Bio-hythane production by thermophilic two-phase anaerobic digestion of organic fraction of municipal solid waste

The increasing interest on hythane, a highly efficent and ultra clean burning alternative fuel (a mixture of hydrogen and methane) led many researchers to attempt hydrogen production by anaerobic digestion of biomass. The wet biomass with high carbohydrate content can be converted to hydrogen and organic acids through the action of fermentative bacteria. The aim of this experimental work was to evaluate the hydrogen and methane production efficency of the organic fraction of municipal solid waste (OFMSW) tratment through the two-phases anaerobic digestion process. The work was carried out at pilot scale, using two CSTRs (100 l and 380 l of working volume the first and second phase respectively) both maintained at thermophilic temperature (55°C) and fed semicontinuosly with organic waste mixed with tap water. The short HRT applied to the acidogenic phase (3 days) and the high temperature, facilitate the solubilisation of waste and the acidification of medium (pH lower than 4), conditions that aid hydrogen formation. The experiment was divide in three period where different organic loading rate were tested (5, 10, 15 kgTVS/m3d) and the gas yields, hydrogen from the fermentative reactor and methane from the anaerobic digestor, were monitored. During the first period, at 5 kgTVS/m3d, 0,005 m3gas/kgTVSf were produced in the fermentative reactor, showing a 60 % CO2 content. The methanogenic phase shown constant stability parameters (pH value 8, VFA 255 mgCOD/l, ammonia 1150 mgN/l) and a specific gas production of 0,73 m3/kgTVSf