Abstract
The wastewater–seawater (WW-SW) integrated reverse osmosis (RO) process has gained much attention in and out of academia due to its energy saving capability, economic benefits, and sustainability. The other advantage of this process is to reduce boron concentration in the RO permeate that can exclude the post-treatment process. However, there are multiple design constraints regarding boron removal that restrict process design in the WW-SW integrated system. In this study, uncertainties in design factors of the WW-SW integrated system in consideration of boron removal have been explored. In comprehensive consideration of the blending ratio of between WW and SW, regulatory water quality standard, specific energy consumption (SEC), specific water cost, and RO recovery rate, a range of 15,000~20,000 mg/L feed turned out to be the most appropriate. Furthermore, boron rejection tests with SWRO (seawater reverse osmosis) and BWRO (brackish water reverse osmosis) membranes under actual WW-SW integration found a critical reduction in boron rejection at less than 20 bar of operating pressure. These findings emphasize the importance of caution in the use of BWRO membranes in the WW-SW integrated RO system.
Highlights
Boron is a common element in the environment and the 10th most abundant ionic species in the ocean [1]
In the mixed solution of treated wastewater (WW) and seawater (SW), the initial boron concentration in SW decreases with dilution by blending WW that contains relatively marginal boron concentration (0.5 mg/L) compared to pure SW
Dilution of seawater with other water sources is one of the efficient ways to reduce permeate boron concentration that improves the overall economics of the WW-SW integrated reverse osmosis (RO) system by excluding additional post-treatment processes
Summary
Boron is a common element in the environment and the 10th most abundant ionic species in the ocean [1]. An acceptable level of boron for potable water in the guideline of the World Health Organization (WHO) was originally set at below 0.5 mg/L but was modified to 2.4 mg/L in 2012, while European Union (EU) and Spanish legislation constantly maintain it as 1.0 mg/L [4,5,6]. This regulation on boron concentration in the final product of seawater desalination acts as a design constraint in the process design.
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