Characteristics And QSAR Of Chlorinated Organics Degradation By Ultrasound Combined With Element Iron

The combination of ultrasound and element iron convenes the advanced ultrasonic oxidation and Fe⁰ reduction together, and could effectively remove POPs from wastewater. This paper attempts to establish the combined system of ultrasound and Fe⁰ (US/Fe⁰), and chlorinated organics are chosen as target pollutants to study the synergetic effect between US and Fe⁰. The mechanism for system parameters influencing on the degradation of chlorinated organics are deeply studied in this paper. And the synergetic mechanism is investigated through researching the characteristics of water solution under US/Fe⁰. The QSAR method is applied to build the quantitative structure-activity relationship model for chlorinated organics degradation activity in the synergetic system.Chloroform (CHCl₃), 1,2,4-trichlorobenzene (TCB), and 2,3,4,6-tetrachlorophenol (TeCP) are chosen as target pollutants and their degradation rate in US/Fe⁰ system are studied. Obvious synergetic effects between the US and Fe⁰ have been proved. The three compounds'degradation rates obey such a order: TCB > TeCP > CHCl₃. The influences of element iron loading, solution initial pH, initial pollutants concentration, ultrasonic power and ionic strength of solution, on the degradation rates of the three compounds in US/Fe⁰ are studied, and their influence mechanism are discussed. The results showed that: 1) There is an optimum Fe⁰ loading for the three pollutants'degradation rate in US/Fe⁰ system; 2) The other four parameters have different influence mechanism on the different pollutants. Some general regularities could be concluded as that, higher degradation rate can be obtained in neutral solution pH, and the degradation rate increases with ultrasonic power increasing; 3) It can be comprehensively deduced that: the chloroform is degraded mainly through pyrolysis inside cavitation bubbles, Fe⁰ reduction has a higher contribution on the TCB degradation, however, the·OH oxidation occurred in the bulk solution predominates the TeCP degradation. A dynamic balance of these five items'concentrations, which includes solution pH, iron ion,·OH and H₂O₂, presents in water solution of US/Fe⁰. The promoting effect of Fe⁰, to the oxidation induced by ultrasonic cavitation, reach highest at 2 g·L^-1 of Fe⁰ loading, when the formation of·OH and H₂O₂ get largest. Alkaline pH is conducive to·OH and H₂O₂ generation in US/Fe⁰.Based on the former research, the pseudo-first-order degradation rate constant for 31 chlorinated organics (which includes 9 chlorinated hydrocarbons, 8 chlorobenzenes, and 14 chlorophenols) in US/Fe⁰ are studied. And 31 molecular structure parameters of 49 chlorinated organics (which includes 18 chlorinated hydrocarbons, 12 chlorobenzenes, 19 chlorophenols) are calculated by quantum chemistry computing software or obtained trough related experimental database. PLS statistical method is used to establish stable and well forecasting QSAR models. And four good models have been achieved, such as chlorinated hydrocarbons'QSAR, chlorobenzenes'QSAR, the total chlorinated organics'QSAR, et al. 49 chlorinated organics'degradation rate constants in US/Fe⁰ are predicted using these models. The degradation rate of the three types of chlorinated organics in US/Fe⁰ roughly follow the following order: chlorobenzenes > chlorinated hydrocarbons > chlorophenols. Such results can be concluded through model analysis: the most important independent variables, which include the electronic parameters describing the characteristic of C-Cl bond (the most positive hydrogen's charges, the most negative carbon's charges, and charges of the chlorine which combined with the most negative carbon), the energy parameters describing molecular total property (zero-point-energy, thermal energy, kinetic energy, potential energy), and octanol-water partition coefficient, can be chosen from the 31 parameters according to their contribution for models. And the degradation mechanisms for chlorinated hydrocarbons and chlorobenzenes could be demonstrated again theoretically.