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There are few examples of collective manure treatment in France. This is why an inventory of collective treatment units or methods has been carried out on a European scale.
The collective units in operation and the treatment methods on the European scale were inventoried by country and by process (phase separation, treatment of liquids and solids, etc.) according to the quantity of effluents treated: on-farm, in medium size units (< 50,000 t/year) or large size units (> 50,000 t/year).
In France, the annual treatment of several tens of thousands of tons of effluent is considered to be large-scale. Given these volumes and the average size of French farms, knowing that only surplus effluents are treated, treatment units of more than 50,000 t/year are collective, as opposed to individual farm units.
Most processes are adapted to collective processing, while the reverse is not possible for reasons of economy of scale and complexity. Collective units are usually few in number, but sometimes dominant in terms of volume treated in certain countries, as in the case of phase separation, anaerobic digestion, and liquid phase treatment in the Netherlands.
The implementation of large units varies greatly among European countries
Some countries are characterized by a high proportion of centralized units in relation to the volume of effluents treated: this is the case in the Netherlands for phase separation and liquid treatment by membrane filtration and nitrification/denitrification. This is also the case in Belgium for liquid phase treatment by nitrification/denitrification and dehydration of solids and in Spain for phase separation, a technique that is mainly individual on a European scale.
For these three countries, the Netherlands, Spain, and Belgium, the proportion of large methane digesters is higher than in other European countries. The large-scale development of solids dehydration in Belgium and phase separation in the Netherlands is related to their need to export solids, in particular phosphorus, to third countries.
Spain is characterized by a wide variety of centralized treatment processes: use of additives and pretreatments (high pressure, high temperature), use of coagulant-flocculants to improve the performance of phase separation, essentially by decanter-centrifuges for these large installations, thermal dehydration, pelletizing and combustion for solids treatment, membrane filtration, and evapo-concentration for the treatment of the liquid phase.
Italy is characterized by a strong development of phase separation based almost exclusively on an individual model. The same applies to anaerobic digestion in Germany, excluding resorption techniques.
Other situations are characterized by considerable diversity: this is the case with composting in Spain, where individual and centralized units coexist. The same happens with anaerobic digestion in Denmark, where there were successive phases of public incentives for individual and centralized models.
In Italy, anaerobic digestion is also well developed with a mix of processes.
The differences in the development of centralized units and in the treatment processes chosen can be explained by multiple factors: national transpositions of European directives, the nature of local regulations, animal production density, the state of communication routes, social acceptability, etc.
Study conducted by IFIP, Itavi, Chamber of Agriculture of Brittany, FR Cuma Ouest, Idele within the framework of the GESTE project financed by ADEME.
Excerpt from the brochure: Filières collectives de gestion et de traitement des déjections animales et des digestats (to be published by the end of 2024).
