Patent ID: 6342378
Filing Date: 2002-01-29
Classification: C12M,C12P,Y02E,Y10S

Abstract:
A method for producing methane by digesting solid agricultural waste having methane generating potential, said method comprising:(a) a hydrolysis phase comprising; (i) contacting said solid agricultural waste with a hydrolytic bacterial culture in a hydrolysis vessel separated into a lower chamber and an upper chamber by a filtration means preventing passage of said solid agricultural waste from said upper chamber into said lower chamber; (ii) incubating said solid agricultural waste and said hydrolytic bacterial culture at a pH of from about 4.5 to about 6.5, thereby hydrolyzing said solid agricultural waste to form an aqueous hydrolysis mixture comprising volatile fatty acids, said aqueous hydrolysis mixture and the solid agricultural waste being retained in said hydrolysis vessel throughout said incubating; (iii) following said incubating, filtering at least a portion of said aqueous hydrolysis mixture through said filtration means into said lower chamber, separating said aqueous hydrolysis mixture from the solid agricultural waste, thereby forming a liquid methanogenesis feedstock essentially free of the solid agricultural waste; (b) a methanogenesis phase comprising; (i) transferring from said lower chamber of said hydrolysis vessel at least a portion of said liquid methanogenesis feedstock into a methanogenesis reactor where said feedstock is contacted with a methanogenic bacterial culture contained in said methanogenesis reactor, thereby forming a methanogenesis mixture having a pH of from about 6.5 to about 7.5; (ii) incubating said methanogenesis mixture, thereby forming methane, said methanogenesis mixture being retained in said methanogenesis reactor throughout said incubation; (ii) collecting said methane formed in step (b(ii)); (iv) transferring at least a portion of said methanogenesis mixture from said methanogenesis reactor into said hydrolysis vessel where said methanogenesis mixture is contacted with said solid agricultural waste; (c) a recycling phase comprising; (i) repeating steps (a(i)-a(ii)) and steps (b(i)-(iv)), to further hydrolyze the solid agricultural waste in sad hydrolysis vessel and continuously generate methane in said methanogenesis reactor, thereby exhausting said methane generating potential of the solid agricultural waste, and forming depleted agricultural waste; (d) following said recycling phase, removing at least a portion of said depleted agricultural waste from said hydrolysis vessel, while said methanogenesis reactor continues to generate methane; and (e) optionally, following step (d), introducing a batch of solid agricultural waste into said hydrolysis reactor, and repeating steps (a(i)-a(ii)), steps (b(i)-(iv)) and step (c).