Airstreams can be purified by passing them through a biologically active filter medium to destroy organic and inorganic contaminants. It is especially useful for low concentrations of VOCs and inorganic chemicals (e.g., sulfur compounds). It has proven helpful for mixed waste air streams and especially applicable for odour reduction. Heavily halogenated compounds present problems
Biofiltration is efficient for aqueous wastes where concentrations are less than 1%. As with all natural method, it requires stable, consistent operating conditions.
Biofiltration is not suitable for highly chlorinated aliphatics, amines, organics, and aromatic compounds. Heavy metals and organic chemicals may kill the microorganisms. Heavy metals and non-biodegradable organics may also accumulate in the sludge. Hydrogen sulfide gas may also be released. Biofiltration swales and strips are vegetated areas that remove pollutants from stormwater runoff as it flows through the vegetation.
Removal mechanisms include filtration and infiltration. In this study, one biofiltration strip and six swales treat highway runoff, while two pieces treat water from maintenance yards (for pretreatment for infiltration trenches). Runoff is captured in drain inlets and routed to the swales, while strips receive sheet flow directly from the pavement. Swales are conveyance channels where stormwater flow passes through the grass. Pieces are broad surfaces with a grass cover that allows stormwater to flow in relatively thin sheets.
Biofiltration swales and strips are giving useful information about vegetation that can filter stormwater pollutants efficiently in dry areas with little rainfall. Specific biofiltration devices can be used for pretreating stormwater going to infiltration BMPs (i.e., trenches and basins). This “treatment train” approach can increase the overall effectiveness of stormwater treatment.