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Bioremediation of Cr(VI)-Contaminated Soil using Bacteria
Published in Maulin P. Shah, Removal of Refractory Pollutants from Wastewater Treatment Plants, 2021
A wide diversity of microorganisms is known to have evolved biochemical pathways through aerobic and anaerobic processes to eradicate toxic compounds. Aerobic bioremediation involves microbial reactions that require oxygen to step forward. The bacteria use a carbon substrate as the electron donor and oxygen as the electron acceptor. The aerobic reduction is a co-metabolic process in which bacteria do not obtain energy or carbon from the degradation of a contaminant, but rather, the contaminant is reduced by a side reaction (EPA, 2006). On the other hand, anaerobic bioremediation involves microbial reactions occurring in the absence of oxygen. This requires many methods, including oxidation, reductive dechlorination, methanogenesis, and the reduction of sulfate and nitrate levels, depending on the contaminant. In anaerobic metabolism, sulfate, nitrate, carbon dioxide, oxidized materials, or organic compounds can substitute oxygen as the electron acceptor. Most of the microorganisms catalyzing redox reactions use the metals or metalloids in anaerobic respiration as terminal electron acceptors. Such microorganisms are both phylogenetically and physiologically diverse, classified as dissimilatory metal-reducing bacteria. Among the different groups of microorganisms, Cr(VI) reduction was investigated in a large number of bacterial species. The mechanisms by which bacterial strains reduce Cr(VI) to Cr(III) are variable and dependent on the species (McLean et al., 2000). Microbial Cr(VI) reduction occurs in two different processes: aerobic conditions and anaerobic conditions. In aerobic conditions, Cr(VI) reduction is found to be co-metabolic (not participating in energy conservation), whereas it is predominantly dissimilatory under anaerobic conditions (Ishibashi et al., 1990).
An analysis of the influence of affordable housing system on price
Published in Dawei Zheng, Industrial, Mechanical and Manufacturing Science, 2015
Gorby, Y. A.; Beveridge, T. J. 2005. Composition, reactivity, and regulation of extracellular metal-reducing structures (nanowires) produced by dissimilatory metal reducing bacteria. Presented at DOE/NABIR meeting, April 20, Warrenton, VA.
Energy harvesting using exoelectrogenic Shewanella oneidensis bacteria
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Young H. Park, Edward Park, Geoffrey Smith
Researches have been conducted to study exoelectrogenic Shewanella oneidensis bacteria that control the redox transformation of heavy metals and other electron acceptors for use in energy conversion (Lies et al. 2005). An important feature of S. oneidensis bacteria is that they produce electrically conductive nanowires that facilitate electron transfer to electron acceptors. Hence, research attempts were made to use S. oneidensis for a mediator-free microbial fuel cell (MFC) that can treat wastewater and produce electricity simultaneously without any synthetic mediators (Kim et al. 2002). The cost of the S. oneidensis based MFC can be reduced and the design simplified compared to MFCs based on bacterial species that are inactive for the transport of electrons and thus need electron transport mediators that shuttle the electrons between microbes and electrodes (Park and Zeikus 2000). In the S. oneidensis based MFC, the electrons are released via catalytic oxidation of organic substrates by S. oneidensis bacteria and transferred to the anode by bacterial nanowires in the anode chamber (Pirbadian et al. 2014; Reguera et al. 2005). The electrons eventually reach the cathode via an external electrical circuit and combine with electron acceptor (oxygen) and the protons that move from the anode chamber to the cathode chamber through a separator; the resulting byproduct is water in the cathode chamber (Bond et al., 2002; Min and Logan 2004). Proton-exchange membranes are widely used as a separator for efficient transport for protons from the anode to the cathode while impeding substrate and oxygen to penetrate. Due to the high cost of these membranes, low cost alternatives such as PVDF-co-HFP (Kumar et al. 2015) and a blend of polybenzimidazole (PBI) and polyvinylpyrrolidone (PVP) (Kumar et al. 2016b) were considered as a separator. Nanomaterial as a nano-filler was also utilized in the blend of a PVDF-co-HFP to increase the efficiency (Kumar et al. 2016a). Shewanella oneidensis is dissimilatory metal-reducing bacteria (DMRB) that can reduce metal compounds. While the anode is engaged in substrate oxidation in the form of wastewater, the cathode can accept electrons produced and catalyze metal oxidation by the DMRB, which can use metals as electron acceptors. Wastewater containing heavy metal such as Co (III) (Huang et al. 2014) and Cr (VI) (Wu et al. 2015) thus can be treated successfully (Wang and Ren 2014) with DMRB. Hence a Shewanella oneidensis based MFC offers potential benefits for environmental sustainability as well as sustainable technology for simultaneous wastewater treatment and electrical power generation (Wu et al. 2018). In this study, we designed a single chamber membraneless bioreactor and harvested energy from the reactor in which electrons were transported from oxidation region to reduction region directly by Shewanella nanowires without an external circuit or a separator.