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Geobacter sulfurreducens is an electroactive bacterium capable of reducing metal oxides in the environment and electrodes in engineered systems1,2. Geobacter sp. are the keystone organisms in electrogenic biofilms, as their respiration consumes fermentation products produced by other organisms and reduces a terminal electron acceptor e.g. iron oxide or an electrode. To respire extracellular electron acceptors with a wide range of redox potentials, G. sulfurreducens has a complex network of respiratory proteins, many of which are membrane-bound3–5. We have identified intracytoplasmic membrane (ICM) structures in G. sulfurreducens. This ICM is an invagination of the inner membrane that has folded and organized by an unknown mechanism, often but not always located near the tip of a cell. Using confocal microscopy, we can identify that at least half of the cells contain an ICM when grown on low potential anode surfaces, whereas cells grown at higher potential anode surfaces or using fumarate as electron acceptor had significantly lower ICM frequency. 3D models developed from cryo-electron tomograms show the ICM to be a continuous extension of the inner membrane in contact with the cytoplasmic and periplasmic space. The differential abundance of ICM in cells grown under different thermodynamic conditions supports the hypothesis that it is an adaptation to limited energy availability, as an increase in membrane-bound respiratory proteins could increase electron flux. Thus, the ICM provides extra inner-membrane surface to increase the abundance of these proteins. G. sulfurreducens is the first Thermodesulfobacterium or metal-oxide reducer found to produce ICMs.

Light-activated photosystem II (PSII) carries out the critical step of splitting water in photosynthesis. However, PSII is susceptible to light-induced damage. Here, results are presented from a novel microbial electro-photosynthetic system (MEPS) that uses redox mediators in conjunction with an electrode to drive electron transport in live

Geobacter sulfurreducens is a ubiquitous iron reducing bacterium in soils, and in engineered systems it can respire an electrode to produce measurable electric current. Its unique metabolism, heavily dependent on an extensive network of cytochromes, requires a unique cell composition. In this work we used metallomics, cell fraction and elemental analyses, and transcriptomics to study and analyze the cell composition of G. sulfurreducens. Elemental composition studies (C,H,O,N, ash content) showed a high C:O and H:O ratios of approximately 1.7:1 and 0.25:1, indicative of more reduced cell composition that is consistent with a high lipid content. Our study shows that G. sulfurreducens cells have a large amount of iron (2 ± 0.2 μg/gdw) and lipids (32 ± 0.5% dw/dw) and that this composition does not change whether the cells are grown with a soluble or an insoluble electron acceptor. The high iron concentration, higher than similar microorganisms, is attributed to the production of cytochromes that are abundant in transcriptomic analyses in both solid and soluble electron acceptor growth. The unique cell composition of G. sulfurreducens must be considered when growing this microorganism for lab studies and commercial applications.ImportanceGeobacter sulfurreducens is an electroactive microorganism. In nature, it grows on metallic minerals by transferring electrons to them, effectively ‘breathing’ metals. In a manmade system, it respires an electrode to produce an electric current. It has become a model organism for the study of electroactive organisms. There are potential biotechnological applications of an organism that can bridge the gap between biology and electrical signal, and as a ubiquitous iron reducer in soils around the world, G. sulfurreducens and its relatives impact the global iron cycle. We measured the concentrations of metals, macromolecules, and basic elements in G. sulfurreducens to define this organism’s composition. We also used gene expression data to discuss which proteins those metals could be associated with. We found that G. sulfurreducens has a large amount of lipid and iron compared to other bacteria — these observations are important for future microbiologists and biotechnologists working with the organism.

Geobacter sulfurreducensis an electroactive bacterium capable of reducing metal oxides in the environment and electrodes in engineered systems1,2.Geobacter sp. are the keystone organisms in electrogenic biofilms, as their respiration consumes fermentation products produced by other organisms and reduces a terminal electron acceptor e.g. iron oxide or an electrode. To respire extracellular electron acceptors with a wide range of redox potentials,G. sulfurreducenshas a complex network of respiratory proteins, many of which are membrane-bound3–5. We have identified intracytoplasmic membrane (ICM) structures inG. sulfurreducens. This ICM is an invagination of the inner membrane that has folded and organized by an unknown mechanism, often but not always located near the tip of a cell. Using confocal microscopy, we can identify that at least half of the cells contain an ICM when grown on low potential anode surfaces, whereas cells grown at higher potential anode surfaces or using fumarate as electron acceptor had significantly lower ICM frequency. 3D models developed from cryo-electron tomograms show the ICM to be a continuous extension of the inner membrane in contact with the cytoplasmic and periplasmic space. The differential abundance of ICM in cells grown under different thermodynamic conditions supports the hypothesis that it is an adaptation to limited energy availability, as an increase in membrane-bound respiratory proteins could increase electron flux. Thus, the ICM provides extra inner-membrane surface to increase the abundance of these proteins.G. sulfurreducensis the first Thermodesulfobacterium or metal-oxide reducer found to produce ICMs.

Chlorinated solvents are some of the most pervasive pollutants found in groundwater and drinking water sources in the United States (U.S.). In the early 2000s, bioremediation emerged as a novel and effective technology, but was limited by challenges to delivery and transport of nutrients and microbes. Electrokinetic bioremediation (EK-Bio) has since emerged as a promising alternative to solve these limitations, delivering successful results at the lab and pilot scale. EK-Bio can be applied at sites where traditional bioaugmentation, the transformation of pollutants via an added microbial culture, is transport limited. The application of direct current in situ in electrokinetic (EK) remediation facilitates transport of the microbial culture and substrate in the subsurface. Despite this recent surge in interest surrounding EK-Bio, it is not clear how this technology would perform at a site with elevated levels of alternative electron acceptors, another common barrier to successful bioremediation. Our objectives were to use bench scale reactors to 1) determine which reactions and processes would dominate when using EK-BIO to treat TCE contamination at a site with high levels of the alternative electron acceptor sulfate, 2) compare EK-Bio to a traditional bioremediation application without electrokinetics, and 3) understand the effect of EK-Bio on the microbial community under these conditions. Our results showed complete transformation of TCE to ethene and acetylene by EK-Bio, while only 15% of TCE was transformed to cis-DCE and VC via traditional bioaugmentation. In the EK-Bio reactor, the majority of the TCE was converted to acetylene, likely due to its electrochemical reduction at the cathode. EK-Bio out performed traditional methods as it facilitated TCE biotic and abiotic transformation. Next generation sequencing analysis showed the microbial community in the EK-Bio reactor was highly enriched by the bioaugmentation culture, and community structure and diversity were minimally affected by the electrokinetic application. These results demonstrate that EK-Bio is an effective and promising remedy for treating chlorinated solvent contamination at transport limited sites with high concentrations of competing electron acceptors. This combined treatment strategy can be used to extend traditional bioaugmentation to a greater number of polluted sites, restoring more contaminated water systems for beneficial use.

Hydrogen (H

The shift towards distance learning brought forth by the pandemic has highlighted the shortcomings of teaching physical skills at a distance. With the emergence of new augmented and connected mediums, new opportunities arise for transferring physical skills that have resisted traditional documentation methods. However, there lacks a framework that allows tutorial authors to capitalize on a new medium’s unique affordances rather than remediating existing tutorial conventions. Our work analyzes a body of tutorials rendered in various mediums for centering clay on a pottery wheel — a foundational skill that exemplifies the difficulties of physical skill transfer. Through the lens of McLuhan’s “The Medium is the Message” we synthesize a taxonomy of medium conventions and themes derived from analyzing a body of centering tutorials and observation of how a tutorial’s medium affects how learners develop physical skills. We leverage our findings to motivate design recommendations to inform how new mediums can support material practices.

This study investigates the effect of sludge stabilization at high rates on a single-chamber microbial hydrogen peroxide (H2O2) producing cell (sMPPC). Unlike a typical microbial fuel cell operation, the use of the sMPPC focuses on sludge treatment instead of power generation. Two different porous separators between the anode and the cathode, glass fiber (GF) and stitchbond polyester fabric (SPF), as well as two circuit modes, closed and open, were explored. The sMPPC in the open-circuit mode (no current generation) had a COD removal rate of 0.89 g COD per L per day (removal flux of 22 g COD per m−2 d−1) due to only passive oxygen diffused through the air-cathode. The sMPPC in the closed-circuit mode equipped with SPF increased the removal rate up to 2.4 g COD per L per day (loading rate of 5 g COD per L per day). The high removal rate resulted from current production, oxygen diffused through the air-cathode, and H2O2 produced, and was higher than that of a conventional anaerobic digester. This arrangement achieved a 52% VSS removal rate and 1.2 × 105 most probable number per gram solids of fecal coliforms, and the values met two important requirements (pathogen indicators and vector attraction reduction) for class B biosolid production. The microbial community in the sMPPC showed stratification of microorganisms at the anode, supporting its crucial roles in aerobic metabolism as well as anaerobic hydrolysis, fermentation, and anode respiration. We demonstrate for the first time how the sMPPC allows direct sludge stabilization at higher organic loads than traditional anaerobic digesters.

Microbiological conversion of CO2 into biofuels and/or organic industrial feedstock is an excellent carbon-cycling strategy. Here, autotrophic anaerobic bacteria in the membrane biofilm reactor (MBfR) transferred electrons from hydrogen gas (H2 ) to inorganic carbon (IC) and produced organic acids and alcohols. We systematically varied the H2 -delivery, the IC concentration, and the hydraulic retention time in the MBfR. The relative availability of H2 versus IC was the determining factor for enabling microbial chain elongation (MCE). When the H2 :IC mole ratio was high (>2.0 mol H2 /mol C), MCE was an important process, generating medium-chain carboxylates up to octanoate (C8, 9.1 ± 1.3 mM C and 28.1 ± 4.1 mmol C m-2 d-1 ). Conversely, products with two carbons were the only ones present when the H2 :IC ratio was low (

Silicone is a transformative design material found within a variety of emerging HCI practices including shape-changing interfaces, soft robotics, and wearables. However, workflows for designing and fabricating silicone forms require a time-intensive mold-cast-cure pipeline that limits the experiential knowledge that can be gained from working directly with silicone. In this work, we conduct a material-centric exploration of silicone and develop designerly workflows for creating inflatable silicone bladders. We present Siloseam, a creative framework that streamlines a bladder design and fabrication process, collects tacit knowledge involved in recovering from errors, and introduces new workflows that reuse existing molds. A set of exemplar artifacts demonstrates an expanded repertoire of silicone forms that leverage various configurations of airtight seams to create playful, haptic interactions. We discuss the remaining challenges in integrating silicone with a broader range of materials and opportunities for developing designerly workflows for other mold-and-cast processes.

There is an increased interest in finding remedies for contamination in low permeability and advection-limited aquifers. A technology applicable at these sites, electrokinetic-enhanced bioremediation (EK-BIO), combines traditional bioremediation and electrokinetic technologies by applying direct current to transport bioremediation amendments and microbes in situ. The effect of this technology on the native soil microbial community has only been previously investigated at the bench scale. This research explored the influence of EK-BIO on subsurface microbial communities at a field-scale demonstration site. The results showed that, similar to the findings in laboratory studies, alpha diversity decreased and beta diversity differed temporally, based on treatment phase. Enrichments in specific taxa were linked to the bioaugmentation culture and electron donor. Overall, findings from our study, one of the first field-scale investigations of the influence of electrokinetic bioremediation on subsurface microbial communities, are very similar to bench-scale studies on the topic, suggesting good correlation between laboratory and field experiments on EK-BIO and showing that lessons learned at the benchtop are important and relevant to field-scale implementation. KEY POINTS: • Microbial community analysis of field samples validates laboratory study results • Bioaugmentation cultures and electron donors have largest effect on microbial community.

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 Thermincola ferriacetica 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 (EKA) and formal redox potential (E°′) under nonturnover conditions. The EKA and E°′ 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 T. fer...

Typical reactions in bioelectrochemical systems (BESs) promote the phenomenon of the pH split between anode and cathode. The pH split results in an undesirable phenomenon which has stimulated several technological solutions to limit its effects, particularly for energy-producing bioelectrochemical systems (BESs). On the other hand, several applications of energy-consuming BESs exploited the pH split to integrate different operations using the bioelectrochemical reactions. Those additional operations, which are directly related to the electric field generated by the bioelectrochemical interphases, include target products extraction, concentration, and recovery. This review offers a comprehensive overview of the different bioelectrochemical applications in which the pH split is used for the integration of bioelectrochemical reactions with products concentration and recovery. By discussing the phenomenon of the pH split in BESs, this paper presents an alternative view to stimulate new niches of applications for the bioelectrochemical processes.

Microbial peroxide producing cells (MPPCs) are microbial electrochemical cells used to synthesize hydrogen peroxide (H2O2) in the cathode chamber. Catholyte hydraulic retention time (HRT), different catholytes and their concentrations, and a ferrochelating stabilizer are varied in a continuous-flow cathode MPPC to evaluate their impacts on performance. Using NaCl catholytes, the MPPC produced as high as 3.1 ± 0.37 g H2O2 L−1 at a 4-h HRT with as little as 1.13 W-h g−1 H2O2 energy input and with up to 57 g Lcathode−1 d−1 at a 1-h HRT. For these conditions, the H2O2 production rate provides more than 3 times the H2O2 required for disinfection or micro-pollutant removal while using 5–25% of the power used in conventional H2O2 production processes. Attempts to improve H2O2-production by adding weak acid buffers or H2O2-stabilizing EDTA fail for different reasons. The addition of the ferrochelator EDTA to prevent H2O2 auto-decay deteriorates MPPC performance, because EDTA diffuses from the cathode to the anode, inhibiting iron utilization by anode-respiring bacteria. Weak acid buffers failed to reduce cathode concentration overpotentials. Buffering catholytes lowered the H2O2 yield due to large pH gradients at the cathode chamber entrance, causing the formation of H2O instead of H2O2 or O2 re-formation from H2O2 auto-decay.

Titanium-dioxide (TiO2) semi-conductors are promising for microbial-fuel-cell anodes, because they can accelerate the biodegradation of refractory organic pollutants while recovering electrical current. To make the coupling of TiO2 photocatalysis and biodegradation a success, the anode’s biofilm must be protected from damage from reactive-oxygen species generated by photocatalysis. In this work, we first realized a photocatalytic bioanode using N-doped TiO2 coated on macroporous carbon-foam that accumulated biofilm inside. Photocatalysis occurred on the outer surface, while bacteria were protected inside the foam matrix; this is a unique manifestation of intimately coupled photobiocatalysis (ICPB). Experiments focused on degradation of 4-chlorophenol (4-CP) and electrochemical characterization of the ICPB-anode. The illuminated photo-anode, non-photocatalytic bio-anode, and ICPB-anode achieved ∼10%, ∼28%, and ∼41% 4-CP degradation efficiency, respectively; clearly, the ICPB anode achieved the best performance for 4-CP removal. The corresponding mineralization efficiency of the ICPB-anode also was the highest, and current generation by the ICPB-anode was 50% greater than that of a bio-anode. Cyclic voltammetry showed that photocatalyst and biofilm had to be present together to achieve high current density, and it also suggested that the electron-transport activity of c-type cytochromes of anode-respiring bacteria played an essential role in the transport of electrons.

Summary An enriched mixed culture of thermophilic (60°C) bacteria was assembled for the purpose of using cellulose to produce current in thermophilic microbial electrolysis cells (MECs). Cellulose was fermented into sugars and acids before being consumed by anode‐respiring bacteria (ARB) for current production. Current densities (j) were sustained at 6.5 ± 0.2 A m−2 in duplicate reactors with a coulombic efficiency (CE) of 84 ± 0.3%, a coulombic recovery (CR) of 54 ± 11% and without production of CH 4. Low‐scan rate cyclic voltammetry (LSCV) revealed a mid‐point potential (E ka) of −0.17 V versus SHE. Pyrosequencing analysis of the V4 hypervariable region of 16S rDNA and scanning electron microscopy present an enriched thermophilic microbial community consisting mainly of the phylum Firmicutes with the Thermoanaerobacter (46 ± 13%) and Thermincola (28 ± 14%) genera occupying the biofilm anode in high relative abundance and Tepidmicrobium (38 ± 6%) and Moorella (11 ± 8%) genera present in high relative abundance in the bulk medium. The Thermoanaerobacter (15 ± 16%) and Brevibacillus (21 ± 30%) genera were also present in the bulk medium; however, their relative abundance varied by reactor. This study indicates that thermophilic consortia can obtain high CE and CR, while sustaining high current densities from cellulose in MECs.

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 signifi...

Microbial fuel cells (MFCs) can treat organic compounds from domestic wastewater without aeration, but an additional procedure is required to remove nitrogen. This study developed a flat-panel air-cathode MFC (FA-MFC) that was comprised of five MFC units connected in series and operated to remove organic and nitrogen compounds from domestic wastewater with a short hydraulic retention time (HRT) of 2.5 h. During eight months of operation, the removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) increased, reaching 85% and 94%, respectively, and the effluent COD and TN concentrations were 20.7 ± 2.5 mg/L and 1.7 ± 0.1 mg/L, respectively. The greatest removals of COD and TN were in the first and second unit (0.62 kg-N/m 3 /d of TN removal rate). The FA-MFC system allowed simultaneous removals of COD and TN from domestic wastewater, although it led to minimal power output (6.3 W/m 3 in the first unit). Because any abiotic ammonia loss was not found under the supplied potential of ∼1.1 V at a short HRT of 30 min, the biological nitrogen removal was thought as a dominant mechanism for TN removal in the FA-MFCs. Microbial community analysis revealed that, near the cathode, Nitrosomonas -like strains contributed to nitrification and Nitratireductor -like strains led to denitrification. Acidovorax -like strains, known for their metabolic diversity, were ubiquitous and appeared to contribute to organics and nitrogen removal in anode and cathode biofilms. This study provides proof of concept that the FA-MFC system has a promise for energy sustainable wastewater treatment.

When anode-respiring bacteria (ARB) respire electrons to an anode in microbial electrochemical cells (MXCs), they harvest only a small amount of free energy. This means that ARB must have a high substrate-oxidation rate coupled with a high ratio of electrons used for respiration compared to total electrons removed by substrate utilization. It also means that they are especially susceptible to inhibition that slows anode respiration or lowers their biomass yield. Using several electrochemical techniques, we show that a relatively high total ammonium-nitrogen (TAN) concentration (2.2 g TAN/L) induced significant stress on the ARB biofilms, lowering their true yield and forcing the ARB to boost the ratio of electrons respired per electrons consumed from the substrate. In particular, a higher respiration rate, measured as current density (j), was associated with slower growth and a lower net yield, compared to an ARB biofilm grown with a lower ammonium concentration (0.2 g TAN/L). Further increases in influent TAN (to 3 and then to 4.4 g TAN/L) caused nearly complete inhibition of anode respiration. However, the ARB could recover from high-TAN inhibition after a shift of the MXC's feed to 0.2 g TAN/L. In summary, ARB biofilms were inhibited by a high TAN concentration, but could divert more electron flow toward anode respiration with modest inhibition and recover when severe inhibition was relieved. Biotechnol. Bioeng. 2017;114: 1151–1159. © 2017 Wiley Periodicals, Inc.

Anaerobic digestion (AD) is a mature anaerobic biotechnology that plays a significant role in wastewater treatment in terms of solids reduction and energy recovery as methane. An alternative anaerobic platform, the microbial electrochemical cell (MXC), has shown similar results to AD in terms of solids reduction, but electron recovery as electrical current has been poor, in large part because of undesired production of methane. The aim of this study was to maximize Coulombic recovery (CR) and minimize methanogenesis by controlling the anode hydraulic retention time (HRT) and pH in a flat-plate microbial electrolysis cell (MEC) fed semi-continuously with primary sludge (PS). Although the PS-fed MEC had ∼60% solids reduction for all HRTs tested (6 to 15 days), the HRT had a strong impact on current density and CR. The maximum current density was >2 A m−2 for 6 and 9 day HRTs, while CR was the highest (34%) for a 9 day HRT. A relatively high pH (∼8.1) in the anode chamber also led to an increase in CR by suppressing methanogenesis. Being the first report of long-term MEC operation with PS, this study demonstrates that CR and sludge treatment can be improved by increasing pH and decreasing HRT in a flat-plate MEC.

We assessed the effects of pH and buffer concentration on current production and growth of biofilms of Thermincola ferriacetica – a thermophilic, Gram-positive, anode-respiring bacterium (ARB) – grown on anodes poised at a potential of − 0.06 V vs. SHE in microbial electrolysis cells (MECs) at 60 °C. T. ferriacetica generated current in the pH range of 5.2 to 8.3 with acetate as the electron donor and 50 mM bicarbonate buffer. Maximum current density was reduced by ~ 80% at pH 5.2 and ~ 14% at 7.0 compared to pH 8.3. Increasing bicarbonate buffer concentrations from 10 mM to 100 mM resulted in an increase in the current density by 40 ± 6%, from 6.8 ± 1.1 to 11.2 ± 2.7 A m− 2, supporting that more buffer alleviated pH depression within T. ferriacetica biofilms. Confocal laser scanning microscopy (CLSM) images indicated that higher bicarbonate buffer concentrations resulted in larger live biofilm thicknesses: from 68 ± 20 μm at 10 mM bicarbonate to > 150 μm at 100 mM, supporting that buffer availability was a strong influence on biofilm thickness. In comparison to mesophilic Geobacter sulfurreducens biofilms, the faster transport rates at higher temperature and the ability to grow at relatively lower pH allowed T. ferriacetica to produce higher current densities with lower buffer concentrations.

Hybrid practices are emerging that integrate creative materials like paint, clay, and cloth with intangible immaterials like computation, electricity, and heat. This work aims to expand the design potential of immaterial elements by transforming them into manipulatable, observable and intuitive materials. We explore one such immaterial, electric heat, and develop a maker-friendly fabrication pipeline and crafting support tool that allows users to experientially compose resistive heaters that generate heat spatially and temporally. These heaters are then used to couple heat and thermoreactive materials in a class of artifacts we term Thermoreactive Composites (TrCs). In a formal user study, we observe how designing fabrication workflows along dimensions of composability and perceivability better matches the working styles of material practitioners without domain knowledge of electronics. Through exemplar artifacts, we demonstrate the potential of heat as a creative material and discuss implications for immaterials used within creative practices.

Tacit knowledge is a type of knowledge often existing in one's subconscious or embodied in muscle memory. Such knowledge is pervasive in creative practices yet remains difficult to observe or codify. To better understand tacit knowledge, we introduce a design method that leverages time-series data (interaction logs, physical sensor, and biosignal data) to isolate unique actions and behaviors between groups of users. This method is enacted in Eluent, a tool that distills hundreds of hours of dense activity data using an activity segmentation algorithm into a codebook - a set of distinct, characteristic sequences that comprise an activity. The results are made visually parsable in a representation we term process chromatograms that aid with 1) highlighting distinct periods of activity in creative sessions, 2) identifying distinct groups of users, and 3) characterizing periods of activity. We demonstrate the value of our method through a study of tacit process within computational notebooks and discuss ways process chromatograms can act as a knowledge mining technique, an evaluation metric, and a design-informing visualization.

An exciting, expanding palette of hybrid materials is emerging that can be programmed to actuate by a range of external and internal stimuli. However, there exists a dichotomy between the physicality of the actuators and the intangible computational signal that is used to program them. For material practitioners, this lack of physical cues limits their ability to engage in a "conversation with materials" (CwM). This paper presents a creative workstation for supporting this epistemological style by bringing a stronger physicality to the computational signal and balance the conversation between physical and digital actors. The station utilizes a streaming architecture to distribute control across multiple devices and leverage the rich spatial cognition that a physical space affords. Through a formal user study, we characterize the actuation design practice supported by the CwM workstation and discuss opportunities for tangible interfaces to hybrid materials.

The aim of this study was to investigate pH effect on stratification of bacterial community in cathodic biofilm of the microbial fuel cell (MFC) under alkaline conditions. A single-chamber MFC with air-cathode was operated with 0.8 g/L maltodextrin and bicarbonate buffer solutions under pH values of 8.5, 9.5, and 10.5, respectively. The cathodic biofilms were characterized by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), confocal laser scanning microscopy (CLSM), freezing microtome and high-throughput sequencing analysis on bacterial communities, respectively. Results showed that the maximum power densities in the MFC increased with the pH values and reached 1221 ± 96 mW/m2 at pH = 10.5 during ∼30 d of operation. With different pH values, the composition and relative abundance of bacterial community significantly changed in the bottom (0–50 μm), middle (50–100 μm), and top (100–150 μm) layers of the cathodic biofilm. With pH = 10.5, aerobic bacteria accounted for 12%, 13%, and 34% of the bacterial community in the top, middle, and bottom layers, respectively. The amount of anaerobic bacteria in the top and middle layers (i.e., 52%, and 50% of the bacterial community, respectively) was higher than that in the bottom layer (22%). The distribution of aerobic and anaerobic bacteria showed a “valley-peak” structure within the layers. The high CO32− concentration facilitates the hydroxyl transfer and the neutralization in the anode of the MFC under high alkali conditions. The results from this study should be useful to develop new catalyst and cathode in the MFC.

Anaerobic digestion treatment of brewer’s spent yeast (SY) is a viable option for bioenergy capture. The biochemical methane potential (BMP) assay was performed with three different samples (SY1, SY2, and SY3) and SY1 dilutions (75, 50, and 25 % on a v/v basis). Gompertz-equation parameters denoted slow degradability of SY1 with methane production rates of 14.59–4.63 mL/day and lag phases of 10.72–19.7 days. Performance and kinetic parameters were obtained with the Gompertz equation and the first-order hydrolysis model with SY2 and SY3 diluted 25 % and SY1 50 %. A SY2 25 % gave a 17 % of TCOD conversion to methane as well as shorter lag phase (

One of the main performance challenges in microbial electrochemical cells (MXCs) is the low voltage efficiency in comparison to other fuel and electrolysis cells. In this study, we aimed to improve the design and operation of microbial electrolysis cells (MECs) to achieve current densities >10 A m −2 with reduced applied voltages, using a thorough analytical framework involving electrochemical techniques such as chronoamperometry, voltammetry and electrochemical impedance spectroscopy. We developed a design that allows high surface area for the anode using carbon fibers, but without creating a large distance between the anode and the cathode ( 10 A m −2 remained 0.3 V of Nernstian concentration overpotential. We showed how by adding CO 2 to the cathode, this overpotential could be reduced to negligible. We also tested two different cathode materials – stainless steel and nickel – to compare the cathode activation overpotentials. Overall, through our design and operation improvements, we were able to reduce the applied voltages from 1.1 to ∼0.85 V, at 10 A m −2 . Our results also provide important guidelines for further optimizations of MXCs.

The energy value of the organic matter in landfill leachate can be captured with a microbial electrolysis cell (MEC), which oxidizes organic compounds at an anode and generates H2 gas at a cathode. Due to the low biodegradability of the organic matter in landfill leachate, MEC performance typically is characterized by low current density (j), coulombic efficiency (CE), coulombic recovery (CR), and organic-matter removal. Here, we evaluated whether or not Fenton oxidation of landfill leachate could enhance MEC performance compared to control MEC fed with raw leachate. Fenton pre-treatment significantly improved the leachate's biodegradability, leading to much higher MEC performance: 52 ± 10% BOD5 removal, 29 ± 3% CE, and 1.42 ± 0.27 A m−2 as j, compared to 3 ± 0.3% BOD5 removal, 1.8 ± 0.5% CE, and 0.11 ± 0.06 A m−2 as j for the raw leachate. This higher performance of the MEC fed treated leachate was associated with an ∼5-fold increase in the biofilm accumulation compared to the control MEC. Acetate-spike experiments in the control MEC revealed that inhibition of fermentation, not anode respiration, was the main factor causing poor COD removal and current density with raw leachate. The microbial community in the biofilm anode with treated leachate was enriched in anode-respiring Geobacteraceae: ∼40% of the sequences, compared to only ∼20% for MEC fed with raw leachate. Bacterioidetes, Firmicutes, Spirochaetes, and Actinobacteria were among the other abundant phyla of fermenting bacteria in the biofilm anode fed with treated leachate. This study provides proof-of-concept that Fenton oxidation of landfill leachate enhanced MEC performance by accelerating fermentation, allowing more biofilm accumulation, and establishing a syntrophic relationship between fermenters and anode-respiring bacteria (ARB).

Failure, whether it be "complete-and-utter" or "a minor setback", occurs in a variety of different creative practices, yet how it is perceived, handled, and recovered from is a lesser explored design space. Failing to address these perceptions of failure can have psychological repercussions, discourage users from continuing a practice, and form cultural stigma such as those associated with STEM fields. However, mediating practices to develop a culture of resiliency and perseverance is key to sustaining a (lifelong) practice and reshaping pedagogical strategies. In this work, we outline the design space of "guardians", or elements of a creative practice that mitigate the psychological effects of failure. Through contextual inquiry, we contribute an inventory of failure-mitigation strategies from a variety of creative disciplines. We synthesize guidelines for the design of new guardians and present a preliminary exploration of guardians for the lasercutting practice -- effigies and test tags.

Practices are emerging which blend both physical and computational techniques and materials. This thesis contributes a framework for understanding how to compose these hybrid elements into rich, reflective new media practices that expand the aesthetic repertoire and facilitate the adoption, sharing, and teaching of hybrid techniques.

The aim of this study was to investigate the combination of two technologies - pulsed electric field (PEF) pre-treatment and semi-continuous pre-fermentation of primary sludge (PS) - to produce volatile fatty acids (VFAs) as the electron donor for microbial electrolysis cells (MECs). Pre-fermentation with a 3-day solids retention time (SRT) led to the maximum generation of VFAs, with or without pretreatment of the PS through pulsed-electric-fields (PEF). PEF treatment before fermentation enhanced the accumulation of the preferred VFA, acetate, by 2.6-fold. Correspondingly, MEC anodes fed with centrate from 3-day pre-fermentation of PEF-treated PS had a maximum current density ∼3.1 A/m(2), which was 2.4-fold greater than the control pre-fermented centrate. Over the full duration of batch MEC experiments, using pre-fermented centrate led to successful performance in terms of Coulombic efficiency (95%), Coulombic recovery (80%), and COD-removal efficiency (85%).

When a mixed-culture microbial electrolysis cell (MEC) is fed with a fermentable substrate, such as glucose, a significant fraction of the substrate’s electrons ends up as methane (CH4) through hydrogenotrophic methanogenesis, an outcome that is undesired. Here, we show that free ammonia-nitrogen (FAN, which is NH3) altered the glucose fermentation pathways in batch MECs, minimizing the production of H2, the “fuel” for hydrogenotrophic methanogens. Consequently, the Coulombic efficiency (CE) increased: 57% for 0.02 g of FAN/L of fed-MEC, compared to 76% for 0.18 g of FAN/L of fed-MECs and 62% for 0.37 g of FAN/L of fed-MECs. Increasing the FAN concentration was associated with the accumulation of higher organic acids (e.g., lactate, iso-butyrate, and propionate), which was accompanied by increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae), lactic-acid production (Lactobacillales), and syntrophic acetate oxidation (Clostridiaceae). Thus, the micr...

Medium-chain fatty acids (MCFA) are important biofuel precursors. Carbon monoxide (CO) is a sustainable electron and carbon donor for fatty acid elongation, since it is metabolized to MCFA precursors, it is toxic to most methanogens, and it is a waste product generated in the gasification of waste biomass. The main objective of this work was to determine if the inhibition of methanogenesis through the continuous addition of CO would lead to increased acetate or MCFA production during fermentation of ethanol. The effects of CO partial pressures (PCO ; 0.08-0.3 atm) on methanogenesis, fatty acids production, and the associated microbial communities were studied in batch cultures fed with CO and ethanol. Methanogenesis was partially inhibited at PCO ≥ 0.11 atm. This inhibition led to increased acetate production during the first phase of fermentation (0-19 days). However, a second addition of ethanol (day 19) triggered MCFA production only at PCO ≥ 0.11 atm, which probably occurred through the elongation of acetate with CO-derived ethanol and H2 :CO2 . Accordingly, during the second phase of fermentation (days 20-36), the distribution of electrons to acetate decreased at higher PCO , while electrons channeled to MCFA increased. Most probably, Acetobacterium, Clostridium, Pleomorphomonas, Oscillospira, and Blautia metabolized CO to H2 :CO2 , ethanol and/or fatty acids, while Peptostreptococcaceae, Lachnospiraceae, and other Clostridiales utilized these metabolites, along with the provided ethanol, for MCFA production. These results are important for biotechnological systems where fatty acids production are preferred over methanogenesis, such as in chain elongation systems and microbial fuel cells.

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 (H

© 2017 ACM. Recent digital fabrication tools have enabled new form-giving using a wide range of physical materials. However, light as a first class creative material has been largely ignored within the design of our electronic objects. Our work expands the illumination design space by treating light as a physical material. We introduce a digital design tool that simulates and visualizes physical light interactions with a variety of materials for creating custom luminaires. We further develop a computational design and fabrication process for creating custom secondary optics elements (SOEs), which provides additional handles for users to physically shape and redirect light to compose, fill, and evenly diffuse planar and volumetric geometries. Through a workshop study with novice electronic designers, we show how incorporating physical techniques to shape light alters how users view the role and function of LEDs and electronics. We produce example pieces that showcase how our approach expands the electronics aesthetic and discuss how viewing light as material can engender novel, expressive artifacts. Copyright is held by the owner/author(s).

The paper report a unique biologically inspired electro-chemical reference electrode based on regulating the breathing of bacteria. Some species of bacteria, named exoelectrogen, have the capability of extracellular electron transfer, which is the transfer of electrons to a solid electron acceptor outside their membrane. We find that it sets the solid electron acceptor at a stable electrochemical potential, which can be used as reference electrode. We pattern thin film platinum as electron acceptor and grow exoelectrogenic biofilm on it. By performing colorimetric analysis of the individual ions in the anolyte solution, we confirmed that the potential of the reference electrode, ∼ −0.5 V versus the Ag/AgCl in 3M NaCl, arises from the electrochemical potential of the reaction. The biologically-inspired reference electrode demonstrates a stability of ±4.2 mV/day for two days. It is integrated in a MEMS microbial fuel cell (MFC) to characterize its electrochemical characteristics.

A microbial fuel cell (MFC) is a bio-electrochemical converter that can extract electricity from biomass by the catabolic reaction of microorganisms. This work demonstrates the impact of a small characteristic length in a Geobacteraceae-enriched, micro-scale microbial fuel cell (MFC) that achieved a high power density. The small characteristic length increased the surface-area-to-volume ratio (SAV) and the mass transfer coefficient. Together, these factors made it possible for the 100-µL MFC to achieve among the highest areal and volumetric power densities - 83 μW/cm(2) and 3300 μW/cm(3), respectively - among all micro-scale MFCs to date. Furthermore, the measured Coulombic efficiency (CE) was at least 79%, which is 2.5-fold greater than the previously reported maximum CE in micro-scale MFCs. The ability to improve these performance metrics may make micro-scale MFCs attractive for supplying power in sub-100 µW applications, especially in remote or hazardous conditions, where conventional powering units are hard to establish.

Biofilms of the anode-respiring bacterium Geobacter sulfurreducens (G. sulfurreducens) demonstrate dynamic potential-dependent changes between two electron transport pathways that are used selectively depending on the anode potential. Electrochemical impedance spectroscopy (EIS) measurements suggest that these pathways (both n=1), with midpoint potentials of -0.155 (± 0.005) and -0.095 (± 0.003) V versus standard hydrogen electrode, are not additive within the biofilm, but are preferentially used depending on the anode potential. Potential step voltammetry and cyclic voltammetry (CV) confirmed rapid changes between the two pathways in minutes when the anode potential is changed. We confirm that the electrochemical response observed in a slow-scan-rate CV (∼1 mV s(-1) ) is often composed of at least the two pathways characterized. Thus, beyond understanding the electron transport pathways in G. sulfurreducens, this study also has implications on the interpretation of previously collected and future potential-dependent datasets.

We investigated the role of green sulfur bacteria inlight-responsive electricity generation in microbial electrochemical cells (MXCs). We operated MXCs containing either monocultures or defined cocultures of previously enriched phototrophic Chlorobium and anode-respiring Geobacter under anaerobic conditions in the absence of electron donor. Monoculture control MXCs containing Geobacter or Chlorobium neither responded to light nor produced current, respectively. Instead, light-responsive current generation occurred only in coculture MXCs. Current increased above background levels only in the dark and declined slowly over 96 h. This pattern suggested that Chlorobium exhausted intracellular glycogen reserves via dark fermentation to supply an electron donor, presumably acetate, to Geobacter. With medium containing sulfide as the sole photosynthetic electron donor, current generation had a similar and reproducible negative light response. To investigate whether this metabolic interaction also occurred without an electrode, we performed coculture experiments in batch serum bottles. In this setup, sulfide served as the sole electron donor, whose oxidation by Chlorobium was required to provide S0 as the electron acceptor to Geobacter. Copies of Geobacter 16S rDNA increased approximately 14-fold in batch bottle cocultures containing sulfide compared to those lacking sulfide, and did not decline after termination of sulfide feeding. These results suggest that products of both photosynthesis and dark fermentation by Chlorobium were sufficient both to yield an electrochemical response by Geobacter biofilms, and to promote Geobacter growthin batch cocultures. Our work expands upon the fusion of MXCs with coculture techniques and reinforces the utility of microbial electrochemistry for sensitive, real-time monitoring of microbial interactions in which a metabolic intermediate can be converted to electrical current. Biotechnol. Bioeng. 2014;111: 223–231. © 2013 Wiley Periodicals, Inc.