Nitrogen and phosphorus requirements for the bioremediation of oil in saltwater

Abstract

Nitrogen and phosphorus are two of the limiting factors in the bioremediation of oil in sea water, Laboratory experiments were conducted to determine the maximal flux of NH4' and P and concentrations of NH4' and P required by microorganisms utilizing oil in water. Treatments were concentrations of NH4+, and P, and inoculum size. Treatments were inoculated with a microbial consortium from Galveston Bay, Texas sea water grown by enrichment on oil. All treatments were incubated at 30'C with shaking to promote aeration. For determination of nutrient flux, disappearance of NH4' and P from the media was analyzed during microbial growth on oil. Microscopic counts of microbial populations using acridine-orange staining were done to determine growth rates of oil degrading microorganisms in sea water at different concentrations Of NH4' and P. Maximal NH4' uptake was 475.5 mg. NH4' L-1 hr-' for oil degrading populations in excess of 5.0 x 107 cells ml-'and maximal P uptake was 85.5 mg. P L" hr-'. Ammonium concentrations of 0.289 mg. NH4+ mL-' and P concentrations of 0.082 [mg P mL" did not limit cell growth so long as the concentrations could be maintained. Rapid generation times for microorganisms grown on oil in sea water generally ranged from 1. 19 to 2.97 hours when NH4+ and P was not limiting and cell populations were below 1.0 x 107 cells mL-1. At high cell populations maintenance of low concentrations of nutrients was difficult due to high microbial consumption. In estuaries concentrations and fluxes of nutrients have the potential to limit microbial utilization of oil in sea water. Concentrations of NH4+ and P that occur in estuaries may not limit microbial growth on oil, provided an adequate flux can be maintained.