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.
Biochar 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 700oC exhibit superior performance in copper removal compared to other types of biochar and granular activated carbon (GAC), the current prevailing adsorbent media.
Adsorption results were 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 moved beyond common empirical isotherm models and employed thermodynamically-based surface complexation modeling to predict metals adsorption under varying solution conditions and incorporating electrostatic effects. These electrostatic models are better equipped to evaluate metals removal by biochar in solutions of varying pH, ionic strength, and metals loading, making them more suitable for application in complex stormwater systems. Model parameters, including surface site density and surface complexation constants, were determined by fitting simulation results to experimental results of potentiometric titrations and copper sorption edges over varied pH. Defining the fundamental pathways for metals removal will inform engineering design to optimize biochar production conditions and advance sustainability.
Researchers and practitioners involved in biochar agricultural and environmental applications, bio-energy and biochar production, and forest management were interviewed to determine what questions remained in their fields that were acting as barrier to widespread biochar implementation. Interviews and questions presented in field workshops were video recorded at US Biochar Initiative (USBI) conference hosted at Oregon State University (OSU) in 2016. The “Burning Questions of Biochar” are presented in this document and a complementary edited video. The goal disseminating these questions is to encourage cross-discipline communication between aspects of the biochar business system, to highlight common barriers and to form collaborative solutions. The most common concern presented from all fields examined was that biochar characteristics are not well-documented in the myriad of published studies. Lack of characterization makes it difficult if not impossible to compare biochar results across studies with varying environmental or biochar production conditions. There was a cross-cutting need to understand mechanisms by which biochar provides benefits to environmental and agricultural applications. Defining mechanisms for soil and water improvement must also be linked to biochar characteristics to understand how biochar will affect target applications based on production and site conditions. Biochar benefits in agricultural and environmental applications need to be confirmed by long-term field-scale trials to understand how environmental conditions affect biochar performance over time.