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Air cleaning

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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Short description

Air washing of unwanted pollutants using water or reagent solutions that specifically target certain compounds.

Best Available Technique: Not indicated
Objective

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.

Level of complexity

Usual scale

Innovation stage

General diagram

Applied to







Typical technology combinations Air cleaning is typically part of manure processing plants. Can also be applied for air treatment in livestock houses.
Pictures

Illustration courtesy of DMT Environmental Technology, The Netherlands (www. dmt-et.nl)

Theroetical fundamentals and process description

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.

Environmental effects

Effects on air (emissions):

  • Nitrogen (N) can be recovered as in the form of ammonium salt (mainly sulphate). Particles and odour reduction.

Effects on water/soil (and management):

  • The process only moves the unwanted substance from the exhaust gases into a liquid solution, solid paste or powder form. This must be disposed off safely, if contain substances that can not be reused.

Other effects:

  • Potentially dangerous or harmful chemicals are needed, such as H2SO4.
  • Nitrogen (N) can be recovered as in the form of ammonium salt (mainly sulphate).
  • The process only moves the unwanted substance from the exhaust gases into a liquid solution, solid paste or powder form. This must be disposed off safely, if contain substances that can not be reused.
Biosecurity aspects
  • Potentially dangerous or harmful chemicals are needed, such as H2SO4.
Technical indicators

Conversion efficiency:


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).

Observations
  • It is necessary to control the process with pH measurements and system discharge (concentrated water <150 g NH4+/L). Replacement of concentrated water is estimated in 70L water/pig or 2L/broiler place according to Melse and Ogink (2005).
  • Dust accumulation in scrubbers can cause air channelling and a decrease in efficiency. It is necessary to perform regular cleaning.
Economic indicators (Economic figures are rough indications, which cannot be used for individual project planning)
  • Investment cost:

    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).

Literature references
  • EPA. Air Pollution Control Technology http://www.epa.gov/ttn/catc/dir1/fbiorect.pdf
  • Hahne, J., Vorlop, K-D. (2001). Treatment of waste gas from piggeries with nitrogen recovery. Landbauforschung Völkenrode, 51 (3), 121-130.
  • http://www.ag.iastate.edu/wastemgmt/Mitigation_Conference_proceedings/CD_proceedings/Animal_Housing-Biofilters_and_Scrubbers/Melse-multi-pollutant_scrubber.pdf
  • MARM (Spanish Ministry of Agriculture). Http://www.marm.es/es/ganaderia/temas/requisitos-y-condicionantes-de-la-produccion-ganadera/ganaderia-y-medio-ambiente/mejores-tecnologias-disponibles-en-avicultura-y-porcino/
  • Melse, R.W., Ogink, NWM. (2005). Air scrubbing techniques for ammonia and odour reduction at livestock operations: Review of on-farm research in the Netherlands. Transactions of the ASAE 48, 2303-2313.
  • Melse, R., Ogink, N., Bosma, B. (2008). Multi-pollutant Scrubbers for Removal of Ammonia, Odor, and Particulate Matter from Animal House Exhaust Air. Proceedings from the National Conference on Mitigating Air Emissions from Animal Feeding Operations Exploring the advantages, limitations, and economics of mitigation technologies.
  • Vrielink, M.G.M., Verdoes, N., Van Gastel, J.P.B.F. (1997). Reducing the ammonia emission with a chemical air scrubber. Report P. 1.178, rosmalen, The Netherlands: Praktijkonderzoek.
Real scale installation references

Acid scrubber for air effluent from the thermal drying unit are installed at:

  • TRACJUSA and VAG pig manure treatment plants (Juneda, Spain)
  • SAVA pig manure treatment plant (Miralcamp, Spain)
  • POLAN and BAÑUELO pig manure treatment plants (Toledo, Spain).
Examples of suppliers
  • Munters AB, http://www.munters.com/en/Global/, is currently testing a chemical air cleaner for its effect to reduce the ammonia emission from the ventilation air in pig stables. The test is performed according to the VERA Test Protocol for Air Cleaning Technologies.