Acidification with sulfur of the separated solid fraction of raw and co-digested pig slurry: effect on greenhouse gas and ammonia emissions during storage

A study was performed to assess: (1) the feasibility to acidify the separated solid fraction of raw and co- digested pig slurry by using a powdery sulfur-based product; and (2) the effect of this acidification method on greenhouse gases and ammonia emissions during manure storage. Samples of raw and co-digested pig slurry were collected at two commercial farms and mechanically separated by a laboratory-scale screw press device. The sulfur powder (80% concentration) was added to the obtained separated solid fractions at three application rates: 0.5%, 1% and 2% (w/w). Carbon dioxide, methane, nitrous oxide and ammonia emissions were afterwards measured during storage of the acidified samples and compared with those measured from untreated samples (Control). Gaseous emissions were determined with dynamic chamber method by Infrared Photoacoustic Detection. Gaseous losses were monitored along 30 and 60 days of storage time for raw solid fraction and digested solid fraction, respectively. The addition of the tested sulfur powder to solid fractions showed to be a reliable and effective method to acidify raw and co-digested solid fractions. Results showed a significant reduction of both greenhouse gases and ammonia emission regardless of the separated solid fraction type. The highest sulfur application rate (2% w/w) led to a reduction of up to 78% of greenhouse gas emission and 65% of ammonia losses from raw separated solid fraction when compared with the Control. Similar results were achieved from the co-digested solid fraction, with emission reduction of up to 67% for ammonia and 61% for greenhouse gas.