TREATMENT OF WASTE WATER PRODUCTING METHANE

The oxygen demand of waste water (5) having a partial organic composition is reduced by feeding the waste water (5) into an anaerobic digester (2) near the top thereof so as to flow downwardly through the interior of the digester (2). The digester (2) is at least partially filled with a high surface area media (30) carrying on its surface a microorganism which preferentially produces methane when in contact with the organic material in the waste water (5) and also reduces the oxygen demand of materials therein. Nutrients (18, 19) are added as necessary to promote growth of the microorganisms. Methane released from the waste water is collected (at 53) and selectively recirculated to the bottom of the digester (at 60) to break up the biomass thereon. Waste water (5) and biomass is recirculated from the bottom of the digester (2) to the top thereof, preferably at a rate of five times the flow of the influent to the digester (2).