What we consider rubbish today can become energy and fertilizer tomorrow: to do this, the system that makes this step possible is essential, the biodigester. This is an increasingly widespread technology, which allows us to reduce emissions, contain costs and make cities more sustainable.
What a biodigester is and what it does
A biodigester is a bit like a large stomach: it takes organic waste and transforms it into two things: compost, therefore fertilizer for the land, and biogas, which after refining becomes biomethane, a natural gas for producing energy. There are four steps in this process, and conceptually they are very similar to our digestion of food.
The first phase occurs in pre-treatment area, which is a bit like it was our mouth. The organic waste arrives here and is shredded in a huge blender and then the other unwanted components, such as plastic or ferrous components, are separated.
The material then ends up inside enormous parallelepipeds, i biodigesters. Just as in our intestine there are enzymes that transform food for digestion, in these cylinders the bacteria degrade organic substances and make them ferment, that is, they transform them into biogas.
The biogas produced internally, however, cannot yet be exploited, because it contains only 60% methane, and the minimum threshold for distribution is 97.5%. For this reason it must be “refined”, that is, the carbon dioxide and other gases present are captured, so as to obtain biomethane. During this process, the captured carbon dioxide is used for other purposes, for example in the food sector.
Now, there’s one last step. What happens at the end of digestion? There is a gap. Similarly, a residue remains in the biodigester, called “digestate”, which becomes compost. In practice, the digestate is dried and mixed with prunings and leaves. Then it is stored in large rooms, the biocellswhere it is fermented for about forty days.
Does the biodigester pollute?
When talking about this type of system, one might feel a sense of skepticism: there is the fear that these systems are harmful to health and the environment, that they make bad smells… and so on. But behind it there is a great deal of study and research on the environmental impact, analyzing in advance all the possible effects of the plant on various factors, from the olfactory impact to atmospheric emissions.
For example, in this plant the processes that could potentially cause bad odors will take place almost entirely in confined spaces. Furthermore, like other types of systems of this kind, there will be an odor abatement system. The emissions will then be constantly monitored to strictly comply with the parameters established by law.
In this case, the environmental impact study also simulated theacoustic impact that the system will have: as regards the operational phase, the noise level will also fall within the legal limits established.
Biodigesters in Rome: projects in the pipeline to manage waste in the capital
Densely populated cities like Rome have a great need for systems of this type. In fact, the capital’s workforce amounts to approximately 250,000 tons per year, which so far has been sent to external biodigestersincluding Friuli Venezia Giulia and Veneto, but this requires high costs which are increasingly less sustainable in the long term.
Precisely to overcome these types of problems, Roma Capitale has decided to build two biodigesters, one in Cesano (whose work began last July) and one in Casal Selce (by 2027) which they will manage efficiently 200,000 tons of organic waste of the city. Each plant will produce approx 9.5 million cubic meters of biomethane and 18 thousand tons of compost per year. In addition to the two biodigesters, two plants will be built for the treatment of paper and plastic, promoting the circularity of resources and sustainable energy production. Added to these is the waste-to-energy plant, which will manage 600 thousand tons of undifferentiated waste per year and will close the waste cycle of Rome Capital.
