Évaluation comparative du cycle de vie mettant en lumière les compromis d'un séparateur-composteur de lisier dans une ferme laitière canadienne

The primary sources of Canada's agricultural greenhouse gas (GHG) emissions are due to the demand for cattle products, mainly from beef and milk. In 2013, an estimated 60 million tonnes (Mt) carbon dioxide equivalents (CO2eq) were emitted directly from the agricultural sector of Canada where 59% of these emissions were due to both livestock related enteric fermentation and manure management, and cattle rearing was responsible for 96% of these livestock GHG emissions. While enteric methane emissions accounted for 42% of total emissions from the agricultural sector, 17% (~10.2 Mt CO2eq) were due to manure, indicating that the improved management of manure represents a sizeable GHG mitigation opportunity with no discernible impact on animal productivity.

The objective of this research was to undertake a detailed comparative dairy (environmental) life cycle assessment based on a dairy farm located in Ontario, Canada that recently adopted an active composting system that incorporated a screw-press solids/liquids separator prior to in-vessel composting. In achieving this goal, farmers and policy makers can become more informed about the environmental trade-offs of utilizing this technology. By undertaking a lifecycle perspective (from cradle to milk at farm gate), all trade-offs between the active manure composting system, and the farm with the conventional liquid slurry storage system can be compared fairly.

Results indicated that the active composter system on this farm reduced the carbon footprint (CF) of milk production by 36% (from 1.92 to 1.23 kg CO2eq kg-1 fat-protein corrected milk). The composter system created other life cycle benefits (no need to import sand for bedding, increased soil carbon sequestration) and burdens (increased on-farm electricity demand for composter operation), however, the relative contributions of these additional trade-offs were small. Given these additional trade-offs were minor, the GHG mitigation potential of this manure composting technology is likely high in any region of application. In addition, the dairy system with the composter created only marginal problem shifting concerns in terms of the non-CF environmental impact categories considered.

The total annual life-cycle GHG emissions estimated for the baseline and composter dairy farm systems were 4.07 and 2.61 kilo-t CO2eq per year, respectively. For this particular farm system, the mitigation opportunity from transitioning to a composter system was estimated to be about 1460 t CO2eq yr-1. If jurisdictions recognize this manure composting technology as a viable carbon offset option, investment in this equipment would likely become worthwhile. For instance, as the price on carbon in Canada increases from $10 (in 2018) to $50 (in 2022) per t CO2eq, the adoption rate of this technology would likely increase since the carbon credits attributed to the separator-composter from the studied farm would increase from around $ 14,000 to over $ 70,000 per year. Therefore, it is recommended that jurisdictions recognize manure composter technologies as a viable GHG mitigation opportunity in their carbon offset programs.