This review covers air scrubbers and biofilters as treatment for the air LEAVING pig and poultry housing. It characterises exhaust air, reviews removal efficiencies for ammonia, odour, particulate matter, nitrous oxide and methane, and identifies the design variables that govern performance: air and liquid flow configuration, packing size and material, water flow rate, water discharge and acid dosage.
The distinction from disease control filtration is total and worth stating plainly, because the shared vocabulary invites confusion. Filtration for biosecurity treats incoming air to keep pathogens out of a building. Scrubbers and biofilters treat outgoing air to keep ammonia, odour and particulate out of the surrounding environment. Different air stream, different target, different regulatory driver, different equipment. Nothing in this review speaks to whether a filter bank will keep PRRSV out of a barn, and nothing in the PRRSV filtration literature speaks to ammonia removal from exhaust.
The driver here is European regulation. Scrubbers entered pig and poultry housing as a low ammonia technique, and the requirements later widened to cover odour and particulate removal efficiencies as well. Producers outside that regulatory environment are generally not operating under the same obligation, which is the main reason this equipment is far more common in northern Europe than in North America. The authors flag low solubility components, odour compounds and methane in particular, as where performance still falls short. For a site weighing neighbour relations or an emissions requirement rather than herd health, this is the relevant literature, and it is one of the few reviews that treats poultry housing on equal terms with pig housing.