Separations 2023 , 10 , 148
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Figure7. FT-IR spectra of wastewater before and after treatment by ozonation and catalytic ozona- tion systems. 3.6. GC-MS Analysis of Pulp and Paper Mill Wastewater before and after Degradation by Different Systems Table 3 shows GC-MS analysis of pulp and paper mill wastewater before and after treatment of the pulp and paper mill wastewater. The wastewater contains a lot of organic compounds and its composition is complex. There are two organic compounds in DCSs [28], namely stilbene and palmitic acid. Stilbene is derived from styrene–butadiene–styrene copolymers and styrene–butadiene rubber, and palmitic acid is usually derived from dispersant, surfactant, or in-pulp sizing agents in the papermaking process [29]. The relative content of stilbene is 2.09%, and it can be degraded in two different treatments. The relative content of palmitic acid decreases from 5.67% to 2.11% after ozonation. In contrast, the catalytic ozonation system completely degrades palmitic acid [30,31]. Meanwhile, nine kinds of ester are detected in pulp and paper mill wastewater, such as dibutyl phthalate and diethyl phthalate, which are common toxic and hazardous organics in pulp and paper mill wastewater and are also included in Annex C of the USA EPA Priority Pollutant Control “Protocol Order” [32]. There is also an ester after ozonation, and the ester is completely degraded after catalytic ozonation, mainly due to the ester having an unsaturated bond, which is easily oxidized by catalytic ozonation. In addition, many of the saturated alkanes, such as dodecane, octadecane, tetradecane, etc., generated after treatment may be due to the oxidation of ample molecular weight organics by ozone with hydroxyl radicals to generate smaller molecular weight alkanes. In general, the ozonation technique is suitable for esters, aromatic rings, long-chain alkanes, halogenates, fatty acids, and other large- molecule volatile organic compounds, which can be decomposed into smaller alkanes, alcohols, esters, and acids (e.g., dodecane, dimethoxyethane, pentadecanoic acid, methoxy acetic acid-tetradecyl ester, and 2-ethyl hexanol) by ozone molecules and hydroxyl radicals.
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