Biofiltration of exhaust air from animal houses: removal efficiencies and practical experiences

Two wood-chip biofilters (capacity and surface area for biofilter #1: 75.000 m3/hour from poultry manure dryer, 68 m2; biofilter #2: 100,000 m3/hour from fattening pig house, 188 m2; media depth: 25 cm) were monitored during 6 - 10 months. Average ammonia (NH3) and odour removal efficiencies were 42 - 62%. NH3 outlet concentrations appeared rather constant and independent of fluctuations in inlet concentrations, so higher inlet concentrations led to higher calculated removal efficiencies. Part of the inlet NH3 was converted to nitrous oxide (N2O). The average N2O production was equal for both biofilters (0.5 g N2O/m2/hour) although NH3 loading rates were very different (30 and 2.4 g NH3/hour). Average air loading rates were 657 and 341 m3/m2/hour, which equal air residence times of 1.4 s and 2.6 s; average pressure drops were 287 and 22 Pa. It is concluded that biofilters have potential for emission reduction at animal houses, but it is recommended that they are professionally designed, operated, and monitored. Especially high pressure drop (clogging/fouling) and homogenous moistening of the biobed need attention.