Effect of Hydrodynamic Dispersion in Denitrifying Wood-Chip Stormwater Biofilters

AbstractStormwater biofiltration systems can include a submerged layer containing a solid organic carbon substrate, such as wood chips, to promote biological denitrification. The objective of this research was to evaluate the effect of biofilter depth and dispersion on the performance of submerged wood-chip biofilters. Tracer and reactive column studies were performed on biofilters with varying depths (30, 45, and 60 cm), which were evaluated with stormwater at varying hydraulic retention times. The results from every tracer test (n=9) indicated that dispersion affected constituent transport. Shorter columns and/or higher hydraulic retention times resulted in dispersion dominated transport, which contributed to greater constituent bypass through the biofilters. Even though a wood-chip biofilter is considered a porous medium, dispersivity values in this layer were an order of magnitude larger than dispersivities of natural porous media (e.g., sand). These results provide evidence that less media volume is ...