FIELD APPLICATION OF A RENEWABLE CONSTRUCTED WETLAND SUBSTRATE FOR PHOSPHORUS REMOVAL

Phosphorus (P) is typically the best target to prevent eutrophication in freshwater, a biological process associated with water quality degradation. Constructed wetlands (CW) and other practices that include P removal by sorption processes in substrates can provide economical treatment of stormwater, but have limitations (e. g., large land requirements, loss of removal over time, lack of P recovery). Over the last three years, a multi-study research program addressed these limitations with a new P management concept. This concept minimizes CW size with a rejuvenation cycle (or rejuvenation) that renews P-sorption capacity in the CW substrates and enables P recovery for productive use. This study, conducted in Blacksburg, Virginia (July-September 2009), tested the efficacy of rejuvenation in the field. Methods included replicate cells of two sand substrates monitored for P removal during prerejuvenation and postrejuvenation filtration runs. One substrate contained cast iron filings as a repository for sorption capacity. Results support the following conclusions: (1) P removal is likely dependent on multiple factors including influent P concentration, previous substrate /solution equilibrium, pH, and time; (2) rejuvenation is capable of releasing P adsorbed during stormwater filtration; (3) inclusion of cast iron in substrate promotes additional P removal and enables further removal after rejuvenation; but (4) inclusion of cast iron may limit release of P during rejuvenation.