Hydrogen oxidizing bacteria are capable of removing orthophosphate to ultra-low concentrations in a fed batch reactor configuration

This paper proposes the use of hydrogen oxidizing bacteria (HOB) for the removal of orthophosphate from surface water as treatment step to prevent cyanobacterial blooms. To be effective as an orthophosphate removal strategy, an efficient transfer of hydrogen to the HOB is essential. A trickling filter was selected for this purpose. Using this system, a removal rate of 11.32 +/- 0.43 mg PO4-3-P/L.d was achieved. The HOB biomass, developed on the trickling filter, is composed of 1.25% phosphorus on dry matter, which suggests that the orthophosphate removal principle is based on HOB growth. Cyanobacterial growth assays of the untreated and treated water showed that Synechocystis sp was only able to grow in the untreated water. Orthophosphate was removed to average residual values of 0.008 mg/L. In this proof of principle study, it is shown that HOB are able to remove orthophosphate from water to concentrations that prevent cyanobacterial growth

Opportunities for visual techniques to determine characteristics and limitations of electro-active biofilms

Optimization of bio-electrochemical systems (BESs) relies on a better understanding of electro-active biofilms (EABfs). These microbial communities are studied with a range of techniques, including electrochemical, visual and chemical techniques. Even though each of these techniques provides very valuable and wide-ranging information about EABfs, such as performance, morphology and biofilm composition, they are often destructive. Therefore, the information obtained from EABfs development and characterization studies are limited to a single characterization of EABfs and often limited to one time point that determines the end of the experiment. Despite being scarcer and not as commonly reported as destructive techniques, non-destructive visual techniques can be used to supplement EABfs characterization by adding in-situ information of EABfs functioning and its development throughout time. This opens the door to EABfs monitoring studies that can complement the information obtained with destructive techniques. In this review, we provide an overview of visual techniques and discuss the opportunities for combination with the established electrochemical techniques to study EABfs. By providing an overview of suitable visual techniques and discussing practical examples of combination of visual with electrochemical methods, this review aims at serving as a source of inspiration for future studies in the field of BESs

Considerations for application of granular activated carbon as capacitive bioanode in bioelectrochemical systems

In the last decades, the research in Microbial Fuel Cells (MFCs) has expanded from electricity production and wastewater treatment to remediation technologies, chemicals production and low power applications. More recently, capacitors have been implemented to boost the power output of these systems when applied as wastewater treatment technology. Specifically, the use of granular capacitive materials (e.g. activated carbon granules) as bioanodes has opened up new opportunities for reactor designs and upscaling of the technology. One of the main features of these systems is that charge and discharge processes can be separated, which offers multiple advantages over more conventional reactor types. In this manuscript, we discuss several aspects to consider for the application of capacitive granules as bioanodes in MFCs and other bioelectrochemical systems, as well as the recent advances that have been made in applying these granules in various reactor systems. Similarly, we discuss the granule properties that are key to determine system operation and performance, and show that biofilm growth is highly dependent on the efficiency of discharge.</p

Quantification of charge carriers and acetate diffusion lengths in intermittent electro-active biofilms using Electrochemical Impedance Spectroscopy

Intermittent anode potential regimes have been used to increase the concentration of charge carriers in electro-active biofilms (EABfs). Even though this increased number of carriers is typically correlated to higher current densities, estimating the concentration of charge carriers in EABfs and linking it to measured current density has never been done. In this study, Electrochemical Impedance Spectroscopy (EIS) and Optical Coherence Tomography (OCT) were used to estimate charge carriers and to study mass transfer limitations in intermittently polarized anodic EABfs. Intermittent potential steps of 20, 60, and 300 s were applied and EABf equilibration times were measured. These times were in the order of 10 s and correlated to the diffusion times obtained from EIS. Acetate consumption rates 100 times faster than the diffusion time of acetate into the EABfs were also estimated with EIS, indicating that current was diffusion limited. Using the capacitance and considering the measured volume of EABf, concentrations of charge carriers ranging from 0.05 molcharge carriers m−3EABf at current densities of 1 A m−2 up to 0.2 molcharge carriers m−3EABf at current densities higher than 2 A m−2 were calculated. This study shows that EIS can be used to study developing EABfs in a non-destructive way and in real-time.</p

Quantification of charge carriers and acetate diffusion lengths in intermittent electro-active biofilms using Electrochemical Impedance Spectroscopy

Intermittent anode potential regimes have been used to increase the concentration of charge carriers in electro-active biofilms (EABfs). Even though this increased number of carriers is typically correlated to higher current densities, estimating the concentration of charge carriers in EABfs and linking it to measured current density has never been done. In this study, Electrochemical Impedance Spectroscopy (EIS) and Optical Coherence Tomography (OCT) were used to estimate charge carriers and to study mass transfer limitations in intermittently polarized anodic EABfs. Intermittent potential steps of 20, 60, and 300 s were applied and EABf equilibration times were measured. These times were in the order of 10 s and correlated to the diffusion times obtained from EIS. Acetate consumption rates 100 times faster than the diffusion time of acetate into the EABfs were also estimated with EIS, indicating that current was diffusion limited. Using the capacitance and considering the measured volume of EABf, concentrations of charge carriers ranging from 0.05 molcharge carriers m−3EABf at current densities of 1 A m−2 up to 0.2 molcharge carriers m−3EABf at current densities higher than 2 A m−2 were calculated. This study shows that EIS can be used to study developing EABfs in a non-destructive way and in real-time.</p

Real-time monitoring of biofilm thickness allows for determination of acetate limitations in bio-anodes

Several studies have reported that current produced by electro-active bacteria (EAB) is dependent on anode potential and substrate concentration. However, information about the relation between biofilm growth and current density is scarce. In this study, biofilm thickness was monitored in-situ and this relation explored at three anode potentials and three acetate concentrations. The highest current densities of 3.7 A·m−2 were obtained for biofilms thinner than 40 μm, even though thicknesses up to 88 μm were measured. Fick's law was used to estimate the acetate penetration depth in the biofilm, acetate diffusion rates in the biofilm, and specific acetate utilization rates. A maximum biofilm thickness of a non-acetate limited biofilm of 55 μm and an acetate diffusion rate of 2.68 × 10−10 m2·s−1 were estimated at −0.2 V vs Ag/AgCl. The results provide information on the target biofilm thickness for which no acetate limitations occur and provide data for modeling works with bio-anodes

Quantification of charge carriers and acetate diffusion lengths in intermittent electro-active biofilms using Electrochemical Impedance Spectroscopy

Intermittent anode potential regimes have been used to increase the concentration of charge carriers in electro-active biofilms (EABfs). Even though this increased number of carriers is typically correlated to higher current densities, estimating the concentration of charge carriers in EABfs and linking it to measured current density has never been done. In this study, Electrochemical Impedance Spectroscopy (EIS) and Optical Coherence Tomography (OCT) were used to estimate charge carriers and to study mass transfer limitations in intermittently polarized anodic EABfs. Intermittent potential steps of 20, 60, and 300 s were applied and EABf equilibration times were measured. These times were in the order of 10 s and correlated to the diffusion times obtained from EIS. Acetate consumption rates 100 times faster than the diffusion time of acetate into the EABfs were also estimated with EIS, indicating that current was diffusion limited. Using the capacitance and considering the measured volume of EABf, concentrations of charge carriers ranging from 0.05 molcharge carriers m−3EABf at current densities of 1 A m−2 up to 0.2 molcharge carriers m−3EABf at current densities higher than 2 A m−2 were calculated. This study shows that EIS can be used to study developing EABfs in a non-destructive way and in real-time.</p

Quantification of charge carriers and acetate diffusion lengths in intermittent electro-active biofilms using Electrochemical Impedance Spectroscopy

Intermittent anode potential regimes have been used to increase the concentration of charge carriers in electro-active biofilms (EABfs). Even though this increased number of carriers is typically correlated to higher current densities, estimating the concentration of charge carriers in EABfs and linking it to measured current density has never been done. In this study, Electrochemical Impedance Spectroscopy (EIS) and Optical Coherence Tomography (OCT) were used to estimate charge carriers and to study mass transfer limitations in intermittently polarized anodic EABfs. Intermittent potential steps of 20, 60, and 300 s were applied and EABf equilibration times were measured. These times were in the order of 10 s and correlated to the diffusion times obtained from EIS. Acetate consumption rates 100 times faster than the diffusion time of acetate into the EABfs were also estimated with EIS, indicating that current was diffusion limited. Using the capacitance and considering the measured volume of EABf, concentrations of charge carriers ranging from 0.05 molcharge carriers m−3EABf at current densities of 1 A m−2 up to 0.2 molcharge carriers m−3EABf at current densities higher than 2 A m−2 were calculated. This study shows that EIS can be used to study developing EABfs in a non-destructive way and in real-time.</p

Methane-Dependent Extracellular Electron Transfer at the Bioanode by the Anaerobic Archaeal Methanotroph “Candidatus Methanoperedens”

Anaerobic methanotrophic (ANME) archaea have recently been reported to be capable of using insoluble extracellular electron acceptors via extracellular electron transfer (EET). In this study, we investigated EET by a microbial community dominated by “Candidatus Methanoperedens” archaea at the anode of a bioelectrochemical system (BES) poised at 0 V vs. standard hydrogen electrode (SHE), in this way measuring current as a direct proxy of EET by this community. After inoculation of the BES, the maximum current density was 274 mA m(–2) (stable current up to 39 mA m(–2)). Concomitant conversion of (13)CH(4) into (13)CO(2) demonstrated that current production was methane-dependent, with 38% of the current attributed directly to methane supply. Based on the current production and methane uptake in a closed system, the Coulombic efficiency was about 17%. Polarization curves demonstrated that the current was limited by microbial activity at potentials above 0 V. The metatranscriptome of the inoculum was mined for the expression of c-type cytochromes potentially used for EET, which led to the identification of several multiheme c-type cytochrome-encoding genes among the most abundant transcripts in “Ca. Methanoperedens.” Our study provides strong indications of EET in ANME archaea and describes a system in which ANME-mediated EET can be investigated under laboratory conditions, which provides new research opportunities for mechanistic studies and possibly the generation of axenic ANME cultures

Safeguarding the microbial water quality from source to tap

Anthropogenic activities and climate change can deteriorate the freshwater quality and stress its availability. This stress can, in turn, have an impact on the biostability of drinking water. Up to now, the microbiological quality of drinking water has been maintained through the selection of high-quality water sources allied to the use of disinfectants and the removal of organic carbon. But as freshwater becomes richer in other nutrients, strategies used so far may not suffice to keep a steady and high-quality supply of drinking water in the future. This article readdresses the discussion on drinking water biostability. We need to reframe the concept as a dynamic equilibrium that considers the available nutrients and energy sources (potential for growth) relative to the abundance and composition of the bacterial community (potential to consume the available resources)