Two-stage anaerobic digestion systems wherein one of the stages comprises a two-phase system

摘要

Low cost, efficient two-stage anaerobic digestion systems for the production of biogas (e.g. methane) are provided. During the first stage, biogas is produced in a first reactor by anaerobic microbes cultured in two phases: a high solids phase and a low solids phase. During the second stage, biogas is produced in a second reactor by a methanogen-rich anaerobic culture cultured in low solids medium. Removal of effluent comprising pH lowering reaction products assists in maintaining a suitable pH in the high solids phase. The transfer of effluent from the second reactor to the first reactor assists in maintaining a suitable pH in the high solids phase, in mixing of the high solids phase, and in reseeding the high solids phase with methanogens. Methane is produced in and recovered from both reactors.

主权项

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.