Effect of co-contaminated soil mixtures as fixed/fluidized bed media on pollutants emission under thermal treatment

Abstract

Thermal treatment of soil polluted by lube oil and heavy metals (cadmium, chromium, copper, and lead) was carried out by using a laboratory-scale incinerator. The effect of co-contaminated soil mixtures as fixed/fluidized bed media was studied with different ratios of sand bed amount to soil feeding. Additionally, the effect of soil moisture content on incineration system was further investigated. The reduction in air input altered the mode of fluidized bed to fixed bed which resulted in an increase in organic pollutants such as benzene, toluene, ethylbenzene, xylene, and polycyclic aromatic hydrocarbons. The combustion efficiency of fixed bed mode was observed to be relatively high at a lower ratio of sand bed amount to soil feeding, whereas high combustion efficiency was found in fluidized bed mode at a higher ratio of sand bed amount to soil feeding. Much higher concentration of organic pollutants in both gas phase and bottom ash is found under a higher soil moisture content. In addition, the increase in moisture content has resulted in an increase in lead, cadmium, and chromium in fly ash while copper was decreased. An important consideration is that the partitioning of heavy metals was randomly distributed in particle sizes of bottom ash. The highest concentration of heavy metals was deposited on fine-sized particle. The distribution of heavy metals in medium-sized and coarse-sized particles to form eutectic species might be produced by the soil–sand aggregation.