A study of theoretical mechanism on wastewater components of paper industry with process generated radicals in gaseous and aqueous phase

Abstract

The paper and pulp industries release a diverse array of hazardous chemicals into the atmosphere, water bodies, and soil. Papermaking is characterized by intricate stages including debarking, pulping, bleaching and washing. Each of these stages possesses the capacity to generate a spectrum of toxic pollutants which may be present in both gaseous and liquid phases. This includes substances such as fatty acids, aromatic compounds, polycyclic aromatic hydrocarbons, acetaldehyde, chlorinated phenols, lignin, cellulose, hemicellulose and wood extractives. Consequently, these industrial discharges contribute to the contamination of wastewater with a complex mixture of harmful compounds. Some of these compounds persist even after the secondary treatment process. The effluent from these industries contains benzaldehyde which is one of the aromatic aldehydes with the highest reported retention time. The present study focuses on the reactions between benzaldehyde and atmospheric radicals (NO, NO2, HO2, O2, and OH radical) using computational methods. The study holds prime importance in understanding reactions involving these compounds and eventually assessing their impact on the environment. Density Functional Theory (DFT) is used to calculate Gibbs’s free energy which shows the spontaneity of reactions. The results show that the production of nitrobenzaldehyde is more feasible with ∼ -53.64 kcal/mol than the other products, and these nitro derivatives are proven to have a role in the formation and growth of the secondary organic aerosols. The aqueous solution environment promotes the production of these compounds, and they have a higher reaction energy of ∼ -3.34 kcal/mol than the gas phase. The products of these reactions adversely impact health and the atmosphere, making it a necessity to decrease the reactivity of these reactions or to take necessary actions to restrict the release of these toxic contaminants before they react with atmospheric radicals.