ABSTRACT
Pollution caused by crude pol; a complex mixture of hydrocarbons that includes aliphatics, aromatics, asphaltenes and resins is one of the most prevalent problems in the environment. Bioremediation of such hydrocarbon contaminated soils exploits the ability of microorganisms to degrade and/or detoxify organic contamination. It has been established as an efficient, economic, versatile and environmentally sound treatment and offers promise in solving the problem of environmental pollution. The most widely used bioremediation procedure is biostimulation of the indigenous microbes by addition of nutrients, as contamination tends to result in rapid depletion of the available pools of major inorganic nutrients such a Nitrogen and Phosphorus. This study examined the possibility of using Diammonium phosphate and Urea as alternative sources of nutrients needed for biostimulation. This was achieved by contaminating soil at three contamination concentrations of 3000, 5000 and 8000mg/kg and treating them using Diammonium phosphate and urea. The total petroleum hydrocarbon, enzyme activity (laccase, lipase, catalase and peroxidase), microbial load (Total Heterotrophic Bacteria, Total Heterotrophic Fungi, Total Hydrocarbon Utilising Bacteria and Total Hydrocarbon Utilising Fungi) and physicochemical properties (Total Organic Carbon, Total Nitrogen, Total Phosphorus) of the soil every 6 days for a period of 30days. Treated soils showed better remediation results with TPH removal levels of over 80% in them as against that of about 45% in untreated soils. Significant difference at α = 0.05 was also observed in laccase, lipase, catalase and peroxidase activities of fertilized and unfertilized contaminated soils, the microbial load of these soils also had similar patterns. Microbial population rapidly increased in treated soils, this increase was rapid till day 12 after which a reduction in their population in their population was observed. This trend varied from that of control that showed a low but steady increase in microbial population over time. Enzymatic activities of laccase reached a peak of 2.38 ± 0.10µmol/h/g in unfertilized soil and 2.64 ± 0.06µmol/h/g in unfertilized soils on day 18 after which a steady decline was observed. Peroxidase and catalase behaved similarly with activity peaks on day 12 followed by a decline in activity; the observed increase and decrease in peroxidase and catalase activity in contaminated soils correlated with decreasing microbial load observed in same soil samples. Lipase activity was measured as µmol/g of soil, it showed increased activity in all soil samples throughout the duration of this study. Total organic carbon increased in unfertilized soils from 1.23 ± 0.01% to 1.27 ± 0.01% after 30 days while fertilized soil showed an average decrease from 1.23 ± 0.00% to 0.70 ± 0.01%. Total phosphorus levels in all soil samples decreased over the 30 day period while total nitrogen concentration continued to flunctuate. In all fertilized soils, all parameters were significantly enhanced pointing to the importance of nutrients in bioegradation, although the effect of biostimulation of the indigenous soil microorganisms declined with time especially after day 12
