U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060gen and proper proportions of carbon, nitrogen and phosphorus. Because oil has compounds containingcarbon, oil is consumed when encountered by the organisms. The products of thebiodegradation process are a stable biomass, water and carbon dioxide. Natural biodegradation ofspilled oil is a slow process. Colonization of bacteria typically takes from one to two weeks andthen biodegradation of the oil can take up to two to six months or more.6.4.2 Enhanced Biodegradation. The biodegradation process is enhanced by adding a nutrientcontaining the proper proportions of nitrogen and phosphorus to the oil slick. A compound containingcarbon may also be added to “jump start” the bacterial process. Laboratory tests show thebiodegradation process can be made up to four times more efficient by the application of nutrientssimilar to agriculture fertilizers.The nutrient must not be soluble in water and must be oleophilic, so that it is available to the oil atthe oil-water interface. A nutrient typically may consist of oleic acid for introduction of carbon, aphosphoric ester for phosphorus and a compound containing nitrogen. Nutrients sometimes aremade as micro-emulsions to aid retention at the oil-water interface.6.4.3 Application. Biological additives are applied at a rate of about one part nutrient to 10 partsoil. Bioremediation is particularly appropriate in remote areas where support of personnel andequipment is difficult, because the process is self-sustaining and requires only periodic monitoring.Biodegradation is effective in cold climates, although microbial action is slowed as temperaturedecreases. Biodegradation makes a slow, but significant contribution to the removal of oilfrom marine environments. As bioremediation cannot remove a spill in a short time, it is of useprincipally as a supplement to mechanical removal.6.4.4 Approval. Procedures for gaining permission to use biological agents for response to an oilspill are the same as the procedures for dispersants. Approved biological additives are included inthe EPA National Contingency Plan Product Schedule.6.5 BURNING AGENTSBurning agents are additives that physically or chemically improve the combustibility of thematerials to which they are applied. Most burning agents function as wicking agents—that is, theyenhance movement of oil to an igniter or source of combustion to sustain burning. Wicking agentssuch as polyurethane foam also insulate oil from cold seawater to enhance combustion. Otherburning agents increase the surface area of oil, add catalysts, oxidizers and low-boiling volatilecomponents and absorb and entrap oil.6.5.1 Burning Operations. Free oil in a slick less than about 0.12 inches thick does not sustaincombustion because of cooling from seawater. Thicker oil slicks usually support combustion untilonly a thin layer that is too cold to burn remains. Combustion is greatest where oil is the thickest.As oil warms, it flows outward, reducing slick thickness so combustion is sustained only towardthe center of the slick. The inward flow of air caused by rising heat slows the outward flow.A greater portion of oil burns when it is contained by boom, ice, etc.6-10