Addressing the low power generation of anodic biocatalysts is pertinent to the advancement of microbial fuel cell technology. While Propionibacterium freudenreichii ssp. shermanii has shown potential as a biocatalyst, its incomplete consumption of the anodic substrate is a persistent issue. This research aims to optimize substrate consumption to increase power generation using Propionibacterium freudenreichii ssp. shermanii as a biocatalyst. The effect of coculturing Geobacter sulfurreducens with Propionibacterium freudenreichii ssp. shermanii was investigated. The cocatalyst and pure culture performance was tested in an air-cathode microbial fuel cell. Geobacter sulfurreducens produced the highest maximum power density among the experimental cases. Power density produced by Propionibacterium freudenreichii ssp. shermanii was improved in the air-cathode design compared to previous experiments performed in an H-type design. The novel cocatalyst was shown to produce electricity, however a full characterization to elucidate the contribution to power generation by each microbe would be desirable to investigate.

Microbial fuel cell (MFC) technology is a renewable energy source that employs microorganisms as biocatalysts to degrade substrates into electrons and protons, and then transfer the electrons to the anode electrode. Electron transfer rates by microorganisms depend on many factors as well as on their diverse electron transfer mechanisms. The present study compared cytochromes, flavoproteins, electron transfer complexes, redoxins and other extracellular membrane proteins that have direct involvement in electron transfer mechanisms in Escherichia coli str. K-12 MG1655, Rhodopseudomonas pulastris DX-1 and Shewanella oneidensis MR-1. Escherichia coli str. The results showed that K-12 MG1655 had a more diverse range of extracellular proteins for electron transfer mechanisms compared to Rhodopseudomonas pulastris DX-1 and Shewanella oneidensis MR-1. Escherichia coli str. K-12 MG1655 expressed more flavoproteins, redoxin and electron transfer complex related proteins that had direct involvement in electron transfer mechanisms compared to two other bacterial species indicating that it may be able to transfer more electrons when employed in MFC technique. Escherichia coli str. K-12 MG1655 expressed 16 cytochromes, 9 flavoproteins, 6 redoxins, 6 electron transport complexes, 1 hypothetical and 1 oxidoreductase proteins. On the other hand, Rhodopseudomonas pulastris DX-1 and Shewanella oneidensis MR-1 expressed 26 and 35 cytochromes proteins. But these two bacterial species expressed less flavoproteins and redoxin related proteins and they didn’t express any electron transport complexes or hypothetical and oxidoreductase related proteins for electron transfer. STRING and SMART results suggested that the identified proteins transferred electrons either by connecting with other types of identified proteins in the constructed gene network or independently by taking part in oxidation-reduction reaction, metal ion reduction reaction or by their FMN binding activities.

Manganese compounds have a high potential for treating wastewater, both for utilizing its oxidation, flocculation ability and catalyst ability in anaerobic nitrification. The promising use of manganese compounds (such as permanganate and manganese dioxide) is regarded as an effective method of treating organic compounds in wastewater from municipal and industrial wastewater. Now it is newly realized possibilities to combine manganese compounds with Microbial Fuel Cell technology. Aiming at reusing the biomass in anaerobic digested sludge for degrading organic pollutants and simultaneously recovering electric energy, Single-chamber Microbial Fuel Cell (SMFC) system was developed and investigated during the main experimental part. Considering the electricity generation rate and characteristics of cathode, MnO2 was used as the reactant on the cathode electrode; meanwhile, the substrate types in anode compartment also were investigated and then extra sodium acetate was added to investigate the power generation performance. Two parts of the research were carried out during the whole project. The chemical treatment part was mainly designed to find out the best dosage of KMnO4 in flocculation when concurrent reacted with magnesium and calcium compounds when treating reject wastewater from digester at Hammarby Sjöstadsverk. The other part was studied to see whether it is possible to improve electricity generation by degrading organic pollutants when MnO2 was used as a cathodic reactant in sediment microbial fuel cell which consisted of anaerobic digested sludge from UASB.

Microbial fuel cell (MFC) has become one of the energy-sustainable technologies for wastewater treatment purpose in the recent years. It combines wastewater treatment and electricity generation together so as to achieve energy balance. By inoculating microorganism in the anode chamber and filling catholyte in the cathode chamber, and also with the help of a proton exchange membrane (PEM) between them, the MFC can transfer protons and produce power. Microbial desalination cells (MDC) are based on MFC’s structure and can fulfill desalination function by the addition of a middle chamber and anion exchange membrane (AEM). This study focuses on ammonium removal and electricity generation in MDC system. Mainly two types of liquid were tested, a solution of Hjorthorn Salt and filtrated supernatant. The experiments were performed at Hammarby Sjöstad research station and laboratory of Land and Water Resources department, Stockholm. It consists of a preparation stage, a MFC stage and a MDC stage. Until the end of MFC stage, biofilm in the anode chamber had been formed and matured. After that, solutions of different initial concentrations (1.5, 2.5, 5, 15 g/L) of Hjorthorn Salt and also filtrated supernatant have been tested. Ammonium removal degree can be obtained by measuring the initial concentration and cycle end concentration, while electricity generation ability can be calculated by voltage data which was continuously recorded by a multimeter. Results showed that this MDC system is suitable for ammonium removal in both of Hjorthorn Salt solutions and supernatant. The removal degrees in Hjorthorn Salt solution at desalination chamber were 53.1%, 52.7%, 60.34%, and 27.25% corresponding to initial NH4+ concentration of 340.7, 376, 376 and 2220 mg/L. The ammonium removal degrees in the supernatant were up to 53.4% and 43.7% under 21 and 71 hours operation, respectively. In power production aspect, MDC produced maximum voltage when potassium permanganate was used in the cathode chamber (217 mV). The power density in solutions of Hjorthorn Salt was relative low (46.73 - 86.61 mW/m3), but in the supernatant it showed a good performance, up to 227.7 and 190.8 mW/m3.

Wastewater treatment is energy intensive, with modern wastewater treatment processes consuming 0.6 kWh/m3 of water treated, half of which is required for aeration. Considering that wastewater contains approximately 2 kWh/m3 of energy and represents a reliable alternative water resource, capturing part of this energy and reclaiming the water would offset or even eliminate energy requirements for wastewater treatment and provide a means to augment traditional water supplies. Microbial electrochemical technology is a novel technology platform that uses bacteria capable of producing an electric current outside of the cell to recover energy from wastewater. These bacteria do not require oxygen to respire but instead use an insoluble electrode as their terminal electron acceptor. Two types of microbial electrochemical technologies were investigated in this dissertation: 1) a microbial fuel cell that produces electricity; and 2) a microbial electrolysis cell that produces hydrogen with the addition of external power. On their own, microbial electrochemical technologies do not achieve sufficiently high treatment levels. Innovative approaches that integrate microbial electrochemical technologies with emerging and established membrane-based treatment processes may improve the overall extent of wastewater treatment and reclaim treated water. Forward osmosis is an emerging low-energy membrane-based technology for seawater desalination. In forward osmosis water is transported across a semipermeable membrane driven by an osmotic gradient. The microbial osmotic fuel cell described in this dissertation integrates a microbial fuel cell with forward osmosis to achieve wastewater treatment, energy recovery and partial desalination. This system required no aeration and generated more power than conventional microbial fuel cells using ion exchange membranes by minimizing electrochemical losses. Membrane bioreactors incorporate semipermeable membranes within a biological wastewater treatment process. The anaerobic electrochemical membrane bioreactor described here integrates a microbial electrolysis cell with a membrane bioreactor using conductive hollow fiber membrane to produce hydrogen gas, treat wastewater and reclaim treated water. The energy recovered as hydrogen gas in this system was sufficient to offset all the electrical energy requirements for operation. The findings from these studies significantly improve the prospects for simultaneous wastewater treatment, energy recovery and water reclamation in a single reactor but challenges such as membrane biofouling and conversion of hydrogen to methane by methanogenesis require further study.

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Sediment microbial fuel cell (SMFC) is a special type of microbial fuel cells that can be deployed in a natural water body for energy production and contaminant removal. This MS project aims to explore whether it will be viable to apply SMFCs for wastewater treatment. Experimental SMFCs were studied in several configurations and operational modes for organic removal, nitrate reduction, and energy recovery. When treating an artificial secondary effluent for nitrate removal, the SMFC could remove 44% of the nitrate, higher than that without electricity generation. The enhanced removal was attributed to the supply of electrons to nitrate reduction in the aqueous phase through oxidizing the organics in the sediment. The lack of a proper separator between the anode and the cathode led to the failure of the SMFC when treating an artificial raw wastewater. Ion exchange membranes were incorporated into the MFCs that were installed in a lab-scale open water pond (150 L in volume). Such a system achieved 100% COD removal and more than 75% removal of ammonium nitrogen. However, denitrification remained as a challenge because of a lack of anoxic zone. To reduce the cost of the cathode catalysts, a polymer-based carbon cloth was investigated and exhibited better performance than bare carbon cloth. The results of this MS project have demonstrated that SMFCs in the absence of a proper separator cannot be applied for wastewater treatment. A membrane-based MFC system integrated with open pond may function as a wastewater treatment system, though nitrogen removal efficiency must be improved. / Master of Science