Abstract
One of the major challenges in reusing cooling tower blowdown water (CTBD) utilizing membrane processes is its remaining organic compounds, e.g., humic substances leading to biofouling. Besides, the possible abundance of chloride in CTBD imposes the concern of the formation of chlorinated by-products. To choose a pre-treatment process for the studied CTBD composition, various advanced oxidation processes (AOPs), including electrooxidation (EO), photocatalytic degradation (PCD), heat-activated persulfate oxidation (PS), UVC/vacuum UV (UVC/VUV), and UVC processes, were evaluated and compared based on two main targets: i) highest removal and mineralization of the organics, especially humic substances; and ii) lowest formation of chlorinated by-products including adsorbable organic halides and oxychlorides. All the processes were conducted in the natural condition of the real CTBD, while solution pH was monitored. Based on results of chemical oxygen demand, total organic carbon, dissolved organic carbon, UV254 absorbance, liquid-chromatography–organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (FEEM), it is concluded that PS leads to complete removal of organic compounds along with the lowest formation of low molecular weight organic acids and organic neutrals. FEEM and LC-OCD data also indicated that EO, PCD, and UVC/VUV processes brought about substantial removal of organic compounds and broke down the humic substances into low molecular weight building blocks and organics. Besides, EO exhibited the highest AOX and oxychlorides formation, while these were limited when using the other AOPs. Summarizing, PS, PCD, and UVC/VUV were efficient processes for the degradation and mineralization of organics without generating significant amounts of chlorinated by-products.
Highlights
Water reuse, especially in industrial applications, is highlighted in the sustainable development goals as one of the promising strategies to avoid freshwater scarcity [1]
Due to the use of boron-doped diamond (BDD) as anode and presence of chloride in the cooling tower blowdown (CTBD), both direct/anodic and indirect/mediated electrooxidation have sup posedly occurred with synergistic action of reactive oxidative species (ROS) and reactive chlorine species for oxidation and mineralization of organic compounds (OCs) [20,24,32]
While the highest chemical oxygen demand (COD) removal was obtained for elec trochemical (EO), the EO’s efficiency for total organic carbon (TOC) removal was similar to that of photo catalytic degradation (PCD) and UVC/VUV processes
Summary
Especially in industrial applications, is highlighted in the sustainable development goals as one of the promising strategies to avoid freshwater scarcity [1]. The study showed that chlorate formation was in forms of HOCl/OCl− and SO4- mediated compounds, which were significantly scavenged by the DOC, eventually inhibiting chlorate formation [18]
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