Full-scale Seawater Reverse Osmosis Research Articles

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

In this work, an operational optimization designed to reduce the operational cost of a full-scale seawater reverse osmosis (SWRO) system was studied under variable operating conditions. To increase operational flexibility and cost savings potential, the storage tank was used as the buffer between freshwater production and supply. With a well-developed mathematical model, which included reverse osmosis (RO) process equations, the storage tank equations and operational cost equations, the optimal problem was formulated in the form of nonlinear DAOPs (differential algebraic optimization problems). To solve the problem effectively, a simultaneous approach was introduced in which the differential and algebraic variables were fully discretized. Then nonlinear solver of IPOPT was used to solve the discretized large-scale nonlinear programming (NLP) problem. Computational results show that the operational optimization has significant potential of more than 26% cost saving over conventional method. Based on the successful solution, the impacts of variable parameters, such as feed temperature, seawater salinity, electricity price and freshwater demand were analyzed in detail. The effect of these parameters on operational cost savings and corresponding key performance indicators was determined, which enhances the understanding of the SWRO process and its optimal control.

Proposed new fouling monitoring indices for seawater reverse osmosis to determine the membrane cleaning interval

This study focuses on how to systematically determine the membrane cleaning interval of the seawater reverse osmosis (SWRO) desalination process by proposing two new fouling indices as well as comparing the fouling model with the fouling-free model. A fouling-free mathematical model of the SWRO desalination process based on the effects of temperature on flux as well as operation data obtained from a full-scale SWRO desalination plant in Korea was developed in order to normalize the permeate flow rate and feed pressure values. The normalized permeate flow rate was monitored in order to determine the proper cleaning interval of the RO membrane based on the membrane manufacturing company's cleaning protocol. The normalized feed pressure was modeled based on the linear cake filtration theory and dynamic fouling indices including an updated slope β and intercept γ that were proposed using the recursive least square (RLS) method. In addition, statistical control charts for the dynamic fouling indices were proposed in order to determine the proper membrane cleaning interval based on standard rules. The proposed fouling model was calibrated by the Monte-Carlo and principal component analysis (PCA). The experimental results from a full-scale SWRO plant in Geojae Island, Korea, indicate that the proposed fouling model and fouling monitoring indices were able to analyze the fouling mechanism of the RO membrane and were also able to determine the optimal membrane cleaning intervals.

Full-scale simulation of seawater reverse osmosis desalination processes for boron removal: Effect of membrane fouling

The objective of this study is to further develop previously reported mechanistic predictive model that simulates boron removal in full-scale seawater reverse osmosis (RO) desalination processes to take into account the effect of membrane fouling. Decrease of boron removal and reduction in water production rate by membrane fouling due to enhanced concentration polarization were simulated as a decrease in solute mass transfer coefficient in boundary layer on membrane surface. Various design and operating options under fouling condition were examined including single- versus double-pass configurations, different number of RO elements per vessel, use of RO membranes with enhanced boron rejection, and pH adjustment. These options were quantitatively compared by normalizing the performance of the system in terms of Emin, the minimum energy costs per product water. Simulation results suggested that most viable options to enhance boron rejection among those tested in this study include: i) minimizing fouling, ii) exchanging the existing SWRO elements to boron-specific ones, and iii) increasing pH in the second pass. The model developed in this study is expected to help design and optimization of the RO processes to achieve the target boron removal at target water recovery under realistic conditions where membrane fouling occurs during operation.

Stochastic cost estimation approach for full-scale reverse osmosis desalination plants

A novel stochastic approach was developed to estimate the construction and operation cost of a seawater reverse osmosis (SWRO) desalination plant. Uncertainties in the future cost of energy (e.g., electricity price) and financing (e.g., interest and inflation rates) were represented by probability distributions, and correlations among these variable parameters (i.e., statistical dependence between two or more variables) were estimated based on past records. The stochastic cost model was further coupled with a process simulation model that predicts performance measures such as water production rate and produced water quality. The coupled model was applied to a case study in which a virtual full-scale SWRO plant is constructed using two configuration options: single-stage single-pass (SSSP) and double-stage single-pass (DSSP). The case study demonstrates the effectiveness of the coupled model in ranking and comparing a large number of design and operating conditions for the full-scale SWRO plant. The main criteria for comparison were (1) the ability to meet the required production rate and water quality standards, such as salt and boron rejection rates, and (2) the unit cost of water production. The results show that cost estimates and relative rankings of various design and operating conditions from the stochastic approach are often different than those determined by the deterministic approach. More importantly, the stochastic model allows the decision maker to quantitatively consider the uncertainties in the cost estimates for this energy-intensive technology.

Institute of African research and studies, Cairo University

Recently, the rapid worldwide growth of seawater reverse osmosis (SWRO) desalination capacity has reignited the boron removal challenge in drinking water. The objective of this review is to discuss the recent advances and patents in boron mitigation strategies in SWRO systems, and to present the energy and environmental concerns of SWRO desalination system with boron rejection. First, the operating parameters of SWRO systems that affect boron removal are presented, before we discuss the reported findings and patents of boron control improvement from the standpoint of membrane materials advancement and from the development of various configurations, such as double pass reverse osmosis and hybrid SWRO processes with other separation technologies like ion exchange (IX), nanofiltration (NF), and electrodeionization (EDI). Thereafter, issues over SWRO desalination’s detrimental environmental impact are reviewed: thus, seawater intake, brine discharge, and energy consumption constitute the main weaknesses. Then, sustainable solutions are proposed to reduce the environmental burdens. As SWRO desalination is an energy intensive process, exergy analysis emerges as a key tool to assess the performance of this process. Therefore, the use of exergy analysis to SWRO desalination in general and, as an example, to a full-scale SWRO desalination plant located in Spain, are discussed. The findings indicate that the SWRO unit is responsible for over 64% of exergy destruction due to the irreversibilities associated with the large pressure drop and the high salinity of the brine.