Caelan Nelson is studying the use of NutriFilters, a floating (or in-pond) biofilter designed by Agriment Services, as a retrofit for stormwater retention ponds. The biofilters feature a tank filled with lightweight expanded clay aggregate (LECA), a substrate that provides high surface area for biofilm development to target nutrients, specifically nitrogen. The key innovation of the NutriFilter is that by controlling water flow within the tank, the system alternates between aerobic and anaerobic conditions, allowing it to target both ammonia and nitrate.

To evaluate performance, the study combines mesocosm trials with field monitoring of two stormwater retention ponds in Wilson, NC, before and after biofilter deployment. Retrofits like the NutriFilter™ offer significant value because they require a minimal footprint and are more cost-effective than replacing existing stormwater infrastructure outright.