Photodegradation of dioxin in contaminated soil in the presence of solvents and nanoscale TiO₂particles

Abstract

Decomposition of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) present in soil under ultraviolet (UV) illumination (350-400nm) was investigated using a combination of nontoxic solvents mixed in soil and nanoscale anatase TiO2 (nTiO2) distributed on 2mm top soil surface. Three types of UV-exposure experiments were conducted: intermittent exposure (8 h/day) for 90 days and 120 days, sequential intermittent (120 days) and continuous (24 h/day) for the next 55 days, and continuous exposure for 55 days. The influence of several factors on dioxin photodegradation efficiency was investigated, including the UV absorption by the targeted dioxin, presence of catalytic nTiO2 on soil surface, solvent evaporation rate, as well as vertical gradients of solvents added into the soil columns. Results of dioxin analysis for the soil samples collected at the end of every experiment condition show that the photodegradation enhanced by the nTiO2 presence on the soil surface considerably increased the dioxin removal. Higher removal efficiencies were found for treatments with 15%wt of nTiO2 mixed in the 2-mm surface soil as compared to the 5%wt nTiO2 treatments. The highest removal efficiency (79.6%) was for the sequential intermittent-continuous UV-exposure experiment with nTiO2. Dechlorinated products of 2,3,7,8-TCDD were generally not detected which suggests degradation of targeted dioxin by C-Cl cleavage was negligible. Further modifications to improve removal efficiencies were proposed. Large-scale engineered systems may employ this integrated treatment approach which can also incorporate the reuse of the top soil containing nTiO2 and solvent vapours. With the utilization of natural sunlight such systems would be promisingly suitable for tropical conditions.

Risk for animal and human health related to the presence of dioxins and dioxin‐like PCBs in feed and food

“…PCDD/Fs in soil are generally bound tightly to particles; hence they are more difficult to destroy by sunlight as compared to PCDD/Fs in the air. As UV radiation cannot penetrate into soil, the photodegradation process of PCDD/Fs in contaminated soil almost exclusively occurs in the top few millimetres of the soil (Binh et al., ). PCDD/Fs are highly resistant to acids and bases, possess a low vapour pressure and are thermally stable below 600°C.…”

Effect of Casein Tablet Made from Goat Milk Yogurt on Liver Histopathological Profile, Dioxin Residue, and Malondialdehyde level in Broiler Exposed to 2,3,7,8-Tetrachlorodibenzo-P-Dioxin

“…The results of the sample filtrate from 2 times the extraction were taken to measure the TCDD residue levels using UV spectrophotometry at a wavelength of 305 nm. This method is based on references from (Binh et al, 2014) with modifications.…”

The potential application of carbazole-degrading bacteria for dioxin bioremediation

“…Dioxins can also be degraded through the photodegradation technology. In the study by Nguyen et al 2014 , the highest dioxin removal efficiency by photodegradation was 79.6% for the sequential intermittent–continuous UV-exposure experiment with nTiO2 (Nguyen et al 2014 ).…”