S.J. McMillen, J.M. Kerr, P.S. Davis, and J.M. Bruney, Exxon Production Research Company, M.E. Moir, and P. Nicholson, Imperial Oil Resources Limited, C.V. Qualizza, Artemis Consulting, and R. Moreau and D. Herauf, Exxon Company, U.S.A.
Two composting field trials have been successfully completed at Exxon Company USA's Big Stick Madison Unit (BSMU) in Billings, North Dakota and Imperial Oil's (Exxon's Canadian affiliate) Willesden Green producing field in the Province of Alberta, Canada. Composting is a bioremediation method in which bulking agents such as manure, wood chips, and straw are added to oily soil/sludge to improve the soil texture, tilth, air permeability, water holding capacity, and organic matter content. The compost mixture is placed in windrows or static piles where heat is generated by microbial breakdown of hydrocarbons and organic matter. Because composting conserves heat generated by biodegradation, it is well suited for bioremediating wastes in cold climates. In addition, the temperature in the piles increases the rate of the biochemical processes responsible for oil degradation and can significantly reduce the time required to achieve a remediation target. Elevated temperatures were observed in both field trials, and in Canada the compost piles remained warm throughout the winter months thereby expanding the normal bioremediation season. Hydrocarbon loss data indicate that clean-up criteria for both sites was met within a few months. Extensive hydrocarbon characterization confirmed that the total petroleum hydrocarbon losses were due to biodegradation. At the BSMU site 71 cubic yards (54 m3) of oily soil were composted in five windrows that were aerated by periodic tilling, and at Willesden Green 1700 cubic yards (1300 m3) of oily soil were composted in three static, passively aerated piles.
Remediation of soils impacted by hydrocarbon wastes generated during oil and gas production can be accomplished by a variety of biological and nonbiological techniques. Biological techniques take a variety of forms from the low intensity management/low input approach of land-treatment to highly managed bioreactors. Land-treatment has long been a popular option for remediating hydrocarbon impacted soils because it is seen as an inexpensive alternative. However, the available time during the year for land-treatment in northerly climates is limited. In addition, extremely long remediation periods are required when more weathered or recalcitrant hydrocarbons are spread on land. More intensive approaches to bioremediation, such as composting, provide a number of possible benefits including:
higher soil temperatures which enhance biological activity and can extend the remediation season to twelve months of the year;
less land is required to treat similar volumes of soil; and
less ongoing maintenance may be required.
Composting has previously been reported to be successful in treating hydrocarbon wastes in a laboratory study and in a field trial. Bulking agents such as manure, wood chips, straw, and/or gypsum are added to compost mixtures to improve the soil texture, tilth, air permeability, water holding capacity, and organic matter content. After the bulking agents are added, the compost mixture can be either placed in windrows (2 to 3 feet high and 4 to 5 feet wide) that are tilled to achieve adequate aeration, or the compost can be placed in piles in which perforated piping is used to force air through the pile. Compost mixtures usually generate their own heat due to microbial breakdown of organics in the compost, and this heat is somewhat conserved due to the size of the piles. Because the process generates and conserves heat, it is well suited for bioremediating wastes in cold climates. This paper describes two composting projects conducted in North Dakota and Alberta using composting in windrows and statically aerated compost piles, respectively. They were monitored using similar analytical methodology.