Control of atmospheric emissions from pig housing

T. Curran, V. Dodd, B. Sheridan and J. Colligan
 

There are continuing difficulties for pig producers in obtaining planning permission and Integrated Pollution Control (IPC) licences for intensive pig units, mainly due to concerns regarding the risk of odour nuisance and water pollution. Exhaust ventilation air from pig housing has been identified as a key source of odour and ammonia. The main aim of this project is to assess the efficacy of biofiltration as a practical technology for the treatment of exhaust ventilation air from intensive pig units in order to minimise the risk of odour nuisance. A secondary objective is to reduce emissions of ammonia which can have a local acidification impact on the surrounding environment

Pilot-scale Biofilter System at Pig Digestion House, UCD Farm (Lyons Estate)

 

Intensive pig production can lead to odour nuisance with the main odours arising from the buildings and the spreading of slurry (1). These complex mixtures of gases can contain over 150 volatile compounds of which 31 are odorous (2). Good progress has been made in the reduction of odours and ammonia associated with spreading through the use of band spreading and soil injection. However, an appropriate abatement method has not yet been determined to control emissions in the exhaust ventilation air from pig housing.

Biofiltration is a proven technology in industrial applications as a method of atmospheric emissions reduction. The operating principle of a biofilter is that the contaminated air from the building is passed through a filter where micro-organisms flocculate. The contaminants in the air transverse to the liquid phase on the biofilm where the micro-organisms degrade them to CO2, H2O, inorganic salts and biomass (3).

 

Methodology
A pilot-scale biofiltration system (Fig. 1) has been developed and constructed at the UCD research farm at Lyons Estate. An experimental unit consisting of two pens each containing 6 pigs in a twelve-pen pig house has been sealed off from the other pens.

The experimental units had their own air inlets and outlets and were heated by radiant electric heaters. Air from each pen was extracted by a variable-speed centrifugal fan and passed through a humidifier and biofilter. Each biofilter consisted of an upright cylindrical metal drum, with an internal diameter of 605 mm and a height of 910 mm. Biofilter 1 contained woodchips of size >20 mm whereas biofilter 2 contained woodchips of size 10 mm-16 mm. Media depth in each biofilter was 500 mm.

The moisture status of each biofilter was monitored using a load cell and automated control of moisture content within each biofilter was maintained using a solenoid valve, which was controlled by LabView software.

Gas samples for sensory analysis were collected into Nalophan NA® bags via a vacuum sampling device and the bags were taken to the olfactometry laboratory in the Department of Agricultural and Food Engineering at Earlsfort Terrace for odour concentration measurement always within 24 h of sampling. Ammonia levels were measured using Draeger tubes.

Fig. 1. Pilot-scale Biofilter System at Pig Digestion House, UCD Research Farm, Lyons Estate, Newcastle, Co. Dublin

 
Main findings
The highest odour and ammonia reduction efficiencies were achieved using the smaller wood chips (media particle size 10 mm to 16 mm). Figure 2 shows that ammonia reduction efficiencies were maintained above 90% even at a volumetric loading rate of 1500 m3 gas m-3 medium h-1.

Biofilter 2 was also more efficient for the removal of odour from the exhaust air. The larger surface area of the smaller wood chips provided more contact between the contaminant air and the biofilm creating a better opportunity for degradation of gaseous components.

It can be concluded from this research that biofiltration can remove odours and ammonia efficiently from exhaust ventilation air from pig housing. Valuable information has been obtained regarding biofilter design parameters such as the air loading rate and media particle size. This can be extrapolated to optimise the design of a commercial scale unit.

Fig. 2. % Ammonia Reduction versus Volumetric Loading Rate for Different Media Particle Sizes

 

Acknowledgements
This research was funded by the Irish Government Department of Agriculture, Food and Rural Development from its research stimulus fund under the 1994-1999 Operational Programme for Agriculture, Rural Development and Forestry, with the assistance of the European Union.

 

References

  1. Curran TP, Dodd VA, 1998. Irish Grassland and Animal Production Association 24th meeting, UCD, Belfield, Dublin 19-20 March 1998. pp. 191-192.

  2. O'Neill DH, Phillips VR, 1992. A review of the control of odour nuisance from livestock buildings: Part 3, Properties of the odorous substances, which have been identified in livestock wastes or in the air around them. Journal of Agricultural Engineering Research 53, pp. 23-50.

  3. Deshusses MA, 1997. Biological waste air treatment in biofilters. Current Opinions in Biotechnology. 8, pp. 335-339