Bioelectrochemical Systems for water streams toxicity monitoring and remediation.

BioElectrochemical Systems (BES) are an emerging technology based on the innate capability of a special group of microorganisms able to transfer electrons in and out of the cell, using solid state electrode as electron donor or electron acceptor. BES research efforts are addressed to a variety of applications, ranging from wastewater treatment and power source in remote area to bioremediation and chemicals production. This thesis is focused on the development, characterization and application of different electroactive biocatalysts for water streams pollution monitoring and remediation. In particular, one approach was based on environmental mixed community bioanodes to sensor water toxicity. The other one was based on pure culture biocathode for water sulfate removal. As described in Chapter 4, mixed-community Bioanodes, originating from freshwater-sediment samples, were developed and deeply characterized, before testing their biosensing capacity. Different acclimation methods and inoculum enrichment strategies were investigated, in order to achieve an efficient and fast developing anodic biofilm. Microbial Fuel Cell (MFC) start-up time was independent of the external resistance applied, while it was influenced by the inoculum pre-enrichment step. A 47 ohm conditioning combined with a General anaerobic enrichment method resulted in a fast MFC start-up time of 5 days and in high values of current density and maximum power point. The deep electrochemical analysis, through 3-electrode Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV), as well as the biological investigation, through fluorescence imaging and microbial community analysis, permitted to understand the better performances achieved by Generally-enriched Bioanodes, compared to the selective enrichment method. In Chapter 5, the sensing ability of Generally-enriched river-sediment Bioanodes towards several pollutants was investigated. BES biosensing experiments were performed in low cost membrane-less single MFCs with open-air cathode. The semi-continuous operation mode of the MFC-based biosensors allowed to obtain high stability of non-toxic current profile, even in non-controlled temperature conditions. The environmental electroactive consortium showed to be sensitive towards different type of toxicants. A linear response was observed with respect to glutaraldehyde within the range of 5-1000 ppm. Moreover, the bioanodes exhibited a full recovery of activity even after the highest concentration of glutaraldehyde, allowing to test the same biosensors towards nickel (II) (2, 20 and 60 mg L-1) and then chromium (III) (2 and 20 mg L-1). According to these findings, the usage of environmental anodic consortium as sensing element in MFCs demonstrated satisfactory versatility and reusability. To effectively analyze the biosensors response and to save energy during data transmission, a novel data analysis methodology was proposed. These results open the door for the application of river-sediment bioanodes as early-warning systems for freshwater on-line toxicity monitoring. Moving from biosensing to bioremediation application, in Chapter 6, a novel electrotrophic microorganism, Desulfosporosinus orientis, was characterized inside the cathode of a H-type BES reactors. This chapter summarizes the results obtained during my six-month research exchange period in the RosenbaumLab at the Institute of Applied Microbiology-RWTH Aachen University (DE). D. orientis is an anaerobic Gram-negative, sulfate-reducing and acetogenic bacterium, which is able to grow chemoautotrophically on H2 and CO2. BES experiments were carried out at different applied potentials in order to investigate the effect of cathodic potential on D. orientis’ bioelectrochemical ability of sulfate reduction and organic acids production, using CO2 gas as substrate. The first test was performed at -0.5V, while the second and the third runs were carried out with a start-up condition of -0.9V vs Ag/AgCl, followed by an electrocatalytic phase of -0.5 or -0.55V vs Ag/AgCl. The reactors with a start-up phase of -0.5V vs Ag/AgCl exhibited contrasting results related to D. orientis’ current consumption ability and maintained a quite constant concentration of sulfate. The start-up phases at -0.9V were characterized by high current consumption, high planktonic biomass growth, high acetate production and high sulfate reduction rate. Conversely, the electrocatalytic phases exhibited constant levels of acetate and sulfate, with a decrease in optical density. These findings pointed at a H2-mediated electron uptake capability of D. orientis. Overall, the highest sulfate reduction rate was achieved during the highest current consumption phase, indicating bioelectrochemical sulfate removal ability. On contrary, the acetate production occurred always during the first days of start-up phase, independently of the applied cathodic potential and the current consumption. D. orientis’ biocathodes exhibited a maximum sulfate removal rate (0.24±0.01 g L-1day-1) higher than the majority of mixed-community sulfate-reducing biocathodes reported in literature for this purpose. These preliminary results highlighted the great potential of D. orientis as biocatalyst for wastewater sulfate removal application, with simultaneous CO2 fixation.