ASHS 2025 Conference

Runoff containing excess nitrogen (N) and phosphorus (P) is detrimental to environmental and human health. Bioreactors are biological treatment systems that can be used to combat these problems, which often consist of a lined trench filled with a carbon-rich media (often woodchips) to promote biological remediation through denitrification and other processes. Various carbon-rich organic materials, such as woodchips and sugarcane bagasse (a byproduct of sugarcane production), can be used to fuel biological processes, whereas inorganic materials, such as expanded shale, can provide binding sites for P adsorption as well as physical stability within medias. Raingarden installations utilize similar concepts for trapping runoff water and remediating contaminants; however, the inclusion of ornamental plants provides aesthetic appeal, an important consideration in urban and suburban areas. Seven unique medias were evaluated to determine potential to a.) remediate N and P from runoff and b.) support plant life. An aged pine bark/sand media commonly used for landscape beds (bed mix; BM) served as the control. Organic carbon sources (woodchips (WC) and sugarcane bagasse (SB) to support bacterial communities) and several inorganic materials (including expanded shale (S) and activated aluminum (AA) to bind P) were blended with BM to provide potential enhancement of nutrient removal capabilities. Media blends were homogenized by hand before being transferred into media containers (MC; 2.36 L of substrate per container), wherein Hibiscus moscheutos ‘Luna Pink Swirl’ seedlings were transplanted. Pots were placed within plastic containers (leachate containers (LC)), which served as a collection receptacle for leachate. Simulated runoff water containing N and P was prepared and applied to each replicate, after which leachate was analyzed and collected as sub-samples. Simulated runoff applications were limited in the initial phase of the study (one application per week; three total) and intensified in the final phase (three applications per week; nine total), with all leachate volumes collected between applications. Health and growth of Hibiscus was assessed via SPAD readings, growth index, and destructive harvest at the termination of the study. While the growth of all Hibiscus replicates was generally equivalent between treatments, it was observed that BM amended with SB produced more shoot biomass. Additionally, leachate nutrient content and water chemistry dynamics were influenced by several of the investigated amendments.