Feasibility of coupling hydrogen and methane production during sewage sludge digestion

Anaerobic digestion is a technology widely used for the stabilisation of sewage sludge in wastewater treatment plants (WWTP). This technology presents several advantages such as the production of energy and the use of this energy to cover the demand of the treatment plant. However, sludge digestion systems may not produce an enough amount of biogas to cover a great fraction of the total energy demand. In the present manuscript is evaluated the introduction of a fermentative hydrogen phase and the effect produced in the system in terms of the energy balance. Food waste were considered as carbohydrate rich co-substrate and batch fermentation of this process is evaluated. The system was modelled using SuperPro designer considering conventional waste activated sludge system for the treatment of wastewater whereas the sewage sludge line was studied under mesophilic regimens. The mass and energy balance indicated an increase between 20 - 60% in the whole valorisation process, reporting as suitable this alternative when using digestate as inoculum source for starting-up the hydrogen process.