Biogas is not circular

Recently, various interventions and reports have been published presenting biogas as a renewable and circular energy source. These are messages that hide the complexity of this technology. To begin with, the projected biogas plants are refineries that produce a non-renewable fuel that needs to be processed. Furthermore, the energy balance of the entire process for biogas production, from cradle to grave, is negative: more energy is consumed than is ultimately produced.The internal operation of the biogas plants themselves can absorb nearly 30% of the energy obtained. To this, approximately an additional 16% must be added for the transport of slurry, manure, and animal waste that feed the plants, as well as the resulting digestate to the farms that will accept it. However, the largest – and often ignored – energy cost is associated with the generation of slurry and manure. These materials are not free; they require a significant energy expenditure in feed, climate control, and farm operations. The meat obtained only recovers approximately 50%-60% of the energy contained in the feed, and the energy invested in producing slurry can be equivalent to 80% of the energy that the biogas plant ultimately generates.And what do these feeds contain? Primarily, soy and cereals. Soy mostly comes from America, transported by ships that consume large quantities of diesel. Both soy and cereals are produced using agricultural machinery – again, diesel – and to make them grow, chemical fertilizers and pesticides are needed. The production of these fertilizers depends on fossil fuels and minerals from mines in the Sahara, Canada, and other distant locations, all of which are finite and non-renewable resources. The expansion of these crops also entails other problems, such as deforestation in the countries where they are produced, contributing directly to climate change.To all this, we must add the industrial inputs that these plants require. The project planned in La Sentiu de Sió (Noguera), the largest currently in Catalonia, would annually require thousands of tons of nitric acid, potassium carbonate, ferric chloride, or methanol, in addition to tens of thousands of tons of water. The associated waste is also considerable: ferrous metals, plastics, and contaminated filters, among others.

The magnitude of this flow of materials and energy contradicts the idea of circularity. A process that begins in mines or plantations around the world and ends in an industrial plant in Lérida or Barcelona is not circular: it is linear. It would be more circular to return the portion of the slurry generated to America, but that is, evidently, absurd. The conclusion is simple: if we talk about circularity, the best option is not to import millions of tons of cereals and soy to maintain an oversized livestock model. Circularity exists when manure and slurry are applied directly to the adjacent fields that produce the soy or cereals that will feed the livestock.The argument that these plants “transform waste into useful resources” is also fallacious. Manure and slurry are not waste: they are not a useless material that must be treated to give it value, but the historical basis for fertilizing fields. The methanization process simply extracts a part of the organic matter from the manure and slurry, that is, a part of its fertilizing value. Biogas plants also do not generate “new organic nutrients”; on the contrary, some projects aim to convert part of the nitrogen from the slurry into chemical fertilizers by adding even more nitrogen, which, evidently, does not solve the nitrate issue but aggravates it. The debate requires balance and context: while in some parts of the country there is an excess of dejections, not all problems of groundwater contamination are the result of these excesses, and what should be done, in any case, is to avoid excesses. But in Ponent, the data indicate that these excesses are so limited that they would not even be enough to supply the Sentiu plant, let alone all the biogas plant projects being considered. The real problem is landless livestock farming, disconnected from agriculture; a disconnection that biogas plants do not resolve. Furthermore, when they try to mix manure and slurry with waste from slaughterhouses and sewage sludge, with all the contaminants they contain, the soil contamination problems where the digestates they produce are applied will be aggravated.In addition to the arguments presented, we cannot fail to consider these energy policies in the recent context of outbreaks of swine fever and nodular dermatosis. The daily movement of hundreds of trucks loaded with slurry, slaughterhouse waste, and carcasses through the regions of Ponent is not a minor risk.In summary, the image of a circular, renewable, and transformative biogas economy is, in large part, a mirage. Behind it lies an industrial model highly dependent on fossil fuels, massive imports, and intensive use of chemical resources. And above all, a model that consolidates intensive livestock farming that is already environmentally and territorially unsustainable today. If we want to address the energy and climate crisis, we must do so with rigor and without simplifications that can end up generating more problems than they aim to solve.Co-authors of this article are Víctor Altés, doctor agricultural engineer, expert in soils and agricultural sustainability, UdL; Gerard Batalla, farmer and sociology graduate, member of Assemblea Pagesa; Jaume Sastre-Juan, doctor in history of science and technology, expert in science, technology and society, UAB; Jaume Valentines, doctor in history of science and technology, expert in science, technology and society, UAB; and the Plataforma Pobles Vius (https://poblesvius.cat/).