A continuous flow, immobilized cell reactor, and bioprocess, for the detoxification and degradation of volatile toxic organic compounds. The reactor is closed, and provided with biocatalysts constituted of specific adapted microbial strains immobilized and attached to an inert porous packing, or carrier. A contaminated groundwater, industrial or municipal waste, which is to be treated is diluted sufficiently to achieve biologically acceptable toxicant concentrations, nutrients are added, and the pH and temperature are adjusted. The contaminated liquid is introduced as an influent to the closed reactor which is partitioned into two sections, or compartments. Air is sparged into the influent to the first compartment to mix with and oxygenate the influent with minimal stripping out of the toxic organic compounds. The second section, or compartment, is packed with the biocatalyst. The oxygenated liquid influent is passed through the second compartment substantially in plug flow, the biocatalyst biodegrading and chemically changing the toxic component, thereby detoxifying the influent. Non toxic gases, and excess air from the first compartment, if any, are removed through a condenser located in the overhead of the reactor. Liquids are recondensed back to the aqueous phase via the condenser.