title: Thermodynamic entropy of organic oxidation in the water environment: experimental evaluation compared to semi-empirical calculation.
abstract: Residual organic matters in the secondary effluent are usually less biodegradable in terms of the total organic carbon content, and when discharged into a receiving water body, their further decomposition most likely mainly occurs due to chemical oxidation. Using this scenario, a semi-empirical method was previously developed to calculate the thermodynamic entropy of organic oxidation to quantitatively evaluate the impact of organic discharge on the water environment. In this study, the relationship between the entropy increase (ΔSC) and excess organic mass (ΔTOC) was experimentally verified via combustion heat measurement using typical organic chemicals and mixtures. For individual organic chemicals, a linear relationship was detected between ΔSCand ΔTOC with the same proportionality coefficient, 54.0 kJ/g, determined in the previous semi-empirical relationship. For the organic mixtures, a linear relationship was also identified; however, the proportionality coefficient was 69.2 kJ/g, indicating an approximately 28 % increase in the oxidation heat required to decompose the same organic mass. This increase in energy can likely be attributed to the synergistic effects of hydrogen bonding, hydrophobic interactions, π-π interactions, and van der Waals interactions between functional groups of different organic compounds. Intermolecular interactions may result in 17-32 % more dissociation energy for organic mixtures compared to the organic components' chemical structures. Because organics discharged into a water body are always a mixture of organic compounds, the proportionality coefficient obtained using organic mixtures should be adopted to modify the previously proposed semi-empirical equation.
authors: International Science & Technology Cooperation Center for Urban Alternative Water Resources Development, Key Lab of Northwest Water Resource, Environment and Ecology, Ministry of Education, Xi'an University of Architecture and Technology, Xi'an, 710055, China.
authors: Li
authors: L
authors: Luo
authors: International Science & Technology Cooperation Center for Urban Alternative Water Resources Development, Key Lab of Northwest Water Resource, Environment and Ecology, Ministry of Education, Xi'an University of Architecture and Technology, Xi'an, 710055, China. xcwang@xauat.edu.cn.
authors: Xiaochang C
authors: XC
authors: Wang
authors: School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, University of Technology, Broadway, Sydney, NSW, 2007, Australia.
authors: Huu Hao
authors: HH
authors: Ngo
authors: School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, University of Technology, Broadway, Sydney, NSW, 2007, Australia.
authors: Wenshan
authors: W
authors: Guo
mesh_terms: D019277:Entropy; D057927:Hydrophobic and Hydrophilic Interactions; D008962:Models, Theoretical; D009930:Organic Chemicals / Q000032:analysis / Q000737:chemistry*; D010084:Oxidation-Reduction; D013816:Thermodynamics; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D014874:Water Pollutants, Chemical
keywords: Chemical oxidation; Entropy increase; Organics; Synergistic effects; Water environment