Continuous fermentative hydrogen production under various process conditions

Hydrogen is a clean energy carrier which has a great potential for an alternative fuel. To produce hydrogen by fermentation of biomass, a continuous process using a non-sterile substrate with a readily available mixed microflora is desirable. This work investigates a continuous procedure at pH 5.2 and 37 degrees C, using heat-treated digested sewage sludge of a wastewater treatment plant and continuous hydrogen production from waste sugar at various stirring speeds and hydraulic retention times (HRT). For continuous biohydrogen production the experimental set-up of three 5.5-L working volume continuously stirred tank reactors (CSTR) having three stirring speed levels (240, 135, 80 rpm) were constructed. At the optimum operation condition, seven HRTs at different organic loading rates (OLR) of 3-11 kg DOC/m(3).d (Dissolved Organic Carbon) were examined. Results indicated that the stirring speed of 135 rpm had a beneficial effect on H-2 fermentation. The best performance was obtained in 135 rpm and 8 h of HRT. The gas amount varied with different OLRs, but could be stabilized on a high level as well as the hydrogen concentration in the biogas was 62-64%. No methane was detected in the HRTs less than 16 h of operation. The most stable result achieved with reactor at 135 rpm. In addition, specific rate of hydrogen production reached its highest value at 2.13 L H-2/L-media.d