy costs by 51.4 % and 60 %, respectively. Overall, the insights from this study have the potential to expedite the realization of sustainable development goals 6, 7, and 13, particularly in developing nations abundant in solar energy resources.

Techno-Economic Analysis of Reverse Osmosis Desalination Plant Powered by Hybridized PV and CSP Systems for Irrigation Water

Large market opportunities exist for solar powered Reverse Osmosis (RO) desalination technologies in fertile but arid areas with large solar and sea water resources. A challenge to realizing these markets is the variable nature of solar resources, which for the desalination plant can lead to high water costs due to low capacity factors (CF) and increased maintenance costs due to repeated start-ups and shut-downs. A potential solution is to power RO plants using both PV and CSP with Thermal Energy Storage (TES) with an aim to reduce shut-downs, and increase CF. In this study, three solar energy systems to power RO are considered: 1) PV only; 2) CSP with central receiver (CR) and TES; 3) PV and CSP with CR and TES. Two RO operational strategies are considered: 1) nominal load only; 2) variable load between minimal and nominal. The performance of these systems is simulated for Mersin, Turkey, using TMY data. The PV and CSP with TES system and variable RO operation achieved the levelized cost of water (LCOW) 1.92 USD m-3 with an RO CF of 60.8%.

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.

Bi-objective optimal design of desalination plants considering the uncertainty of renewable energy sources

Desalination systems are commonly used in isolated areas to supply drinking water. However, they usually rely on fossil fuels, which emit greenhouse gases. Renewable energy sources can be used to power desalination systems, but they are intermittent. To address this, the power generation or the capacity of energy and/or water storage can be increased, but this increases the cost. In this paper, we present a bi-objective optimization methodology for designing a desalination system that is powered by renewable energy sources. The methodology aims to maximize reliability while minimizing the levelized cost of water (LCOW) by including the inherent uncertainty in renewable energy generation. We applied this methodology in the Guajira Peninsula, a region of Colombia with serious problems of drinking water scarcity, to evaluate photovoltaic (PV), wind, and PV/wind hybrid systems, determining the optimal combination of wind turbines, photovoltaic (PV) modules, desalination unit characteristics, water storage capacity, and batteries. We also introduced a new indicator, the Reliability - LCOW ratio (RLR), to assist in selecting the optimal configuration. Our results indicate that the renewable systems are feasible, achieving reliability levels between 92% and 95% and LCOW values between 0.82-0.84 USD/m3, when compared to fossil fuel configurations. Despite this, the PV-only system exhibited a significantly higher installed capacity when compared to wind and hybrid systems, while the latter two showed relatively similar characteristics. An analysis about the use of the water tank as a natural battery compared with electricity storage proved that the battery bank was more effective for the PV-only system, while the water tank was more suitable in systems where the use of wind power is predominant. Furthermore, an analysis of the direct CO2 emissions of the fossil fuel configurations shows that the renewable solutions reduce emissions by over 150 tons-eq/y.

A theoretical analysis on upgrading desalination plants with low-salt-rejection reverse osmosis

Brackish water/seawater reverse osmosis (RO) desalination is a key solution to global freshwater scarcity. However, the water recovery (Rw) in conventional RO desalination plants is limited by the operating pressure (∆P). As a novel staged RO technology, low-salt-rejection RO (LSRRO) can potentially enhance the Rw in the desalination plants. In this study, we perform process modeling and techno-economic analysis to evaluate the viability of upgrading current RO desalination plants with LSRRO. Based on the results from process modeling, in typical brackish water RO (BWRO) and seawater RO (SWRO) desalination plants, adding an LSRRO stage can effectively enhance the Rw by 21 and 53 %, respectively, and the energy efficiencies are not compromised with the enhanced Rw. From techno-economic analysis, upgrading RO desalination plant with LSRRO is highly viable. Specifically, after adding an LSRRO stage in a BWRO plant, the Rw can be enhanced from 71 to 81 % without notably increasing the levelized cost of water (LCOW), and adding an LSRRO stage in the SWRO plant with zero brine discharge can reduce the LCOW by 30 %. The findings in our study highlight the vast potential of adopting LSRRO in brackish water/seawater desalination plants, and shed lights on the design of future desalination plants.

Techno‐enviro‐economic design of small‐scale membrane‐based seawater desalination systems integrated with hybrid autonomous renewable power systems

AbstractThis article aims to search the technical, environmental, and economic model of an off‐grid hybrid power generation system that supplies electricity to a seawater reverse osmosis (RO) system. Net present cost (NPC) and levelized cost of electricity (LCOE) values were used to determine the optimal system sizing powering a reverse osmosis desalination system for different sites where is located south and west coast of Türkiye. In the proposed power systems, PV panels, wind turbines, diesel generators, lead‐acid batteries, and converters were used. In the instance where the lowest LCOE of 0.301$/kWh is calculated, the optimal system comprises of a 25.7 kW PV array, one wind turbine (rated at 10 kW), 152 kWh LA batteries, and a 6.76 kW converter. The levelized cost of water (LCOW) value for this case was calculated as 1.168 $/m3. The LCOE value was calculated as 0.529 $/kWh for the power system, which is considered as a base case and consists of only a diesel generator, where no renewable energy source is used. For the base case, the carbon footprint of electricity generation is 35,127 kg/year. According to CO2 sequestration analysis result, the number of trees (Pinus Brutia) to be planted was calculated as approximately 164 tree/year over the lifetime of the power system for base case.

Water harvesting system in greenhouses with liquid desiccant technology

The study aimed to investigate the feasibility of utilizing atmospheric water generation systems (AWG) in the agricultural sector by implementing a liquid desiccant-based moisture harvesting system. The system was modeled using an adiabatic simulation approach to evaluate the performance of the system in terms of moisture removal rate during the dehumidification process. Additionally, an economic analysis was conducted to compare the costs and payback period of three different water extraction scenarios for the agricultural sector in Jordan. The scenarios considered the Levelized Cost of Water (LCOW) and payback period over a 20-year life cycle. The results of the study showed that the average annual water extracted during the tomato cultivation period was 2,198 m3 and 1,451 m3 for the strawberry cultivation period. The payback period for non-subsidized water selling prices was between 6 and 12 years and between 3 and 4 years if water was purchased from artesian wells. The LCOW for the different scenarios ranged from 1.92 USD/m3 to 2.91 USD/m3, depending on the type of crop and the desiccant solution used. Overall, the study demonstrated that the implementation of an AWG system in the agricultural sector can be a viable option with a reasonable payback period and cost-competitive LCOW.

Life cycle assessment and life cycle costing of a building-scale, solar-driven water purification system

Water purification systems require material resources and energy to build and operate, thus leading to environmental burdens. Mature water treatment technologies such as reverse osmosis and multi-effect distillation have been extensively studied for their environmental impacts. There is still a lack of such studies in one of the promising technologies, namely, air gap membrane distillation (AGMD). This study performs a cradle-to-grave life cycle assessment (LCA) and a life cycle costing of a solar-driven AGMD water purification system. This research also assesses the cost competitiveness of the system compared to local bottled water using a levelized cost of water (LCOW) approach. The study shows that the environmental impacts of the water purification systems (using a functional unit of 590 m3 of drinking water produced over a time period of 15 years) are: 27,224 kg CO2eq (climate change), 2,408 kg 1.4-DCB (human carcinogenic toxicity), 3,100 kg 1.4-DCB (marine ecotoxicity), and 2,286 kg 1.4-DCB (freshwater ecotoxicity). The solar PV sub-system and solar thermal sub-system have a much higher impact than the water purification sub-system. The LCOW calculations show that the system, with its current runtime of six hours using solar energy, has a levelized cost of 0.46 USD/L. Alternative scenarios, such as the use of grid electricity and end-of-life treatment of generated wastes, are also evaluated. A sensitivity analysis is performed on four parameters, i.e., component lifetime, maintenance frequency, discount rate, and AGMD module production cost. This study could be useful to local governments, investors, and potential customers interested in the water purification system's environmental footprint and cost competitiveness.

Predictive performance and costing model for Membrane Capacitive Deionization (MCDI) at operational scale

A model that can be used to predict the performance of Membrane Capacitive Deionization (MCDI), including current efficiency, flowrate of the product water, water recovery and energy consumption is established in this work. The model was developed using a Response Surface Model approach that considers the influence of influent conductivity, flowrate passing by the electrodes and applied current on MCDI system performance rather than relying on electrochemical principles or the description of the intrinsic properties of the carbon electrodes and ion exchange membranes. In the scenarios tested here, flowrate contributes the most towards MCDI performance. The appropriateness of using NaCl for an MCDI performance model is confirmed. The model can be applied to extensive applications with two examples detailed here including a small town potable application of 100 m3/day with influent water of 2000 μS/cm and an industrial wastewater application of 1000 m3/day with influent water of 4000 μS/cm. A costing model is developed and applied to the two scenarios with the optimised levelized cost of water (LCOW) found to be US$0.74/m3 for the small town and US$1.08/m3 to US$1.41/m3 for the industrial wastewater (product water quality dependent). By maximising the production rate, the LCOW can be minimised. The model presented here can be applied to a wide range of applications or used as a framework for efficient performance modelling of other MCDI configurations.

Desalinated Water Costs from Steam, Combined, and Nuclear Cogeneration Plants Using Power and Heat Allocation Methods

This work presents a detailed thermo-economic analysis of unit water costs from dual-purpose cogeneration plants. The power levelized cost was first calculated for stand-alone steam, nuclear, and combined-cycle power plants. The cost of energy needed to operate the desalination systems connected to power plants was evaluated based on two different approaches: power- and heat-allocated methods. Numerical models based on the heat and mass balances of the power and desalination plants’ components were developed and validated. Comprehensive and updated data generated using Desaldata libraries were correlated to estimate the capital, labor, overhead, and maintenance costs for different desalination systems. The levelized water cost produced by multi-effect distillation, multi-effect distillation with vapor compression, multi-stage flash, and reverse osmosis systems connected to different power plants was estimated. The impact of various controlling parameters, including the price of natural gas, nuclear power plant installation cost, and the desalination capacity on water cost, was investigated. For all simulated cases, the levelized water cost evaluated using the heat-allocated method was found to be lower by 25–30% compared to that estimated using the power-allocated method. The cost of water produced using reverse osmosis remains below that produced by other desalination technologies. However, using the heat-allocated method to estimate the levelized water cost narrows the gap between the costs of water produced by multi-effect distillation and that produced by seawater reverse osmosis. The results also show that the use of the multi-effect distillation process in a cogeneration configuration rather than multi-effect distillation with vapor compression can result in a lower water cost. The profit analysis shows slight differences between the profit of a power plant connected to a reverse osmosis system and the profit of a power plant connected to a plain multi-effect distillation system.

Analysis of variable reverse osmosis operation powered by solar energy

The use of solar photovoltaic (PV) to power reverse osmosis (RO) plants and produce water will enhance the sustainability of water supplies in several dry remote coastal areas. Varying the operating power level of the RO plant has been proposed in the literature as a solution to accommodate intermittent PV power sources. Such variable operation is intended to match the RO load to the available PV power. Nevertheless, such operation has not been used outside research laboratories and small pilot plants. In this work, we used different case studies to evaluate the benefit of using variable operation and its effects on system design, system operation and levelized cost of water (LCOW). A simulation model for the optimal operation of the system is developed using three-dimensional dynamic programming (DP) to determine the power levels of the battery, diesel generator, and RO plant while optimal sizing of these plants and associated water tanks and PV generators was solved using an ordinal optimization (OO) approach. The use of OO permitted the examination of a large design search space quickly but exhaustively using a simple model. We then ranked the different designs in increasing cost order and assessed a reduced number of these using an accurate model to simulate the system on an hourly basis for all the days of a year. This approach relies on the fundamental tenet of OO: “order is robust to the noise introduced by the simple model”. Different power modulation strategies are investigated, and their implications on the hydraulic operating parameters are presented. In this respect, we investigate the operation of the RO system at varying power levels and different sizes of backup systems (battery and diesel generator). This ability to vary the RO operating level helped in a better matching of the system load to the available, yet variable, PV power, even when the backup and storage systems were at a minimum. Operating an RO plant with PV and backup systems is found to be far more cost effective than operation without backup systems, reducing costs by 37–55% for the case studies considered.

Cost optimization of low-salt-rejection reverse osmosis

Low-salt-rejection reverse osmosis (LSRRO) is an emerging membrane-based desalination technology for concentrating brines with potentially lower energy consumption and cost than thermally driven processes. We assess the technoeconomic performance of LSRRO by using an optimization model that minimizes the levelized cost of water (LCOW). We develop detailed models for the RO module and other equipment using WaterTAP (Water treatment Technoeconomic Assessment Platform), an open-source simulation and optimization software for water treatment. We improve upon previous LSRRO cost optimization studies by optimizing the salt permeability for each stage, which has significant implications for technoeconomic performance. We present the cost-optimal design, operation, and performance for three cases: 35 g/L TDS feed at 70 % recovery, 70 g/L at 55 %, and 125 g/L at 35 %. The cost-optimal LCOW and specific energy consumption (SEC) for these cases are 0.70, 1.89, and 7.41 $/m3 and 3.9, 8.4, and 30.4 kWh/m3, respectively. For each case, we use sensitivity analyses to provide guidance on key factors that impact economic viability. We also present the cost-optimal LCOW and SEC for feed concentrations between 5 and 220 g/L TDS and recoveries between 30 and 90 %. Lastly, we compare LSRRO to other high-salinity desalination technologies and find that it may be cost-competitive below feed concentrations of 125 g/L.