Nitrogen fixing bacteria enhanced bioremediation of a crude oil polluted soil

Abstract

The use of nitrogen fixing bacteria to enhance bioremediation of a crude oil polluted soil was investigated in a 56-day study period. Soil pH ranged between 5.3 - 6.8. Soil moisture content ranged between 10-30%. Counts of heterotrophic bacteria ranged between 4.5 x 106 - 6.0 x lO7Cfu/g. Counts of hydrocarbon-utilizing bacteria ranged between 2.5 x 106 - 2.0 x lO7 Cfu/g. Levels of total organic carbon, nitrogen, phosphorus and hydrocarbons decreased with time during the study period except in the kill control cell. The highest percentage loss of crude oil (84%) was recorded in cells, which contained seeds of Phaseolus vulgaris (White beans) and 5g slurry of Bacillus polymyxa. Cells in which 5g slurry of Anacystis (Chroococcus) sp., 5g slurries each of Azotobacter sp., Bacillus polymyxa and Anacystis (Chroococcus) sp. were applied, recorded 56% and 80% losses of crude oil respectively. Cells in which 5g slurry of Azotobacter sp., 5g slurries each of Azotobacter sp. and Bacillus polymyxa were applied, recorded 80% loss of crude oil. The fertilizer (NPK 15:15:15) treated cell showed a 64% loss of crude. The cell containing fertilizer (NPK 15:15:15) with seeds of Phaseolus vulgaris, and the cell containing fertilizer NPK 15:15:15 with 5g slurry of Anacystis (Chroococcus) sp showed 64% and 72% losses of crude oil respectively. The cell in which all treatment options were applied showed 56% loss of crude oil. The cell in which tilling alone was employed showed 72% loss of crude oil. The kill control cell recorded the least percentage loss of crude oil (24%) at the end of the study period. Results indicate that at 0.05 (95%) level of significance, there is a significant difference between nutrient level arising from treatment option and hydrocarbon level in soil samples. Thus the % losses of crude oil recorded in treatment cells were due to treatment options applied (at 95% level of significance) The results indicated a higher bioremediation rate when nitrogen-fixing bacteria were used instead of when inorganic nutrient (fertilizer) were applied. Key words: - Nitrogen fixing bacteria, Bioremediation, Crude oil, Polluted soil, Fertilizer. (Global Journal of Pure and Applied Sciences: 2002 8(4): 455-470)