A predictive controller for a heaving buoy producing potable water

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

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

Numerical study of a point absorber wave energy converter with different power take-off systems

Conceptual designs of integrated process for simultaneous production of potable water, electricity, and salt

GWECS: An indicator to describe the energy absorption characteristics of wave energy converter arrays in real sea states

Study on the energy capture spectrum (ECS) of a multi-DoF buoy under random waves

The demand for freshwater is increasing globally, particularly in areas with limited water resources. Desalination, the process of removing salt and other minerals from seawater, is one solution that can help meet this demand. However, traditional desalination methods can be energy-intensive and generate significant amounts of waste. To help address these issues, a hybrid wave-to-water desalination system that combines reverse osmosis (RO) with supercritical water desalination (SCWD) can be used to produce freshwater from seawater. SCWD is used to treat the brine produced by RO, while the RO system produces fresh water at a lower energy cost. The system utilizes a wave energy converter (WEC) to harness the energy of ocean waves to power the desalination process by using the motion of waves to directly pressurize the seawater feeding into the RO system. Using ocean waves as an energy source makes the system renewable and reduces the carbon footprint of the desalination process. This paper presents a numerical model of a small-scale zero-waste desalination system powered by off-grid renewable energy along with a sensitivity analysis to determine the optimal configuration of key parameters of the system. An oscillating surge wave energy converter (OSWEC) was selected for the current study to directly pressurize the ocean water to meet the minimum pressure requirement of the RO. The numerical model of the water desalination system was developed using MATLAB-Simulink. WEC-Sim was used to develop the wave energy converter subsystem. A sensitivity analysis was conducted using an irregular wave pattern with a wave height of 0.117 m and a period of 1.68 s to determine the optimal combination of the power take-off (PTO) volumetric displacement, accumulator size, and RO membrane type for the system. Results showed that the type of RO membrane and the PTO volumetric displacement had a much larger impact on the water production rate than the accumulator volume.

Experimental evaluation of a multi-skid reverse osmosis unit operating at fluctuating power input

Modeling of wave energy converters by GPUSPH and Project Chrono

Performance evaluation of two RO membrane configurations in a MSF/RO hybrid system

Agricultural activities in arid regions, like Kuwait, require large volume of water for irrigation purposes. Saline groundwater quality, shortage in treated wastewater supply, and expensive freshwater force farmers to use on-site brackish groundwater reverse osmosis (RO) units to treat brackish to saline groundwater. One of RO units’ primary limitations is the large volume of concentrated brine (reject water) that is generated from these units. Due to the absence of proper policies and regulations to handle reject water from RO units, it is often disposed of illegally over open land surface or unlined pits. Concentrated reject water could have negative impacts on groundwater quality, and uncontrolled pumping of groundwater could affect groundwater levels. Soil salinization due to brine disposal has negative impacts on crops, threatening partial food security attempts of the authorities. The study presented here has been conducted with the objective to assess the impact of RO reject brine on groundwater quality and levels in agricultural farms of Kuwait. This paper presents the initial activities and results of the study to evaluate impacts of RO reject water on groundwater quality and levels and recommend rational utilization of available water reserves for agricultural purposes. Groundwater levels and salinity were measured, and first round of sample collection was carried out from groundwater wells serving the feed water for RO units, product water and reject water from RO units. Samples are analyzed for major ions, trace metals and nutrients. Groundwater levels are regularly monitored to evaluate their fluctuations. Initial results indicate the decline in groundwater table and quality deterioration over the period of time. Preliminary data of this ongoing study and future plans is discussed in this paper.

The origin of Chronic Kidney Disease of unknown etiology (CKDu) that is rapidly invadingthe dry zone of Sri Lanka has not yet been identified. However, occurrence of the disease isthought to be linked with excess levels of fluoride and hardness in drinking water. Hence, thestudy herein focuses to evaluate the suitability of domestic Reverse Osmosis (RO) units;which introduced in CKDu affected areas to remove excess fluoride and hardness.Accordingly, the drinking water quality in CKDu prevalent areas in terms of fluoride andhardness was simulated in the laboratory and the removal of aforesaid constituents usingdomestic ROs was investigated.According to water quality analyses, domestic RO units effectively removed hardness even atextremely high initial concentrations, such as 1,730 mg/L (as CaCO3). Excessive removal ofCalcium and Magnesium by the RO units was observed, thus remineralization of thepermeate up to 80-100 mg/L as CaCO3 is required to ensure health benefits. Meanwhile,fluoride removal was observed to be highly dependent upon initial fluoride and hardnessconcentrations. It was not possible to suggest an „optimum removal level‟ for fluoride, wherepermeate fluoride concentration exceeded the maximum permissible WHO Drinking WaterGuideline value of 1.5 mg/L. However, it may arise at a point where fluoride and hardnessconcentrations in raw water fall within 1.7-3.5 mg/L and 570-1,130 mg/L as CaCO3,respectively.Plausible reasons for ineffective removal of fluoride could be the relatively small size andlow ionic charge of fluoride. Additionally, high concentration of heavy ions may interferewith fluoride adsorption of activated carbon filter in the domestic RO unit. Effective fluorideremoval could be achieved by adopting appropriate pre-treatment methods for hardnessremoval. Separate threshold levels for fluoride and hardness levels in drinking water shouldbe defined, especially for CKDu patients.Keywords: Chronic Kidney Disease, Domestic reverse osmosis units, Fluoride, Hardness

A wave energy converter (WEC) system has the potential to convert the wave energy resource directly into the high-pressure flow that is needed by the desalination system to pump saltwater to the reverse-osmosis membrane and provide the required pressure level to generate freshwater. In this study, a wave-to-water numerical model was developed to investigate the potential use of a wave-powered desalination system (WPDS) for water production. The model was developed by coupling a time-domain radiation-and-diffraction method-based numerical tool (WEC-Sim) for predicting the hydrodynamic performance of WECs with a solution-diffusion model that was used to simulate the reverse-osmosis (RO) process. The objective of this research is to evaluate the WPDS dynamics and the overall efficiency of the system. To evaluate the feasibility of the WPDS, the wave-to-water numerical model was applied to simulate a desalination system that used an oscillating surge WEC device to pump seawater through the system. The hydrodynamics WEC-Sim simulation results for the oscillating surge WEC device were validated against existing experimental data. The RO simulation was verified by comparing the results to those from the Dow Chemical Company’s reverse osmosis system analysis (ROSA) model, which has been widely used to design and simulate RO systems. The wave-to-water model was then used to analyze the WPDS under a range of wave conditions and for a two-WECs-coupled RO system to evaluate the influence of pressure and flow rate fluctuation on the WPDS performance. The results show that the instantaneous energy fluctuation from waves has a significant influence on the responding hydraulic pressure and flow rate, as well as the recovery ratio and, ultimately, the water-production quality. Nevertheless, it is possible to reduce the hydraulic fluctuation for different sea states while maintaining a certain level of freshwater production, and a WEC array that produces water can be a viable, near-term solution to the nation’s water supply. A discussion on the dynamic impact of hydraulic fluctuation on the WPDS performance and potential options to reduce the fluctuation and their trade-offs is also presented.

Arsenic Removal in Drinking Water Sources by Reverse Osmosis Units in Real Life Scenarios

In the reverse osmosis (RO) desalination process, a salt water solution is pressurized to overcome the osmotic pressure across a semi-permeable membrane. A few groups have proposed that a wave energy converter (WEC) having a seawater based, hydraulic power take-off can could be used to pressurize the feedwater for an RO system. However, coupling the wave energy harvesting process and the RO desalination process imposes unique design constraints on the fluid power system, such as pressure limits of conventional RO system components. In this study, a fluid power circuit with a switch-mode power transformer is used to transfer power while keeping the pressure of the power take-off and RO processes relatively decoupled. The switch-mode power transformer studied herein adds fewer costly components and less significant loss mechanisms to the system than a conventional hydraulic transformer performing the same function. The switch-mode power transformer uses the inertia of a hydraulic motor driven electric generator and switching of the hydraulic motor inlet between high and low-pressure sources to decrease the pressure at which power is being transmitted to the RO process. This process is analogous to DC-DC switching power transformers in the electrical domain. This study seeks to demonstrate this unique switch-mode system as a potential solution for coupling the wave-energy harvesting process with the reverse osmosis process. The system is modeled and studied in the context that the transformer and RO system are onshore, 500 meters from the WEC. Power captured from the WEC is transmitted through a long pipeline to shore. A distributed parameter model is used to model the pipeline dynamics, simultaneously revealing the significance of these dynamics and the robustness with which the switch-mode transformer decouples the pressure dynamics at the RO feed from the pipeline dynamics. The switch-mode power transformer is estimated to be 76% efficient while the system, as a whole, is estimated to be 45% efficient.