Microbial electrochemical systems (MESs) use microorganisms to covert the chemical energy stored in biodegradable materials to direct electric current and chemicals. Compared to traditional ...treatment-focused, energy-intensive environmental technologies, this emerging technology offers a new and transformative solution for integrated waste treatment and energy and resource recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. All MESs share one common principle in the anode chamber, in which biodegradable substrates, such as waste materials, are oxidized and generate electrical current. In contrast, a great variety of applications have been developed by utilizing this in situ current, such as direct power generation (microbial fuel cells, MFCs), chemical production (microbial electrolysis cells, MECs; microbial electrosynthesis, MES), or water desalination (microbial desalination cells, MDCs). Different from previous reviews that either focus on one function or a specific application aspect, this article provides a comprehensive and quantitative review of all the different functions or system constructions with different acronyms developed so far from the MES platform and summarizes nearly 50 corresponding systems to date. It also provides discussions on the future development of this promising yet early-stage technology.
Metal contaminated wastewater posts great health and environmental concerns, but it also provides opportunities for precious metal recovery, which may potentially make treatment processes more ...cost-effective and sustainable. Conventional metal recovery technologies include physical, chemical and biological methods, but they are generally energy and chemical intensive. The recent development of bioelectrochemical technology provides a new approach for efficient metal recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. While dozens of recent studies demonstrated the feasibility of the bioelectrochemical metal recovery concept, the mechanisms have been different and confusing. This study provides a review that summarizes and discusses the different fundamental mechanisms of metal conversion, with the aim of facilitating the scientific understanding and technology development. While the general approach of bioelectrochemical metal recovery is using metals as the electron acceptor in the cathode chamber and organic waste as the electron donor in the anode chamber, there are so far four mechanisms that have been reported: (1) direct metal recovery using abiotic cathodes; (2) metal recovery using abiotic cathodes supplemented by external power sources; (3) metal conversion using bio-cathodes; and (4) metal conversion using bio-cathodes supplemented by external power sources.
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•Reviews the new bioelectrochemical technology for metal recovery from wastewater.•Categorizes the four different mechanisms in bioelectrochemical metal recovery.•Discusses the potentials and challenges of this new metal recovery approach.
Wood-based biochars were used as microbial fuel cell electrodes to significantly reduce cost and carbon footprint. The biochar was made using forestry residue (BCc) and compressed milling residue ...(BCp). Side-by-side comparison show the specific area of BCp (469.9m(2)g(-1)) and BCc (428.6cm(2)g(-1)) is lower than granular activated carbon (GAC) (1247.8m(2)g(-1)) but higher than graphite granule (GG) (0.44m(2)g(-1)). Both biochars showed power outputs of 532±18mWm(-2) (BCp) and 457±20mWm(-2) (BCc), comparable with GAC (674±10mWm(-2)) and GG (566±5mWm(-2)). However, lower material expenses made their power output cost 17-35US$W(-1), 90% cheaper than GAC (402US$W(-1)) or GG (392US$W(-1)). Biochar from waste also reduced the energy and carbon footprint associated with electrode manufacturing and the disposal of which could have additional agronomic benefits.
The microbial fuel cell (MFC) technology offers sustainable solutions for distributed power systems and energy positive wastewater treatment, but the generation of practically usable power from MFCs ...remains a major challenge for system scale up and application. Commonly used external resistors will not harvest any usable energy, so energy-harvesting circuits are needed for real world applications. This review summarizes, explains, and discusses the different energy harvesting methods, components, and systems that can extract and condition the MFC energy for direct utilization. This study aims to assist environmental scientists and engineers to gain fundamental understandings of these electronic systems and algorithms, and it also offers research directions and insights on how to overcome the barriers, so the technology can be further advanced and applied in larger scale.
Exceptional points are singularities of open systems, and among their many remarkable properties, they provide a way to enhance the responsivity of sensors. Here we show that the improved ...responsivity of a laser gyroscope caused by operation near an exceptional point is precisely compensated by increasing laser noise. The noise, of fundamental origin, is enhanced because the laser mode spectrum loses the oft-assumed property of orthogonality. This occurs as system eigenvectors coalesce near the exceptional point and a bi-orthogonal analysis confirms experimental observations. While the results do not preclude other possible advantages of the exceptional-point-enhanced responsivity, they do show that the fundamental sensitivity limit of the gyroscope is not improved through this form of operation. Besides being important to the physics of microcavities and non-Hermitian photonics, these results help clarify fundamental sensitivity limits in a specific class of exceptional-point sensor.
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•We analyse the scarcity-weighted fossil fuel footprint of China at the provincial level.•A scarcity evaluation indicator is introduced to reflect relative scarcity of fossil fuel ...flows.•Interregional export is a major driver of fossil fuel depletion in less-developed regions.•Our study can help Chinese regions to identify fossil fuel supply risk.
Supply risks and shortages of fossil fuels are major challenges to the sustainable development of countries. In response to this challenge, the 12th main goal of the Sustainable Development Goals emphasizes the importance of sustainable consumption and production patterns for resource (including fossil fuels) sustainability. However, for China, the world's largest energy consumer, the availability and criticality of fossil fuels to economic development have not been studied at sub-national scales. Understanding these can help fossil fuel management and the implementation of policies in different regions. This study is the first to analyse the scarcity-weighted fossil fuel footprint in China at the provincial level for 2012 using an environmentally extended multi-regional input-output model and a newly proposed scarcity evaluation indicator. Using scarcity-weighted indicators allows us to identify supply insecurities that are not revealed when focusing on fossil fuel extraction. The scarcity-weighted fossil fuel indicators identify new critical regions such as Hunan and Hubei. We also find that interprovincial export is a major driver of fossil fuel depletion in less-developed regions (e.g., 83% for Shanxi). This study can help regions in China identify fossil fuel supply risks from the viewpoint of their natural capital endowment and resource depletion in relation to final demand. More importantly, the research findings provide a valuable reference for policymakers when reassessing sustainability not only for fossil fuels but also for other natural resources at multiple scales within and beyond China.
Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance. To transfer these capabilities from the ...laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence. Here, we bridge conventional semiconductor lasers and coherent optical systems using CMOS-foundry-fabricated microresonators with a high Q factor of over 260 million and finesse over 42,000. A five-orders-of-magnitude noise reduction in the pump laser is demonstrated, enabling a frequency noise of 0.2 Hz2 Hz−1 to be achieved in an electrically pumped integrated laser, with a corresponding short-term linewidth of 1.2 Hz. Moreover, the same configuration is shown to relieve the dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms. The simultaneous realization of this high Q factor, highly coherent lasers and frequency combs using foundry-based technologies paves the way for volume manufacturing of a wide range of coherent optical systems.Using CMOS-ready ultra-high-Q microresonators, a highly coherent electrically pumped integrated laser with frequency noise of 0.2 Hz2 Hz−1, corresponding to a short-term linewidth of 1.2 Hz, is demonstrated. The device configuration is also found to relieve the dispersion requirements for microcomb generation that have limited certain nonlinear platforms.
The increasing awareness of the energy–environment nexus is compelling the development of technologies that reduce environmental impacts during energy production as well as energy consumption during ...environmental remediation. Countries spend billions in pollution cleanup projects, and new technologies with low energy and chemical consumption are needed for sustainable remediation practice. This perspective review provides a comprehensive summary on the mechanisms of the new bioelectrochemical system (BES) platform technology for efficient and low cost remediation, including petroleum hydrocarbons, chlorinated solvents, perchlorate, azo dyes, and metals, and it also discusses the potential new uses of BES approach for some emerging contaminants remediation, such as CO2 in air and nutrients and micropollutants in water. The unique feature of BES for environmental remediation is the use of electrodes as non-exhaustible electron acceptors, or even donors, for contaminant degradation, which requires minimum energy or chemicals but instead produces sustainable energy for monitoring and other onsite uses. BES provides both oxidation (anode) and reduction (cathode) reactions that integrate microbial–electro-chemical removal mechanisms, so complex contaminants with different characteristics can be removed. We believe the BES platform carries great potential for sustainable remediation and hope this perspective provides background and insights for future research and development.
Optical gyroscopes are among the most accurate rotation measuring devices and are widely used for navigation and accurate pointing. Since the advent of photonic integrated components for ...communications, and with their increasing complexity, there has been interest in the possibility of chip-scale optical gyroscopes1. Besides the potential benefits of integration, such solid-state systems would be robust and resistant to shock. Here, we report a gyroscope using Brillouin ring lasers on a silicon chip. Its stability and sensitivity enable measurement of Earth’s rotation, representing a major milestone for this new class of gyroscope.A Sagnac gyroscope based on Brillouin ring lasers on a silicon chip is presented. The stability and sensitivity of this on-chip planar gyroscope allow measurement of the Earth’s rotation, with an amplitude sensitivity as small as 5 deg h−1 for a sinusoidal rotation, an angle random walk of 0.068 deg h−1/2 and bias instability of 3.6 deg h−1.
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