By-products valorisation - Anaerobic Digestion of by-products
Conversion of the residual wastewater (by-products) into valuable end-products is necessary to achieve economic viability. The choice for producing biogas is justified by many facts. Anaerobic digestion of liquid organic wastewater is a mature technology. It should allow reaching full conversion of all the polysaccharides in biofuel and valorising the NPK minerals naturally contained in the biomasses. Currently the most typical valorisation of the vinasses from distillation and other residual wastewater is cogeneration of the concentrated solids (mainly lignin) to produce steam and electrical energy which is totally or partially recycled in the plant. This strategy is relevant in terms of energy efficiency and cost reduction when the plant requires much energy to operate, notably to run the pretreatment process.
In the case of the project where less heat is required thanks to the mild conditions of the new pretreatment, more biogas will be exportable whether for injection in the natural gas network or for storage as biofuel for transport. The small-scale production model is well adapted to farming activity. For instance in France, the biogas production in small methanation units run by agricultural cooperatives is developing as a solution to valorise organic residues from the farms. So there is a favourable background for the linking of biogas production units to ethanol production plants. Each business case will be subject to a specific study in cooperation with the local users and stakeholders to define the best strategy for the exportation of methane and mineral fertilizer at local level.