Supercritical fluid process for removal of polychlorodibenzodioxin and dibenzofuran from fly ash

Abstract

A process is proposed for the decontamination of fly ash from an urban solid‐waste incineration facility (USWI), where the target contaminants are polychlorodibenzodioxins (PCDDs) and dibenzofurans (PCDFs), a class of highly toxic tricyclo‐polychlorinated organics. In general, the ash waste requires inertization and disposal into a controlled landfill. Here, we propose an inertization process based on the reduction of the PCDDs and PCDFs content before dumping. Inertization is brought about by extraction with a solvent consisting of supercritical carbon dioxide modified with a co‐solvent (10% toluene). The plant would run in semibatch mode, with continuous flow of fluid through a packed bed of fly ash. Then, carbon dioxide and the co‐solvent would be separated and recycled. Favorable extraction conditions were found in the laboratory at 300 bar and 60°C. Under these conditions, the removal efficiency of native PCDDs and PCDFs is around 50% refereed to the extraction of the same sample using the EPA method 1613 (Soxhlet extraction with toluene). A techno‐economic appraisal of a treatment facility is presented for a medium sized incineration plant (50,000 ton urban waste yearly) producing 1,500 ton of fly ash/y. The ash production would be inertised in a specially designed supercritical fluid (SCF) extraction unit, located on‐site at the incineration facility.

Characterization of fly ash from a hazardous waste incinerator in Medellin, Colombia

“…However, in Colombia fly ash is mixed with household waste and landfilled without either previous treatment or use of appropriate human protection. Although characterization studies also reveals that the levels of dioxins in fly ash vary widely depending on specific combustion parameters, particle size and the air pollutant control device (APCD) used for dust collection [19,21] and [25], 1-3 ng I-TEQ/g of PCDD/Fs is accepted as an adequate value for landfill disposal in developed countries [25,26]. Nevertheless, fly ash collected from incinerators in Colombia usually contains higher dioxin concentrations [4,5] requiring additional treatment before land filling.…”

“…Several methods for dioxin detoxification of incineration fly ash have been proposed both in solid phase [26][27][28][29][30][31][32][33] and in liquid fly ash extracts [34][35][36][37]. Among them, liquid phase catalytic hydrodechlorination (LP-HDC) over Pd supported catalyst is a promising technique for fly ash dioxin degradation since high conversions are obtained after short reaction times under moderate reaction conditions [34][35][36][37].…”

Supercritical fluid extraction process for removing polychlorinated biphenyl from a DOE job control waste

“…Extraction temperature is an important operating condition for both analytical and remediation SFE. The critical temperature of carbon dioxide is 31" C. Based on previous bench-scale studies and engineering design [6,11,151, the extraction temperature was set at either 40" C or 80" C. Table 2 shows that high temperature did slightly improve the extraction efficiency. When the extraction temperature was increased from 40" C to 80" C, 2CBP recoveries increased about 4 to 7%.…”

“…The effects of extraction pressure on PCB extraction have also been studied by several authors in bench-scale extraction [6,11,221. The common pressure range is 1,500-6,000 psi for these studies.…”

Supercritical Fluid Extraction of the Pesticides Carbosulfan and Imidacloprid from Process Dust Waste

“…Recently published papers concerning process-scale studies have shown the usefulness of SFE for the remediation of soil (Zaragosa et al, 1998), decontamination of fly ash (Gabarra et al, 1999), and removal of oil for recycling of steel (Fu et al, 1998). Thus, the development of a large-scale process for the extraction of pesticides from a solid matrix as dust waste seems to be possible.…”