Bioremediation of an Experimental Oil Spill on the Shoreline of Delaware Bay

TLDR

In 1994, a field experiment in Delaware released light crude oil onto beach plots to assess bioremediation potential. The study aimed to statistically evaluate whether adding mineral nutrients and/or microbial inoculum improves crude oil removal from sandy beaches and to quantify intrinsic and enhanced biodegradation rates. Biodegradation was monitored by GC/MS of selected hydrocarbons, with concentrations corrected for abiotic loss via hopane normalization, using a randomized block design that compared a control, nutrient addition, and nutrient plus indigenous inoculum treatments. Untreated plots showed substantial hydrocarbon biodegradation, but nutrient addition significantly increased alkane and aromatic degradation rates; however, adding an indigenous inoculum offered no additional benefit, and the high intrinsic rates were attributed to background nitrogen, suggesting that exogenous nutrients may be unnecessary when natural levels are sufficient.

Abstract

In the summer of 1994, a field study was undertaken in Delaware in which light crude oil was intentionally released onto plots to evaluate bioremediation. The objectives were to obtain credible statistical evidence to determine if bioremediation with inorganic mineral nutrients and/or microbial inoculation enhanced the removal of crude oil contaminating a sandy beach and to compute intrinsic and enhanced biodegradation rates. Biodegradation was tracked by GC/MS analysis of selected components, and the measured concentrations were corrected for abiotic removal by hopane normalization. A randomized block design was used to assess treatment effects. Three treatments were evaluated: a no-nutrient addition control, addition of water-soluble nutrients, and addition of water-soluble nutrients supplemented with a natural microbial inoculum from the site. Although substantial hydrocarbon biodegradation occurred in the untreated plots, statistically significant differences between treated and untreated plots were observed in the biodegradation rates of total alkane and total aromatic hydrocarbons. First-order rate constants for the disappearance of individual hopane-normalized alkanes and PAHs were computed, and the patterns of loss were typical of biodegradation. Significant differences were not observed between plots treated with nutrients alone and plots treated with nutrients and the indigenous inoculum. The high rate of oil biodegradation that was observed in the untreated plots was attributed to the background nitrogen that was measured at the site. Even though oil loss was enhanced by nutrient addition, active bioremediation in the form of exogenous nutrient addition might not be appropriate in cases where background nutrient levels are already sufficiently high to support high intrinsic rates of hydrocarbon biodegradation.