Hazardous waste dewatering and dry mass reduction through hydrophobic modification by a facile one-pot, alkali-assisted hydrothermal reaction.

Hazardous waste dewatering is important for volume reduction and further treatment. Hazardous organic wastes with low ratio of free to bound water, and low flash point are difficult to dewater and pose an explosion risk for conventional thermal drying. Here, we develop a facile one-pot, alkali-assisted hydrothermal treatment (AHT) method for cost-efficient hazardous waste dewatering, dry mass minimization and volume reduction. Wet paint sludge (WPS), a hazardous organic waste, was reduced (79% by total weight and 52% by dry mass) by dewatering through AHT hydrophobic modification, and the product was nonflammable. Conversion of bound water to free water enhanced WPS dissolution for further decomposition. Alkali was critical for boosting ether demethylation in the solid phase, and cleavage of ethers forming alcohols that facilitated transfer of solid mass into the liquid phase. Polar functional groups were eliminated through AHT, which increased the relative abundance of hydrophobic functional groups on the surface of solid residues and promoted dewatering. We also demonstrate that AHT can be widely adapted and scaled up to treat various hazardous organic waste streams, which is of significant industrial and environmental interest.

Oxidation products and degradation pathways of 4-chlorophenol by catalytic ozonation with MnOx/γ-Al2O3/TiO2 as catalyst in aqueous solution.

To identify the intermediates of 4-chlorophenol (4-CP) and bring forward the degradation pathways in the process of catalytic ozonation of 4-CP, 4-CP was ozonated with MnOx/γ-Al2O3/TiO2 (MAT) catalyst, and 4-CP was almost decomposed within 30 min, the mineralization reaching above 94.1% at 100 min. The evident reduction of the degradation with the addition of the radical scavenger tert-butanol (TBA) and the stronger spin-adduct signals of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) indicated that 4-CP was oxidized primarily by hydroxyl radical (·OH). Analysis of GC-MS, HPLC and IC confirmed that aromatic compounds and carboxylic acids were predominant oxidative organic intermediates of 4-CP in catalytic ozonation.The main degradation steps were hydroxylation of 4-CP and the formation of hydroquinone, 4-chlororesorcinol and 4-chlorocatechol. The low molecular weight (LMW) acids, such as malic, malonic, oxalic, acetic, and formic acid, were formed from the further oxidation of the intermediates.