Abstract
It is well known that reverse osmosis (RO) is the leading desalination technology. As an energy intensive technology, the exploitation of renewable energy sources (RES) to power RO systems is a attractive option. A strategy to take advantage of all the available energy of an off-grid renewable system is to work with the RO system under variable operating conditions. This implies additional challenges in terms of water production and permeate quality, among others. Boron rejection is one of the main concerns in seawater RO (SWRO) systems. The aim of this work was to evaluate the performance and boron rejection of a single-stage SWRO system with 7 membrane elements per pressure vessel under variable operating conditions. The initial permeability coefficients of two SWRO membranes (TM820L-440 and TM820S-400) were calculated from experimental data of a full-scale SWRO desalination plant. These coefficients and the characteristics of the membranes were introduced in a simulation algorithm to estimate the behavior of the SWRO system. The results show that, compared with the TM820S-400 membrane, the TM820L-440 performed better in terms of boron rejection in the form of boric acid, but worse in terms of water production. When RES-powered SWRO systems are designed to work under variable operating conditions, consideration needs to be given to the safe operation window in terms of boron concentration in the permeate and to variation of the permeability coefficient of the membranes.
Highlights
Boron is an important nutrient, especially for plant growth (Darwish et al, 2020)
Boron rejection is a major concern in seawater reverse osmosis (SWRO) desalination plants (Cengeloglu et al, 2008; Koseoglu et al, 2008b)
Determination of the initial water permeability coefficient (A), salt permeability coefficient (Bs) and boron permeability coefficient (BB) was carried out using the experimental data of the initial operating point of a fullscale SWRO desalination plant with TM820L-440 and TM820S-400 membranes installed
Summary
Boron is an important nutrient, especially for plant growth (Darwish et al, 2020). The margin between a deficient and a toxic concentration of boron is very small and the regulations in this respect are usually quite restrictive (Ruiz-García et al, 2019). Boron concentration in seawater is around 5 ppm and is in the form of boric acid (H3BO3) (Hilal et al, 2011). This is an uncharged weak acid and the separation of species by reverse osmosis (RO) membranes depends mainly on their charge (Qasim et al, 2019). Considerable efforts have been made to make new RO membranes that increase boron rejection (Li et al, 2020; Jung et al, 2020). Another well-developed research line is related to proposals for alternative processes to RO that separate boron from aqueous
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