Field-test evaluation of digestate solid fraction land-spreading quality: Method and first results

Évaluation de terrain de l'épandabilité de la fraction solide du digestat : méthode et premiers résultats

Roux, J.C. ; Heritier, P. ; Piron, E. ; Girault, R. ; Guiziou, F.

Type de document
Communication scientifique avec actes
Affiliation de l'auteur
Résumé / Abstract
With the recent development of anaerobic digestion plants in France, farmers should manage new organic products often more concentrated in N or P fertilizer. In the same time they have to decrease the use of inorganic fertilizers in order to minimize environmental damages. In agriculture, organic fertilizer are spread using big band robust spreader, because of the product specificities, variabilities, etc. Intrinsic fertilizer value is more and more considerate nowadays and application quality in the field has to be always better, as well to maximize agronomical return as to minimize environmental impacts. This new method, named IMOB (Irstea Method or Mobile Organic Bench) has been developed in order to test and evaluate solid organic matter spreading on soil, particularly for solid fraction of digestate applications. Objective is to evaluate land-spreading performances regarding spreader and organic fertilizer characteristics, in order to improve land-spreading quality. This test provides the volumetric three dimensional spread pattern and its correspondence with the mass (transverse distribution represents the mass of organic matter distributed perpendicularly to the travel direction while longitudinal distribution represents evolution of the rate along the total spreading time). Also criteria which are defined in the European standard EN 13080 can be estimated using this method: optimum working widths, transverse variation coefficient, application rate, flow characteristics, stretch within the tolerance zone and longitudinal variation coefficient. 3D spread pattern distribution and land-spreading flow are measured during the same spreader unloading. A globally plan and horizontal area is required in order to install mobile axle weighing system which supports the spreader and the tractor. In a relatively short time (around one hour) and without complicated and fastidious works, land-spreading measurements are performed. Innovation in the measurement is the use of a 3D laser scanner (FARO® Laser scanner Focus 3D) which allows measuring the topography of the global fertilizer mass distributed during the unloading. This land-spreading topography is obtained computing the difference between the laser measurement after the unloading and the one before unloading, the spreader being fixed during the test, weighted continuously by the static platforms to register the mass flow. Using the land-spreading obtained map, transversal distribution is calculated adding fertilizer densities column by column in the travel direction, as required in the European standard EN 13080. The laser telemeter is handly positioned because of its small size and weight (around 5kg), and the precision of each of the measured distances is less than 2mm. Samples of obtained spread patterns have been compared using the specific Irstea test bench 'CEMOB' which validated the method. For these test, material used during land-spreading was a solid fraction obtained from a mechanical separation of digestate. Results give information about spreader / matter interactions and allow improving land-spreading efficiency. Using correctly user machine instructions and obtained test data, high quality land-spreading can be obtained. Many working width variation coefficients are computed in order to define the optimal working width regarding different settings. In a small time, without complicated and costly devices, the global picture of the obtained land-spreading can be measured. It has been showed to be very closed to the 3D spread pattern measured using CEMOB device, even if it represents the distribution of the total amount for the unloading. The volumetric measurement which is performed by the scanner, crossed with the unloading value measured using static platforms, provides a consistent measurement of the land-spreading performance. In the future, this new test could be an alternative to perform improvement test easily and everywhere. Manufacturer could use it in order to improve spreader design and construction, and so minimise environmental damages and optimise fertilization. For existing spreaders, this method could be used in order to identify correct settings and land-spreading requirements for different product to be spread. User’s manual should be more precise by this way. This new test method should be proceeded to encourage farmers and spreader users, to realize better spreading.
10th International Conference on “Circular Economy and Organic Waste”, 25/05/2016 - 28/05/2016, Heraklion, GRC

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