SWRO brine reuse by diaphragm-type chlor-alkali electrolysis to produce alkali-activated slag

Seawater desalination generates concentrated brine, which may pose a threat to marine ecosystems upon discharge into the ocean. This study was conducted to evaluate possibility possible novel approach for electrochemical post-treatment of seawater reverse osmosis (SWRO) discharge brine and reuse without further additional brine enrichment processes. A synthetic brine and real brine from a SWRO plant were electrolyzed under controlled conditions to obtain a mild alkaline solution using a diaphragm-type chlor-alkali cell. Under a 100 mA/cm2 current density and 37.5–45 min of hydraulic retention time (HRT), a maximum NaOH concentration of 3.3 wt% was obtained from real SWRO brine (initially 1.7–1.9 times the salinity of seawater) with 63% chloride removal via electrolysis. In electrolyzed brine reuse, a solid alkali-activated slag (AAS) product resulted from mixing 3.5 and 2.0 wt% NaOH alkali effluents (as an alkaline activator of slag) produced via electrolysis of synthetic brine and ground granulated blast furnace slag (GGBFS) from steelworks. For the specimens cured for 3–28 days, relatively high compressive strengths of 12.9–15.3 MPa and 9.8–11 MPa, respectively, were obtained.