Patent ID: 6966983

Claim:
A continuous flow, enclosed and heat insulated, multistage gas-liquid contacting system for the thermophilic aerobic digestion, pasteurization and stabilization of concentrated wastewater sludge, wherein: a) each gas-liquid contacting stage contains a separate sludge liquid volume, an enclosed separate gas headspace above the sludge liquid and a gas-liquid contacting device to contact the sludge liquid with the gas in the headspace; b) the sludge liquid flows from the feed liquid stage serially through the entire multistage system; c) the gas feed to the multistage system contains at least 20 volume percent oxygen gas and flows directly from the feed gas headspace to one or more other gas headspaces in the multistage system in a predetermined sequence; and d) the sludge liquid temperature reaches a minimum of 58° C. in at least one stage at a sufficient residence time to ensure pasteurization.