An in situ groundwater remediation process,termed EGCW,was developed in this study by integrating in-well groundwater electrolysis into groundwater circulation well.Groundwater circulation carries electrolytically generated O2 and H2 into the impacted aquifer for in situ biodegradation of contaminants.In a two-dimensional tank filled with field sandy sediments,simulated trichloroethylene(TCE)-contaminated groundwater was circulated between an injection well with electrodes inside and a pumping well.Results from a 50-day EGCW experiment show that in-well electrolysis oxygenated most region near the injection well,and 10mg/L TCE was mainly biodegraded aerobically to about 2.7 mg/L(73％removal)by the indigenous microbes.Aerobic TCE degradation was enhanced by the pulsed addition of acetate.Together with the proofs of stable carbon isotope fractionation(enrichment factor:-0.57％o--1.53％o)and microbial community variation after EGCW treatment,aerobic cometabolism was proposed to be the most likely mechanism for TCE degradation.It is interesting to find that the intrinsic organic carbon in aquifer matrix could fuel the aerobic TCE degradation,particularly at low TCE concentrations.EGCW treatment is advantageous in terms of supplying appropriate dosages of electron acceptor(O2)and donor(H2)for in situ bioremediation because groundwater electrolysis and circulation are expedient and controllable.