Bioremediation of oil shale chemical industry solid wastes using phytoremedition and bioaugmentation

Abstract

Although the production of oil shale energy and oil has decreased steadily during the last years with a corresponding decrease in wastes, the semi-coke mounds constitute one of the major adverse environmental challenges in Estonia The processed oil shale (semicoke) contains several organic and inorganic compounds (oil fractions, sulphides, phenolic compounds, polycyclic aromatic hydrocarbons). Laboratory and field experiments were carried out in order to test the effect of phytoremediation and bioaugmentation for remediation of pollutants in semi-coke. Four pilot test plots (50 m2 ) were established at semi-coke depository in July 2001. For bioaugmentation experiment the set of bacteria consisting of three biodegradative strains isolated from nearby area was selected. Several molecular microbiological methods were used to assess and compare the microbial community structure and diversity as well as the presence and diversity of biodegradative genes in collected samples. The dominant bacterial species based on 16S rDNA sequences in semi-coke samples were also identified. These analyses revealed that semi-coke microbial community is characterized by few dominant populations and possesses low diversity. The phytoremediation increased the number of bacteria and diversity of microbial community in semi-coke. Within a one and half year period starting from establishment of test plots, the concentration of phenolic compounds decreased up to 50% and oil products up to three times at plots with vegetation compared to control. Bioaugmentation experiment, performed in summer 2002 increased biodegradation intensity of oil products up to 50% compared to untreated planted controls. The plots, which were supplemented with laboratory-selected bacteria, were characterized by higher microbial activity and showed changes in microbial community structure. Our findings also indicate that plant growth; particularly rooting depth and belowground biomass could be enhanced by adding mixture of selected bacterial strains to semi-coke.