Removal of dissolved nitrogen, phosphorus and carbon from stormwater by biofiltration mesocosms
Biofiltration systems are becoming a popular treatment device in water sensitive urban design. However, very limited data exists on the effectiveness of these systems for nutrient removal, and no results for carbon removal have yet been reported in the technical literature. Experimental small-scale biofiltration systems have been tested to determine the treatment efficiency of these devices for dissolved nutrients (nitrogen and phosphorus and carbon). Three different media were tested (gravel, sand and sandy-loam), in vegetated and non-vegetated treatments.
Vegetated experimental biofiltration systems were very effective in removing nitrogen (63-77% removal) and phosphorus (85-94% removal) from synthetic stormwater. Carbon data are currently being analysed. Vegetated treatments removed significantly more nutrients than non-vegetated treatments. Extending the retention time from 24 hours to 72 hours slightly improved the removal of total nitrogen from vegetated biofiltration systems, yet worsened total nitrogen removal from non-vegetated systems. When the biofiltration systems were leached with fresh water, nutrients leached from non-vegetated systems, but were retained by the vegetated systems. Filtration effectiveness changed very little even after 6 months of regular dosing (14 events). Vegetated sand or vegetated sandy-loam provided the best overall treatment. Thus, vegetated biofiltration systems for stormwater treatment offer an excellent opportunity to turn landscaping constraints (Stormwater Quality
Improvement Devices) into landscaping assets (vegetated green space).