Simulating Biodegradation of Hydrocarbon Pollutants under Slow Nutrient Delivery Conditions

Aim: Bacterial growth and petroleum hydrocarbon degradation kinetics was studied under controlled laboratory conditions, to determine and numerically simulate the fate of hydrocarbon pollutants.

Study Design: A 35-day study was setup to investigate crude oil degradation and bacterial growth dynamics in water, using slow-release fertilizer formulations.

Place and Duration of Study: This study was carried out in the Environmental Microbiology Laboratory, University of Port Harcourt, Nigeria, between January and June 2015.

Methodology: Crude oil degradation studies were carried out in six (6) 500 ml capacity conical flask containing 200 ml mineral salt solution and 0.25% crude oil. The setups were inoculated with suspensions of 24-h old pure cultures of bacterial isolates (Pseudomonas sp., Bacillus sp. and Micrococcus sp.).

Results: At the end of the study, the crude-oil concentration (S) was reduced from an initial value of 11250 ppm to 6360.6 ppm and 1471.3 ppm at weeks 5 and 10, respectively. The bacterial biomass on the other hand increased from 4.69 at the start of the experiment, to 19.36 and 34.03 (Log.10 cfu/ml) at weeks 5 and 10, respectively. Results from the numerical simulations showed that a 50% variation (reduction) on the maximum degradation rate (qmax) led to 332.32% biodiversity gain in hydrocarbon substrate (S) and a concomitant 43.11% biodiversity loss on bacterial biomass (X) after a ten-week period of simulation. Also, an 80% variation (reduction) on qmax led to a 132.93% biodiversity gain on hydrocarbon substrate and a 17.24% biodiversity loss on bacterial biomass.

Conclusion: This study revealed that lower rates of crude oil utilization leads to increased volume of petroleum hydrocarbon in the environment as well as a concomitant loss in species diversity. Nutrient amendment as well as seeding with bacteria consortium is recommended for faster rates of crude oil degradation.