Abstract
Laboratory studies were developed to compare the effectiveness of inoculated bacteria consortia and indigenous microorganisms on diesel-polluted soil for 18 days. Bacteria isolated from the unpolluted soil sample were: Pseudomonas spp. (LBI), Pseudomonas cepacia (LB5), Micrococcus luetus (LB2), Bacillus subtilis (LB3) and Bacillus cereus (LB4). Their ability to degrade different substrates were first studied by the presence of growth in minimal salt broth. All the isotates were unable to grow in hexane. LB1 and LB2 had a strong growth in n-dodecane and n-hexadecane. Only LB1, LB4 and LB5 were able to grow in paraffin. LB1 and LB5 had poor growth on xylene. LB1 and LB3 had moderate growth in phenol. All the isolates had little growth in kerosene and only LB3 and LB4 grow in diesel. The three most promising of the isolates, with moderate to strong growth (LB2, LB4 and LB5) on crude oil were further used for diesel bioremediation. The bacterial population in the augmented diesel-contaminated soil showed a reduction in the population density from days 15 to 18, an indication of nutrients (diesel oil) exhaustion. While the un-augmented diesel-polluted soil samples showed potential of more days of increased bacterial population after the 18th day of observation, a pointer of more diesel in the soil samples that can be metabolized/utilized by the microorganisms present in soil samples. The consortia of Bacillus coagulans, Citrobacter koseri and Serratia ficaria was effective in the removal of 73.8% diesel oil from the diesel-polluted soil sample while natural attenuation resulted in 41.0% diesel oil removal and 35.8% in the control. Key words: Bioaugumentation, consortia, diesel, effectiveness, pig dung, soil.
Highlights
The contaminated soil in the tray was inoculated with 200 mL of 8.8 x 10-3 cfu/ml of bacteria (Bacillus coagulans, Citrobacter koseri and Serratia ficaria) capable of degrading hydrocarbon and supplemented with 200 g of pig dung thoroughly mixed and was subsequently designated A
The bacteria isolated from the soil sample were: Pseudomonas spp., Pseudomonas cepacia, Micrococcus luetus, Bacillus subtilis and Bacillus cereus
Bioremediation of diesel-contaminated soil which involves the use of augmented bacteria and pig dung to reduce high levels of diesel to levels that can be harmless/safe and as a result, will minimize the subsequent damages caused to the environment
Summary
Biodegradation is a biologically catalyzed oxidation or reduction reaction involving complex chemical compounds This process can be based on either growth (organic pollutants are used as the sole source of carbon and energy) or co-metabolism. Cometabolism is the breaking down of organic compounds in the presence of a growth substrate which is used as the primary carbon and energy source (Das and Chandran, 2011) These microbial activities occur with effective cooperation from the soil (Laleh et al, 2016). Exploring different microbial species, their optimum degrading parameters, co-substrates or nutrient supplements with high efficiency to breakdown/degrade hydrocarbons, is of importance in the bioremediation of crude oil and its products. The objective of this study was to investigate the bioremediation of dieselpolluted soil using augmented bacteria and pig dung as nutrient supplement
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