Laboratory studies of the biodegradation of chemically dispersed oil: effect of droplet size and nutrient amendment

Oil spills could have devastating effects on the shorelines, and for this reason, chemical dispersants are commonly used to disperse the oil slick in the water column, preventing it from reaching the shorelines. However, the long term fate of dispersed oil depends on its biodegradation by indigenous microorganisms, which in turn depends on the concentration of nutrients in water and on the droplet size distribution. Using water from the shorelines of Atlantic City, we placed the water with oil and dispersant inside EPA Baffled Flasks and placed them on rotatory shakers. We selected two speeds: high (250 rpm) and low (125 rpm). We also added excess nutrient for some of the flasks to evaluate the role of nutrient. The experiments reflected the following situations: HSHN, HSLN, LSHN, and C, where HS and LS mean high (250 rpm) and low (125 rpm) speed mixing, respectively. HN and LN means high and low nutrient, respectively. C means control, which was HSLN with azide added to inhibit bacterial activity, and subsequently oil biodegradation. The initial median oil droplet was 3.00 microns, 3.15 microns, 4.34 microns, and 3.48 microns for the HSHN, HSLN, LSHN, and C, respectively. The biodegradation rates for HSHN, HSLN, LSHN was 82%, 87%, and 51% respectively. Thus, smaller droplet sizes promoted the biodegradation of oil