July 19, 2017

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Duane Graves Article Published in Journal of Environmental Management

Duane Graves (Tennessee) co-authored an article entitled "Biogeochemical Oxidation of Calcium Sulfite Hemihydrate to Gypsum in Flue Gas Desulfurization Byproduct Using Sulfer-Oxidizing Bacteria" published in the Journal of Environmental Management online in Volume 201 on pages 357-365 on July 7, 2017.

The article outlines the application of microbial physiology. It also addresses flue gas desulfurization, its composition, and its capabilities. The article concludes that the conversion rate of calcium sulfite hemihydrate to gypsum is around five percent each day.

His co-authors were Jacques J. Smith, Linxi Chen, Allison Kreinberg, Brianna Wallace, and Robby White.

Duane Graves is a Senior Principal Scientist based in Tennessee with more than 30 years of experience focused on environmental biotechnology; environmental forensics; in situ groundwater, soil, and sediment remediation; evaluation of airborne biological contaminants; and remediation of groundwater in karst formations.

He specializes in the development, selection, feasibility evaluation, design, and deployment of remedial solutions for hazardous, radioactive, and mixed-waste, contaminated soil, sediment, and groundwater; odor and biological agent investigation and mitigation; environmental forensics; and environmental biotechnology. His project involvement includes the development of technical approaches, hazardous waste treatability studies, remedial investigations and feasibility studies (RI/FS), corrective measures studies (CMS), corrective action plans, remedial designs, and interpretation and reporting of data to regulatory agencies, clients, and the public.


Flue gas desulfurization (FGD) is a well-established air treatment technology for coal and oil combustion gases that commonly uses lime or pulverized limestone aqueous slurries to precipitate sulfur dioxide (SO2) as crystalline calcium salts. Under forced oxidation (excess oxygen) conditions, FGD byproduct contains almost entirely (>92%) gypsum (CaSO4·2H2O), a useful and marketable commodity. In contrast, FGD byproduct formed in oxygen deficient oxidation systems contains a high percentage of hannebachite (CaSO3·0.5H2O) to yield a material with no commercial value, poor dewatering characteristics, and that is typically disposed in landfills. Hannebachite in FGD byproduct can be chemically converted to gypsum; however, the conditions that support rapid formation of gypsum require large quantities of acids or oxidizers. This work describes a novel, patent pending application of microbial physiology where a natural consortium of sulfur-oxidizing bacteria (SOB) was used to convert hannebachite-enriched FGD byproduct into a commercially valuable, gypsum-enriched product (US Patent Assignment 503373611). To optimize the conversion of hannebachite into gypsum, physiological studies on the SOB were performed to define their growth characteristics. The SOB were found to be aerobic, mesophilic, neutrophilic, and dependent on a ready supply of ammonia. They were capable of converting hannebachite to gypsum at a rate of approximately five percent per day when the culture was applied to a 20 percent FGD byproduct slurry and SOB growth medium. 16S rDNA sequencing revealed that the SOB consortium contained a variety of different bacterial genera including both SOB and sulfate-reducing bacteria. Halothiobacillus, Thiovirga and Thiomonas were the dominant sulfur-oxidizing genera.

More Information

For more information regarding the article, visit: http://www.sciencedirect.com/science/article/pii/S0301479717305947.
For more information on biogeochemical oxidation of calcium sulfite hemihydrate, contact Duane Graves at This email address is being protected from spambots. You need JavaScript enabled to view it..
To learn more about Duane see his profile at: https://www.geosyntec.com/people/duane-graves