The effect of temperature and hydraulic retention time (HRT) on the
homoacetogenesis and on .the morphological characteristics of hydrogen
producing granules was investigated. Hydrogen was produced using an
expanded granular sludge blanket (EGSB) reactor, fed with glucose and Larabinose,
under mesophilic (37ºC), thermophilic (55ºC), and hyperthermophilic
(70ºC) conditions. Apparent homoacetogenesis was observed only at
mesophilic conditions. Glucose was utilized preferentially over L-arabinose at
thermophilic and hyper-thermophilic conditions. Higher yields of hydrogen
production were linked to the decrease of lactic acid and the increase of nbutyrate,
in all temperatures tested. Under mesophilic conditions with an
organic loading rate (OLR) of 5KgCOD/m3/d the total filaments length per VSS
(TL/VSS) increased and the apparent granules density (VSS/TA) dropped off.
With the application of OLR 10 and 16KgCOD/m3/d, TL/VSS decreased and the
VSS/TA augmented suggesting an increase of granules density. Under
thermophilic conditions the enhance of TL/VSS and the diminish of VSS/TA only
occurred with the application of OLR16KgCOD/m3/d, while under
hyperthermophilic conditions it happened since the beginning of operation with
the application of OLR10KgCOD/m3/d. Granules size was not affected by
temperature but the application of higher OLR promote a decline on the
percentage of projected area of aggregates with equivalent diameter (Deq)
larger than 1 mm.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/29823/2006, SFRH/BPD/24221/2005,
projecto POCTI/ENR/57786/200
