Bioremediation of Petroleum Hydrocarbons in Louisiana\u27s Saltwater Marshes: Sediment Oxygen Demand Model.

Laboratory core studies were conducted to determine sediment oxygen demand (SOD) in petroleum hydrocarbon contaminated salt marshes. Natural degradation processes in salt marshes such as aerobic respiration, nitrification and sulfate reduction were investigated to quantify SOD. Oxygen demand in oiled/fertilized cores was greater than control and fertilized cores due to increased oxygen consumption by oil degradation and oxidation of reduced chemicals; sulfide and ammonium. SOD under non-flooded condition was greater than flooded condition due to an increased area of oxic-anoxic interface during air exposure. This may indicate that significant biodegradation of crude oil only occurs when the surface of the salt marsh is exposed to the atmosphere. Simultaneous measurements of total CO2 production and 35SO4 2- reduction were performed to partition carbon flow pathways between aerobic respiration and sulfate reduction in crude oil contaminated salt marsh sediment. Crude oil and fertilizer stimulated sulfate reduction rates and highest sulfate reduction rates were observed in the top 2-cm depth. Sulfate reduction was a major sink of oxygen demand. Mineralization kinetics of 14C-hexadecane and -phenanthrene were determined from core studies. The obtained zero-order rate constants at different level of nitrogen loading rates indicate that biodegradation of crude oil was enhanced when ammonia nitrogen concentration in pore water was maintained above 200 ppm. A SOD model was successfully applied to estimate SOD in oil contaminated salt marshes. Carbonaceous and nitrogenous sediment oxygen demand models were calibrated through a non-linear regression technique. Oil sediment oxygen demand (OSOD) model which simulates oxygen uptake, cell growth and oil degradation simultaneously was solved numerically and compared with experimental data. Field study was conducted to measure sediment oxygen demand, sulfate reduction and oil sediment oxygen demand over six months. SOD (flooded and non-flooded) in control, oiled, and oiled/fertilized (ammonia nitrate treated) salt marsh soils was measured. Higher SOD under oiled and oiled/fertilized conditions indicates that aerobic biodegradation of crude oil is occurring and thus increasing O2 demand. Although sulfate reduction consumes a significant amount of oxygen demand, major portion of the demand is caused by aerobic respiration due to crude oil degradation