published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

The treatment of acid mine drainage (AMD) by sulfate-reducing bacteria (SRB) has been reported in the literature as a possible alternative to chemical treatment. The overall objective of this study was to implement such a treatment process at the mine site and specifically within the open mine pit itself. The first step of this study was to characterize process parameters. To accomplish this, a reactor was designed and built to simulate hydrodynamic conditions found in the mine pit. This reactor contained a 6$ sp{ prime prime}$ deep gravel bed in which a mixed population of SRB was inoculated. The operation of this reactor demonstrated that treatment of a continuous flow of AMD by SRB was possible, however, the response to changes in the composition of the AMD and to flow conditions was limited. The results indicated that further studies should be directed at the gravel bed itself since this was where the SRB are located and is the active site within the system. / The role of various physical parameters of a gravel bed in the biological treatment of AMD by SRB was examined. This was accomplished by using gravel of different sizes (0.25$ sp{ prime prime}$ vs. 0.5$ sp{ prime prime})$ and composition (granite vs limestone) to form 12$ sp{ prime prime}$ beds in a series of column reactors. The difference in size results in variations in the total surface area, the void volume and various volume ratios within the system. The effect of potential geological buffering by limestone was examined by using and comparing with beds composed of granite. / The gravel beds were inoculated with a mixed culture of SRB and overlaid with 6 L of AMD. After the SRB were established, a series of experiments were performed in which 16.7%, 25%, 75% and 100% of the water column was replaced with an equivalent quantity of fresh AMD. Changes in pH, ORP, electric conductivity, and concentrations of metal and sulfate were monitored for at least 28 days. Sulfate and metal removal at days 7 and 28 of each experiment were compared. The SRB can tolerate a wide range of disturbances, however, an increase in the load of fresh AMD decreased the performance of the system. The results indicated that the total surface area is of greater importance than the void volume in the overall treatment process by SRB. / A dimensionless number was constructed to describe the relationships between the physical parameters of the gravel bed. A plot of the proportion of sulfate removed and this dimensionless number could provide essential information for the sizing of a gravel bed for the purposes of sulfate reduction. This was done for each type of gravel and comparison of the two curves indicated that there was no significant difference between the two gravels. / The importance of the physical substrate for the SRB has been reported in the literature. However, no known attempt has been made to quantify the relationships between the physical parameters and the biological activity. Such information would be useful for the sizing of wetlands and other passive treatment system that uses SRB activity for the purposes of treating AMD. This study is a step towards filling this void.

No description available.

The main aim of this study was to investigate biological hydrogen production from sucrose and molasses by purple non-sulphur bacteria (PNS). The hydrogen production capacities of four different PNS bacteria (Rhodobacter capsulatus (DSM 1710), Rhodobacter capsulatus YO3 (Hup-), Rhodopseudomonas palustris (DSM 127) and Rhodobacter sphaeroides O.U.001 (DSM 5864)) were tested on sucrose and molasses. The photobiological hydrogen production were performed in 50 ml and 150 ml small scale photobioreactors, in batch mode. The produced hydrogen quantities, bacterial growth profiles and pH of the media were recorded through the photobiological hydrogen production processes. Organic acids and sucrose consumption rates were determined by HPLC during the experiments. The maximum hydrogen productivitiy of 0.78 (mmol/lc.h) and 0.55 (mmol/lc.h) was obtained by R. palustris (DSM 127) on sucrose and molasses, respectively. Secondly, co-cultivation of these bacterial strains was studied. The maximum hydrogen productivity by co-cultivation of R. sphaeroides O.U.001 (DSM 5864) and R. palustris (DSM 127) was found as 1.0 (mmol/lc.h).

Mercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in aquatic and terrestrial food webs as monomethylmercury (MeHg). Anaerobic microbes are largely responsible for MeHg production, which depends on the bioavailability of inorganic Hg substrates to methylators. Hg redox cycling pathways such as Hg reduction play a key role in determining Hg’s availability in the environment. Although abiotic photochemical Hg reduction typically dominates in oxic surface environments, Hg reduction pathways mediated by photosynthetic and anaerobic microbes are thought to play an important role in anoxic habitats where light is limited and MeHg production occurs. Currently, the physiological mechanisms driving phototrophic and anaerobic Hg reduction remain poorly understood. The main objective of my thesis is to provide mechanistic details on novel anaerobic and phototrophic Hg reduction pathways. I used a combination of physiological, biochemical and trace Hg analytical techniques to study Hg reduction pathways in a variety of anaerobic and photosynthetic bacteria. I demonstrated that Hg redox cycling was directly coupled to anoxygenic photosynthesis in aquatic purple non-sulphur bacteria that reduced HgII when cells incurred a redox imbalance. I discovered that terrestrial fermentative bacteria reduced Hg through pathways that relied on the generation of reduced redox cofactors. I also showed that sulphur assimilation controlled Hg reduction in an anoxygenic phototroph isolated from a rice paddy. In addition, I developed methods to explore cryptic anaerobic Hg redox cycling pathways using Hg stable isotope fractionation. At its core, my thesis underscores the intimate relationship between cell redox state and microbial Hg reduction and suggests a wide diversity of microbes can participate in anaerobic Hg redox cycling.