Chloroform aerobic cometabolism in a continuous-flow sand-filled bioreactor fed with alternate oxygen and growth substrate pulses

Chlorinated Aliphatic Hydrocarbons (CAHs) are common contaminants of groundwaters and industrial wastewaters. Several lab- and field-scale studies showed that aerobic cometabolism with aliphatic and aromatic hydrocarbons as growth substrates can lead to the rapid and complete dechlorination of a wide range of CAHs, including high-chlorinated compounds such as tetrachloroethylene. In this study, a process of chloroform (CF) aerobic cometabolic biodegradation by a butane-growing consortium was investigated for 354 days in a 2-m continuous-flow sand-filled reactor. The study was aimed at a) investigating the oxygen/substrate pulsed injection technique as a tool to control the clogging of the porous medium, to attain a long bioreactive zone and to reduce substrate inhibition on CF cometabolism; b) identifying guidelines for optimizing the oxygen/substrate supply schedule; c) developing a reliable model of CF cometabolism in porous media. While the continuous supply of butane rapidly led to the clogging of the porous medium due to excessive biomass growth near the reactor inlet, the testing of six types of oxygen/substrate pulsed feeding led to the identification of a feeding schedule capable to prevent aquifer clogging and to lead to the development of a long bioreactive zone and to satisfactory CF degradation performances (CF removal = 82%; CF degradation rate = 0.035 mg Lreactor d-1; ratio of CF degraded to butane consumed (CF/B) = 0.27 mg mg-1). The tested model of aerobic cometabolism in porous media led to a suitable interpretation of the experimental data (average percent error = 19%) as long as the CF/B ratio was ≤ 0.27 mg mg-1. A long-term simulation of the best-performing schedule of pulsed oxygen/substrate supply indicated the attainment of a steady state condition characterized by lower bioremediation performances than those obtained experimentally, evidencing the need for a further, model-based optimization of the pulsed injection technique.