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Anno 2021 Numero 3-4

Bioenergy
March - April 2021

Biogas and biomethane, the new frontiers of innovation

In relation to the growing need for energy from renewable sources, the production of biogas from the anaerobic decay of new waste materials offers significant advantages. By extending interest to those organic matrices rich in cellulose, hemicellulose and lignin that today can’t be exploited. The several lines of research, we will be able to obtain sustainable biofuels from woody biomass recovered from our fields

In order to tackle the great complexity of the current situation, characterised by the explosive mixture of a triple crisis - health, environmental and economic - it is necessary to act systematically, rapidly and on several fronts with the awareness that no problem can be solved by neglecting the solution of the others. With this vision in mind, the Italian National Recovery and Resilience Plan (NRRP) has been allocated economic resources on an unprecedented scale. In fact, our NRRP will absorb about 28% of the funds allocated to Europe as a whole for the period 2021-2027: 209 billion euros of which 1/3 (as much as 69) will go to "Mission 2 - Green Revolution and Ecological Transition" which is divided into the following four "Components": I.Sustainable agriculture and circular economy (€ 5.2 billion + 300 million ReactEu); II. Renewable energy, hydrogen and sustainable mobility (EUR 17.5bn + EUR 680m ReactEu); III. Energy efficiency and building renovation (EUR 30.4 bn + 320 ml ReactEu); IV. Protection of land and water resources (EUR 14.3 bn + 200 ml ReactEu).

In these areas, a broad involvement of society must be stimulated, and FederUnacoma is also called upon to make concrete contributions to the achievement of these objectives.

We have learned from the pandemic that the well-being of people and the environment go hand in hand, and for the Covid-19 recovery, circular economy, sustainable agriculture and energy are among the central themes. These are all elements that fall squarely within the agricultural models of the biogas-biomethane chain. These models, which are very widespread and advanced in Italy, have so far exploited biomass (residual or cultivated ad hoc) that can be fermented and therefore degraded in the natural process of anaerobic digestion by specific bacterial consortia.

In the future, in order to further expand the productivity of this technology, one of the aspects to be considered is the full exploitation of the methanogenic potential (BMT) of the different organic matrices. Not all organic matter can be digested as such by the microorganisms responsible for biogas production. For example, compounds such as cellulose, hemicellulose and especially lignin are difficult to biodegrade. Therefore, pre-treatments are needed to increase the solubility of the organic solids and to accelerate and improve the rate of degradation. There are different types of techniques: physical/mechanical, thermal, chemical, biological-enzymatic, and the role of research and technological innovation is essential to meet the challenges of the future. Today, ENEA's Casaccia Research Centre has a system that generates high-voltage, low-intensity pulsed electric fields (commercially known as BioCrack), which opens gaps in the cell membrane. In collaboration with the Department of Industrial Civil Engineering of the University of Rome La Sapienza (Dr. Danilo Morriello), this system has been integrated into a small pilot anaerobic digestion plant (1 m3 in volume) for the pre-treatment of biomass with a high lignocellulosic content that is fed into it. A maize silage with a fairly high cellulose and hemicellulose content and a mixture of vegetable products with a much lower cellulose and hemicellulose content were chosen as the working matrices for experimentation. Both were the feed mix for an industrial biogas plant. Analysis of the experimental data obtained from the BMPs showed that this pretreatment system produces the expected effects on matrices with a high cellulose content. In fact, BioCrack mainly damages the three-dimensional structure of cellulose and hemicellulose, reducing the cross-linking of polysaccharide chains ("crystallinity"). This, in a nutshell, increases the surface area available for the microorganisms’ action, increases the solubility of the organic matter, and also the methane potential of lignocellulosic biomass. On the other hand, the effect of BioCrack on matrices with a low lignocellulosic content is nil or even counterproductive.

In addition to this chemical and physical pre-treatment, it is possible to use biochemical processes that are very common in nature. In fact, herbivorous mammals and numerous xylophagous insects do not produce enzymes capable of degrading the cellulose of ingested plant material and to this end develop symbioses with pools of microorganisms present in their intestinal tract. Within this consortium, ruminal anaerobic fungi (ARF) play a key role. A characteristic of these micro-organisms is that they are among the most active degraders of cellulosic material and produce a large number of enzymes and enzyme complexes capable of attacking the plant cell wall and plant fibres ingested by the host animal. As the degradation of lignocellulosic material is currently considered the main bottleneck in the anaerobic digestion process, great developments are expected from the study of these organisms. The use of ARFs opens up the possibility of "in situ" co-treatment by enhancing this community in anaerobic digesters. According to studies carried out by the University of Tuscia and ENEA, the use of an integrated inoculum of ARFs (Neocallimastix sp. and Orpinomyces sp.) and a selected consortium of other hydrogen-producing micro-organisms has led to significant increases in biogas production from chitin and wheat straw.

For a possible industrial application of ruminal fungal strains capable of improving biogas production processes, after testing the ability to grow in small benchtop bioreactors, the next step is industrial scaling up to full-scale use of such inocula. On the latter front, process results are encouraging, which is not to be taken for granted given the difficulty for some microorganisms in the fungal community to grow and develop on large-volume culture media.

The challenge on the front of lignocellulosic biomass for anaerobic digestion is also played out in the field of agricultural mechanization. Indeed, on this depends the ability to contain the cost of supplying raw materials, from collection to processing, transport and storage. Finally, given that biomethane can also be obtained from the digestion of this renewable resource, it would be an important sign of ecological transition to be able to use this biofuel to power the engines of agricultural machinery used in our fields. A major breakthrough in the sphere of the circular bio-economy.

by Matteo Monni

Keywords: Biogas Biomethane
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