Biodegradation of the organic matter in a coking plant soil and its main constituents

In contaminated soils, several natural processes (e.g. biodegradation, oxidation) can induce degradation of organic pollutants. To evaluate the effects of biodegradation on the organic matter and the main organic constituents (coal and coal tar) of a coking plant soil, we conducted a batch incubation experiment, whereby mineral nutrient solution and a microbial inoculum from the coking plant soil were added to the different samples. Microbial counts were monitored during the 9 months of the biodegradation experiment and the mineralization rate was quantified by measuring the CO2 produced and the content, molecular weight (MW) distribution and molecular composition of the solvent extractable organic matter. The microbial enumeration and mineralization rate demonstrated no biodegradation with the coal tar but biodegradation was observed for the coal and coking plant soil samples. The coking plant soil exhibited the highest biodegradation rate, probably due to complex interactions between the different organic and mineral phases and the presence of various nutrient and carbon sources. Biodegradation of the kerogen with subsequent production of lower MW compounds (n-alkanes and isoprenoids) was observed for both coal and coking plant soil samples. The results indicate that the kerogen could be a potential source of carbon for the microorganisms and showed the central role of coal in the changes observed for the coking plant soil.