Heavy metals, such as copper, zinc, and cadmium, are ubiquitous in stormwater and potentially toxic to aquatic organisms at low concentrations. Removal of heavy metals contamination by conventional treatment is expensive and does not always reduce metals concentrations low enough to ensure safety of all aquatic species. This research seeks to evaluate the effectiveness of biochar as a low-cost, sustainable solution for the remediation of heavy metals in stormwater. Pyrogenic Carbonaceous Matter (PCM) has proven effective in removing metals; however, specific sorption mechanisms and reactive properties are not well defined. In this work, different biomass feedstocks (Douglas fir chips and hazelnut shells) were pyrolyzed at varying temperatures to determine the effects of biomass feedstock and production conditions on biochar characteristics and metals removal. Adsorption experiments were conducted in batch reactors and constant flow fixed-bed column filtration experiments. Results of copper removal from batch adsorption experiments were used to select an optimal thermally-altered media for further characterization and evaluation in column filtration experiments. Batch and fixed-bed column results indicate that hazelnut shells pyrolyzed at 700°C exhibit superior performance in copper removal compared to other types of biochar and granular activated carbon (GAC), the current prevailing PCM adsorbent. Adsorption results are being used in conjunction with biochar characterization and modeling techniques to elucidate the mechanisms for metals removal by biochar. Modeling of batch and continuous flow experiments will move beyond common empirical isotherm models and employ thermodynamically-based surface complexation modeling to predict metals adsorption under varying solution conditions and incorporate electrostatic effects. These electrostatic models are better equipped to evaluate metals removal by PCM in solutions of varying pH, ionic strength, and metals loading, making them more suitable for application in complex stormwater systems<b>. </b>Model parameters, including surface site density and surface complexation constants, were determined by fitting simulation results to experimental results of copper sorption edges over varied pH and potentiometric titrations. Defining the fundamental pathways for metals removal will inform engineering design to optimize biochar production conditions and advance sustainability.

Evaluating biochar in sustainable stormwater treatment of heavy metals

255th National Meeting (2018)

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