Aerobic/anaerobic/aerobic sequenced biodegradation of a mixture of chlorinated ethenes, ethanes and methanes in batch bioreactors

[Display omitted] ► Aerobic/anaerobic/aerobic treatment biodegrades complex chlorinated solvent mixture. ► First aerobic step: low- and medium-chlorinated solvents degraded by cometabolism. ► Anaerobic step: tetrachloroethene degraded to cis-dichloroethene or trichloroethene. ► Second aerobic step: cis-dichloroethene or trichloroethene degraded by cometabolism. ► The anaerobic step is likely fed with dead cells grown during the aerobic step. A novel aerobic/anaerobic/aerobic treatment was implemented in batch reactors containing aquifer materials from a site contaminated by tetrachloroethylene (PCE), trichloroethylene (TCE), vinyl chloride (VC), 1,1,2-trichloroethane (1,1,2-TCA) and chloroform (CF). Consortia grown aerobically on methane, propane, n-pentane and n-hexane completely biodegraded the chlorinated solvent mixture, via aerobic cometabolism of VC, CF, TCE and 1,1,2-TCA, followed by PCE reductive dechlorination (RD) to 1,2-cis-dichlorothylene (cis-DCE) or TCE, and cis-DCE/TCE cometabolism in a further aerobic phase. n-Hexane was the best substrate. No electron donor was supplied for RD, which likely utilized cellular material produced during the aerobic phase. Chloride release was stoichiometric with chlorinated solvent biodegradation. According to the Lepidium sativum ecotoxicity test, a decreased toxicity was observed with propane, n-pentane and n-hexane, but not methane. A kinetic study of PCE RD allowed to estimate the PCE maximum specific rate (0.57±0.07mgmgprotein-1day-1) and half-saturation constant (6.7±1.5mgL-1).