Seawater Reverse Osmosis Desalination Research Articles

Simulation of reverse osmosis seawater desalination system based on virtual reality technology

Simulation of reverse osmosis seawater desalination system based on virtual reality technology

Potential biofoulants in open-ocean SWRO desalination station in Jeddah, KSA

Abstract Currently, water desalination is an essential solution for the high demand for water worldwide. A sea water reverse osmosis (SWRO) facility fulfills the need for pure water. Conventionally, these plants use open-ocean water that is rich with natural organic matter (NOM) and transparent exo-polymers (TEP). Marine flora increases the demand for fouling the membrane in the SWRO facility that raises the pressure and results in the halting of the station. Therefore, water samples were collected from SWRO stages during high-pressure problems to probe the factors that play a key role in membrane biofouling. NOM and TEP particles physically disappeared after the dual-media filter (DMF). However, turbidity significantly increased after the DMF stage, which is indicative of the fragmentation of NOM and TEP particles. Chlorophyll and phycoerythrin disappeared after the DMF stage but were observed in the reject stage (brine). Therefore, NOM and TEP are playing a role indirectly in membrane biofouling. Fifteen potential species of heterotrophic prokaryotes are identified and recorded in all stages of the SWRO. The characteristics of these species imply that they form a cooperative consortium that potentially creates the biofilm in the RO membrane. Therefore, SWRO facilities that use open-ocean water must develop highly sophisticated pretreatment technology to eliminate the seeds of the biofilm that fouls RO membranes.

Role of Seawater Desalination in the Management of an Integrated Water and 100% Renewable Energy Based Power Sector in Saudi Arabia

This work presents a pathway for Saudi Arabia to transition from the 2015 power structure to a 100% renewable energy-based system by 2050 and investigates the benefits of integrating the power sector with the growing desalination sector. Saudi Arabia can achieve 100% renewable energy power system by 2040 while meeting increasing water demand through seawater reverse osmosis (SWRO) and multiple effect distillation (MED) desalination plants. The dominating renewable energy sources are PV single-axis tracking and wind power plants with 243 GW and 83 GW, respectively. The levelised cost of electricity (LCOE) of the 2040 system is 49 €/MWh and decreases to 41 €/MWh by 2050. Corresponding levelised cost of water (LCOW) is found to be 0.8 €/m3 and 0.6 €/m3. PV single-axis tracking dominates the power sector. By 2050 solar PV accounts for 79% of total electricity generation. Battery storage accounts for 41% of total electricity demand. In the integrated scenario, due to flexibility provided by SWRO plants, there is a reduced demand for battery storage and power-to-gas (PtG) plants as well as a reduction in curtailment. Thus, the annual levelised costs of the integrated scenario is found to be 1–3% less than the non-integrated scenario.

Fouling indicators for field monitoring the effectiveness of operational strategies of ultrafiltration as pretreatment for seawater desalination

The applicability of fouling indicators for real time performance assessment of UF feed pretreatment in RO seawater desalination was explored in a field study using an integrated seawater UF-RO desalination pilot plant. Fouling indictors were evaluated with respect to quantification of UF backwashability, unbackwashed fouling resistance and UF fouling rate. Feed water quality and coagulant dose demonstrated measurable impact on both UF fouling rate and effectiveness of foulant removal via UF backwash. Increased coagulant dose promoted higher rate of cake formation and in turn improved backwash efficiency. However, there was a maximum coagulant dose beyond which there was no further backwash improvement. Backwash effectiveness increased with higher backwash flux and duration, up to threshold upper limits, but declined as the filtration period increased above a threshold limit. Field tests during periods of temporally varying feed quality demonstrated that higher fouling rate (promoted by inline coagulation) resulted in more effective backwash and correspondingly lower progressive rise in post-backwash UF resistance. The study results suggest that real-time UF fouling indicators, based on UF filtration resistance metrics and backwash effectiveness, should be potentially useful for tracking UF performance and thus for deployment of UF feed-back control for optimal performance of UF feed pretreatment.

Wind-driven SWRO desalination prototype with and without batteries: A performance simulation using machine learning models

In this paper, two studies are carried out related to the performance simulation and analysis of a wind-powered seawater reverse osmosis (SWRO) desalination plant prototype installed on the island of Gran Canaria (Spain). Three machine learning techniques (artificial neural networks, support vector machines and random forests) were implemented to predict the performance (pressure, feed flow rate and permeate flow rate, and permeate conductivity) of the SWRO desalination plant. Subsequently, plant operation was analysed in two different operating modes: a) constant pressure and flow rate through connection with a wind-battery microgrid, b) variable pressure and flow rate as a function of the power supplied by a stand-alone wind microgrid without energy storage. The paper supports two main outcomes. First, support vector machines and random forests are significantly (5% significance level) better predictors of the plant's performances than neural networks. Second, over one year, the operating mode that considers variable pressure and flow rate operates more continuously (higher operating frequencies and lower stop/start frequencies) than the constant pressure and flow rate alternative; however 1.2 times less permeate with 1.08 higher conductivity is produced on an annual basis.

A novel autonomous PV powered desalination system based on a DC microgrid concept incorporating short-term energy storage

Seawater reverse osmosis (SWRO) desalination units coupled with renewable energy technologies such as photovoltaics are a very appealing suggestion, especially in remote areas, such as islands and coastal regions, which often face lack or low quality fresh water coupled with electrical energy shortages. This paper regards an experimental investigation of a PV powered small-scale SWRO desalination system which employs hydraulic energy recovery, based on a DC microgrid concept and incorporates a short term electric energy storage in the form of hybrid capacitors and a short term hydraulic energy storage in the form of pressure vessels. Α multi-agent decentralized energy management system which relies on intelligent agents and employs Fuzzy Cognitive Maps for its implementation, allowing for efficient operation of the desalination system under variable conditions (variable feed pressure), was developed and implemented. The experimental results show that it is feasible to operate efficiently such PV powered SWRO system. Furthermore, the desalination unit produces potable water during daytime even at periods when the produced energy from the PV array is not sufficient to operate the desalination unit. Moreover, the SWRO system shows a continuous and smooth operation, meaning small feed water pressure variations at sharp rapid solar irradiation intensity variations due to the incorporated short-term storage. In addition, the intelligently managed PV powered SWRO system with short term storage produces considerably more fresh water, especially at days with variable solar irradiation, as compared to the same SWRO system directly PV driven without storage and any control.

Learning Curve for Seawater Reverse Osmosis Desalination Plants: Capital Cost Trend of the Past, Present, and Future

AbstractSeawater reverse osmosis (SWRO) desalination is expected to play a pivotal role in helping to secure future global water supply. While the global reliance on SWRO plants for water security increases, there is no consensus on how the capital costs of SWRO plants will vary in the future. The aim of this paper is to analyze the past trends of the SWRO capital expenditures (capex) as the historic global cumulative online SWRO capacity increases, based on the learning curve concept. The SWRO capex learning curve is found based on 4,237 plants that came online from 1977 to 2015. A learning rate of 15% is determined, implying that the SWRO capex reduced by 15% when the cumulative capacity was doubled. Based on SWRO capacity annual growth rates of 10% and 20%, by 2030, the global average capex of SWRO plants is found to fall to 1,580 USD/(m3/d) and 1,340 USD/(m3/d), respectively. A learning curve for SWRO capital costs has not been presented previously. This research highlights the potential for decrease in SWRO capex with the increase in installation of SWRO plants and the value of the learning curve approach to estimate future SWRO capex.

Effect of chemical and physical factors on the crystallization of calcium sulfate in seawater reverse osmosis brine

A major challenge of seawater reverse osmosis (SWRO) desalination process corresponds to the management of concentrated brine waste because discharging the brine back into the sea influences the marine ecosystem and incurs additional costs to plants. A membrane distillation crystallizer (MDC) can further produce clean water and simultaneously recover valuable resources from the concentrated brine; this is more environmentally and economically optimal. SWRO brine contains salts, which contribute to scaling development during the MDC operation. Hence, the main goals of this study was to observe the crystallization tendency of calcium sulfate (CaSO4) under high salinity and, to examine other inorganic and organic compounds and operational conditions that affect the CaSO4 crystallization. The crystallization tendency of CaSO4 in SWRO brine was examined with respect to different temperatures; changes in pH values; and in the presence of co-existing ions, chemical agents, and organic matters as well as physical factors. The results showed that the size and quantity of crystals formed increased at higher temperatures. Furthermore, an increase in the pH values increased the crystal size. At higher pH, the complexion of NaCl along with CaSO4 was created. Moreover, stirring enhanced CaSO4 crystal formation due to the kinetic mechanism.

해수 담수화 공정의 고압펌프 가변속 운전에 따른 동력 절감

In seawater reverse osmosis desalination plant, pumps consume nearly 90% of the electrical energy. The purpose of this study is to compare the energy consumptions of the high pressure pump before the installation of inverter and after the installation of the inverter and to evaluate the performance of variable speed driven high pressure pump. Calculated energy saving of the variable speed driven high pressure pump was around 14% at relatively clean condition of the membrane. However, the certain extent of the saving should be continuously monitored year by year depending on the fouling and aging of the membranes.

Cfd simulation of the effects of extended angle on the mixing performances of rotary pressure exchanger

By directly contacting with the high and low-pressure fluids, rotary pressure exchanger(RPE) can efficiently recover the high pressure energy of the concentrated salt water and achieve pressure energy transfer, as well as reduce the operation cost of reverse osmosis desalination. Therefore, controlling the radial mixing caused by the direct contact between different fluids is a critical technology for the RPE development to reduce the energy consumption. In this paper, RPE models were built based on the background of reverse osmosis seawater (SWRO) desalination system. On the basis of RPE extended angle concept, the mixing performances of the turbulence model were firstly simulated by CFD software. Then, the structure and operation parameters were changed to analyse the flow field information and reveal the unsteady flow mechanism in RPE. And the flow characteristics of unsteady flow field and the development of high and low- pressure fluid mixing properties in the rotor duct were investigated. The simulation results showed that when the extended angle was ±30˚, smaller volume mixing rate can be obtained compared with no extended angle. The study results can provide a basis for the design and optimization of RPE, and also establish a theoretical guidance for controlling the hydraulic driven rotary device.

Investigation of Algal Biotoxin Removal during SWRO Desalination through a Materials Flow Analysis

The operation of seawater reverse osmosis (SWRO) desalination facilities has become challenged by the increasing frequency and severity of harmful algal blooms (HABs). The efficiency of algal toxins removal during SWRO and pretreatment processes has critical human health implications. Therefore, a probabilistic materials flow analysis (pMFA) was developed to predict the removal of algal toxins in source water by various pretreatment configurations and operations during SWRO desalination. The results demonstrated that an appreciable quantity of toxins exists in the SWRO permeate (ng/L–µg/L levels), the backwash of pretreatment, and final brine rejects (µg/L–mg/L levels). Varying the pretreatment train configuration resulted in statistically significant differences in toxin removals, where higher removal efficiencies were evidenced in systems employing microfiltration/ultrafiltration (MF/UF) over granular media filtration (GMF). However, this performance depended on operational practices including coagulant addition and transmembrane pressures of MF/UF systems. Acute human health risks during lifetime exposure to algal toxins from ingestion of desalinated water were benign, with margins of safety ranging from 100 to 4000. This study highlights the importance of pretreatment steps during SWRO operation in the removal of algal toxins for managing marine HABs.

Energy-saving “NF/EDR” integrated membrane process for seawater desalination. Part II. The optimization of ED process

For the high pressure and high energy consumption of Seawater reverse osmosis (SWRO) desalination technology, an energy-saving “NF/EDR” integrated membrane process for seawater desalination was proposed in our study. The seawater desalination by Nanofiltration (NF) membrane with high desalination capacity has been reported in our previous paper. This manuscript is the second part of this system about the optimization of electrodialysis (ED) process, where ED process with polarity reverse (EDR) was applied to treat the NF output with the conductivity of 8790μS/cm. A series of operation parameters of the ED process were optimized. More specifically, the effects of the concentrate and dilute flow, internal water flow model, as well as temperature of raw water on separation performances were well investigated. Besides, the optimal period of polarity reverse was determined. The results showed that with the dilute stream flow of 150L/h, concentrate stream flow of 120L/h and the ED stack consisted of one stage with two passages, with the proportion of 27/23 in cell pairs, together with suitable raw water temperature, the desalination rate of ED process could be about 90% and the energy consumption was 0.98KWh/(m3 produced water). Furthermore, the membrane fouling could be effectively avoided by EDR with a period of reversing electrodes at 3h. All the results demonstrated that the optimization of ED process is beneficial to the increasing of desalination rate as well as the decreasing of energy consumption in the “NF/EDR” integrated system, besides, it provided research basis and data support for the pilot-scale system of the “NF/EDR” integrated membrane process.

Reducing specific energy consumption of seawater desalination: Staged RO or RO-PRO?

Specific energy consumptions (SECs) in seawater RO desalination employing staged RO and RO-PRO with energy recovery devices are investigated using systematic mathematical methods. The SECs in both configurations are minimized by solving a constrained nonlinear optimization model which optimally selects operating conditions and allocates membrane area between different membrane units. It is shown that both staged RO and RO-PRO are noticeably advantageous over single-stage RO only if a dimensionless parameter γtotal=AtotalLpπ0/Q0 is sufficiently large. The RO-PRO outperforms staged RO when internal concentration polarization is not severe, water recovery is low (e.g., 30%) and/or membrane area is abundant (e.g., γtotal ≥ 1.6). The staged RO is likely to excel at a high water recovery (e.g., 60%) even though the high-salinity brine enhances the driving force for osmotic energy recovery in the RO-PRO. Both configurations have comparable SECs based on water recoveries of 40% and 50% and a γtotal of 0.8, a representative value in industrial seawater RO plants.

Treatment of cleaning waters from seawater desalination reverse osmosis membranes for reutilization purposes. Part II: Application of photo-Fenton and photocatalysis processes

This is the second part of the study of cleaning waters from seawater desalination reverse osmosis membranes treatment, with the aim of reclaiming them for reuse. In the first part, Fenton process was applied in these wastewaters and a TOC removal of 67% and a final BOD5 value of 14.8mgL−1 O2 were achieved by using 4000mgL−1 of H2O2 and 200mgL−1 of Fe2+. In this part, photo-Fenton and photocatalysis processes were explored in order to enhance mineralization degree. The highest elimination was achieved with the photo-Fenton process at pH 3, where 79% of TOC removal was obtained with 1400mgL−1H2O2 and 70mgL−1 Fe2+ (3 times lower than in the Fenton process) under solar radiation after 60min, and 85.6% after 157min, with the total removal of sodium dodecyl sulfate and obtaining a suitable water for irrigation. This photo-Fenton reaction could also be performed at pH 7, as after 157min, the same elimination is reached. The addition of P25 accelerates the photo-Fenton process, although after one hour of treatment, similar elimination was reached for both conditions. 77% of TOC removal after 180min was obtained under solar radiation at pH 3 by adding 1200mgL−1 of H2O2 with 250mgL−1 of P25 instead of Fe.

Treatment of cleaning waters from seawater desalination reverse osmosis membranes for reutilization purposes. Part I: Application of Fenton process

The scope of the present work is the study of the Fenton process applied to the removal of the organic load of cleaning waters from seawater desalination reverse osmosis membranes in order to be reused for irrigation or in other stages of the process and contribute to the concept of zero discharge in a reverse osmosis desalination plant. Fenton experiments were performed at pH 3 after selecting ratios of H2O2/COD (wt.) between 1.9 and 20, and H2O2/Fe2+ (wt.) between 0.13 and 82.80. For the studied conditions, it was observed that the optimal reaction time was 157min and the optimal reagents doses were above 4000mgL−1 of H2O2 and 200mgL−1 of Fe2+. This combination achieved a maximum TOC removal of 67% and a final BOD5 value of 14.8mgL−1 O2.

Electricity system based on 100% renewable energy for India and SAARC.

The developing region of SAARC (South Asian Association for Regional Cooperation) is home to a large number of people living below the poverty line. In future, providing affordable, universally accessible, reliable, low to zero carbon electricity in this region will be the main aim. A cost optimal 100% renewable energy system is simulated for SAARC for the year 2030 on an hourly resolved basis. The region was divided into 16 sub-regions and three different scenarios were set up based on the level of high voltage direct current (HVDC) grid connections. The results obtained for a total system levelised cost of electricity (LCOE) showed a decrease from 71.6 €/MWh in a decentralized to 67.2 €/MWh for a centralized grid connected scenario. An additional scenario was simulated to show the benefits of integrating industrial gas production and seawater reverse osmosis desalination demand, and showed the system cost decreased by 5% and total electricity generation decreased by 1%. The results show that a 100% renewable energy system could be a reality in the SAARC region with the cost assumptions used in this research and it may be more cost competitive than nuclear and fossil carbon capture and storage (CCS) alternatives. One of the limitations of this study is the cost of land for installation of renewables which is not included in the LCOE calculations, but regarded as a minor contribution.

Adaptive Expert Generalized Predictive Multivariable Control of Seawater RO Desalination Plant for a Mineral Processing Facility

In this paper an adaptive expert generalized predictive multivariable controller (AEGPMC) is developed for control of a seawater reverse osmosis desalination plant, which supplies freshwater for a mineral processing facility. Based on the use of subspace system identification algorithms a dynamic multivariable model, which considered the permeate flow rate and the permeate conductivity as the controlled variables, is derived and its parameters are computed from experimental data. This model is used in the design of the AEGPMC. The obtained simulation results demonstrate that the performance of the control system with the designed AEGPMC is much more appropriate and robust than with the other multivariable GPC.

Fractional Order Robust Control of a Reverse Osmosis Seawater Desalination Plant

A fractional-order robust controller to control a reverse osmosis desalination plant is proposed. The dynamics of this plant was experimentally identified. A multivariable mathematical model was obtained which showed large plant parameter variations. The proposed control system is composed of a decoupler, a diagonal compensator of the less variable dynamics, and a fractional order PI controller in each of the two loops. The fractional orders of these last controllers were optimized in order to improve the phase margin robustness. It was shown that these controllers outperformed the robustness achieved using PI controllers.

PCA as tool for intelligent ultrafiltration for reverse osmosis seawater desalination pretreatment

A novel fouling monitoring methodology based on principal component analysis (PCA) has been validated using transmembrane pressure (TMP) data of a pilot-scale pressurized ultrafiltration (UF) system operated with seawater. The evolution of membrane fouling was investigated to determine its relation to the used cleaning strategy on the one hand and the quality of the raw seawater on the other hand. The developed models showed that in terms of cleaning efficiency there are no significant differences between the standard and optimized backwashing protocols that were employed. This confirms the hypothesis of being able to use the optimized operation in a sustainable manner and benefit from lower cleaning frequencies. In addition, it has been demonstrated that the use of PCA as a monitoring technique to detect abnormal fouling behaviour is a robust tool. By using PCA, decisions on cleaning sequences or frequencies could be taken dynamically instead of running the system with fixed cycles.

Theoretical performance prediction of a reverse osmosis desalination membrane element under variable operating conditions

Sea Water Reverse Osmosis (SWRO) desalination systems powered by Renewable Energy (RE) can reduce drastically costs, specific energy consumption and CO2 emissions. A direct connection of a SWRO desalination system with RE technologies such as photovoltaics, can result in lowering the specific energy consumption due to the part-load operation of the desalination unit. However, due to the variable nature of solar energy, the membranes could operate outside of their nominal operating ranges. Therefore, research is needed to investigate the effect of the variable operation (non-stable pressure and flow rate) on the membranes. This paper presents the development of a dynamic mathematical model of a spiral wound reverse osmosis membrane module aiming to investigate the mass transfer in the membrane under non-constant operating conditions. The main pursue of the model is to investigate the physical compaction, as well as the raise of the concentration polarization in order to predict the performance of the membrane under variable operating conditions. The results show a water flux drop of 0.2×10−3kg/m2·s due to the sudden increase in the applied pressure, when the impact of physical membrane compaction was taken into consideration under non-constant operating conditions.