The WaterNOx nitrogen removal system from Waterloo Biofilter Systems can be installed following any aerobic treatment unit. Featuring a nontoxic carbon source, nitrified effluent from the treatment unit is then 100 percent denitrified in the system. It uses a permanent, absorbent filtration medium, can be installed above or below ground, uses very little energy, and requires little maintenance and no backwashing. It recovers quickly from upsets such as disinfectant use at the facility. Used for both new installations and to retrofit underperforming systems, total nitrogen concentrations of less than 5 mg/L can be consistently achieved with proper design and maintenance. 866/366-4329; www.waterloo-biofilter.com.