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Storage systems

Facilities for storing of livestock manure with a minimal loss of nutrients

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Short description

Application of an acidic reagent resulting in a decreased pH, which may be desired for the inactivation of pathogens and/or reduction of especially ammonia emissions.

Best Available Technique: in DK
Objective

The main objective of acidification of liquid manure is to lower the level of pH in the manure, and thereby increase the concentration of ammonium (NH4-N) at the expense of ammonia (NH3) – which will result in reduced free ammonia emission.

Level of complexity

Usual scale

Innovation stage

General diagram

Applied to







Typical technology combinations
Pictures

Tank for sulphuric acid (http://www.jhstaldservice.dk).

Theroetical fundamentals and process description

Addition of acid to the slurry leads to a decrease of the slurry pH, whereby the amount of ammonia nitrogen increasingly is transformed into ammonium (NH4+) that does not evaporate. By adding 4-6 kg concentrated sulfuric acid (H2SO4) per 1,000 kg pig slurry reduces the slurry pH to between pH 5.5 and 6.0. The acidification unit to treat the slurry, consists of the following main components: valve pit, process tank and acid tank. When processed, the manure from a number of slurry basins in the stable is pumped to the process tank via the valve pit. In the process tank, sulfuric acid is added so that the slurry pH is decreased to 5.5 (target), during stirring and combined with aeration. After treatment, the main part of the slurry is pumped back to the basins in the stable, while the rest is pumped to the storage tank. Treatment frequency depends on the slurry pH measured before each treatment, meaning the frequency increases with increasing initial pH. Normally, all the slurry in a herd will be treated 1-3 times daily. All processes are controlled and monitored automatically.

Environmental effects

Effects on air (emissions):

  • The acidification proces can reduce risk of gaseous emisssions (COV, CH4, NH3) and odour problems. A Danish study has shown that frequent adjustment of the pH of pig slurry in a pig house (fattening pigs) with 1/3 drained floor and 2/3 slats reduced ammonia volatilization by 70% (Pedersen, 2004). Acidification of slurry also results in reduced ammonia volatilization from the slurry storage. A single trial (Kai et al., 2008) estimated losses from acidified slurry being less than 20% of the emission from an untreated uncovered storage facility. Ammonia losses during storage of manure are expected to be reduced by 50% compared with untreated slurry with naturally established crust (floating layer). Acidification of slurry reduces ammonia volatilization during and after field application as well. An experiment has shown that the accumulated ammonia measured seven days after application with trailing hoses was about 67 % lower for acidified pig slurry compared to untreated slurry (Kai et al., 2008). A possible effect of adding more acid and thereby lowering pH further will be minimum, because nearly all ammonia will be as ammonium at pH 5.5. There have been conducted olfactometric odor measurements for the two trials of acidification of slurry in slaughter houses (Pedersen, 2004 and 2007). The experiments showed no statistically significant effect in terms of odor by acidification. There are examples, that increased odor problems have been discovered locally around the process tank of the acidification unit. Elimination of the problem by mounting a carbon filter at the process tank. A laboratory study has shown that emissions of methane from the sulfuric acid treated cattle slurry was 90% lower than the untreated control slurry by measurements over 100 days in a semi-field systems (Petersen and Eriksen, 2008). Another laboratory study showed that emissions of methane from cattle manure stored for seven weeks was 67% lower than the untreated slurry (Hansen, 2008). The experiments provide no basis for clarifying the effect of acidification of slurry, but it can be concluded that acidification has a markedly negative effect on methane production during storage. The effect on methane emissions from pig stables and storage of pig manure is not known but it is expected that there will be a significantly reducing effects due to the ongoing acidification and aeration of the slurry. There are not assumed any net effect of slurry acidification on nitrous oxide emissions. Only through the substitution of nitrogen in commercial fertilizers with saved ammonia volatilization in the field fertilizer level, you can expect a lower nitrous oxide emission (IPCC, 2006).

Effects on water/soil (and management):

Not indicated

Other effects:

  • The acidic media can inhibit some pathogens or microorganisms growth. The impact of this process over pathogens survival must be evaluated.
Biosecurity aspects
  • The acidic media can inhibit some pathogens or microorganisms growth. The impact of this process over pathogens survival must be evaluated.
Technical indicators

Conversion efficiency:


By adding 4-6 kg concentrated sulfuric acid (H2SO4) per 1,000 kg the pig slurry pH can be reduced up to pH value of 5.5-6.0. The acidification process has proven to be able to reduce the ammonia emission from pig houses and slurry storage by 65-70 %.

  • Net energy consumption - explanation:

    Pedersen (2004) calculated an increased consumption of approx. 3 kWh/m3 slurry by using slurry acidification. The calculation is based on runtime and pump power and is therefore subject to some uncertainty. For the Infarm plant located in Randers (Report 4. Annex B), treating 10,000 m3/y the estimated electricity consumption is 1.8 kWh/m3.

  • Reagent 1 - explanation:

    In the process there will be added approximately 4-6 kg concentrated sulfuric acid (H2SO4) per 1,000 kg pig slurry. The amount of reagent needed to attain a given pH is linked to the alkalinity of the manure. Treatments such as nitrification or CO2 stripping may help in reducing such reagent requirements (possible volatilization must be considered).

Observations
  • Sulfuric acid addition to manure can have negative consequences for the sustainability of some types of concrete because of a sulphate reaction. Recommendations for selection of concrete should be followed. Also sulphuric acid manipulation should be performed under safety protocols.
  • Ammonia is concentrated in the manure/slurry. Consequently, if the target of the adopted treatment is to concentrate nutrients in a fertilizing product (as pellets or concentrates obtained in evaporation or drying processes), acidification must be considered as a pre-requisite or pre-treatment for those process combination.

Economic indicators (Economic figures are rough indications, which cannot be used for individual project planning)
  • Investment cost:

    There is a basic investment in the range of 100,000 € at farm level (including storage tanks, pumps and controllers) but dependent on farm size and types of stables and other local parameters.

  • Quantifiable income - text:

    Acidification of slurry is a technology that reduces ammonia emissions from both stables, storage facilities and at land application. Based on standard figures for manure (2008) it can be estimated that net saving is 17-19 kg NH3-N volatilization from stables, storage facilities and at application per. animal unit using acidification in pig houses. Acidification of manure means that the content of nitrogen in the manure at storage is 7-13% higher than in normal manure handling. By application with trail hoses of acidified slurry a 20-25% increase in fertilizer effect (bio-availability) is expected (Kai et al., 2008), while the nitrogen effect by injection of acidified slurry is not increased, because of the high nitrogen effect of injection already (Sørensen and Eriksen, 2009).

Literature references
  • Miljøstyrelsens Teknologiliste - http://www.mst.dk/Virksomhed_og_myndighed/Landbrug/Husdyrgodkendelser/bat/Teknologiliste_ny.htm (Technology Sheet: Acidification of slurry (2011), Environmental Protection Agency, Danish Ministry of the Environment).
  • IPCC (2006): IPCC Guidelines for National Greenhouse Gas Inventories. Volume 4 Agriculture, Forestry and Other Land Use.
  • Kai, P., Pedersen, P., Jensen, J.E., Hansen, M.N., and Sommer, S.G. (2008): A whole-farm assessment of the efficacy of slurry acidification in reducing ammonia emissions. Eur. J. Agron. 28:148-154. 
  • Pedersen, P. (2004): Svovlsyrebehandling af gylle i slagtesvinestald med drænet gulv. Meddelelse nr. 683, Landsudvalget for Svin, pp. 12. 
  • Pedersen, P. (2007): Tilsætning af brintoverilte til forsuret gylle i slagtesvinestald med drænet gulv. Meddelelse nr. 792 fra Dansk Svineproduktion, Den rullende Afprøvning, pp. 14. 
  • Petersen og Eriksen (2008): Acidic slurry more climate-friendly. www.agrsci.dk
  • Sørensen, P, og J. Eriksen (2009): Effects of slurry acidification with sulfuric acid combined with aeration on the turnover and plant availability of nitrogen. Agriculture, Ecosystems and Environment 131, 240-246.
Real scale installation references
  • Pigfarmer, Mr. Mogens Sommer Jensen Amstrupgårdsvej 40 8940 Randers SV Tel. +45 86 44 71 59 Mob +45 2191 3575
Examples of suppliers