New Methods For The Degradation Of Phenolic Compounds

Phenolic compounds are a class of important environmental contaminants. Phenolic wastewater is one of the most hazardous and widespread industrial wastewater. The effluents from industry such as gas, coking, oil refining, metallurgy, machinofacture, petrochemical industry, organic synthesis, plastic, medicine, pesticide, paint, etc. generally contain phenolic compounds, which may lead to serious environmental pollution and health risk as well. In recent years, alkylphenol, bisphenols, phenolic pharmaceuticals and natural steroid hormones have received extensive attention due to their ubiquity, endocrine disruption effects and other biological toxicity. In the present study, we used bisphenol A and acetaminophen as model compounds to investigate two novel methods for the degradation of phenolic compounds.(1) The oxidative degradation of bisphenol A and its mechanism using zero valent aluminum (ZVAl)-acid system under air-equilibrated conditions was investigated. The results showed that ZVAl possesses an excellent capacity to remove bisphenol A under pH < 3.5 acidic conditions. More than 75% of bisphenol A was eliminated within 12 h in pH 1.5 reaction solutions initially containing 4.0 g/L aluminum and 2.0 mg/L bisphenol A at 25°C. In the range of aluminum loading 0⁴.0 mg/L, the removal of bisphenol A was accelerated with increasing aluminum loadings. Higher temperature and lower initial pH also facilitated bisphenol A removal. The addition of Fe2+ into the ZVAl-acid system significantly accelerated the reaction likely due to the enhancing transformation of H₂O₂ to HO·via Fenton reaction. Furthermore, the primary products or intermediates including monohydroxylated bisphenol A, p-hydroquinone, 2-(4-hydroxyphenyl)propane and 4-isopropenylphenol, were identified and a possible reaction scheme was proposed.(2) The reactivity of acetaminophen with synthetic manganese dioxide (δ-MnO₂) was investigated. The results showed that manganese dioxide demonstrated an excellent efficiency in removing aqueous acetaminophen. More than 99% of acetaminophen was eliminated in 40 min in a pH 4.5 buffer solution containing 100μM MnO₂ and 2.0 mg/L acetaminophen. The reactivity of MnO₂ with acetaminophen in different pH solutions followed the order pH 4.5 > pH 5.0 > pH 5.5 > pH 9.6 pH 8.6 > pH 7.5 pH 6.5. The co-solutes NaCl, CaCl2, FeCl3 and humic acid generally had negative effects on the reaction and the inhibitory effects were exacerbated with increasing co-solute concentration. Moreover, the aging effect of MnO₂ with co-solutes was for the first time evaluated, the reactivity of MnO₂ with acetaminophen decreased as the contacting time of MnO₂ with co-solutes increased, likely due to the occupation of surface reactive sites by metal ions and the enhancing dissolution of MnO₂ to Mn2+ by humic acid. This work demonstrated that ZVAl/H+/O₂ system andδ-MnO₂ have effiective capacity to remove phenolic compounds, offering two potentially practicable technologies for treatment of phenolic compound-containing wastewater.