Hydrogen sulfide (H2S) generation in construction and demolition (C&D) debris landfills has been associated with the biodegradation of gypsum drywall. Laboratory research was conducted to observe H2S generation when drywall was codisposed with different C&D debris constituents. Two experiments were conducted using simulated landfill columns. Experiment 1 consisted of various combinations of drywall, wood, and concrete to determine the impact of different waste constituents and combinations on H2S generation. Experiment 2 was designed to examine the effect of concrete on H2S generation and migration. The results indicate that decaying drywall, even alone, leached enough sulfate ions and organic matter for sulfate-reducing bacteria (SRB) to generate large H2S concentrations as high as 63,000 ppmv. The codisposed wastes show some effect on H2S generation. At the end of experiment 1, the wood/drywall and drywall alone columns possessed H2S concentrations > 40,000 ppmv. Conversely, H2S concentrations were < 1 ppmv in those columns containing concrete. Concrete plays a role in decreasing H2S by increasing pH out of the range for SRB growth and by reacting with H2S. This study also showed that wood lowered H2S concentrations initially by decreasing leachate pH values. Based on the results, two possible control mechanisms to mitigate H2S generation in C&D debris landfills are suggested.
Thiothrix spp., sulfide‐oxidizing mixotrophic bacteria, were sampled from visible colonies in the Floridan aquifer in several underwater caves, sinkholes, and springs below the water table in North Florida. Bacteria samples were collected by cave divers certified by the National Speleological Society/Cave Diving Section. Sites sampled were ecological niches in the aquifer where visible colonies had a white slimy or filamentous appearance indicative of Thiothrix spp. Sterile sampling methods were adapted to the underwater cave setting. Bulk water samples for media preparation were collected by divers from bacteria sampling sites. Bacteria were isolated and cultured in growth media prepared with cave or spring water. Thiothrix spp. were identified by microbiological and immunological methods. Monoclonal antibodies specific for Thiothrix spp. were utilized in fluorescent antibody assays and enzyme‐linked im‐munosorbent assays (ELISA). Thiothrix was found in six of eight underwater caves sampled. Three of these caves had no discernible water flow at the time of sampling, indicating that Thiothrix in the Floridan aquifer does not necessarily require constantly flowing water. Most of the visible bacterial colonies that tested negative for Thiothrix were biofilms growing on limestone and iron oxyhydroxide substrates on the walls of clear‐water and high‐flow caves. The sulfur cycle in phreatic limestone conduits is described. The reactions and bacteria involved in the HS‐ cycle and pyrite cycle are discussed. Thiothrix generates sulfuric acid, which has the potential to dissolve limestone below the water table. Results of this study should contribute to a better understanding of the role of colorless sulfur bacteria in the development of porosity in carbonate rocks and microbial ecology in these karst aquifer settings.
Toxicity bioassays of solvent extracts of sediments are used to evaluate the toxicological effects of extracted hydrophobic organic contaminants. However, this type of bioassay assesses the toxicity of all extracted compounds, natural or anthropogenic. Sediment extracts are typically subjected to cleanup procedures before chemical analysis to remove interfering, coextracted substances. This study evaluated the effect of cleanup procedures on the toxicity of acetonitrile extracts of contaminated sediments by using the Microtox® bioluminescence bioassay. Extract cleanup significantly reduced toxicity of most extracts when copper powder was added to remove coextracted sulfur. Microtox was shown to be highly sensitive (EC50 of 24.7-35.8 μg/L) to elemental sulfur dissolved in several organic solvents. Toxicity tests utilizing solvent extracts of sediments must take into account the toxic effects of coextracted sulfur on bioassay organisms to accurately assess the environmental impacts of extracted hydrophobic contaminants.
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