Date of Award
Doctor of Philosophy (PhD)
Chemistry and Biochemistry
James W. Lee
Patrick G. Hatcher
Lesley H. Greene
Smokeless biomass pyrolysis with application of biochar as a soil amendment could be a significant approach for carbon sequestration to possibly control climate change for energy and environmental sustainability. If biochar were to be utilized as a soil amendment and a carbon sequestration agent at Gt C scales, the release of potentially toxic compounds into soils and associated hydrological systems, through soil rainwater runoff and leaching, might have negative consequences, in both agro-ecosystems and aquatic environmental systems. Therefore, the main focus of this dissertation was to study the sources and chemical composition of biochar water extractable (soluble) organic compounds and their effects on aquatic microorganisms.
To evaluate the effects of biochar water extractable substances on the growth of aquatic microorganisms, rapid phytotoxicity assays were performed and showed that pinewood derived biochar water extracts inhibited the growth of both cyanobacteria, Synechococcus sp., and eukaryotic green algae, Desmodesmus sp., while peanut shell and chicken litter derived biochar water extracts did not inhibit growth. Because of its ultrahigh resolution, mass precision and effectiveness for analyzing water soluble compounds, electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) was utilized to analyze biochar water extracts at a molecular level to enhance our initial understanding of the toxic nature of pinewood-derived biochar water extracts as compared to benign peanut shell-derived biochar water extracts. The molecular composition of pinewood-derived biochar water extracts showed unique carbohydrate ligneous components and sulfur containing condensed ligneous components which were both absent from peanut shell-derived biochar water extracts.
Finally, sources of biochar water soluble organic compounds (WSOC) were investigated as a function of biomass materials including cellulose and lignin and pyrolysis temperature from 300°C to 500°C in relation to their potential toxicity to freshwater blue-green algae, Synechococcus. The amount of WSOC extracted from biochar, irrespective of biomass starting material, decreased significantly as a function of pyrolysis temperature. Algal bioassays and advanced 2D GC×GC mass spectrometry analyses revealed that toxic WSOC extracted from pinewood-derived biochar was most likely due to mono-, di- and tri-substituted phenolic compounds derived from lignin, while toxic WSOC extracted from cellulose-derived biochar was acidic and bio-oil like in nature.
Smith, Cameron R.. "Possible Sources and Impacts of Biochar Water Extractable Organic Compounds on Aquatic Microorganisms" (2016). Doctor of Philosophy (PhD), dissertation, Chemistry and Biochemistry, Old Dominion University, https://digitalcommons.odu.edu/chemistry_etds/10