Titolo della tesi: Development of bioelectrochemical systems for biomethane and biohydrogen production
The raising energetic demand has brought the concentration of greenhouse gases in atmosphere at the highest value ever registered. Especially the concentration of CO2 is at the center of every environmental debate. To reduce the CO2 emission, lots of efforts were made and more must be made to enhance the production of renewable energy. Unfortunately, the electric current produced by wind farms, hydroelectric plants, solar and geothermal plants is not enough. Furthermore, some of those technologies are dependent on the weather along with its fickleness. For those reasons humanity is looking for new efficient renewable technologies to produce electric current. In addition, the production of waste has raised along with the enhancement of the world population. Therefore, the recycling of waste must be a priority in order to preserve the environment. Anaerobic digestion (AD) is a waste treatment process which transforms the organic waste into digestate and biogas. Biogas is rich in CH4, therefore can be burned to produce thermal and electric energy in combined heat and power generation plants (CHP) (Szarka et al., 2013). A valid alternative is to purify and upgrade biogas to biomethane (with a content of CH4 > 95%), which has the same properties as the compressed natural gas (Ryckebosch et al., 2011; Villadsen et al., 2019). Those steps are very expensive, therefore only few AD plants have systems to transform biogas to biomethane. However, the recent European investment politics on biogas upgrading have changed the inertia in such manner to push the biogas upgrading in a product with an added value like biomethane.
An innovative technology capable of upgrade biogas is represented by the bioelectrochemical systems (BES) which exploit the ability of particular microorganisms to interact with a solid-state electrode. This ability permits to build systems capable of doing the most varied processes like environmental bioremediation(Zeppilli, Matturro, Dell’Armi, Cristiani, et al., 2021), nutrient recovery(Kuntke et al., 2014), chemicals production(Marshall et al., 2013) and biofuels production (Nelabhotla & Dinamarca, 2018; Rousseau et al., 2020). In order to render this technology commercial, is fundamental to lower the costs and to obtain high and reliable performance.
With the same technology is possible to produce biohydrogen using wastewaters (WW) like digestates or the domestic WWs(Roubaud et al., 2018). Hydrogen is the lightest fuel usable for combustion, but due its dangerousness hydrogen motors are not widespread. Furthermore, hydrogen is used in chemistry as source of reducing power and nowadays the 96% of it is produced by steam reforming, water shift reaction and methane pyrolysis (Nikolaidis & Poullikkas, 2017). On the other hand, hydrogen is the only combustible (between coal, wood, oil and methane) which its combustion does not produce carbon dioxide but only water. For this reason, the production and the distribution of hydrogen could lower the greenhouse gases production. Knowing this, the European union has decided to invest strongly on green hydrogen(Zappa et al., 2019).
Producing biomethane from organic waste and biohydrogen from wastewaters using microorganisms and low energetic consumptions demonstrates that a circular economy is not only feasible but also desirable.
Here six different investigations with five different MECs aimed to bioproduction of hydrogen and methane, are described showing how the scaling up process is going.