Thermal desorption is widely used for remediation of soil contaminated with volatiles, such as solvents and distillates. In this study, a soil contaminated with semivolatile polychlorinated biphenyls (PCBs) was sampled at an interim storage point for waste PCB transformers and heated to temperatures from 300 to 600 °C in a flow of nitrogen to investigate the effect of temperature and particle size on thermal desorption. Two size fractions were tested: coarse soil of 420-841 μm and fine soil with particles <250 μm. A PCB removal efficiency of 98.0 % was attained after 1 h of thermal treatment at 600 °C. The residual amount of PCBs in this soil decreased with rising thermal treatment temperature while the amount transferred to the gas phase increased up to 550 °C; at 600 °C, destruction of PCBs became more obvious. At low temperature, the thermally treated soil still had a similar PCB homologue distribution as raw soil, indicating thermal desorption as a main mechanism in removal. Dechlorination and decomposition increasingly occurred at high temperature, since shifts in average chlorination level were observed, from 3.34 in the raw soil to 2.75 in soil treated at 600 °C. Fine soil particles showed higher removal efficiency and destruction efficiency than coarse particles, suggesting that desorption from coarse particles is influenced by mass transfer.

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Waste can be converted into energy and value-added products by thermochemical processes. Pyrolysis represents the thermal degradation of the material under a non-oxidant atmosphere leading to generation of three products: charsolid, oil-liquid and pyrolysis gas. Pyrolysis process means a complex mechanism of reactions, endothermic and/or exothermic chemical reactions that occurs simultaneously and/or subsequently. The use of lignocellulosic and plastic waste for energy purposes leads to the production of solids that could replace much of the conventional fuels once energy conversion technologies will prove profitable. In this chapter the authors proposed to describe, analyze and apply analytical methods for the heating value estimation of the solid products generated by pyrolysis of different wood and plastic materials. Our results obtained by experimental studies and empirical formulas will be evaluated and compared. The impact of the thermochemical process operational conditions on the variation of chars and biochars heating value will be also discussed in this chapter.