Biogas is produced by using the anaerobic decomposition of organic materials that occurs when biodegradable matter from a living or once-living organism decays with the help of microorganisms in an oxygen-free environment. B4B biogas plant is composed by three principle components, two digesters and a gas holder. The digesters are an airtight container in which local organic waste and selected algae are introduce and than decomposed by bacteria producing gases such as carbon monoxide, methane, hydrogen, and nitrogen. The gasholder is a tank that harnesses the gases emitted by the slurry.
The following Figure depicts clearly the plant for production of biogas to be carried out in Sicily. The inputs for open ponds are:
- industrial purified water available in situ, to be used directly in the open ponds and to dampen the solid biomass to carry out anaerobic fermentation;
- biowaste to be used for algae growth: it will be selected for its availability and collection system .
- Manure is mentioned because it can provide the right amount of nitrogen requested for algae growth and can be easily found in adjacent farms;
- CO2 to be insufflated into the algae broth, from the boiler (since starting of macroalgae cultivation) and the upgrading plant (from the beginning of the third year);
- clarified effluents from the Archimede rotors;
- output of the protoplasts incubator.
As outputs, with the exception of CO2 already mentioned above, there are:
- heat and electricity from the co-generator (20 m3/h since biogas treatment starting);
- residual from the Archimede rotors
-solid fraction to be used for pellets and fertilizers production;
- liquid fraction of residual (clarified effluents) to be re-used as input in the algae broth (about 10 m3/day). - biomethane from the cryogenic upgrading plant (10 m3/h). The biogas upgrading process will start since the second half of the second year.
All inputs will be introduced in 4 PVC open ponds where the selected macroalgae http://www.biowalk4biofuels.eu/algae-biogas/types-and-species/ will be cultivated. This allows the control of the cultivation parameters unlike at open sea. Jet air connected with the ponds will provide water and CO2 to the algae broth guaranteeing biomass mixing. At the same time eutrophicational agents (coming from the biodigestors) will be introduced, after an appropriate treatment, achieving a closed cycle. This cultivation assures a strict control of several parameters (pH, nitrogen compounds, phosphates, etc.) avoiding water exchange with the open sea (“controlled open ponds”). The mentioned plant will be built in Augusta.