The TANAIS project deals with the exploitation of industrial waste biomasses as renewable energy source and the optimization of the anaerobic digestion process to increase the methane yield.
The theme of energy from biomass is of foremost importance worldwide and the decarbonisation strategy to support the energy demand is shared -albeit with some differences- at European level.
To increase the potential production of renewable energy, one opportunity is represented by the exploitation of waste from industrial processes through the conversion in biogas by means of anaerobic digestion (AD). To make the AD competitive versus others options, three different aspects could be optimized: the first is the choice of un- or under-exploited biomasses such as the liquid industrial wastes that are relevant to the region in terms of quality and quantity and/or are -up to now- treated with disposal costs; second point is the increase of the methane yield in the process; the third aspect is the recovering from the digested sludge of useful compounds with high added value e.g. phosphates and nitrates.
The present project aims to increase the production of methane assessing the potential for processing three different industrial organic wastes. The three biomasses chosen are whey from cheese production (CW), because it represents one of the largest organic waste flows of the Cantone Ticino, the fermentation wastewater from pharmaceutical processes (FWW), and the soapstocks from food processing companies (SK). Nowadays these wastes of key industrial sector in Ticino are not really valorized but just disposed with extra costs.
To increase the bio-methane yield, the hydrolysis/acidogenesis/acetogenesis (HAA) step of the AD process is physically separated from the final methanogenesis step using an innovative two-stages bioreactor, dimensioned also with microbial kinetic parameters.
At first, the best methane yields has been assessed for each waste in single stage bioreactor to be used as reference. The operational parameters and the maximum methane yield is recorded. Then the three industrial waste have been tested separately with the operational parameters that gave the best performance in the reference tests. A yield greater than 30% for one substrate is deemed satisfactory to reach the milestone set in the project.
The proposed process is innovative respect to the state of the art as a network of reactors are operated to foster ad hoc selected metabolic pathways. In this way, in each bioreactor a specific active microbial community transforms the organic matter with unique kinetics parameters. The sensitive step of the methanogenic phase is enriched by developing biofilm structures to have a stable, resistant and resilient acetoclastic methanogens community, less subject to washout.
Among the three substrates tested, FWW and SK experienced not satisfactory methane yields due to physical chemical characteristics such as sulphur compound presence and difficult solubility. Instead CW gave the most promising results obtaining a methane yield about two times higher than the reference tests. The data will have to be validated in a scale up phase in strict collaboration with the industrial partner involved.
