Air treatment for abatement of gaseous emissions in pigsties

Reducing ammonia emissions in pigsties increases animal welfare and reduces environmental impact. The economic burden of applying the related techniques is significant, and cannot be left entirely to the farmer. A research project carried out by the University of Milan with LIFE European funds aims to scientifically measure the polluting parameters and to experiment the effective solutions

In Italy there are about 26500 active pig farms, for a total of 8.6 million head. Most of the farms are located in the northern regions, namely Lombardy, Emilia-Romagna, Piedmont and Veneto, which alone account for about 87% of the animals bred in Italy. About 50% of the national pig population is raised in Lombardy, with one of the highest densities of animals in Europe. Also because of this, these intensive livestock farms are the main producers of atmospheric emissions of ammonia, particulate matter (PM10 and PM2.5) and odours.

In general, farms (particularly livestock and fertilizer) are responsible for more than 90 percent of ammonia emissions. This gas plays an important role in our environment, since it participates in the formation of secondary atmospheric particulate matter, which is particularly harmful to human health since it is capable of penetrating the deep layers of the lungs. Among the disorders attributed to the uptake of fine and ultrafine particulate matter (PM10 and especially PM2.5) are acute and chronic respiratory (asthma, bronchitis, emphysema, allergy, cancer) and cardiovascular diseases.

Ammonia emissions from pig farms are mainly due to housing (29%) and manure management (storage, 27-57%, and spreading, 24-31%).

The Directive 2010/75/EU specifies the types of livestock farms that are obliged to prevent and reduce pollution. In the case of pigs, farms with at least 2000 production pigs weighing more than 30 kg or with at least 750 sows are involved. The concept of Best Available Techniques (BAT) is also introduced: more in detail, regarding the reduction of emissions of dust, ammonia and volatile organic compounds from inside the shelters, for the air treatment the BATs contemplate the use of water scrubbers, acid scrubbers solution or bioscrubbers. These solutions are extremely effective, but until now have only been implemented in farms with forced ventilation, i.e. in conditions different from those found in Italian farms, where ventilation inside the pigsties is usually natural.

In this objectively "complicated" setting, starting from October 2019 the project "Smart computing system to monitor and abate the indoor concentrations of NH3, CH4 and PM in pig farms (LIFE-MEGA)" has been developed, funded by the EU through the LIFE programme, and coordinated by the Department of Environmental Sciences and Policies of the University of Milan.

The project aims to reduce ammonia, particulate matter, and odour concentrations in pigsties to improve air quality. In addition to the use of wet and dry scrubbers, the aim is to develop a "smart" control unit capable of activating the operation of two different filtering systems in the pigsties, so as to ensure the best air quality, benefiting not only animal welfare, but also the health of the operators. The air treatment is carried out with a dry filter, already tested in the bakery sector, and a prototype of wet filter, made by Rota Guido Srl of Corte de' Frati (CR). The expected benefits concern not only the reduction of environmental impacts of processes more directly related to ammonia (e.g. acidification, formation of secondary particulate matter, eutrophication of water, etc.), but also the reduction of respiratory diseases in animals, a factor that can lead to a worsening of the food conversion index.

 

An application case

This is the application of a wet scrubber in one of the partner farms of the mentioned project.

The company is specialized in the production of heavy pigs, in a "closed cycle" breeding, which includes both the reproduction and the fattening phase. For a UAA of 100 hectares entirely cultivated with corn for grain, about 9,800 animals are raised, including more than 700 sows in the stages of parturition and gestation. The animals are sold for about 1,775 t/year of live weight, with a consumption of about 5,100 t of feed of non-farm origin, in addition to the internal one.

A classic scenario, i.e. without any air quality improvement intervention and with traditional farming methods, and an alternative scenario (in a different room of the same pigsty), where the wet scrubber air treatment is installed, were compared.

The scrubber has a total mass of 2,000 kg, and essentially consists of two stainless steeltanks: the first contains only water, while in the second a solution of water and citric acid is introduced.

Indeed, contrary to the most commonly used wet scrubbers, the prototype does not work with sulfuric acid, but with citric acid, which is much less dangerous for the animals and also for the operators. Other important components of the scrubber are the fan, for the suction of air and its subsequent re-introduction into the barn after treatment, and the pumping apparatus.

The fan draws air from inside the pigsty and forces it to pass into the two tanks; in the first, water acts as an absolute filter and breaks down particulate matter, while in the second, ammonia is removed, reacting with citric acid and precipitating as ammonium citrate.

The water and aqueous citric acid solution are sprayed against the air to be treated, which after purification is returned to the pigsty. Keep in mind that ammonium citrate can be exploited as a fertilizer.

 

Possible benefits

The tests carried out showed a lower abatement efficiency compared to that found in the farms of central and northern Europe where, thanks mainly to forced ventilation, considerable ammonia reduction values are achieved (even higher than 90-95%), with scrubbers that however work with sulfuric acid. More in detail, the prototype has shown an efficiency of about 60-70%, which implies a tangible improvement of the conditions inside the pigsty, accompanied by a reduction of the feed conversion index (i.e. less feed ingested for the same weight gain) and a healthier lung condition of the animals.

The only negative aspect, a slight increase in mortality, which however appears random and not related to the presence of the scrubber, which in any case is located outside the shelters.

From an environmental perspective, the balance of the installation and operation of the scrubber resulted in a slight increase in climate change impacts (+ 2.8%), but a reduction of nearly 10% in terrestrial acidification and eutrophication.

However, the economic balance is negative (for the farmer), since the increased cost of operating the scrubber is not offset (except to a small extent) by the reduction in the feed conversion index. It is therefore clear that in order to ensure adequate economic sustainability it is necessary that first processors and then the consumer are willing to pay a higher price for pigs, and/or that special incentives are provided in the RDPs of the various regions.

In general, the reduction of emissions of pollutant compounds from livestock activity cannot disregard the adoption of appropriate solutions for the storage and application of wastewater, but also in the phase of animal housing. Each solution must be evaluated not only from a technical standpoint, but also from an environmental standpoint. While there are operational and operator safety benefits, the adoption of citric acid in wet scrubbers instead of other more hazardous acids results in increased GHG emissions. Conversely, it benefits other environmental impacts and undoubtedly animal welfare.