Laboratory Tests of Biochars as Absorbents for Use in Recovery or Containment of Marine Crude Oil Spills

Absorption capacity of biochar for crude oil and the mineralization potential of the absorbed oil in seawater were determined in laboratory-scale experiments. Texas, South Louisiana, or Qua-Iboe (Nigeria) crude oils were contacted with each of four commercial hardwood biochars and six synthesized biochars in seawater from the Gulf of Mexico and Long Island Sound (U.S.). Synthesized biochars were made from maplewood anoxically at different heat treatment temperatures (HTT) from 300 degrees C to 700 degrees C. Oil absorption capacity of the biochars determined in dip tests using oil on seawater ranged from 3.6 to 6.3 g/g. Oil-imbibed biochar particles were buoyant. Seawater enhanced absorption capacity in relation to the H/C ratio. Oil was less effectively absorbed in the form of weathered water-in-oil microemulsion (chocolate mousse'') than in as-received form. Absorption capacity peaked at HTT about 400 degrees C and correlated poorly with %C, H/C ratio, O/C ratio, surface area, and porosity. It is proposed that swelling, in addition to macropore filling is responsible for the high capacities of biochar. In biometer tests, CO2 evolution from subcapacity levels of Texas crude in biochar suspended in seawater was stimulated relative to oil in the absence of biochar in three tests; whereas, stimulation in a fourth test was not statistically significant. Thus, biochar may prime biodegradation by providing a favorable solid support and an interstitial reservoir of hydrocarbons for degrader biofilms. While less absorptive than many experimental high-tech absorbents, biochar may serve as an inexpensive alternative for recovery of marine oil spills in a form suitable as a fuel or as an aid to natural attenuation.