PROJECT DESCRIPTION
BACKGROUND
Unmanaged livestock waste is an important source of diffuse emissions of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). According to an annual GHG report, the agricultural sector is responsible for 21% of global greenhouse gas (GHG) emissions (Food and Agriculture Organization, 2016). Intensive livestock farms are the largest emitters of these gases due to the concentration of animals in small spaces. Manure management generates around 106-230 tCO2eq/year, with pigs being responsible for 40% of these emissions. Methane and nitrous oxide are the main gases emitted in agricultural production, especially from the management of livestock and their manure. The management of waste through anaerobic biodigestion processes prevents the generation of these emissions, while producing biogas that, after undergoing a purification treatment (upgrading) can become biofuel (biomethane). The use of biomethane as fuel in vehicles, replacing conventional fossil fuels, further entails the reduction of CO2e emissions (2 kg CO2 per m3 of biomethane produced). Similarly, compressed natural gas (CNG) combustion engines have a lower emission of volatile particles and NOx than diesel engines used in vehicles and agricultural machinery.
OBJECTIVES
The main objective of the LIFE SMART AgroMobility project was to demonstrate the technical, economic and environmental viability of a new management model for livestock discharges (pig manure) through biodigestion with innovative low-cost biodigesters. The resulting digestate was valorised as a high-value biomass for its use as a biofertiliser/biostimulant. This was achieved through the treatment and fixation of nitrogen (N) and phosphorus (P) by microalgae, which, in turn, acted as a biological biogas-refining system and transformed this into biomethane. The final product was biomethane for use in agricultural vehicles and biofertilisers.
The project thus contributed to the implementation of the EU Renewables Energy Directive (2018/2001/EU), through the production of biomethane, of the Energy Efficiency Directive (2012/27/EU), through the transformation of waste into energy, and of other EU policies relating to sustainable agriculture and biofuels.
RESULTS
The main results of the project were:
- the construction of a low cost biodigester for pig manure, with a total capacity of 150 m3. A total of 1,368 m3 of slurry managed per year;
- the creation of a prototype of a new technology (microalgae and bacteria for simultaneous removal of CO2 and H2S) to obtain biomethane. The biological refining treatment has an area of photobioreactors for microalgae culture of 1,500 m2, which can allow the treatment of a flow of 80 m3/day of biogas. This flow corresponds to 82% of the biogas produced in the digester, the rest being consumed to generate heat;
- a biomethane production output of 9.9 m3/day, although it was expected to reach 80 m3/day. The lower-than-expected production was due to technical issues with the heater, which prevented operation within the mesophilic range (35ºC). As a result, the digester functioned in the psychrophilic range (0-35ºC), leading to significantly lower production. Despite these technical difficulties, operating in the psychrophilic range represents a more realistic scenario for some farms, as it reduces initial investment costs. Therefore, although production was lower, this outcome presents a valuable insight for future business plan;
- a new refining process (i.e., the removal of trace contaminants such as volatile organic compounds, NH3, H2S) and biomethane compression based on a multi-phase procedure. As a result of the last phase of treatment, high-purity biomethane is obtained, compressed at a pressure of 250 bar and suitable for supplying to vehicles by means of special petrol station developed for this purpose;
- the real-scale demonstration of the use of the biomethane produced to supply fuel to a vehicle. The project produced enough biomethane for a vehicle to travel 89,014 km/year;
- the production of 4,500 kg/day of fertiliser from the digestate and 730 kg/day from microalgae.
