The use of microbial fuel cells to generate electrical current is increasingly being seen as a viable source of renewable energy production In this Progress article, Bruce Logan highlights recent advances in our understanding of the mechanisms used by exoelectrogenic bacteria to generate electrical current and the important factors to consider in microbial fuel cell design There has been an increase in recent years in the number of reports of microorganisms that can generate electrical current in microbial fuel cells Although many new strains have been identified, few strains individually produce power densities as high as strains from mixed communities Enriched anodic biofilms have generated power densities as high as 69 W per m2 (projected anode area), and therefore are approaching theoretical limits To understand bacterial versatility in mechanisms used for current generation, this Progress article explores the underlying reasons for exocellular electron transfer, including cellular respiration and possible cell–cell communication

Exoelectrogenic bacteria that power microbial fuel cells

A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production.

A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy.

Waste biomass is a cheap and relatively abundant source of electrons for microbes capable of producing electrical current outside the cell. Rapidly developing microbial electrochemical technologies, such as microbial fuel cells, are part of a diverse platform of future sustainable energy and chemical production technologies. We review the key advances that will enable the use of exoelectrogenic microorganisms to generate biofuels, hydrogen gas, methane, and other valuable inorganic and organic chemicals. Moreover, we examine the key challenges for implementing these systems and compare them to similar renewable energy technologies. Although commercial development is already underway in several different applications, ranging from wastewater treatment to industrial chemical production, further research is needed regarding efficiency, scalability, system lifetimes, and reliability.

http://science.sciencemag.org/content/sci/337/6095/686.full.pdf

Conversion of wastes into bioelectricity and chemicals by using microbial electrochemical technologies.

In seeking greater sustainability in water resources management, wastewater is now being considered more as a resource than as a waste-a resource for water, for plant nutrients, and for energy. Energy, the primary focus of this article, can be obtained from wastewater's organic as well as from its thermal content. Also, using wastewater's nitrogen and P nutrients for plant fertilization, rather than wasting them, helps offset the high energy cost of producing synthetic fertilizers. Microbial fuel cells offer potential for direct biological conversion of wastewater's organic materials into electricity, although significant improvements are needed for this process to be competitive with anaerobic biological conversion of wastewater organics into biogas, a renewable fuel used in electricity generation. Newer membrane processes coupled with complete anaerobic treatment of wastewater offer the potential for wastewater treatment to become a net generator of energy, rather than the large energy consumer that it is today.

Domestic Wastewater Treatment as a Net Energy Producer–Can This be Achieved?

Microbial fuel cell (MFC) research is a rapidly evolving field that lacks established terminology and methods for the analysis of system performance. This makes it difficult for researchers to compare devices on an equivalent basis. The construction and analysis of MFCs requires knowledge of different scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. Describing MFC systems therefore involves an understanding of these different scientific and engineering principles. In this paper, we provide a review of the different materials and methods used to construct MFCs, techniques used to analyze system performance, and recommendations on what information to include in MFC studies and the most useful ways to present results.

Microbial Fuel Cells: Methodology and Technology†

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.

https://pubs.acs.org/doi/pdf/10.1021/acs.est.5b03694

Critical Materials Recovery from Solutions and Wastes: Retrospective and Outlook

Abstract. 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 is relatively well understood, the patterns of local moisture recycling and the main variables that impact it remain unknown. We calculate the local moisture recycling ratio (LMR) as the fraction of evaporated moisture that precipitates within a distance of 0.5∘ (typically 50 km) of its source, identify variables that correlate with it over land globally, and study its model dependency. We derive the seasonal and annual LMR using a 10-year climatology (2008–2017) of monthly averaged atmospheric moisture connections at a scale of 0.5∘ obtained from a Lagrangian atmospheric moisture tracking model. We find that, annually, an average of 1.7 % (SD of 1.1 %) of evaporated moisture returns as precipitation locally, although with large temporal and spatial variability, and the LMR peaks in summer and over wet and mountainous regions. Our results show that wetness, orography, latitude, convective available potential energy, wind speed, and total cloud cover correlate clearly with the LMR, indicating that wet regions with little wind and strong ascending air are particularly favourable for a high LMR. Finally, we find that spatial patterns of local recycling are consistent between different models, yet the magnitude of recycling varies. Our results can be used to study the impacts of evaporation changes on local precipitation, with implications for, for example, regreening and water management.


/pdf/local-moisture-recycling-across-the-globe-q9y6awwl.pdf

Local moisture recycling across the globe

/pdf/maximum-thickness-of-non-buffer-limited-electro-active-5mwm78m1.pdf

Bert Hamelers

Papers

Microbial Fuel Cells: Methodology and Technology†

Critical Materials Recovery from Solutions and Wastes: Retrospective and Outlook

Local moisture recycling across the globe

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

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