- Recent studies have discovered that salmon, specifically juvenile Coho Salmon, have their olfactory senses inhibited by the presence of low concentrations of copper concentrations at very low concentrations. Much of this copper is deposited on roadways by car brake pads during their use. The copper is carried with stormwater into nearby waterways during rainfall events and placed into contact with salmon populations. Many different types of adsorbent materials are being investigated as possible methods to remediate the copper in stormwater before it reaches nearby waterways. Biochar, similar to granular activated carbon (GAC), is one of these adsorbent materials and can be made as a byproduct of bioenergy production, which makes it less expensive than many other adsorbents. Biochars can be made from various different feedstocks and under varying production conditions, allowing them to have a wide range of properties.
This study assesses six different biochars (hazelnut shells and Douglas fir feedstocks at 3 different pyrolysis temperatures) for their ability to adsorb copper and determines through characterization experiments which properties of the biochars are correlated to the best copper adsorption. Knowing which properties are important to the
biochar’s ability to adsorb copper allows biochars to be tailored toward the real life application of remediating the copper polluted stormwater. Batch isotherm experiments were performed and the data was analyzed using Langmuir and Freundlich isotherms. For the copper concentrations relevant to stormwater remediation H700 (hazelnut shells at 700°C), H500, and D700 biochars performed the best. Copper adsorption was observed to increase with increasing pyrolysis temperature. The addition of natural organic matter (NOM) to mimic realistic stormwater conditions reduced the copper adsorption by the biochar due to the copper complexing with the NOM.
Other trends noted were that increased adsorption of copper onto biochars correlates to higher biochar pH, increased fixed carbon content, and higher surface area. Although increased surface area does correlate to improved adsorption of copper by biochars, it does not appear to be the determining factor as the Douglas Fir biochars had a higher surface area (SA) compared to the Hazelnut shell biochars, but did not adsorb the copper as well. Based off FTIR spectra results for the hazelnut chars, aliphatic hydrocarbons are the only functional group type present at all three of the pyrolysis temperatures in addition to being the only functional group measured in the H700 char. Further investigation is recommended into the functional group analysis to determine if a specific group is responsible for increased copper adsorption. Overall, the H500 and H700 biochars performed the best out of all six and it is recommended that these be used for any future testing related to implementing them in-situ to remediate stormwater.
Key Words: Biochar, Stormwater, Copper, Remediation, Salmon, Environmental, Adsorbent, Isotherm, Langmuir, Freundlich, FTIR, BET, Characterization
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