Development of composite alginate bead media with encapsulated sorptive materials and microorganisms to bioaugment green stormwater infrastructure†

Abstract

Green stormwater infrastructure (GSI) is being increasingly implemented in urban areas as a nature-based solution to improve water quality and increase groundwater recharge. Nevertheless, GSI is inefficient at removing many trace organic contaminants (TOrCs) and dissolved nutrients, potentially risking groundwater contamination. We developed and characterized novel engineered geomedia to rapidly capture stormwater pollutants via sorption, including TOrCs and dissolved nutrients, while bioaugmenting microorganisms to subsequently degrade captured contaminants in GSI. We created “BioSorp Bead” geomedia by encapsulating powdered activated carbon [PAC] (sorbent), iron-based water treatment residual [FeWTR] (density, sorbent), wood flour [WF] (growth substrate), white-rot-fungi [WRF] (model biodegrading organism), and AQDS (model electron shuttle) in cation-alginate matrices (Ca²⁺, Fe³⁺). We thoroughly mixed WRF culture with autoclaved PAC, FeWTR, AQDS, and WF in 1% alginate. This mixture was added dropwise via peristaltic pump into 270.3 mM CaCl₂/FeCl₃ (on a platform shaker) to instantaneously form beads that were then air-dried. Encapsulated fungi remained viable in dried beads over an extended period (3 months at room temperature), demonstrating potential for bioaugmentation applications. We quantified bead physical properties (i.e., surface area, pore volume, mechanical strength, swelling, leaching), demonstrating that properties can be customized by adjusting composition parameters (e.g., crosslinking with FeCl₃vs. CaCl₂ increased bead mechanical strength). We also conducted preliminary sorption experiments to evaluate capture potential for imidacloprid (neonicotinoid insecticide) from synthetic stormwater runoff. The envisioned goal of the BioSorp Beads is to facilitate rapid contaminant capture during infiltration of storm events and support microorganisms that subsequently degrade sorbed chemicals, thus renewing GSI sorption capacity in situ.