Anaerobic bioconversion of organic waste into biogas by hot water treatment at near-critical conditions: application in bioregenerative life support.
The feasibility of nearly-complete conversion of lignocellulosic waste (70% food crops, 20% faecal matter and 10% green algae) into biogas was investigated in the context of a Life Support Project. The treatment comprised a series of processes, i.e. a mesophilic laboratory scale CSTR (continuously stirred tank reactor), an upflow biofilm reactor and a hydrothermolysis system in near-critical water. By the one-stage CSTR, a biogas yield of 75% with a specific biogas production of 0.37 l biogas g(-1) VSS (volatile suspended solids) added at a HRT (hydraulic retention time) of 20 d was obtained. Biogas yields further increased with 10-15% at HRT > 20 d, indicating the hydrolysis of lignocellulose to be the rate-limiting conversion step. The solids present in the CSTR-effluent were subsequently treated by hot water treatment (T approximately 310-350 degrees C, p approximately 240 bar), resulting in effective carbon liquefaction (50-60% without and 83% with carbon dioxide saturation) and complete hygienisation of the residue. Subsequent anaerobic digestion of the hydrolysate allowed further conversion of 48-60% on COD (chemical oxygen demand) basis. Thus, the total process yielded biogas corresponding with a COD conversion up to 90% of the original organic matter. It appears that mesophilic digestion in conjunction with hydrothermolysis at near-critical conditions offers interesting features for (nearly) complete, non-toxic and hygienic carbon and energy recovery from human waste in a bioregenerative life support context.
Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure L 653, B-9000 Ghent, Belgium.
Geert
G
Lissens
Willy
W
Verstraete
Tobias
T
Albrecht
Gerd
G
Brunner
Christophe
C
Lasseur
D000693:Anaerobiosis; D002482:Cellulose; D004867:Equipment Design; D007700:Kinetics; D008031:Lignin; D009930:Organic Chemicals; D012037:Refuse Disposal / Q000295:instrumentation / Q000379:methods*
D009930:Organic Chemicals; C036909:lignocellulose; D002482:Cellulose; D008031:Lignin