Comparing semi-continuous air sampling versus 24-hour bag samples from two flat-bed biofilters with new woodchip media

Efforts to manage gas emissions from animal feeding operations are expected to create a need for economical and effective methods to assess mitigation practices. The purpose of this project was to compare gas concentrations measured using semi-continuous sampling with dedicated gas analyzers versus concentrations obtained using a system that fills 50 L bags over 24-h periods. Sampling was done on two flat-bed biofilters with new media, 5 cm or 10 cm, treating air from swine nurseries. Concentration ratios and percent reductions were calculated and compared using concentrations from both sampling methods. The results indicate that 24-h bag concentrations and percent reductions tracked the semi-continuous concentrations and percent reductions well. Ratio means for NH₃, CO₂ and N₂O were close to one indicating similar concentrations using the two methods. The H₂S ratio mean was over 1.65 and CH₄ ratio means were less than one. Mean percent reduction differences were mixed. CH₄ and N₂O mean percent reduction differences were near zero but H₂S mean percent reduction differences were negative and NH₃ mean percent reduction differences were inconsistent. The flat-bed biofilter with 10 cm media removed 61 to 73% of the NH₃emitted while the flat-bed biofilter with 5 cm media removed between 6 and 15%. Both biofilters removed between 42 and 65% of the H ₂S. The 10 cm media did not generate N₂O.