Bioremediation of Petroleum Contaminants: Evaluation of Biochar Feedstocks Inoculated with Hydrocarbon-Degrading Bacteria.

Biochar, a carbon–rich soil amendment, has been reported to reduce the bioavailability of heavy metals and hydrocarbon contaminants, improve soil structure, enhance nutrient and soil moisture retention, and allow for greater microbial population by providing niches for colonization. These properties of biochar could make it a desirable additive to bioremediation strategies utilizing hydrocarbon-degrading bacteria (HDB). The objectives of this study were to a) evaluate and compare the effectiveness of various biochars to degrade hydrocarbon contaminants, b) determine if inoculation of biochars with HDB will improve hydrocarbon degradation, and c) examine the interaction effect of biochar and HDB on soil properties and bioremediation of a contaminated soil. A soil incubation study using sandy soil artificially spiked with gasoline and diesel fuel (1% contaminant level in a 1:1 ratio) was conducted in pots placed outdoors to simulate natural weathering. After ageing for four weeks, the spiked soil was amended with one of three biochars (softwood pellets, miscanthus straw pellets, or oilseed rape straw pellets). Four weeks after biochar incorporation, the soil was drenched with one of three HDBs: Pseudomonas putida 33015, P. putida 17484, or Rhodococcus sp. or an uninoculated control (Luria Bertani broth). Soil samples were taken prior to spiking (T0), after spiking and ageing (T1), after ageing and with biochar (T2), prior to soil drenching (T3) and four weeks after drenching (T4), and either air-dried for physio-chemical and hydrocarbon contaminant analyses or shock frozen in liquid N₂ for microbial analyses. Serial dilutions of T4 soils were performed to determine heterotrophic and HDB population on R2A and M9 plates amended with diesel fuel as the sole carbon source, respectively. Soil toxicity assays using Lolium perenne and Panicum virgatum L. were conducted on T4 soils to determine whether inoculated biochar amended soils could reduce contaminant levels prior to seeding for phytoremediation.