Method for the anaerobic degradation of organic material

Claim 1

In a process for the anaerobic bacterial degradation of organic material present in an aqueous medium waste stream comprising introducing the influent waste stream into a system comprised of a holding tank and a fluidized bed anaerobic reactor, recycling at least in part the waste stream between the fluidized bed and the holding tank to anaerobically degrade organic material present in the waste stream in the fluidized bed, and discharging treated effluent from the system, the improvement comprising: introducing a high strength aqueous medium waste stream having a BOD concentration of at least 1,500 mg/l first into a holding tank of sufficient size and having a sufficient population of anaerobic bacteria therein to conduct degradation of organic components in the influent waste stream whereby said holding tank functions as a contact reactor under anaerobic conditions; pumping the aqueous medium waste stream from the contact reactor into a fluidized bed reactor maintained under anaerobic conditions, having an effective volume not more than 0.35 times the effective volume of the contact reactor and containing a bed of finely divided inert solid supporting a population of substantially anaerobic bacteria, at a rate effective to maintain the bed in a fluidized state and to also conduct degradation of organic components in the waste stream; treating the aqueous medium waste stream in said contact reactor and fluidized bed reactor under temperature conditions and for a residence time sufficient to generate methane, both in said contact reactor and said fluidized bed reactor; returning at least a part of the aqueous medium waste stream, which has passed through the fluidized bed reactor, to the contact reactor at a rate effective to achieve multiple passage of the aqueous medium through the contact reactor and the fluidized bed reactor; and withdrawing a treated effluent stream from at least one of the fluidized bed reactor and the contact reactor whereby higher purification levels can be attained than when conducting purification in a fluidized bed reactor connected to a holding tank.