Optimum Nitrogen Concentration Supporting Maximum Crude Oil Biodegradation in Microcosms

ABSTRACT The purpose of this study was to determine the minimum nitrogen concentration needed by microorganisms to biodegrade crude oil hydrocarbons attached to sand particles in a microcosm simulating a low energy marine beach. The experimental approach involved mixing clean sand with weathered Alaska North Slope crude oil and monitoring biodegradation in continuous-flow beach microcosms over a 40-day time period. Two experiments were conducted with different nitrate-N concentrations in the feed (0, 0.25, 0.5, 1.0, 2.5, 5.0 mg/L in the first experiment and 2.5, 5.0, 10, 25, and 50 mg/L in the second). Experimental results indicated that nitrate concentrations below approximately 10 mg/L limited the rate of crude oil biodegradation. This conclusion was supported by oxygen uptake, CO2 production, nitrate consumption, and biomass growth data.