Q&A: 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 officially reported any labour accidents in connection to use of professional 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 needs for use of personal protection gear.