Water Recovery from Bioreactor Mixed Liquors Using Forward Osmosis with Polyelectrolyte Draw Solutions

This paper reports on the use of forward osmosis (FO) with polyelectrolyte draw solutions to recover water from bioreactor mixed liquors. The work was motivated by the need for new regenerative water purification technologies to enable long-duration space missions. Osmotic membrane bioreactors may be an option for water and nutrient recovery in space if they can attain high water flux and reverse solute flux selectivity (RSFS), which quantifies the mass of permeated water per mass of draw solute that has diffused from the draw solution into a bioreactor. Water flux was measured in a direct flow system using wastewater from a municipal wastewater treatment plant and draw solutions prepared with two polyelectrolytes at different concentrations. The direct flow tests displayed a high initial flux (>10 L/m2/h) that decreased rapidly as solids accumulated on the feed side of the membrane. A test with deionized water as the feed revealed a small mass of polyelectrolyte crossover from the draw solution to the feed, yielding an RSFS of 80. Crossflow filtration experiments demonstrated that steady state flux above 2 L/m2·h could be maintained for 70 h following an initial flux decline due to the formation of a foulant cake layer. This study established that FO could be feasible for regenerative water purification from bioreactors. By utilizing a polyelectrolyte draw solute with high RSFS, we expect to overcome the need for draw solute replenishment. This would be a major step towards sustainable operation in long-duration space missions

H₂O₂ Production in Microbial Electrochemical Cells Fed with Primary Sludge

We developed an energy-efficient, flat-plate, dual-chambered microbial peroxide producing cell (MPPC) as an anaerobic energy-conversion technology for converting primary sludge (PS) at the anode and producing hydrogen peroxide (H₂O₂) at the cathode. We operated the MPPC with a 9 day hydraulic retention time in the anode. A maximum H₂O₂ concentration of ∼230 mg/L was achieved in 6 h of batch cathode operation. This is the first demonstration of H₂O₂ production using PS in an MPPC, and the energy requirement for H₂O₂ production was low (∼0.87 kWh/kg H₂O₂) compared to previous studies using real wastewaters. The H₂O₂ gradually decayed with time due to the diffusion of H₂O₂-scavenging carbonate ions from the anode. We compared the anodic performance with a H₂-producing microbial electrolysis cell (MEC). Both cells (MEC and MPPC) achieved ∼30% Coulombic recovery. While similar microbial communities were present in the anode suspension and anode biofilm for the two operating modes, aerobic bacteria were significant only on the side of the anode facing the membrane in the MPPC. Coupled with a lack of methane production in the MPPC, the presence of aerobic bacteria suggests that H₂O₂ diffusion to the anode side caused inhibition of methanogens, which led to the decrease in chemical oxygen demand removal. Thus, the Coulombic efficiency was ∼16% higher in the MPPC than in the MEC (64% versus 48%, respectively)

Anode Biofilms of <i>Geoalkalibacter ferrihydriticus</i> Exhibit Electrochemical Signatures of Multiple Electron Transport Pathways

Thriving under alkaliphilic conditions, <i>Geoalkalibacter ferrihydriticus</i> (<i>Glk. ferrihydriticus</i>) provides new applications in treating alkaline waste streams as well as a possible new model organism for microbial electrochemistry. We investigated the electrochemical response of biofilms of the alkaliphilic anode-respiring bacterium (ARB) <i>Glk. ferrihydriticus</i> voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. We observed there to be at least four dominant electron transfer pathways, with their contribution to the overall current produced dependent on the set anode potential. These pathways appear to be manifested at midpoint potentials of approximately −0.14 V, −0.2 V, −0.24 V, and −0.27 V vs standard hydrogen electrode. The individual contributions of the pathways change upon equilibration from a set anode potential to another anode potential. Additionally, the contribution of each pathway to the overall current produced is reversible when the anode potential is changed back to the original set potential. The pathways involved in anode respiration in <i>Glk. ferrihydriticus</i> biofilms follow a similar, but more complicated, pattern as compared to those in the model ARB, <i>Geobacter sulfurreducens</i>. This greater diversity of electron transport pathways in <i>Glk. ferrihydriticus</i> could be related to its wider metabolic capability (e.g., higher pH and larger set of possible substrates, among others)

Kinetic, Electrochemical, and Microscopic Characterization of the Thermophilic, Anode-Respiring Bacterium <i>Thermincola ferriacetica</i>

<i>Thermincola ferriacetica</i> is a recently isolated thermophilic, dissimilatory Fe­(III)-reducing, Gram-positive bacterium with capability to generate electrical current via anode respiration. Our goals were to determine the maximum rates of anode respiration by <i>T. ferriacetica</i> and to perform a detailed microscopic and electrochemical characterization of the biofilm anode. <i>T. ferriacetica</i> DSM 14005 was grown at 60 °C on graphite-rod anodes poised at −0.06 V (vs) SHE in duplicate microbial electrolysis cells (MECs). The cultures grew rapidly until they achieved a sustained current density of 7–8 A m^–2 with only 10 mM bicarbonate buffer and an average Coulombic Efficiency (CE) of 93%. Cyclic voltammetry performed at maximum current density revealed a Nernst–Monod response with a half saturation potential (<i>E</i>_KA) of −0.127 V (vs) SHE. Confocal microscopy images revealed a thick layer of actively respiring cells of <i>T. ferriacetica</i> (∼38 μm), which is the first documentation for a gram positive anode respiring bacterium (ARB). Scanning electron microscopy showed a well-developed biofilm with a very dense network of extracellular appendages similar to <i>Geobacter</i> biofilms. The high current densities, a thick biofilm (∼38 μm) with multiple layers of active cells, and Nernst–Monod behavior support extracellular electron transfer (EET) through a solid conductive matrix – the first such observation for Gram-positive bacteria. Operating with a controlled anode potential enabled us to grow <i>T. ferriacetica</i> that can use a solid conductive matrix resulting in high current densities that are promising for MXC applications

Kinetic, Electrochemical, and Microscopic Characterization of the Thermophilic, Anode-Respiring Bacterium <i>Thermincola ferriacetica</i>

<i>Thermincola ferriacetica</i> is a recently isolated thermophilic, dissimilatory Fe­(III)-reducing, Gram-positive bacterium with capability to generate electrical current via anode respiration. Our goals were to determine the maximum rates of anode respiration by <i>T. ferriacetica</i> and to perform a detailed microscopic and electrochemical characterization of the biofilm anode. <i>T. ferriacetica</i> DSM 14005 was grown at 60 °C on graphite-rod anodes poised at −0.06 V (vs) SHE in duplicate microbial electrolysis cells (MECs). The cultures grew rapidly until they achieved a sustained current density of 7–8 A m^–2 with only 10 mM bicarbonate buffer and an average Coulombic Efficiency (CE) of 93%. Cyclic voltammetry performed at maximum current density revealed a Nernst–Monod response with a half saturation potential (<i>E</i>_KA) of −0.127 V (vs) SHE. Confocal microscopy images revealed a thick layer of actively respiring cells of <i>T. ferriacetica</i> (∼38 μm), which is the first documentation for a gram positive anode respiring bacterium (ARB). Scanning electron microscopy showed a well-developed biofilm with a very dense network of extracellular appendages similar to <i>Geobacter</i> biofilms. The high current densities, a thick biofilm (∼38 μm) with multiple layers of active cells, and Nernst–Monod behavior support extracellular electron transfer (EET) through a solid conductive matrix – the first such observation for Gram-positive bacteria. Operating with a controlled anode potential enabled us to grow <i>T. ferriacetica</i> that can use a solid conductive matrix resulting in high current densities that are promising for MXC applications

pH Dependency in Anode Biofilms of <i>Thermincola ferriacetica</i> Suggests a Proton-Dependent Electrochemical Response

Monitoring the electrochemical response of anode respiring bacteria (ARB) helps elucidate the fundamental processes of anode respiration and their rate limitations. Understanding these limitations provides insights on how ARB create the complex interfacing of biochemical metabolic processes with insoluble electron acceptors and electronics. In this study, anode biofilms of the thermophilic (60 °C) Gram-positive ARB <i>Thermincola ferriacetica</i> were studied to determine the presence of a proton-dependent electron transfer response. The effects of pH, the presence of an electron donor (acetate), and biofilm growth were varied to determine their influence on the electrochemical midpoint potential (<i>E</i>_KA) and formal redox potential (<i>E</i>°′) under nonturnover conditions. The <i>E</i>_KA and <i>E</i>°′ are associated with an enzymatic process within ARB’s metabolism that controls the rate and energetic state of their respiration. Results for all conditions indicate that pH was the major contributor to altering the energetics of <i>T. ferriacetica</i> anode biofilms. Electrochemical responses measured in the absence of an electron donor and with a minimal proton gradient within the anode biofilms resulted in a 48 ± 7 mV/pH unit shift in the <i>E</i>°′, suggesting a proton-dependent rate-limiting process. Given the limited energy available for anode respiration (<200 mV when using acetate as electron donor), our results provide a new perspective in understanding proton-transport limitations in ARB biofilms, one in which ARB are thermodynamically limited by pH gradients. Since the anode biofilms of all ARB that perform direct extracellular electron transfer (EET) investigated thus far exhibit an <i>n</i> = 1 Nernstian behavior, and because this behavior is affected by changes in pH, we hypothesize that the Nernstian response is associated with membrane proteins responsible for proton translocation. Finally, this study shows that the <i>E</i>_KA and <i>E</i>°′ are a function of pH within the physiological range of ARB, and thus, given the significant effect pH has on this parameter, we recommend reporting the <i>E</i>_KA and <i>E</i>°′ of ARB biofilms at a specific bulk pH

Bacterial composition at the class level as determined by 454 pyrosequencing of the V2-V3 region of the 16S rRNA gene.

<p>The outer pie charts (A–C) represent the relative abundance of select classes in the Cuzdrioara uncontaminated soil, (B) Carolina uncontaminated sediment, and (C) Parris Island contaminated sediment. The inner pie charts (A'–C') show the five most abundant classes in the respective soil/sediment-free enrichment cultures, ZARA-10, LINA-09, and ISLA-08. The classified taxa presented contributed to at least 1% of the total relative abundance and are organized in alphabetical order.</p