Biochar-Mediated Reduction of Nitro Herbicides and Explosives Seok-Young Oh 1 , Jong-Gil Son 1 , Pei C. Chiu 2 1 Department of Civil and Environmental Engineering University of Ulsan, South Korea 2 Department of Civil and Environmental Engineering University of Delaware, U.S.A. 2 US Biochar Conference oma State Univ., July 31, 2012
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Biochar-Mediated Reduction of Nitro Herbicides and Explosives
2012 US Biochar Conference Sonoma State Univ., July 31, 2012. Biochar-Mediated Reduction of Nitro Herbicides and Explosives. Seok-Young Oh 1 , Jong-Gil Son 1 , Pei C. Chiu 2 1 Department of Civil and Environmental Engineering University of Ulsan, South Korea - PowerPoint PPT Presentation
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Biochar-Mediated Reduction of Nitro Herbicides and Explosives
Seok-Young Oh1, Jong-Gil Son1, Pei C. Chiu2
1Department of Civil and Environmental EngineeringUniversity of Ulsan, South Korea
2Department of Civil and Environmental EngineeringUniversity of Delaware, U.S.A.
2012 US Biochar ConferenceSonoma State Univ., July 31, 2012
Black Carbon (BC)
• Soot, charcoal, char, coke, coal, and kerogen• Composed of polycyclic aromatic carbon (so-called graphene) sheets• Important geosorbent for small molecules, such as PAHs and PCBs• Sorption mechanism: π-π electron donor-acceptor (EDA) interaction (Pignatello et al., 2004)• The basis of a current remediation approach: addition of BC materials as sorbents to sediments to reduce the bioavailability and ecotoxicity of PCBs or PAHs (Cho et al., 2009)
Are organic compounds sorbed to BC chemically inert?
Not always. Graphene moiety of BC may play a role of electron conductor to mediate reductive transformation of the sorbed redox-sensitive compounds.
BC-mediated reduction of 2,4-dinitrotoluene by dithiothreitol
Conceptual schematic diagram for BC-mediated reduction of NACs by
reductants
(Oh et al., 2012, EG&H )
Possible Hypothesis on Mechanisms of BC-Mediated Reduction
1. Graphitic structure (graphene) of BC may be responsible for BC-mediated reduction: BC is a sorption site as well as electron conductor (Oh and Chiu, 2009).
2. Surface functional groups (i.e., quinone) of BC may account for BC-mediated reduction (Kemper et al., 2008).
Biochar
• Char derived from pyrolysis of biomass• Carbon sequestration: biochar remains in soils for hundreds or thousands of years
→ long-term sink of CO2
• Improve the fertility of soils and biomass production• However, still costly compared to trading CO2 value ($4/ton)
Other indirect benefits from biochar?
How about sorbent and electron transfer catalyst for redox-sensitive contaminants in soils and sediments?
Objective
• Examine the roles of biochar both as a sorbent and as a redox mediator, in the transformation of nitro herbicides and explosives
Hypothesis
• Similar to other BC, biochar can also act as a redox mediator to promote the reductive transformation of organic compounds and impact the fate of redox-sensitive chemicals in the environment.
• Black carbon1.Poultry litter biochar (37.1% C, S.A.: 2.3 m2/g. at 400oC for 4 h)2.Biosolid biochar (31.8% C, S.A.: 2.0 m2/g, at 400oC for 8 h)3.Graphite powder (99.9% C, S.A.: 13.6 m2/g)4.GAC (86.1% C, S.A.: 738 m2/g)
• Reductant: dithiothreitol (Eh= -0.33V at pH 7)
Batch Experiments
- At 25oC-150 rpm shaking- In a glove box
250-mL amber vial 250 mL of solution (no head space) - N2 purging (30 min) - pH 7.0 (20 mM phosphate) - 120 mg of dithiothreitol - 1% of methanol (due to low solubility) - Pendimethalin = 0.0355 mM - Trifluralin = 0.0686 mM
1 g of biochar 0.1 g of graphite powder 0.05 g of GAC
Mininert™ valve
Two control experiments- sorption control: without reductant- reduction control: without black carbon
A cyclization product:2-ethyl-7-nitro-1-propyl-5-(trifluoromethyl)-1H-benzimidazole
Mass spectrum of a cyclization product (93.9% match)
Gas chromatogram of of hexane extract of trifluralin solution with dithiothreitol and PL biochar after reaction for 120 min
Conclusions
• Biochar can catalyze the reduction of DNT and RDX by dithiothreitol.
• The reduction of pendimethalin and trifluralin by dithiothreitol can also be enhanced in the presence of biochar.
Environmental Implication
• BC may be involved in the abiotic natural attenuation of nitro herbicides and explosives in subsurface environments
• A potential novel site remediation and/or waste treatment approach: BC and other graphitic materials may be applied to soils or sediments contaminated with nitro herbicides and explosives.
• Biochar may play a role of catalyst for nitro herbicides and explosives during biochar sequestration.
Acknowledgments
• Korea Research Foundation Grant 2009-0064688
• Research Grant from Ulsan Green Environment Center
• 2nd stage Brain Korea 21
• Professor Mingxin Guo of Delaware State University