Performance evaluation and boron rejection in a SWRO system under variable operating conditions

Reverse osmosis (RO) technology has been widely applied to water treatment such as seawater desalination, and large RO plants are many in operation around the world. Moreover, much larger plants will be required to secure sufcient water resource in the near future because global water shortage and quality problems are still getting more serious. Mega-ton Water System project was carried out for sustainable management of water environment and for low-carbon path to develop advanced key technologies of water treatment. Lowpressure RO membrane for seawater desalination has been studied in the project as a part of the core technologies to realize mega plant that is capable of producing 1,000,000 m3 of freshwater per day. Fundamental and scientifc research for RO membranes based on fne structure analyses by means of transmission electron microscopy with a special technique was conducted, and practical tools for designing new innovative RO membrane were acquired by the structure analyses to quantify the physicochemical and chemical properties of RO membranes. As the result of studying on structural design of RO membrane, low pressure SWRO membrane was obtained to reduce energy consumption compared to conventional ones in the past of SWRO. The vision of the “Mega-ton Water System” is sustainable desalination and reclamation. The missions are: 1) energy reduction (20-30%), 2) water production cost reduction (50%), and 3) low environmental impact (fewer chemical operations). Water cycle in “Mega-ton Water System” is separated into two parts including i) Seawater RO (SWRO) system, and ii) Seawater RO system with PRO system. The main challenge of development goal is the construction of mega-ton-scale system for seawater desalination for half the current cost. Accordingly, we developed the world’s frst low-pressure, multi-stage, high yield RO system, using a low-pressure seawater desalination membrane, and as a result of incorporating into it the elemental technologies gained from research in subthemes, such as highly-efcient pressure energy recovery, low-cost and highly durable plastic piping, pretreatment without the use of chemicals.

Many desalination plants still struggle to control biological fouling in seawater reverse osmosis (SWRO) systems as there are no standard methods to monitor this type of fouling. Strategies to control biofouling in SWRO systems have been proposed such as antifouling coating and lowering biofouling potential in SWRO feedwater through pretreatment processes. Measuring biofouling potential in the pretreatment and SWRO feedwater has gained increased interest due to its direct link to biofouling. Moreover, this approach can be used as an early warning system allowing for taking corrective actions in the pretreatment processes to meet the required SWRO feedwater quality. This article presents the biofouling potential methods/tools developed for seawater, their applications to monitor and assess raw seawater, SWRO pretreatment and SWRO feedwater, and how these methods are employed to control SWRO biofouling membrane systems. The reported removal efficiency of biofouling potential during SWRO pretreatment processes was found to be low to moderate. Threshold values for biofouling limitation were then proposed based on several lab and plant studies. Research on biofouling potential has provided insight into SWRO pretreatment performance optimisation and biofouling control. Future research is anticipated to determine better pretreatment processes and to identify robust threshold values for mitigating biofouling in SWRO membranes.

Seawater reverse osmosis (SWRO) system is popular in most islands and coastal areas around the world with limited fresh water resources. A SWRO system was designed to fulfil 50% of the population water demand in Cape Town, South Africa, which can lead up to 383,353 m3/day in the next 15 years. The total dissolved solid (TDS) within the product (i.e. drinking water) was lowered to 600 ppm by referring to standard guideline stated by the World Health Organization (WHO). Design flowrate was set at 766,704 m3/day and the parameters such as feed, permeate, concentrate flowrate, number of vessels, number of membrane elements, number of stages, seawater chemical composition, temperature, pressure, and system configuration were considered in this study. Reverse Osmosis System Analysis (ROSA) 2017 software was integrated the design with simulation to further understand how different parameters affect one another in SWRO system. The TDS standard value of 600 ppm in the products were 73.76 ppm and 181.13 ppm after further optimisation. The efficiency of the SWRO system recovery rate was 75.87% and specific energy consumption (SEC) was 6.18 kwh/m3, greater than the previous value of 50% and 9.7 kwh/m3 in terms of recovery percentage and SEC respectively. The findings indicate that a lower amount of feed and energy is needed to achieve the desired production value. Hence, it is also resulting in major savings in terms of operating cost for SWRO system.

Seawater desalination is increasingly being used as a means to augment freshwater supplies in regions with high water stress, and reverse osmosis is increasingly the technology of choice because of the low energy consumption. However, seawater reverse osmosis (SWRO) systems suffer from various types of fouling, which can increase energy consumption and the use of chemicals during SWRO operation. In practice, pre-treatment systems are put in place to reduce the particulate and biological fouling potential of SWRO feed water. However, simple, reliable and accurate methods to assess the extent to which biological fouling potential is reduced during pre-treatment are not available for seawater. This research developed a new method to measure bacterial growth potential (BGP) using the native bacterial consortium in seawater. New reagents to extract and detect ATP in microbial cells were specifically developed for seawater. The new lysis and detection reagents overcame the salt interference in seawater and allow low detection of total ATP, free ATP and microbial ATP in seawater. Incorporating a filtration step further increased the sensitivity of the method six fold, enabling ATP detection of ultra-low levels of microbial ATP in seawater. The newly developed ATP-based BGP method was applied to monitor and assess the pre-treatment of five full-scale seawater desalination plants around the world. A good correlation was observed between BGP measured in SWRO feed water and the pressure drop increase in the SWRO systems, suggesting the applicability of using the ATP-based BGP method as a biofouling indicator in SWRO. Furthermore, a safe level of BGP (<70 µg/L) is proposed for SWRO feed water in order to ensure a chemical cleaning frequency of once/year or lower. However, to validate this conclusion, more SWRO plants with different pre-treatment systems need to be monitored. In the future, on-line monitoring of BGP in SWRO feed water may further reduce the consumption of chemicals and energy and improve the overall sustainability of seawater desalination by reverse osmosis.

More than 30% energy saving seawater desalination system by combining with sewage reclamation

On the feasibility of community-scale photovoltaic-powered reverse osmosis desalination systems for remote locations

Operational cost optimization of a full-scale SWRO system under multi-parameter variable conditions

Membrane technology has emerged as a dominant solution to seawater desalination due to its superior advantages such as stable output water quality, lower energy consumption, ease of operation and smaller footprint. However, the design of spiral wound reverse osmosis (RO) membranes used in desalination does not allow for backwash or air scouring, thus rendering the RO membrane highly susceptible to fouling. Pretreatment for the RO system is therefore essential to ensure a long service life of the RO membranes. For waters containing suspended solids of up to 75 mg/L (such as that in the SingSpring Desalination Plant at Tuas, Singapore), conventional pretreatment methods (such as dissolved air floatation and filtration (DAFF), chemical dosing and cartridge filtration) require regular operator intervention to produce a permeate of reasonably quality. Ultrafiltration (UF) as a pretreatment for seawater desalination can offer better treated water, lower operating costs, a smaller footprint, and flexibility in dealing with poor or varying feed water quality. By improving the pretreatment permeate water quality, reducing operating costs and the footprint, capital expenses can be lowered. Greater stability is also achieved during times of poor or variable feed water conditions (such as periods of algalbloom). A pilot study was conducted at SingSpring to track the performance of Hyflux's Kristal® 2000 hollow fiber UF membranes as pretreatment for the seawater reverse osmosis (SWRO) system. The results of the pilot study will enable the design of future large-scale UF-SWRO membrane projects for seawater desalination.

Reverse osmosis (RO) is the most widely used desalination technology for both seawater and brackish water. Unfortunately, RO remains an energy intensive technology despite the efforts being made to overcome this drawback. One of the factors that could help to minimize this issue is the optimal design and operation of RO systems. Membrane manufacturers are continuously improving and releasing new spiral wound membrane modules (SWMMs) that nonetheless need to be studied in order to determine how to achieve the best highest possible performance from them. The aim of this study was to evaluate the safe operating windows (SOWs) of 9 commercial SWMMs in pressure vessels (PVs) with 7 of these elements in a single stage seawater reverse osmosis (SWRO) system. The permeability coefficients of the SWMMs were taken from a novel membrane open database. These coefficients and the characteristics of the SWMMs were introduced in a simulation algorithm to estimate the behavior of the SWRO system. SOWs were determined without considering any energy recovery device, although these were considered for the calculation of the minimum energy consumption. The SWMMs were compared and the optimal operating points were identified for each one. The results showed the highest difference was around 0.2 kWhm−3 between SWMMs in their optimal operating point with respect to the minimum specific energy consumption. It was also found that this difference increases slightly with rises in feedwater concentration. For a wide range of PV power inputs, the SWMMs were able to reach quite similar maximum flux recovery rates. Experimental work is needed to obtain more reliable predictions of SWRO systems working in wide operating ranges.

Energy and environmental issues of seawater reverse osmosis desalination considering boron rejection: A comprehensive review and a case study of exergy analysis

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

Removal of boron in a multistage SWRO system with pre-crystallization

Institute of African research and studies, Cairo University

Optimization of two-stage seawater reverse osmosis membrane processes with practical design aspects for improving energy efficiency

Antiscalants for near complete recovery of water with tandem RO process