Effect of Mixing on the Biological Degradation of Toluene under Aerobic Conditions

The effectiveness of in-vessel bioremediation in reducing the concentration of toluene in contaminated soil under continuous and intermittent mixing conditions using invessel composting system. The results showed that there was a startup period (60 h) during which the average temperature rose from 21 to 32 and 40°C (and then remained constant) for the bioreactors with continuous and intermittent mixing, respectively. The increase in the temperature demonstrated the conversion of the complex organic carbon into H₂O, CO₂ and energy during mineralization (cell respiration process) of carbon. The lower temperature of the bioreactor with continuous mixing (8-9°C) mixing during the steady state period indicating that more heat was lost with exhaust gas from this bioreactor. Little changes were observed in the moisture contents of the mixture. Most of the moisture losses were through the exhaust gas. The analysis of the exhaust gas samples did not show identifiable toluene peaks but some unidentifiable peaks were present. By day 15, about 96.35 and 89.07% of the initial toluene were removed by the bioreactors with intermittent and continuous mixing, respectively. These results indicate that in addition to reducing the energy requirement by 50%, the bioreactor with intermittent mixing also reduces the time required for complete degradation. This method of bioremediation is very effective in removing toluene but the production of toluene derivatives during the biodegradation process should be investigated.