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Frequently Asked Questions


Does acidification reduce the smell of the slurry?

A reduction in smell could be beneficial to farmers and nearby communities. Some say acidification could help a little.

An inevitable part of livestock production is manure and therefore, some issues with smell. Sometimes the smell can limit the efficient use of manure, since the spreading of slurry on fields near habitation, especially under certain weather conditions, can be bothersome to communities. If the smell of slurry could be reduced farmers would have more flexibility to spread the slurry when and where they see fit, without worries of bothering neighbours and nearby communities. Understandably, many are looking for ways of reducing the smell, and one of the most frequently asked questions related to slurry acidification is whether it can help with this.

The answer to this question is two-fold. First, what is of course known is that ammonia smells bad, so reducing ammonia emissions through acidification should reduce the smell. However, the smell of slurry comes only partially from ammonia, and there isn’t much confirmed evidence of acidification notably reducing the smell of the slurry. The lack of evidence can to some degree be attributed to the fact that the reduction in smell is difficult to measure. Second, even though a significant reduction in smell hasn’t been conclusively proven in studies, people working with acidified slurry have reported a reduction in smell, and acidification is commonly thought to reduce the smell of the slurry.


Why is acidification done using sulphuric acid?

A variety of acids can be used for lowering the pH of slurry, but using sulphuric acid in slurry acidification has become the norm. There is a number of reasons for that.

Sulphuric acid changes ammonia into ammonium (which is a plant-available form of nitrogen that doesn’t evaporate) very efficiently and is the most cost-effective of all the alternatives. Furthermore, it supplies sulphur, which is a macronutrient that plants need, resulting in a decreased need to utilize a sulphur fertilizer.

Other strong acids that have been considered for slurry acidification have proven to be problematic: hydrochloric acid is very corrosive to all materials, and using nitric acid or phosphoric acid would be counterproductive from an environmental perspective. Nitric acid reacts with organic material and releases nitrogen to the air. Phosphoric acid contains phosphorus, and therefore contributes to more phosphorus going onto fields and to eutrophication if not deficit in soil. Weaker acids are not suitable, either, because they require unmanageably large volumes to acidify the manure.

Sulphuric acid is the most suitable for slurry acidification, but it is undeniably dangerous. Therefore, Baltic Slurry Acidification project has compiled a report considering the safety needs for handling acids. The report considers working environment and safety related regulations in all BSR countries. Recognizing the risks in relation to working with sulphuric acid, the below recommendations were compiled in the project group to be used if implementing slurry acidification technology on farm level:

  • Find a safety advisor.
  • Make a risk analysis.
  • Chose the safest technology (no or little risk of contact acid handling).
  • Get training.
  • Follow maintenance program from supplier.
  • Use protection equipment.
  • Be prepared for accidents and know what to do.

In Denmark, where slurry acidification has been used commercially in more than 15 years, there has so far not been any officially reported labour accidents in connection to the professional use of SATs. Nevertheless, rumours are that accidents have happened in Denmark in connection to amateurish handling of sulphuric acid by persons, who were not trained, did not use professional SAT technology, and neither understood or respected the need to use personal protection gear.

Find the whole safety and working environment report here.

A summary exploring the suitability of other acids for slurry acidification can be found here.




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