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Abstract Internally staged design (ISD) was introduced as a method to lower front reverse osmosis (RO) element fluxes, yielding operational benefits. Systematic selection of the best ISD combinations has not been conducted as it is dependent on operating conditions (i.e., RO recovery and average flux). This study aimed to optimize seawater reverse osmosis (SWRO) operations using ISD for better product water quality and energy efficiency. A total of 36 ISD combinations were configured with three commercial SWRO membranes and systematically examined under varying operating conditions which were simulations of typical SWRO operation. A Pareto-optimal front, a non-dominated feasible solution set, was created to understand the tradeoff relationship between permeate quality and specific energy consumption while considering all parameters. The Pareto-optimal front was classified into five phases, and an analysis of phase changes provided optimal parameter settings for SWRO operation. However, the occurrence of colloidal fouling altered optimal ISD combinations on the Pareto-optimal front. Particularly, when SWRO membranes were fouled at high-recovery and -flux conditions, ISD combinations employing three different membrane types exhibited superior performance in terms of energy efficiency. With these results, the best SWRO operation was suggested depending on its performance requirements, and the advantages of ISD were further delineated. Graphical abstract fx1 Highlights • SWRO with ISD was optimized to achieve better water quality and energy efficiency. • Efficient SWRO performance control was examined by Pareto-optimal front analysis. • Colloidal fouling changes the best ISD combinations on the Pareto-optimal front. • ISD with three SWRO membrane types is feasible at high-recovery and -flux operations. • The optimal SWRO operation mode is proposed based on its performance requirements. [ABSTRACT FROM AUTHOR]

Brine management systems are imperative for sustainable water supply and for securing valuable resources from desalination plants. The utilization of membrane brine concentrators has recently been focused on because of their high energy and cost efficiencies compared with those of thermal brine concentrators. In this paper, we investigated the recent candidates of membrane concentrators in terms of their future potential in brine management systems and categorized the types of utilized membranes into two groups: single solution passing (SSP)-type membranes and double solution passing (DSP)-type membranes. The current membrane technologies for manufacturing these types of membranes were critically analyzed, and future directions for membrane development towards efficient brine management systems were suggested. SSP-type membranes and their accompanying systems should be durable at pressures higher than 230 bar to utilize membrane brine concentrators. On the other hand, DSP-type membranes should exhibit high-pressure durability (higher than 40 bar) and low structure parameters (less than 50 μm). This study examines the current status of membrane systems and presents the technical specifications of membranes required for membrane brine management systems. [Display omitted] • Brine management systems using membrane concentrators are summarized and analyzed. • Two types of membranes are classified in the applications of membrane concentrators. • The required specifications of membranes are determined for membrane concentrators. • Future directions for membrane development are suggested towards brine management. [ABSTRACT FROM AUTHOR]

While single-stage is the general configuration for seawater reverse osmosis (SWRO), the two-stage design can increase the overall recovery of an SWRO system. Due to its high-recovery operation, the specific energy consumption (SEC) of two-stage SWRO is higher than that of single-stage. Thus, the two-stage configuration has not been extensively applied in the current desalination market. In contrast, recent studies have reported that the two-stage design can lower the SEC of SWRO compared to that of single-stage. However, the analyses were biased towards SEC, and the practical design aspects (e.g., permeate quality, water flux, and design ratios) were not systemically considered. Thus, this study examines the applicability of a two-stage SWRO system with a capacity of 100,000 m3/d that employs 1200 pressure vessels (PVs). Two-stage SWRO actually consumed a greater amount of energy than that of single-stage for typical SWRO recovery with the same number of PVs. In contrast, single- and two-stage SWRO produced permeate similar in quality, while the two-stage exhibited superior water-flux distribution along the PVs. Additionally, optimal ratios of permeate flow rate and number of PVs were determined by energy recovery devices type, where the ratio of 1:2 was selected for the reverse osmosis system with a pressure exchanger and 2:1 for that with a Pelton turbine. Considering SEC and other operational aspects, the use of two-stage SWRO was feasible at a 50–70% recovery rate. Image 1 • Two-stage SWRO is fundamentally analyzed and optimized for seawater desalination. • SEC of two-stage SWRO is higher than that of single-stage in typical recovery. • Water quality of single- and two-stage SWRO is similar at the same average flux. • Optimal ratios of permeate flow rate and number of PVs vary depending on ERD types. • Two-stage SWRO is more energy-efficient at a high recovery rate (e.g., 50–70%). [ABSTRACT FROM AUTHOR]

• Critical review of energy consumption of seawater reverse osmosis plants. • Collection of more than 70 datasets for large-size seawater reverse osmosis plants. • Investigation of trends in the application of seawater reverse osmosis plants. • Analysis of factors associated with energy consumption of seawater reverse osmosis. • Future directions to reduce energy consumption of seawater reverse osmosis plants. High specific energy consumption (SEC) is the main barrier for the expansion of seawater reverse osmosis (SWRO). Therefore, the main objective of current SWRO research is to lower the SEC of SWRO plants. However, SEC of SWRO plants has not been systemically explored or analyzed, despite the need for information to develop appropriate strategies to reduce SEC. Therefore, this study aims to review and analyze SWRO plants for a comprehensive understanding of their SEC. First, trends in SWRO application are investigated using more than 70 datasets on large-scale SWRO. The analysis explains the increasing number of large-size SWRO plants, the SEC reduction by isobaric energy recovery devices (ERDs), and the use of different SWRO configurations to meet the energy and quality requirements. Factors associated with SEC (i.e. , feed conditions, target conditions, and equipment efficiency) are also analyzed. High salinity increases energy demand, whereas the temperature effect on energy consumption is not entirely clear. High-efficiency ERDs and pumps can reduce SEC, but overall SEC cannot be explained by these factors alone. SEC is also affected by target water quality and quantity. Moreover, specific SWRO designs can improve the system to efficiently achieve the established goals. Furthermore, future directions to develop low-energy SWRO plants are discussed. [ABSTRACT FROM AUTHOR]

Reverse osmosis (RO) is widely accepted for water reuse because it ensures clean water production. However, innovation in the RO process is necessary for water reuse to enhance its recovery while mitigating membrane fouling and reducing the increase in specific energy consumption (SEC). Therefore, circle sequence reverse osmosis (CSRO) adopts a staged design with flow reversal (FR) and a semi-batch design with a jet pump to enhance water flux distribution and energy efficiency for high-recovery water reuse. This study examined the water flux distribution and SEC of CSRO. When the distribution of water flux was compared, CSRO demonstrated a 7.7 % reduction in water flux in the front element compared to semi-batch reverse osmosis (SBRO). This reduction was attributed to advanced designs in SBRO, such as the two-stage design and an FR operation. The SEC of RO systems was also compared under high-recovery conditions. While both SBRO and CSRO achieved SEC reduction of 20–25 % or 9–18 % compared to two-stage RO depending on the feed salinity, CSRO was slightly more energy-efficient for high-saline feed. It is expected that CSRO has excellent potential for high-recovery water reuse, considering the improvement in water flux distribution and energy efficiency. [Display omitted] • Circle sequence reverse osmosis (CSRO) is newly proposed for water reuse. • CSRO adopts a staged design with FR and a semi-batch design with a jet pump. • Design advancements of CSRO were compared with two-stage RO and SBRO. • CSRO effectively concentrated the feed with evenly distributed water flux in RO. • CSRO was more energy-efficient than SBRO for concentrating the high TDS feed. [ABSTRACT FROM AUTHOR]