(156g) Prediction of the Reactivity of Chemical Compounds with Ozone in Water

The wastewater discharged from chemical plants and pharmaceutical factories contains various chemical compounds. To prevent negative impacts on the environment and human health, these compounds need to be decomposed. Microorganism wastewater treatment is the most common method because of its low cost. However, some chemical compounds, called non-biodegradable compounds, are difficult to decompose by microorganisms. Ozonation is an effective method to decompose non-biodegradable compounds, because of ozone’s high oxidizability. To apply ozonation for wastewater, reactivity or reaction rate constants of ozone and chemical compounds in the wastewater are critical information. However, the reactivity with ozone differs from compound to compound.

Thanks to the development of density functional theory (DFT) calculation method and the improvement of computer performance, DFT calculation has been more widely applied to reveal chemical reactions or various properties of chemical compounds. Reaction rate constants of chemical compounds are calculated with transition states and activation energies which obtained from DFT calculations. However, optimization to transition state in DFT calculation requires chemical intuition and try-and-error.

In this research, we developed a model to predict reaction rate constants of ozone and chemical compounds in water with DFT calculations of relaxed states. Experimentally measured rate constants for about 100 compounds in previous research by other groups were used to develop the model. These compounds contain various kinds of compounds, such as aromatic compounds, carboxylic acids and alcohols. We applied DFT calculations to these compounds to obtain physical properties, such as highest occupied molecular orbital (HOMO) energies and dipole moments. We also calculated degrees of unsaturation and molecular weights from chemical formulas. With these physical and chemical properties, we constructed a regression model to predict the rate constants. The model can be used to predict the rate constants even by people with little knowledge and experience in quantum chemistry calculation, and it would be useful for judging the applicability of ozone wastewater treatment.

Furthermore, we developed another model to predict chemical oxygen demand (COD) decrease of non-biodegradable compound aqueous solution by ozone treatment. COD is one of the most important indexes of waste water. Our model to predict rate constant was incorporated in to the model to predict COD decrease.