Aerobic cometabolic bioremediation of trichloroethylene- and 1,1,2,2-tetrachloroethane-contaminated groundwater in a packed bed bioreactor

The aim of this study was to develop a packed bed reactor (PBR) process for the on-site aerobic cometabolic bioremediation of a groundwater contaminated by trichloroethylene (TCE) and 1,1,2,2-tetrachloroethane (TeCA). With regard to the growth substrate selection, the comparison of the CAH degradation performances obtained with 5 candidate substrates led to the selection of butane and to the development from the site’s indigenous biomass of a suspended-cell consortium capable to degrade TCE (TCE first-order constant = 96 L gprotein-1 d-1 at 30 °C and 4.3 L gprotein-1 d-1 at 15 °C) with a 90% mineralization of the organic Cl. Based on PCR-DGGE analysis of the 16S rRNA genes followed by band excision and sequencing, the microbial consortium enriched was mainly composed of Bacteroidetes and Alpha- and Beta-Proteobacteria that were distantly related to known CAH-cometabolizing bacteria. The low TeCA degradation rate by the developed consortium suggested the introduction of a chemical pre-treatment based on the TeCA to TCE conversion via -elimination, a very fast reaction at alkaline pH. The choice of the best-performing carrier was made by means of a 2-level procedure: the 1st level consisted of batch tests, operated both at 30 and 15 °C, whereas the 2nd level consisted of continuous-flow tests, operated at 30 °C. A porous ceramic carrier named Biomax resulted the best-performing one. On the basis of the kinetic parameters relative to TCE aerobic cometabolic biodegradation by the selected consortium, a 31-L packed-bed reactor, consisting of 14 columns connected in series, packed with Biomax and immerged in a temperature-controlled bath, was designed and set-up. The preliminary data, obtained by operating the plant with a 4-day residence time, indicate the attainment of a 0.1 mg L-1 d-1 TCE biodegradation rate.