Best available techniques to reduce emissions in swine production

Livestock farming, like any other human activity, releases a series of emissions into the atmosphere, mainly in the form of gases (both pollutants and greenhouse gases). The "emission ceilings Directive" (Directive (EU) 2016/2284), establishes reduction commitments for ammonia to be achieved by 2030. However, instead of decreasing, over the last few years emissions have been stable or have increased, so there must be a greater effort in reduction, particularly in the swine industry.

To prevent these emissions or reduce them as much as possible, a series of specific techniques are employed, some of which have been used for millennia, such as the frequent removal of slurry from animal housing, the covering of manure, or its immediate burial, with the aim of improving animal health or preventing the loss of nutrients during storage and use.

These techniques are still considered today to be the Best Available Techniques (BAT) in EU regulations (Implemention Decision (EU) 2017/302) to decrease ammonia emissions as they meet the conditions of the BAT definition, i.e. effective, practically applicable, and economically viable measures (in addition to the added benefits of health improvement and contribution to the circular economy). In this article, we will focus on these three measures since their adequate widespread application would be sufficient to meet the established requirements.

Frequent slurry removal

Frequent removal of slurry from the pits of the barn (at least twice a week) reduces methane and also ammonia emissions. If it is not possible to remove the slurry this often, one can also choose to acidify the slurry, install scrubbers at the air outlets, or implement any of the measures proposed in the Community decision on the BATs or in the UNECE Framework Code for Good Agricultural Practice for Reducing Ammonia Emissions.

However, this removal must be done on a mandatory monthly basis to avoid methane emissions.

Slurry storage

The next source of ammonia emissions is in the storage of slurry, and measures must therefore be taken at the storage lagoon. The simplest and most effective approach is still to cover the surface, allow for natural crusting (as long as it completely covers the surface), or add spheres, geometric forms, or floating elements (which is not very recommended in places where there is a tendency to form a natural crust). If coverage cannot be guaranteed, it will be necessary to resort to techniques that allow an equivalent or higher percentage of reduction, choosing from the techniques proposed in the Decision or the UN/ECE code, which include covering with movable or fixed covers of various materials or the use of other techniques such as acidification or anaerobic digestion, for example. If the latter option is used, the methane produced and retained must be used for energy purposes.

Use of slurry as fertilizer

Finally, the use of slurry in the field is an important source of emissions that will have to be reduced by using the corresponding techniques, the most common being the localized application by means of a trailing hose or shoe or its injection into the soil by means of injectors. Immediate burial by plow or moldboard is very effective if done within four hours after application, less effective if buried 12 hours later, or practically ineffective if done after 24 hours. As in the above cases, the EC decision and the UN/ECE code include other measures with similar effectiveness that will be equally acceptable.

Although these techniques are indicative and not exclusive (meaning that other techniques can be used that demonstrate a similar level of efficacy), they have been tested. Thus, if other techniques are used, they must demonstrate equivalent efficacy.

Perhaps one of the most complex aspects is estimating the emissions of nitrogen, phosphorus, ammonia, or greenhouse gases emitted by the farm as a whole. In the specific case of Spain, the Ministry of Agriculture, Fisheries and Food (MAPA) will provide farmers with a tool that allows these estimates to be made as simply as possible. The farmer may opt for other calculation systems as long as he demonstrates that the results are equivalent.

It is not possible to recommend BATs that are applicable to all farms, since the specific conditions of each farm may require completely different actions. As a guideline, MAPA has published a document in which all available techniques recommended by international organizations are listed, including their advantages, disadvantages, costs, and applicability, which are summarized in the following table:

Source: Guía de las mejores técnicas disponibles para reducir el impacto ambiental de la ganadería. MAPA (2017)