Pyrolysis of heavy metal contaminated biomass: Characterization of obtained pyrolysis oils and study of derived activated carbon

Abstract

Widespread heavy metal contamination in soils gives rise to problems; not only in Flanders, but in every location this contamination exists. These problems include (1) a risk of further spreading the contamination. e.g. to larger areas or contamination of groundwater and (2) lost income due to the impossibility to perform conventional agricultural activities (food production). Therefore, an onsite sanitation is required in order to reduce the impact on the environment. These problems may be overcome by the application of phytoremediation. During phytoremediation, plants incorporate the heavy metals slowly from the soil, into their biomass. Application of the plants enhances the soil, so that the problem (1) of further spreading out of the contamination or contamination of the groundwater is strongly reduced. And, the produced biomass can generate income which may replace the lost income of conventional agricultural activities (problem 2) . The phytoremediation biomass itself is contaminated with heavy metals and therefore it can not be burnt directly for energy, or composted for soil enhancer. Therefore, the produced biomass from phytoremediation is considered as "waste". In this study, pyrolysis is put forward to process the contaminated biomass into useful products, i.e. pyrolysis oil and pyrolysis char. Pyrolysis is a thermal process which operates at a controlled, moderate temperature and in absence of oxygen. Under these circumstances, the biomass breaks down and is converted into gas, oil and a solid residue. In view of processing heavy metal contaminated biomass, pyrolysis has the benefit of the possibility to produce pyrolysis oil that does not contain significant levels of heavy metals. By varying the pyrolysis circumstances. it is possible to influence the amounts of produced gas, oil and char in which the heavy metals are concentrated . The pyrolysis gasses are not studied in this work. Besides the oi l, which can be applied for fuel applications, another interesting option is the conversion of pyrolysis char into high grade activated carbons.