Optimized conditions for diesel bioremediation with addition of surfactants

Petroleum hydrocarbon contamination has caused critical environmental and health defects. To enhance the mobility and bioavailability of petroleum compounds, sixteen operations were tested in order to determine the best condition for diesel bioremediation. Sandy loam soil, with controlled moisture of 18% to 24% and pH variation of 6.8 to 7.2, were contaminated in the laboratory with commercial diesel and placed in 16 glass bioreactors. Sixteen runs were tested with different combinations of the following components: (1) concentrations of TPH-d (3,200 or 15,000 mg/kg); (2) surfactants (Tween 80 or rhamnolipid); (3) concentrations of the surfactants (10 or 80 mg/kg), and (4) soil turnover rate (once in two days or once in ten days). The results indicated the 2-day agitation group created effective ventilation which resulted in a better degradation rate than that of the 5-day agitation group. The groups with low diesel addition tended toward no significant difference in TPH-d degradation, and the resultant TPH-d concentrations were degraded to less than 1000 mg/kg within 80 days. Diverse performance was found among the groups with high diesel addition: low levels of rhamnolipid resulted in the optimal TPH-d removal rates, 89.8% and 52.4% in 2-day and 10-day turnover, respectively. High levels of Tween 80 resulted in the worst removal rates. Generally speaking, 2-day turnover performs better than 10-day turnover in terms of the first order rate constant and the TPH-d removal rate, 0.013-0.041 and 68% to 95%, 0.005 to 0.025 and 25.8% to 83.3%, respectively. Insignificant different bacteria counts among the operations indicated the problem of unsuccessfully high TPH-d degradation was not caused by toxicity to microorganisms.