Patent ID: 9567611
Date: 2017-02-14
CPC Classifications: C12M,C12P,Y02E

Claim:
1. A method of producing biogas, comprising the steps of i) in a first reactor, culturing at least one anaerobic microbial consortium in a high solids medium comprising 10 to 20% solids and having a pH in the range of from 6.0 to 7.5, for a period of time sufficient to produce biogas containing methane and to form a high solids phase and a low solids phase within said first reactor, wherein a) said high solids phase is positioned within a top portion of said first reactor and floats directly on said low solids phase, and wherein oxygen tolerant microorganisms within said high solids phase hydrolyze and produce VFAs from biodegradable solids, and b) said low solids phase is positioned beneath said high solids phase within a bottom portion of said first reactor, wherein microbial populations within said low solids phase perform anaerobic processes that produce biogases; and wherein said high solids phase and said low solids phase are in direct contact with each other; ii) culturing, in a second reactor, at least one methanogen-rich anaerobic culture in a low solids medium comprising at most 1% solids and having a pH in the range of from 6.5 to 8.5, for a period of time sufficient to generate methane; iii) during one or both of step i) of culturing and step ii) of culturing, removing effluent containing volatile fatty acids (VFAs) from said low solids phase in said first reactor at a rate that is sufficient to at least partially offset a decrease in pH within said high solids phase; iv) transferring effluent removed from said low solids phase in said first reactor to said second reactor; v) removing effluent from said low solids medium in said second reactor; vi) transferring effluent removed from said second reactor to said first reactor at a rate that is sufficient to at least partially offset said decrease in pH within said high solids phase; and vii) recovering biogas produced in at least one of said first and second reactors.