Kinetics of pseudo-continuous flow bioreactor treatment of diesel contaminated soils

A bioremediation treatability study was evaluated on a laboratory scale for its effectiveness in treating a sandy soil contaminated at 1500 mg kg super(-1) wet weight by No. 2 diesel fuel. A continuous type reactor system was used and by continuously loading different reactors at different levels, a variation in mean cell age was obtained. Adequate nutrients, moisture, and oxygen were available at all times so that the fuel was the only limiting nutrient and was measured in terms of TPH. The off-gases CO sub(2) and volatile hydrocarbons were also monitored. At steady state, biokinetic equations which conform with microbial physiology and growth kinetics were evaluated and included the following coefficients: specific growth rate, specific substrate utilization rate, substrate affinity (half-saturation constant), microbial decay rate and growth yield. The solids retention time for evaluating final TPH concentration of 100 mg kg super(-1) were also calculated. The reactors reached steady state conditions at 70 days based on biomass and TPH levels. This preliminary study shows that a continuous bioreactor system is effective in reducing diesel fuel concentration over a given period of time, and that the kinetics of the process can be evaluated. Removal efficiencies up to 80% were attainable.