Chlorinated solvent aerobic biodegradation via cometabolism in a continuous-flow column reactor

Chlorinated Aliphatic Hydrocarbons (CAHs) are common contaminants of groundwaters and industrial wastewaters. Aerobic cometabolism represents a promising technology for the treatment of CAH-contaminated sites and wastewaters. However, with specific regard to the implementation of this technology for the remediation of CAH-contaminated sites, several issues still need to be addressed, such as the risk of a complete consumption of the supplied growth substrate within a short distance from the injection wells and the fact that aquifer clogging can result from an excessive biomass growth. This study, focused on chloroform (CF) cometabolism by butane-grown bacteria, was conducted in a 2-m continuous-flow column reactor simulating a portion of saturated aquifer. The main goals were: a) to investigate the pulsed injection of growth substrate and oxygen as a tool to control clogging of the porous medium and to attain a wide bioreactive zone; and b) to identify a suitable kinetic and fluid-dynamic model to fit the experimental data of butane utilization and CF cometabolism. A preliminary group of tests was aimed at determining the main fluid-dynamic parameters required for the modelling of the process. The reactor was then run in continuous mode for about 6 months, with subsequent changes of the schedule of pulsed injection of oxygen and butane, with the goal to maximize CF degradation and to minimize butane consumption. The experimental results indicate that a satisfactory injection scheme was finally attained, which resulted in an 80% average CF removal and in an apparently sustainable cometabolic process. The results were successfully simulated with a model of aerobic cometabolism with competitive inhibition. A representative profile of the concentrations of butane, oxygen and CF during the initial period of column operation is provided in Figure 1, together with the corresponding model simulation. Overall, this work provides encouraging indications on the successful application of aerobic cometabolism for the in-situ remediation of CAH-contaminated sites.