Remediation of Heavy Hydrocarbon Contaminated Soils with Biochar Amendment.

Low-tech, sustainable and eco-friendly methods for reducing measurable total petroleum hydrocarbons (TPH) in shallow soils contaminated with heavy hydrocarbons (HH) continue to present a challenge to the petroleum industry.  Amending HH-contaminated soils with locally obtained pyrolyzed agricultural waste biomass (biochar) is proposed as a strategy for both stabilizing and increasing biodegradation of the components of HH contamination.  Three HH contaminated soil and biochar made from two feedstocks (walnut nutshells, pine wood) at similar pyrolysis temperature (900 °C) were characterized for physical and chemical properties.  Batch incubations (25 °C) were used to investigate sorption of contaminants to biochar and evaluate extractability of total petroleum hydrocarbon (TPH) from biochar-amended soils. Soil (50 g) was amended with biochar at three application rates (2, 5 and 10% w/w). Mineral solution (for essential nutrients) and ethanol (for mobilization of TPH) were added to each treatment. The treatments were set-up in triplicate using a randomized block design and maintained at water holding capacity (WHC) of 65-75 %. Appropriate incubations were conducted for 60 days after which soils were destructively sampled.  Results show addition of mineral fertilizer alone can reduce TPH in all the contaminated soils.   Pine wood biochar addition (at 5%) can further enhance this reduction to below regulatory limits, particularly in soils with light crude, achieving this within 60 days. The walnut shell was not as effective in reducing TPH. These results suggest biochar does impact biodegradation of HH contaminated soils and if well understood, this work will provide a low-tech and relatively low-cost method for dealing with extensive shallow HH contamination.