Organic pollutants from diverse agricultural, municipal and industrial facilities, and waste sites partition preferentially into the soil, water or air phases and spread rapidly throughout the environment. Many of these materials, even in small concentrations, adversely affect life forms, and create serious environmental threats. Toxicity, carcinogenicity, and mutagenicity are the most critical biological properties of a potential pollutant, a very large number of organics of which have been identified by the U.S. Environmental Protection Agency as particularly threatening. For example, the widespread use over the last few decades of herbicides, pesticides and related high risk chemicals, e.g., organochlorines, polychlorobiphenyls (PCB's) and chlorinated phenols, have resulted in serious environmental metal problems. In application Ser. No. 519,793 filed May 7, 1990 by David D. Friday and Ralph J. Portier, there is disclosed 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.
In the reactor described in the application, supra, the air in the form of a high velocity jet is sparged into the first compartment of the reactor and combined with the conditioned liquid influent at high gas/liquid shear conditions, under pressure, to create very fine bubbles. The mixed phases of air and liquid are flowed through a bed packed with a solid inert packing, e.g., glass beads, then through an open tubular column to a packed bed of biocatalyst. Good mixing, with minimum stripping of the toxic organic compounds from the liquid, is obtained. The pressure increases the oxygen driving force, and the high gas shear provided by the method of contact between the gas and liquid, and solid inert packing, under pressure minimizes bubble diameter and increases the interfacial transfer area between the phases. By small bubble formation and good mixing with good air/liquid contact at elevated pressure, the volume of air that is introduced into the reactor is minimized. Consequently, a lesser amount of the volatile organic compounds are stripped from the liquid and a greater concentration of the volatile organic compounds are contacted, with the biocatalyst and mineralized to detoxify the influent stream. Whereas the apparatus described in this application has proved admirably suitable for admixing the liquid and oxygen influent phases introduced into the reactor, with minimal stripping of the volatile organics by the gas, there nonetheless remains need for alternate bubble generation devices, as well as a need for improved bubble generation devices. There also remains a need for reactors of improved design for carrying out these types of reactions due principally to the volatility of many of the chemical toxicants targeted for detoxification biodegration.