The advantages of anaerobic waste treatment, such as low energy requirement, low biomass production, and energy generation are still offset by the low throughput rate of this method of treatment. Throughput rates, comparable to those of aerobic waste water processing, have been achieved for some special types of waste water, containing dissolved organic compounds. Results from single and two-stage reactors for the microbial generation of methane, from a mixed substrate, containing solids, are compared. The reactors were partially optimized for the boundary conditions of shear rate and sedimentation.