Effective strategies to reduce methane emissions from livestock

摘要

It is the target of the Dutch government to reduce the emissions of all non-CO_2 greenhouse gases in The Netherlands by 8 Mton CO_2-eq in 2010. Livestock contributes for about 40 percent (10 Mton CO_2-eq) to the emissions of methane. Enteric fermentation is responsible for 32 percent (8 Mton CO_2-eq) and slurry for 8 percent (2 Mton CO_2-eq). In the Netherlands, slurry is the most common manure system. Low-cost and effective options to reduce methane emissions, without increasing emissions of ammonia and nitrous oxide, are covering the outdoor slurry storage, shortening the indoor storage time, lowering the storage temperature and filtration of the air from the livestock house and storage facility. Other less favorable options are aeration, acidification, feed adjustments and controlled anaerobic digestion. Covering of outdoor storages is mandatory in the Netherlands to reduce ammonia emissions. The methane emission reduction of a well-covered outdoor storage with the slurry at rest is around 60percent. In The Netherlands the average temperature of outdoor storage is less than 10.2 deg C. Methane emissions will decrease by 66 percent if the slurry temperature is decreased from 20 deg C to 10 deg C. For pig houses the main source of methane is the slurry stored under the slatted floor. The slurry surface is nearly at indoor temperature (20 deg C). It is most effective for pig slurry to reduce the indoor storage time. Also for ruminants some reduction may be expected from shortening the indoorstorage time of slurry. In addition measurements showed a reduction of more than 50 percent methane emission for well covered storages with slurry at rest. Therefore, the methane emission from an outdoor storage may be neglected. Reduction of the indoorstorage time can result in methane emission reduction from slurry by 50 percent or 1 Mton CO_2-eq. Since most of the methane is produced in the livestock house, i.e. methane from enteric fermentation and from slurry, it is evident that filtering the methane from the ventilation air can be an effective mitigation option. Methane filters are technically possible, but they are still under development and not yet available for practical application. Air filters can result in a reduction of up to 50 percentof the total methane emission from livestock or up to 5 Mton CO_2-eq.