NOVELTY - Pressurized digester biogas reactor (801) comprises mixing tank; double channel central draft tube; pump (850) for forcing inlet fluid downward through central channel in double channel central draft tube into bottom portion of tank; the outer draft channel having inlet weir (877) for channeling mixing tank fluid into secondary channel; where pump supplies minimum of 20 feet/second flow rate to the inlet fluid to form vacuum at bottom end of outer draft channel; where slurry in the tank producing biogas; and central mixing zone having slurry outlet to release liquid.    USE - For anaerobically treating organic wastes such as wastewater sludge and thickening of digesting slurry to improve fuel gas quality while reducing volatile solids in environment which extends the residence time of hard-to-digest solids.    ADVANTAGE - The digester is designed to maintain vessel pressure sufficiently high to create high concentration of dissolved gas in the slurry during digester operation and allowing regenerative thickening process within the reactor and thus, improves fuel gas quality while reducing volatile solids in environment that extends the residence time of hard-to-digest solids. The present digester mixer is nested nozzle mixer which is less expensive than other digester mixing systems. The installation cost of the present mixing system is also lowest of all reactor mixer types. The digester mixer has a single unit configuration which can be completely removable without reactor draining. There is no need of electrical components in classified reactor zone to be inspected and maintained and also no need of permanent mechanical equipment in reactor zone.    DETAILED DESCRIPTION - Pressurized digester biogas reactor comprises mixing tank, where bottom portion of tank having smaller diameter than central portion; double channel central draft tube; pump for forcing inlet fluid downward through central channel in double channel central draft tube into bottom portion of tank; the central channel having primary nozzle (895) facing downstream; outer draft channel housing the central channel; where annular space between outer draft channel and central channel forms secondary channel; the outer draft channel having secondary nozzle (896) facing downstream; where primary nozzle is located above secondary nozzle, and both nozzles share common longitudinal axis; outer draft channel having inlet weir for channeling mixing tank fluid into secondary channel; where pump supplies minimum of 20 feet/second flow rate to the inlet fluid to form vacuum at bottom end of outer draft channel; where vacuum induces mixing tank fluid into weir and out the secondary nozzle; where combined flow from primary and secondary nozzles impinge bottom of mixing tank; slurry in the tank producing biogas; pressure controller located at top portion of tank to maintain operating pressure in tank in the range of 30-100 psi; the bottom portion of the tank having heater; pump having inlet in central mixing zone of tank for inlet fluid; and central mixing zone having slurry outlet to release liquid. The pressurized digester biogas reactor further comprises pressurized raw sludge injector into the tank; biogas removal module, hydrogen sulfide (H2S) removal module, biogas compression module, water removal module and biogas polishing module.    DESCRIPTION OF DRAWING(S) - The figure shows cross sectional view of reactor vessel.    Reactor (801)    Pump (850)    Weir (877)    Mixer (888)    Primary nozzle (895)    Secondary nozzle (896)