Semi-Continuous Air Sampling versus 24-Hour Bag Samples to Evaluate Biofilters on a Swine Nursery in Warm Weather
Abstract. Economical and effective methods are needed to assess practices that reduce gas emissions. This project compared gas concentrations measured using semi-continuous sampling with dedicated gas analyzers versus concentrations obtained using 50 L FlexFoil bags filled over 24 h. Sampling was done over four months in summer and early fall of 2010 and 2011 from four biofilters (flat-bed with old media, A-frame, and two flat beds with either 10 cm or 5 cm screen birch mulch) treating air from deep manure pits below swine nurseries. Concentration ratios and percent reductions were calculated and compared using both sampling methods. The NH 3 , H 2 S, CO 2 , CH 4 , and N 2 O concentration data indicated that the 24 h bag sampling concentrations and percent reductions tracked the semi-continuous sampling concentrations and percent reductions well. Most (77%) of the NH 3 concentrations differences (24 h bag sample minus semi-continuous) were within ±2 ppm of the semi-continuous concentrations, 78% of the H 2 S concentration differences were within ±200 ppb, 87% of the CH 4 concentration differences were within ±10 ppm, and 88% of the N 2 O concentration differences were within ±75 ppb. Ratio means for NH 3 , CO 2 , and N 2 O were close to one (between 0.95 and 1.09). H 2 S ratio means varied from 0.61 in 2010 to 1.68 in 2011. Semi-continuous percent reduction results indicated that the four biofilters reduced NH 3 , H 2 S, and CH 4 emissions. For three of the four biofilters, mean percent NH 3 reductions ranged from 53% to 86%, mean percent H 2 S reductions ranged from 41% to 74%, and mean percent CH 4 reductions ranged from 8% to 39%. One biofilter reduced N 2 O concentrations by 17% to 22%, while three biofilters generated N 2 O by 8% to 81%. The 24 h bag sampling system tested was an effective method for measuring gas concentrations and percent reductions of an air treatment system in the field based on NH 3 , CH 4 , and N 2 O.