Effect Of Hyperthermophilic Pretreatment On Methane And Hydrogen Production From Garden Waste Under Mesophilic And Thermophilic Conditions

Anaerobic digestion of garden waste was investigated in a two-stage process consisting of hyperthermophilic pretreatment followed by mesophilic or thermophilic fermentation. The greatest digestion performance was achieved when the substrates were first treated at 70 degrees C for 3 days with no inoculation, and then mixed with inoculum (anaerobic sludge) and subjected to anaerobic digestion at 55 degrees C. Under such conditions, the maximum methane and hydrogen yields from grass were 517 NmlCH(4)/kgVS and 52 NmlH(2)/kgVS, whereas the corresponding values for leaves were 421 NmlCH(4)/kgVS and 23 NmlH(2)/kgVS, and these figure were far greater than the yields obtained in experiments with no hyperthermophilic stage. A metagenomic analysis of hyperthermophilic environments revealed the appearance of thermophilic and hyperthermophilic bacteria showing hydrolytic activity against lignocellulosic materials, including Caldicellulosiruptor, Thermovenabulum, Thermoanaerobacter, Moorella, Tepimicrobium, Geobacillus and Thermobacillus at a genus level. A noticeable methane production in the hyperthermophilic stage could be linked to the presence of Methanothermobacter sp.