Influence of treatment techniques for pig slurry on methane emissions during subsequent storage
Influence des techniques de traitement des lisiers de porcs sur les émissions de méthane lors du stockage
Résumé
Methane (CH4) is an important greenhouse gas and recent inventories have suggested that livestock manure management systems greatly influence the global CH4 emissions. The present study was conducted to evaluate this assumption using pig slurry as the representative livestock manure. Methane emissions rates were determined through a series of four laboratory experiments comparing, during a 50 day storage monitoring period, the evolution of a range of raw, separated, dilute, aerated or chemically amended slurries. The experiments were performed using 60 litre storage reactors equipped to allow a continuous measurement of the biogas (CH4 and CO2) emitted. The laboratory procedure based on a discontinuous replenishment of the air above the stored slurry, enabled the production curve for carbon emissions to be established.A range of pig slurries were studied including four raw slurries differing in their dry matter content, two dilute slurries (slurry to water ratios of 1:1, 1:2), two differently separated slurries (screened or centrifuged), two aerated slurries, and three slurries chemically amended by the use of commercial additives. From raw slurries, the average daily rate of methane emission comprised between 9 and 77 g [CH4 C] m-3 [slurry] day-1, cumulating in a total methane emission of up to 3.6 kg [CH4 C] m-3 [slurry] for the 50 day monitoring period. The percentage of carbon emissions (CH4 C + CO2 C) varied from 5 to 30% of the total initial carbon content. Biogas emissions from separated slurry were rather similar to that of the raw slurries. The dilution of the slurry tended to decrease the production and the emission of methane. The two aerated slurries had very low methane emissions, showing a 70% to near 100% reduction of emissions compared to the untreated slurry. The use of the three additives lowered the methane emissions from 47 to 64%.For all experiments, the physico-chemical changes of the slurries during storage is reported including total solids (TS), total carbon (TC), chemical oxygen demand (COD), biochemical oxygen demand (BOD) and the volatile fatty acids (VFA).
Le méthane (CH4) est un gaz à effet de serre important et de récents inventaires suggèrent que les systèmes de gestion des déjections animales influencent fortement les émissions globales de CH4. L'étude présentée a été réalisée pour vérifier cette hypothèse en utilisant le lisier de porc. Les taux d'émission de CH4 ont été déterminés à travers une série de 4 essais en laboratoire évaluant sur une période de 50 jours, l'évolution de lisiers bruts, séparés, dilués, traités par aération biologique ou traités par ajout d'additifs commerciaux. Les taux d'émission journaliers issus de lisier de porc sont compris entre 9 et 77 g [C-CH4]m-3[lisier]jour-1, soit un cumul allant jusqu'à 3.6 kg [C-CH4]m-3[lisier] pour la totalité de la période de 50 jours étudiée.Les lisiers préalablement aérés montrent de très faibles émissions de CH4 avec un taux de réduction de 70 à 100% comparativement au témoin. L'utilisation d'additifs permet également de diminuer les émissions de méthane de 47 à 64%.Pour l'ensemble des essais conduits, l'évolution des caractéristiques physico-chimiques lors du traçage comprenant la MS, le carbone total, la DCO, la DBO et les acides gras volatils est présentée.