Biological aerated filters (BAF) use submerged granular media to support biological growth and act as filtration medium, eliminating the need for clarifiers. If aerated, the filter can be used for carbon removal and nitrification. In an unaerated mode and in the presence of sufficient carbon source, this technology provides denitrification. BAF can be installed in separate stages for carbon removal, nitrification, and denitrification.
The first large-scale installation with a capacity of 14 mgd has been operating in Roanoke, VA, for two years, and similar size plants in Minnesota are starting up. Two large plants with peak flows close to 100 mgd are now under construction in Binghamton and Syracuse, NY, corresponding to hundreds of installations with different BAF systems in the UK, German-speaking countries, France, Scandinavia, and Japan.
Biologically active filtration is also applied in drinking water to reduce the biodegradable matter which might lead to regrowth of bacteria in distribution systems using ozone to enhance pollutant bioavailability and supply oxygen, downstream contactors of activated carbon or anthracite provide growth surfaces for biomass.
In contact times of 5 to 10 minutes, a significant amount of biodegradable matter can be removed, lowering the necessary disinfection dosage and reducing the formation of halogenated byproducts. The world’s largest plant with ozone/biofiltration is currently being completed at Southern Nevada Water Authority’s Alfred Merrit Smith water treatment plant in Las Vegas, with a daily flow of up to 600 mgd from Lake Mead.