Analysis of bio-anode performance through electrochemical impedance spectroscopy

In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm− 2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture. In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm− 2. The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 Ω·cm2 and 34 Ω·cm2, respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the Butler–Volmer relationship that needs further exploration.The authors wish to acknowledge funding from the European Union Seventh Framework Programme (FP7/2012-2016) project ‘Bioelectrochemical systems for metal production, recycling, and remediation’ under grant agreement no. 282970. AtH is supported by a NWO VENI grant no. 13631. OS was supported by the French environmental agency ADEME, by the Region Bretagne and by Rennes Metropole when doing the experiments. This work was performed in the cooperation framework of Wetsus, Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is co-funded by the Dutch Ministry of Economic Affairs and Ministry of Infrastructure and Environment, the European Union Regional Development Fund, the Province of Fryslân, and the Northern Netherlands Provinces

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

Starvation combined with constant anode potential triggers intracellular electron storage in electro-active biofilms

The accumulation of electrons in the form of Extracellular Polymeric Substances (EPS) and poly-hydroxyalkanoates (PHA) has been studied in anaerobic processes by adjusting the access of microorganisms to the electron donor and final electron acceptor. In Bio-electrochemical systems (BESs), intermittent anode potential regimes have also recently been used to study electron storage in anodic electro-active biofilms (EABfs), but the effect of electron donor feeding mode on electron storage has not been explored. Therefore, in this study, the accumulation of electrons in the form of EPS and PHA was studied as a function of the operating conditions. EABfs were grown under both constant and intermittent anode potential regimes and fed with acetate (electron donor) continuously or in batch. Confocal Laser Scanning Microscopy (CLSM) and Fourier-Transform Infrared Spectroscopy (FTIR) were used to assess electron storage. The range of Coulombic efficiencies, from 25 to 82%, and the biomass yields, between 10 and 20%, indicate that storage could have been an alternative electron consuming process. From image processing, a 0.92 pixel ratio of poly-hydroxybutyrate (PHB) and amount of cells was found in the batch fed EABf grown under a constant anode potential. This storage was linked to the presence of living Geobacter and shows that energy gain and carbon source starvation were the triggers for intracellular electron storage. The highest EPS content (extracellular storage) was observed in the continuously fed EABf under an intermittent anode potential, showing that constant access to electron donor and intermittent access to the electron acceptor leads to the formation of EPS from the excess energy gained. Tailoring operating conditions can thus steer the microbial community and result in a trained EABf to perform a desired biological conversion, which can be beneficial for a more efficient and optimized BES.</p

Local moisture recycling across the globe

Changes in evaporation over land affect terrestrial precipitation via atmospheric moisture recycling and consequently freshwater availability. Although global moisture recycling at regional and continental scales are relatively well understood, the patterns and drivers of local moisture recycling remain unknown. For the first time, we calculate the local moisture recycling ratio (LMR), defined as the fraction of evaporated moisture that rains out within approximately 50 km from its source, and identify its drivers over land globally. We derive seasonal and annual LMR from multi-year (2008–2017) monthly averaged atmospheric moisture connections at a scale of 0.5° obtained from a Lagrangian atmospheric moisture tracking model. We find that, annually, on average 1.6 % of evaporated moisture returns as rainfall locally, but with large temporal and spatial variability, where LMR peaks in summer and over wet and mountainous regions. We identify wetness, orography, latitude, and convective available potential energy as drivers of LMR, indicating a crucial role for convection. Our results can be used to study impacts of evaporation changes on local precipitation, with widespread implications for, for example, regreening and water management

THE INTEGRATION OF BIOWASTE AND URBAN AGRICULTURE: PROSPECTS AND ISSUES

ABSTRACT Presently, Metropolitan Manila (MM) generates about 6,000 tons of municipal solid wastes per day of which 2,800 tons is estimated to be biodegradable. Despite a legal framework and policy that aims at recycling 25% of the biodegradable wastes, presently (only) 160 tons/d of these biowastes (ca 6%) is source-separated and processed in 22 small-scale composting plants. Evaluation of the performance of 3 of these plants revealed flaws in obtaining compost with the officially required quality standards. A survey among 50 horticultural farmers showed that only 34% of them use organic fertiliser. The main impediments for increased compost application are low expectations about the yields of compost versus inorganic fertilizers, the relatively high price and cumbersome handling of the bulky product. At 25% recycling in MM an agricultural area in the order of 20,000 ha would have to apply municipal biowaste-based compost in quantities of ca 10 tons/ha/yr, which is far more than the agricultural area within the city&apos;s boundaries. Enhancement of the municipal biowaste reuse chain in MM would require synchronous expansion of the markets, the composting and the collection of segregated wastes. In order to develop a vision on chain enhancement a research programme covering Manila and several other South East Asian megacities is proposed. A determined collaboration of the stakeholders involved in the chain, farmers, compost producers, waste generators, waste collectors and waste managers, is seen as a prime prerequisite in the development of this vision

Microbial community structure elucidates performance of Glyceria maxima plant microbial fuel cell

The plant microbial fuel cell (PMFC) is a technology in which living plant roots provide electron donor, via rhizodeposition, to a mixed microbial community to generate electricity in a microbial fuel cell. Analysis and localisation of the microbial community is necessary for gaining insight into the competition for electron donor in a PMFC. This paper characterises the anode–rhizosphere bacterial community of a Glyceria maxima (reed mannagrass) PMFC. Electrochemically active bacteria (EAB) were located on the root surfaces, but they were more abundant colonising the graphite granular electrode. Anaerobic cellulolytic bacteria dominated the area where most of the EAB were found, indicating that the current was probably generated via the hydrolysis of cellulose. Due to the presence of oxygen and nitrate, short-chain fatty acid-utilising denitrifiers were the major competitors for the electron donor. Acetate-utilising methanogens played a minor role in the competition for electron donor, probably due to the availability of graphite granules as electron acceptors

Dataset for 'Reversible fouling by particulate matter from natural seawater reduces RED performance while limiting biofouling'

This dataset contains data collected during experiment on foulant fractionation of seawater in reverse electrodialysis (RED). For explanation of the experimental setup we refer you to the published paper. It is being made public both to act as supplementary data for publication and in order for other researchers to use this data in their own work

Moisture recycling in five different regions with Mediterranean climates around the world

Weather extremes are predicted to be more intense and recurrent in the future because of climate change. Previous studies show that Mediterranean regions around the world are especially vulnerable to extreme events that depend on the hydrological cycle, such as droughts and floods. Land use and land cover changes may enhance these events, as they influence the exchange of moisture and energy between the land surface and atmosphere. To better understand the role of extremes in a future climate, we need to improve our understanding of the impact of climate change on the terrestrial hydrological cycle. Atmospheric transport of moisture is an important element of this cycle as it determines the allocation of evaporated moisture. We are especially interested in the sink-source relations. So, how land contributes to the moisture recycling over land further away, and the origin of the precipitation over, the so-called precipitation-shed. Tuinenburg et al. (2020) recently published a dataset with high-resolution global atmospheric moisture connections from evaporation to precipitation, allowing novel detailed insight. We used this dataset to study temporal variability in atmospheric moisture connections for five different regions with Mediterranean climates. We investigated the dependency of different Mediterranean regions on local and remote moisture sources, and how this dependency varies throughout the year. Large differences in the spatial pattern of moisture recycling over land showed to exist between the Mediterranean regions on the Northern and Southern Hemisphere. Additionally, of all regions, the Mediterranean Basin shows the largest temporal variability. This information is essential to study how local changes in land use and land cover have and will further affect the hydrological cycle in local and remote regions. This helps us to understand how climate extremes could change in the future as a result of land use and land cover changes

Critical Materials Recovery from Solutions and Wastes: Retrospective and Outlook

One of the greatest challenges facing society in the 21st century is providing better living standards to all people while reducing and minimizing the impact of human activities on Earth’s global environment and climate. During the past decade, sustainability has emerged as a unifying framework for addressing the global environmental, economic, and societal challenges facing the world. The Brundtland Commission of the United Nations defined “sustainable development” as “that which meets the needs of the present without compromising the ability of future generations to meet their own needs” (available online at http://www.un-documents.net/ocf-02.htm). Materials are the building blocks and pillars of a sustainable society and global economy. There is a growing realization that the implementation of clean-energy technologies of the 21st century will require large amounts of critical metals including rare-earth elements (REEs), platinum group metals, copper, lithium, gallium, and precious metals (e.g., silver and gold). Significant amounts of phosphorus (P) will also be needed as the world faces the daunting challenge of doubling the amount of food it currently produces in order to feed around 9 billion people by 2050. As a society, we utilize and consume large amounts of minerals, metals, P, and other materials produced by mining with little or no recycling. Thus, our current management and stewardship of Earth’s mineral and metal resources are not sustainable. Increasingly, impaired water (e.g., seawater, brines, and municipal/industrial wastewater) and solid wastes (e.g., discarded consumer products and sludge) are being viewed as alternative sources of critical metals and valuable elements to address global materials availability and supply challenges. Thus, in the next decades, environmental scientists/engineers, business leaders, and policy/ decision makers will be confronted with a new set of exciting opportunities and challenges to advance the viability of critical materials recovery from impaired water and solid wastes. In this special issue of Environmental Science & Technology (ES&T), we highlight recent advances on the recovery of critical/valuable metals and P from “wastes”. Two key goals of this special issue are to (1) provide a retrospective and outlook of the state-of-the-field; and (2) bring into focus crosscutting scientific, technological, and environmental challenges along with corresponding societal and regulatory issues

Maximum thickness of non-buffer limited electro-active biofilms decreases at higher anode potentials

The accumulation of protons in electro-active biofilms (EABfs) has been reported as a critical parameter determining produced currents at the anode since the very beginning of the studies on Bio-electrochemical systems (BESs). Even though the knowledge gained on the influence of this parameter on the produced currents, its influence on EABfs growth is frequently overlooked. In this study, we quantified EABfs thicknesses in real-time and related them to the produced current at three buffer concentrations, two anode potentials and two acetate concentrations. The thickest EABfs (80 μm) and higher produced currents (2.5 A.m−2) were measured when a 50 mM buffer concentration was used. By combining the measured EABfs thicknesses with the pH in the anolyte, a simple model was developed to identify buffer limitations. Buffer limited EABfs with thicknesses of 15 and 42 μm were identified at −0.3 V vs Ag/AgCl when 10 and 50 mM buffer concentrations were used, respectively. At −0.2 V vs Ag/AgCl, the thicknesses of buffer limited EABfs decreased to 13 and 20 μm, respectively. The model also estimated buffer and acetate diffusion rates in EABfs and allowed to determine the boundary between a buffer and acetate limited EABfs. The diffusion rates reported in this study and the definition of the boundary between buffer and acetate limited EABfs provide a powerful tool to avoid limitations, leading to higher produced currents at the anode