Methods applied to clean exhaust ventilation air from livestock houses, or process air used during some manure treatment (i.e. exhaust air from composting, or from venting of storage systems). The descriptions of these livestock manure processing technologies were originally based on 'Flotats, Xavier, Henning Lyngsø Foged, August Bonmati Blasi, Jordi Palatsi, Albert Magri and Karl Martin Schelde. 2011. Manure processing technologies. Technical Report No. II concerning “Manure Processing Activities in Europe” to the European Commission, Directorate-General Environment. 184 pp."
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Air washing of unwanted pollutants using water or reagent solutions that specifically target certain compounds.
The objective of air scrubbing is to reduce/recover particles and pollutants from air streams by means of liquid-reagent wash. In the field of manure/slurry treatment the main focus of scrubbing techniques is to treat/control gas emissions from raw/digested slurries: mainly ammonia (NH3), sulphur (H2S) and odours (VOCs) by acid scrubbing.
Illustration courtesy of DMT Environmental Technology, The Netherlands (www. dmt-et.nl)
A packed tower air scrubber is a reactor that has been filled with an inert or inorganic packing material. The packing material usually has a large porosity, or void volume, and a large specific area. Water is sprayed on top of the packed bed and consequently wetted. Contaminated air is introduced, either horizontally (crosscurrent) or upwards (counter-current), resulting in intensive contact between air and water, and enabling mass transfer from gas to liquid phase. A fraction of the trickling water is continuously recirculated; another fraction is discharged and replaced by fresh water (Melse and Ogink, 2005).
The mass transfer of ammonia (from air inlet to water) is regulated by the equilibrium reaction (below), that is influenced by pH and temperature, in a similar way than explained in Stripping Technology chart (section 7.4). To improve process efficiency, an acid reagent (mainly sulphuric acid) is usually added into water recirculation stream.
NH3(g)+H2O(l)↔NH3(aq)+H2O(l) ↔ NH4+(aq)+OH-(aq)
The efficiency of odour removal by an acid scrubber is the result of dissolution of the odorous compounds in the water phase and the water discharge rate. As the water solubility of odorous compounds may vary from very low to very high, odour removal efficiencies vary as well (Melse and Ogink, 2005).
The treatment of exausted air at farms is hardly used in practice in general. In Flanders there exist regulations obligating to this treatment. In other countries, the regulation demanded by authorities are based on minimum distances (from farm to population) to avoid odour problems. In a context where minimum distance can not be kept (business expansion), that technology can be demanded (Hahne and Varlop, 2001). Also air treatment may be of major importance for compliance with current and future PM10 and PM2.5 standards (particulate matter).
Ammonium salts are usually delivered to fertilizers production companies.
Effects on air (emissions):
Effects on water/soil (and management):
Up to 95% NH3 and 29% odour removal in full-scale piggery farms acid scrubbers (Melse and Ogink, 2005).
Net energy consumption - explanation:
Electricity consumption for ventilation. For piggery on-farm emission control is estimated in 50kWh/place year (Vrielink et al., 1997).
Reagent 1 - explanation:
H2SO4 to maintain pH<4. Acid is normally added to the recirculation water (3.0-3.5 L H2SO4/pig place).
1.3 $/broiler place and 42 $/growing-finishing pig (Melse and Ogink,2005).
Operational costs - explanation:
0.47 $/broiler place year and 14.82 $/growing-finishing pig year (Melse and Ogink, 2005).
Quantifiable income - text:
Not quantified. Possible income by ammonium salt water market (function of its concentration and purity).
Non economically quantifiable benefits:
Odour reduction (animals healthy improvement, reduction of environment emissions, benefits for surrounding population).
Acid scrubber for air effluent from the thermal drying unit are installed at: