Coupling Bio/Phytoremediation with Switchgrass to Biofuel Feedstock Production in Mixed-Contaminant Soils.

ABSTRACT

Soil contamination with anthropogenic chemicals is a worldwide concern. The situation is complicated further by the presence of mixtures of chemicals at most contaminated sites. Potentials exist for deploying bio/phytoremediation strategies with warm season perennial grasses (WSPGs) to clean up mixed contaminant (MC) soils with simultaneous production of bioenergy feedstocks. This study investigated use of vermicompost (VC) and mycorrhizae - Glomus etunicatum (Ge) and Scutellospora heterogama (Sh) respectively, to enhance biomass productivities of model bioenergy feedstock switchgrass (SG) in MC soils. Designated portions of soils were contaminated with mixture of 50 mg·kg^–1 Cr and coal fly ash (10% FA (w/w)) representing inorganic contaminants, and with the nursery insecticide bifenthrin (10 mg·kg^–1) representing an organic contaminant. After eight weeks of growth in moisture replacement soil microcosms (MRS), biomass productivity of switchgrass was not significantly inhibited in the presence of mixed contaminants in soil. SG yield was enhanced slightly, but not significantly, by the application of VC amendment, mycorrhizal inoculation, or both to the MC soil (1.09, 0.98, 1.09, 1.14 and 1.10g, compared to unamended-MC soil, 0.96g). There was a significant decrease in Cr in switchgrass rhizosphere with Ge inoculation alone, by combination of Ge inoculation and VC amendment, and by combination of Sh inoculation and VC amendment (64.4, 65.5, and 57.1 mg·kg^–1 respectively, compared to the initial Cr concentration in the MC soil, 76.67 mg·kg^–1). Accumulation of Cr in SG roots was significantly higher than Cr accumulation in SG shoots for all treatments. Roots of SG grown with VC amendment or AMF inoculation in MC soil contained less Cr than those grown in unamended MC soil. The above observation suggests the potential of VC and AMF in phytostabilization of Cr, and the importance of phytostabilization in the fate of Cr. Results also showed that between 41 and 50% of initially added bifenthrin to the MC soil had dissipation after eight weeks. This suggested strongly, the importance of bioremediation in the fate of bifenthrin in soil. Overall the study shows that SG and associated rhizosphere microbial communities have the potential to bio/phytoremediate mixed contaminant soil and simultaneously produce biomass for biofuel feedstock.

Key Words: Switchgrass; warm season perennial grass; mixed-contaminant soil; bio/phytoremediation; coal fly ash; bifenthrin; mycorrhizae; vermicompost.