Up to now, a continuous scaled-up process for sustainable fermentative H2 production has not been reported in the literature. Only very few studies, are available so far, regarding the fermentation of sugars to hydrogen, at pilot scale. Ren et al. (2006) performed a pilot scale study in a continuous flow anaerobic fermentative reactor with an active volume of 1.48 m3 and using molasses as substrate. The reactor operated under the organic loading rates of 3.11-85.57 kg COD/m3 reactor/d and produced 5.57 m3 H2/m3 reactor/d or 8240 L H2/d with a hydrogen yield of 26.13 mol/kg COD removed. The effluent which was produced, contained primarily acetate and ethanol and was as high as 3000 L/d. This, rich in acetate, effluent could be further exploited for hydrogen production through a subsequent photoeterotrophic stage, which could increase hydrogen production by 317%.

Vatsala et al. (2008) evaluated the feasibility of hydrogen production from a sugar cane distillery effluent using co-cultures of Citrobacter freundii 01, Enterobacter aerogenes E10 and Rhodopseudomonas palustris P2, at 100 m3 scale. The reactor operated at batch mode for 40 hours, and the hydrogen production was 21.38 kg with an average yield of 2.76 mol H2/mol glucose and a rate of 0.53 kg/100 m3/h. The results showed that distillery effluent could be used as a source of hydrogen providing insights into treatment for industrial exploitation.

Since data for real applications are not available so far, we can design such a process based on the respective lab-scale experiments. The problem is that the hydrogen productivity and yields depend significantly on the prevailing conditions, the feedstocks as well as the inoculum used. However, from laboratory-scale work on continuous processes, it could be suggested that such a process may operate at a mesophilic temperature, at a pH around 5.5 and an HRT approximately 8-12 hours, for simple substrates. Higher HRTs are indicative for complex carbohydrate-rich feedstocks. Finally, such a process may use as microbial inoculum, heat-treated sludge form aerobic or anaerobic process or the indigenous microbial species available in the feedstock/waste, which has often proved to work optimally (Antonopoulou et al., 2008a; 2008b).