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&[美]Bruce E.Rittmann，[美]Perry L. McCarty著
&清华大学出版社
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[美]Bruce E.Rittmann，[美]Perry L. McCarty著
清华大学出版社
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本书介绍了用于保护和改善环境的微生物过程的基本原理及其实际应用。不仅涉及环境生物技术的传统应用，还介绍了新兴的应用，如有害化合物的脱毒、生物修复、饮用水的生物过滤等。
中国植物志第十八卷+
中国科学院中国植物志编辑委员会[编]
中国植物志 第十九卷+
中国科学院中国植物志编辑委员会编
农业生物学研究与农业持续发展/牛德水+
牛德水主编
Study on Calligonum plants in China/在中国沙拐枣属植物的研究
山西植物志.第二卷/刘天慰+
刘天慰主编
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这是该教科书的最新版（2009）。该书是一本不可多得的高级计量经济学入门教科书。区区两百页，涉及到高级计量的几乎全部领域，并且注重应用而非数学证明。非常适合已经修完基础计量，希望进一步提升自己计量研究水平的同学。为了回馈常年以来支持我的兄弟姐妹，这本书不收取任何论坛币，完全免费！
1 Introduction 11.1 Economic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Observational Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Economic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Regression and Projection 32.1 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Conditional Density and Mean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.3 Regression Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.4 Conditional Variance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.5 Linear Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.6 Best Linear Predictor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.7 Technical Proofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Least Squares Estimation 143.1 Random Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.2 Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.3 Least Squares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.4 Normal Regression Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.5 Model in Matrix Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.6 Projection Matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.7 Residual Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.8 Bias and Variance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.9 Gauss-Markov Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.10 Semiparametric E& ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.11 Multicollinearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.12 In.uential Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.13 Technical Proofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.14 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Inference 324.1 Sampling Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.2 Consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3 Asymptotic Normality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.4 Covariance Matrix Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.5 Alternative Covariance Matrix Estimators . . . . . . . . . . . . . . . . . . . . . . . . 394.6 Functions of Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.7 t tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.8 Con.dence Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424.9 t-ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42i4.10 Wald Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434.11 F Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444.12 Normal Regression Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464.13 Semiparametric E& ciency in the Projection Model . . . . . . . . . . . . . . . . . . . 484.14 Semiparametric E& ciency in the Homoskedastic Regression Model . . . . . . . . . . 494.15 Problems with Tests of NonLinear Hypotheses . . . . . . . . . . . . . . . . . . . . . 514.16 Monte Carlo Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544.17 Estimating a Wage Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564.18 Technical Proofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.19 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625 Additional Regression Topics 655.1 Generalized Least Squares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655.2 Testing for Heteroskedasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685.3 Forecast Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685.4 NonLinear Least Squares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695.5 Least Absolute Deviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715.6 Quantile Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725.7 Testing for Omitted NonLinearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735.8 Omitted Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745.9 Irrelevant Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.10 Model Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765.11 Technical Proofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785.12 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806 The Bootstrap 836.1 De.nition of the Bootstrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836.2 The Empirical Distribution Function . . . . . . . . . . . . . . . . . . . . . . . . . . . 836.3 Nonparametric Bootstrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856.4 Bootstrap Estimation of Bias and Variance . . . . . . . . . . . . . . . . . . . . . . . 856.5 Percentile Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866.6 Percentile-t Equal-Tailed Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886.7 Symmetric Percentile-t Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886.8 Asymptotic Expansions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896.9 One-Sided Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906.10 Symmetric Two-Sided Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916.11 Percentile Con.dence Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926.12 Bootstrap Methods for Regression Models . . . . . . . . . . . . . . . . . . . . . . . . 936.13 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
。。。。。。（more chapters in the book ...）
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谢谢，学习学习
不客气。互相学习吧：）
谢谢楼主~~~
3Q too much !!
楼主，太谢谢你了！
曾经看过Hansen的文章，有些地方不太明白，希望这本书能够对我有所帮助。
Hansen在顶级计量刊物上发文章太多了，可以在他的个人网页上看到。
没错，他的名气确实了得！
他的这本教材，可以说对有一些计量基础的人，读起来不会觉得吃力，是比较浅显易懂的。希望能对你有所启发：）
对了，顺便指出，这本书是完全的电子版，并非扫描版。
谢谢楼主~~~~~~~~~~~~~~~~~~··
好东西大家共享！
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论坛法律顾问：王进律师Bruce E Logan | Pennsylvania State University, PA | Penn State | Department of Civil and Environmental Engineering | ResearchGate
635Research items96,976Reads48,093CitationsUniversity Park, PA, United StatesView AllZhejiang UniversityPennsylvania State UniversityPennsylvania State UniversityTsinghua UniversityPennsylvania State UniversityView AllZhejiang UniversityPennsylvania State UniversityPennsylvania State UniversityTsinghua UniversityPennsylvania State UniversityView AllDongguk UniversityNational Scientific and Technical Research CouncilAksaray ?niversitesiFederal University of Technology, AkureSirindhorn International Institute of Technology (SIIT)View AllWetsusCarleton UniversityOregon State UniversityPennsylvania State UniversityYale UniversityProjectimprove the efficiency, reduce the energy consumptionProjectDevelopment of a thermally regenerative ammonia battery
to convert low-grade waste heat to electrical powerMar 2018Electrochemically active bacteria (EAB) on the cathodes of microbial fuel cells (MFCs) can remove metals from the catholyte, but the fate of metals in the cells has not been examined in the presence of multiple metals. To study the relative uptake and fate of Cr(VI) and Cd(II) in cells, fluorescence probes were used to determine the amount and location of these metals in four different EAB on the biocathodes of MFCs. When both metals were present, less Cr(VI) was removed but Cd(II) uptake was not appreciably affected. As a consequence, the imaging of Cr(III) ions was lower than that using individual fluorescence probes for single Cr(III) ions in each EAB, compared to negligible changes in images for Cd(II) ions in the presence of either both Cr(VI) and Cd(II) or Cd(II) alone. The concentration of Cr(III) ions in the cells consistently increased over time, while that of Cd(II) ions decreased following an initial increase. Cr or Cd uptake could not be detected using a scanning electron microscope coupled with an energy dispersive spectrometer, reflecting the high sensitivities of the fluorescence probes to these metals. More chromium was found in the cytoplasm while cadmium preferentially accumulated in the cell envelope. These results demonstrate that the fate of chromium and cadmium in EAB was different when both metals were present, compared to controls containing a single metal. These results provide direct and visible results on the fate of the metals in the EAB when these metals are co-present in the catholyte of MFCs.Mar 2018[...]A migration electric-field assisted electrocoagulation (MEAEC) system was developed to increase phosphate removal from domestic wastewater, with reduced energy consumption, using a titanium charging (inert) electrode and a sacrificial iron anode. In the MEAEC, an electric field was applied between the inert electrode (titanium) and an air cathode to drive migration of phosphate anions towards the sacrificial anode. Current was then applied between the sacrificial anode (Fe or Al mesh) and the air cathode to drive electrocoagulation of phosphate. A MEAEC with the Fe electrode using primary clarifier effluent achieved 98% phosphate removal, producing water with a total phosphorus of 0.3 mg/L with &6 min total treatment time ( each 10 s inert electrode charging, and 1 min electrocoagulation), at a constant current density of 1 mA/cm2. In the absence of the 10 s charging time, electrocoagulation required 15 min for the same removal. With an aluminum anode and the same phosphorus removal, the MEAEC required 7 cycles (7 min total treatment, 1 min 10 s total charging), while conventional electrocoagulation required 20 min. The energy demand of Fe-MEAEC was only 0.039 kWh/m3for 98% phosphate removal, which was 35% less than with the Al-MEAEC of 0.06 kWh/m3, and 28% less than that previously obtained using an inert graphite electrode. Analysis of the precipitate showed that a less porous precipitate was obtained with the Al anode than with the Fe anode. The phosphorus in precipitate of Fe-MEAEC was identified as PO43-and HPO42-, while the Fe was present as both Fe2+and Fe3+. Only HPO42-and Al3+were identified in the precipitate of the Al-MEAEC. These results indicated that the MEAEC with a titanium inert charging electrode and iron anode could achieve the most efficient phosphate removal with very low energy demands, compared to previous electrochemical approaches.Feb 2018Long-term operation of wastewater-fed, microbial fuel cells (MFCs) with cathodes made of activated carbon and stainless steel (SS) current collectors can result in decreased performance due to cathode fouling. Copper has good antimicrobial properties, and it is more electrically conductive than SS. To demonstrate that a copper current collector could produce a more fouling resistant cathode, MFCs with air cathodes using either SS or copper current collectors were operated using domestic wastewater for 27 weeks. The reduction in biofouling over time was shown by less biofilm formation on the copper cathode surface compared to SS cathodes, due to the antimicrobial properties of copper. Maximum power densities from 17–27 weeks were 440 ± 38 mW/m2 using copper and 370 ± 21 mW/m2 using SS cathodes. The main difference in the microbial community was a nitrifying community on the SS cathodes, which was not present on the copper cathodes.Feb 2018In two-chamber microbial electrolysis cells (MECs) with anion exchange membranes (AEMs), a phosphate buffer solution (PBS) is typically used to avoid increases in catholyte pH as Nernst equation calculations indicate that high pHs adversely impact electrochemical performance. However, ion transport between the chambers will also impact performance, which is a factor not included in those calculations. To separate the impacts of pH and ion transport on MEC performance, a high molecular weight polymer buffer (PoB), which was retained in the catholyte due to its low AEM transport and cationic charge, was compared to PBS in MECs and abiotic electrochemical half cells (EHCs). In MECs, catholyte pH control was less important than ion transport. MEC tests using the PoB catholyte, which had a higher buffer capacity and thus maintained a lower catholye pH (&8), resulted in a 50% lower hydrogen production rate (HPR) than that obtained using PBS (HPR = 0.7 m?-H2 m?? d??) where the catholyte rapidly increased to pH = 12. The main reason for the decreased performance using PoB was a lack of hydroxide ion transfer into the anolyte to balance pH. The anolyte pH in MECs rapidly decreased to 5.8 due to a lack of hydroxide ion transport, which inhibited current generation by the anode, whereas the pH was maintained at 6.8 using PBS. In abiotic tests in ECHs, where the cathode potential was set at -1.2 V, the HPR was 133% higher using PoB than PBS due to catholyte pH control, as the anolyte pH was not a factor in the performance. These results show that maintaining charge transfer to control anolyte pH is more important than obtaining a more neutral pH catholyte.Jan 2018Thermally regenerative ammonia batteries (TRABs) have shown great promise as a method to convert low-grade waste heat into electrical power, with power densities an order of magnitude higher than other approaches. However, previous TRABs based on copper electrodes suffered from unbalanced anode dissolution and cathode deposition rates during discharging cycles, limiting practical applications. To produce a TRAB with stable and reversible electrode reactions over many cycles, inert carbon electrodes were used with silver salts. In continuous flow tests, power production was stable over 100 discharging cycles, demonstrating excellent reversibility. Power densities were 23 W m -2-electrode area in batch tests, which was 64% higher than that produced in parallel tests using copper electrodes, and 30 W m -2 (net energy density of 490 Wh m -3-anolyte) in continuous flow tests. While this battery requires the use a precious metal, an initial economic analysis of the system showed that the cost of the materials relative to energy production was $220 per MWh, which is competitive with energy production from other non-fossil fuel sources. A substantial reduction in costs could be obtained by developing less expensive anion exchange membranes.Jan 2018[...]Dec 2017[...]Low-grade heat from geothermal sources and industrial plants is a significant source of sustainable power that has great potential to be converted to electricity. The two main approaches that have been extensively investigated for converting low-grade heat to electrical energy, organic Rankine cycles and solid-state thermoelectrics, have not produced high power densities or been cost-effective for such applications. Newer, alternative liquid-based technologies are being developed that can be categorized by how the heat is used. Thermoelectrochemical cells (TECs), thermo-osmotic energy conversion (TOEC) systems, and thermally regenerative electrochemical cycles (TRECs) all use low-grade heat directly in a device that generates electricity. Other systems use heat sources to prepare solutions that are used in separate devices to produce electrical power. For example, low-temperature distillation methods can be used to produce solutions with large salinity differences to generate power using membrane-based systems, such as pressure-retarded osmosis (PRO) or reverse electrodialysis (RED); or highly concentrated ammonia solutions can be prepared for use in thermally regenerative batteries (TRBs). Among all these technologies, TRECs, TOEC, and TRBs show the most promise for effectively converting low-grade heat into electrical power mainly due to their high power productions and energy conversion efficiencies.Nov 2017[...]h i g h l i g h t s g r a p h i c a l a b s t r a c t A battery based on ammonia and copper salts was used to produce electricity. Quaternary ammonium-based poly(-phenylene oxide) membranes were tested. The synthesized membranes had different ion exchange capacities and thicknesses. The power density of the BTMA membrane (40% DF, 50 mm thick) was 106 ± 7 W m ?2. Energy recovery was estimated to reach 7.0% relative to the Carnot efficiency. a b s t r a c t Thermally regenerative ammonia-based batteries (TRABs) can be used to harvest low-grade waste heat as electrical power. To improve TRAB performance, a series of benzyltrimethyl quaternary ammonium-functionalized poly(phenylene oxide) anion exchange membranes (BTMA-AEMs) were examined for their impact on performance relative to a commercial AEM (Selemion AMV). The synthesized AEMs had different degrees of functionalization (DF; 25% and 40%), and thicknesses (50, 100 and 150 mm). Power and energy densities were shown to be a function of both DF and membrane thickness. The power density of TRAB increased by 31% using a BTMA-AEM (40% DF, 50 106 ± 7 W m ?2) compared to the Selemion (81 ± 5 W m ?2). Moreover, the energy density increased by 13% when using a BTMA-based membrane (25% DF, 150 350 Wh m ?3) compared to the Selemion membrane (311 Wh m ?3). The thermal-electric conversion efficiency improved to 0.97% with the new membrane compared to 0.86% for the Selemion. This energy recovery was 7.0% relative to the Carnot efficiency, which was 1.8 Journal of Power Sources 342 (3 times greater than the highest previously reported value of a system used to capture low-grade waste heat as electricity.Nov 2017[...]Microbial fuel cell (MFC) cathodes rapidly foul when treating domestic wastewater, substantially reducing power production over time. Here a wipe separator was chemically bonded to an activated carbon air cathode using polyvinylidene fluoride (PVDF) to mitigate cathode fouling and extend cathode performance over time. MFCs with separator-bonded cathodes produced a maximum power density of 190 ± 30 mW m(-2) after 2 months of operation using domestic wastewater, which was ~220% higher than controls (60 ± 50 mW m(-2)) with separators that were not chemically bonded to the cathode. Less biomass (protein) was measured on the bonded separator surface than the non-bonded separator, indicating chemical bonding reduced external bio-fouling. Salt precipitation that contributed to internal fouling was also reduced using separator-bonded cathodes. Overall, the separator-bonded cathodes showed better performance over time by mitigating both external bio-fouling and internal salt fouling.Nov 2017While stainless steel (SS) cathodes have shown great promise due to their low cost and high specific surface areas in microbial electrolysis cells (MECs), they have mainly been examined under static (no flow) conditions. Several different SS materials with different 3-dimensional structures (mesh, fiber felt, wool, and brushes) were compared in the absence and presence of fluid flow (0.05, 0.1 and 0.2 cm/s) past the cathode by catholyte recirculation. MECs with wool produced the highest hydrogen production rate with 1.3 ± 0.3 L-H2/L-reactor/d, which was the same as the Pt control at a catholyte recirculation of 40 mL/min (applied voltage of 0.9 V). In the absence of flow, hydrogen production rates of SS materials decreased by 52% (wool) to 28% (brush). The high hydrogen production rate using wool was likely a result of its high specific surface area (480 m?/m?-reactor volume), and reduced cathode overpotential due to gas removal by catholyte recirculation.Oct 2017[...]Few microorganisms have been examined for current generation under thermophilic (40-65°C) or hyperthermophilic temperatures (≥80°C) in microbial electrochemical systems. Two iron-reducing archaea from the family Archaeoglobaceae, Ferroglobus placidus and Geoglobus ahangari, showed electro-active behavior leading to current generation at hyperthermophilic temperatures in single-chamber microbial electrolysis cells (MECs). A current density (j) of 0.68±0.11A/m(2) was attained in F. placidus MECs at 85°C, and 0.57±0.10A/m(2) in G. ahangari MECs at 80°C, with an applied voltage of 0.7V. Cyclic voltammetry (CV) showed that both strains produced a sigmoidal catalytic wave, with a mid-point potential of -0.39V (vs. Ag/AgCl) for F. placidus and -0.37V for G. ahangari. The comparison of CVs using spent medium and turnover CVs, coupled with the detection of peaks at the same potentials in both turnover and non-turnover conditions, suggested that mediators were not used for electron transfer and that both archaea produced current through direct contact with the electrode. These two archaeal species, and other hyperthermophilic exoelectrogens, have the potential to broaden the applications of microbial electrochemical technologies for producing biofuels and other bioelectrochemical products under extreme environmental conditions.Sep 2017New electrochemical technologies that use capacitive or battery electrodes are being developed to minimize energy requirements for desalinating brackish waters. When a pair of electrodes is charged in capacitive deionization (CDI) systems, cations bind to the cathode and anions bind to the anode, but high applied voltages (&1.2 V) result in parasitic reactions and irreversible electrode oxidation. In the battery electrode deionization (BDI) system developed here, two identical copper hexacyanoferrate (CuHCF) battery electrodes were used that release and bind cations, with anion separation occurring via an anion exchange membrane. The system used an applied voltage of 0.6 V, which avoided parasitic reactions, achieved high electrode desalination capacities (up to 100 mg-NaCl/g-electrode, 50 mM NaCl influent), and consumed less energy than CDI. Simultaneous production of desalinated and concentrated solutions in two channels avoided a two-cycle approach needed for CDI. Stacking additional membranes between CuHCF electrodes (up to three anion and two cation exchange membranes) reduced energy consumption to only 0.02 kWh/m? (approximately an order of magnitude lower than values reported for CDI), for an influent desalination similar to CDI (25 mM decreased to 17 mM). These results show that BDI could be effective as a very low energy method for brackish water desalination.Aug 2017Dissolved methane and a lack of nutrient removal are two concerns for treatment of wastewater using anaerobic fluidized bed membrane bioreactors (AFMBRs). Membrane aerators were integrated into an AFMBR to form an Aeration membrane fluidized bed membrane bioreactor (AeMFMBR) capable of simultaneous removal of organic matter and ammonia without production of dissolved methane. Good effluent quality was obtained with no detectable suspended solids, 93±5% of chemical oxygen demand (COD) removal to 14±11 mg/L, and 74±8% of total ammonia (TA) removal to 12±3 mg-N/L for domestic wastewater (COD of 193±23 mg/L and TA of 49±5 mg-N/L) treatment. Nitrate and nitrite concentrations were always low (& 1 mg-N/L) during continuous flow treatment. Membrane fouling was well controlled by fluidization of the granular activated carbon (GAC) particles (transmembrane pressures maintained &3 kPa). Analysis of the microbial communities suggested that nitrogen removal was due to nitrification and denitrification based on the presence of microorganisms associated with these processes.Aug 2017Power generation using microbial fuel cells (MFCs) must provide stable, continuous conversion of organic matter in wastewaters into electricity. However, when relatively small diameter (0.8cm) graphite fiber brush anodes were placed close to the cathodes in MFCs, power generation was unstable during treatment of low strength domestic wastewater. One reactor produced 149mW/m(2) before power generation failed, while the other reactor produced 257mW/m(2), with both reactors exhibiting severe power overshoot in polarization tests. Using separators or activated carbon cathodes did not result in stable operation as the reactors continued to exhibit power overshoot based on polarization tests. However, adding acetate (1g/L) to the wastewater produced stable performance during fed batch and continuous flow operation, and there was no power overshoot in polarization tests. These results highlight the importance of wastewater strength and brush anode size for producing stable and continuous power in compact MFCs.Jul 2017The application of immobilized redox mediators (RMs) in microbial fuel cells (MFCs) is an emerging technology for electricity generation with simultaneous azo dye decolorization due to facilitated electrons transfer from bacteria to anodes and azo dyes. The use of immobilized RMs avoids the requirement of their continuous dosing in MFCs, which has been the main limitation for practical applications. Two strategies of anthraquinones-2,6-disulphonic salt (AQDS) immobilization, AQDS immobilized with polyvinyl alcohol particles and AQDS immobilized on anodes by electropolymerization, were evaluated and compared to achieve simultaneous reactive red 2 (RR2) dye reduction and bioelectricity generation. The AQDS immobilized by electropolymerization showed the highest power density (816 ± 2 mW/m?) and extent of RR2 decolorization (89 ± 0.6%). This power density is one of the highest values yet achieved in the presence of a recalcitrant pollutant, suggesting that immobilization was important for enabling current generation in the presence of RR2.Jun 2017[...]Activated carbon (AC) is an inexpensive and sustainable catalyst for oxygen reduction in air-cathodes of microbial fuel cells (MFCs), but its electrical conductivity is relatively poor. To improve cathode performance, five different more conductive materials were added to AC: three carbon materials (carbon black, mesoporous carbon, and carbon nanotubes), and two metal powders (inexpensive copper and inert gold). Carbon-based particles improved maximum power densities by 6%–14% compared to plain AC due to reduced charge transfer resistance. Copper powder had reduced performance, likely due to toxicity effects on anode bacteria, while gold particles were similar to that of plain AC. Heat treated AC mixed with carbon black produced the highest power density of 1900±76 mW m-2, 41% higher than the widely used Pt air-cathode (1350±55 mW m-2). The use of inexpensive carbon black with heat treatment was therefore the most effective and economical approach for improving cathode performance in MFCs.Jun 2017[...]Jun 2017[...]Nafion is commonly used as a catalyst binder in many types of electrochemical cells, but less expensive binders are needed for the cathodes in microbial electrolysis cells (MECs) which are operated in neutral pH buffers, and reverse electrodialysis stacks (RED),which use thermolytic solutions such as ammonium bicarbonate. Six different binders were examined based on differences in ion exchange properties (anionic: Nafion, BPSH20, BPSH40, S-R cationic: Q-R and neutral: Radel, BAEH) and hydrophobicity based on water uptake (0%, R 17–56% for the other binders). BPSH40 had similar performance to Nafion based on steady-state polarization single electrode experiments in a neutral pH phosphate buffer, and slightly better performance in ammonium bicarbonate. Three different Mo-based catalysts were examined as alternatives to Pt, with MoB showing the best performance under steady-state polarization. In MECs, MoB/BPSH40 performed similarly to Pt with Nafion or Radel binders. The main distinguishing feature of the BPSH40 was that it is very hydrophilic, and thus it had a greater water content (56%) than the other binders (0–44%). These results suggest the binders for hydrogen evolution in MECs should be designed to have a high water content without sacrificing ionic or electronic conductivity in the electrode.May 2017Differences in microbial fuel cell (MFC) architectures, materials, and solution chemistries, have previously hindered direct comparisons of improvements in power production due to new cathode materials. However, one common reactor design has now been used in many different laboratories around the world under similar operating conditions based on using: a graphite fiber brush anode, a platinum cathode catalyst, a single-chamber cube-shaped (4-cm) MFC with a 3-cm diameter anolyte chamber, 50 mM phosphate buffer, and an acetate fuel. Analysis of several publications over 10 years from a single laboratory showed that even under such identical operational conditions, maximum power densities varied by 15%, with an average of 1.36 ± 0.20 W m–2 (n=24), normalized to cathode projected area (34 W m–3 liquid volume). In other laboratories, maximum power was significantly less, with an average of 1.03 ± 0.46 W m–2 (n=11), despite identical conditions. One likely reason for the differences in power is cathode age. Power production with Pt catalyst cathodes significantly declined after one month of operation or more to 0.87 ± 0.31 W m–2 (n=18) based on studies where cathode aging was examined, while in many studies the age of the cathode was not reported. Using these studies as a performance baseline, we review the claims of improvements in power generation due to new anode or cathode materials, or changes in solution conductivities and substrates.May 2017[...]May 2017[...]Supplementary Figures, Supplementary Tables, Supplementary Note and Supplementary ReferencesMay 2017[...]Thermally regenerative ammonia-based batteries (TRABs) have been developed to harvest low-grade waste heat as electricity. To improve the power production and anodic coulombic efficiency, the use of ethylenediamine as an alternative ligand to ammonia was explored here. The power density of the ethylenediamine-based battery (TRENB) was 85 ± 3 W m??-electrode area with 2 M ethylenediamine, and 119 ± 4 W m?? with 3 M ethylenediamine. This power density was 68% higher than that of TRAB. The energy density was 478 Wh m??-anolyte, which was ~50% higher than that produced by TRAB. The anodic coulombic efficiency of the TRENB was 77 ± 2%, which was more than twice that obtained using ammonia in a TRAB (35%). The higher anodic efficiency reduced the difference between the anode dissolution and cathode deposition rates, resulting in a process more suitable for closed loop operation. The thermal-electric efficiency based on ethylenediamine separation using waste heat was estimated to be 0.52%, which was lower than that of TRAB (0.86%), mainly due to the more complex separation process. However, this energy recovery could likely be improved through optimization of the ethylenediamine separation process.May 2017[...]Applying microbial electrochemical technologies for the treatment of highly saline or thermophilic solutions is challenging due to the lack of proper inocula to enrich for efficient exoelectrogens. Brine pools from three different locations (Valdivia, Atlantis II and Kebrit) in the Red Sea were investigated as potential inocula sources for enriching exoelectrogens in microbial electrolysis cells (MECs) under thermophilic (70°C) and hypersaline (25% salinity) conditions. Of these, only the Valdivia brine pool produced high and consistent current 6.8 ± 2.1 A/m?-anode in MECs operated at a set anode potential of +0.2 V vs. Ag/AgCl (+0.405 V vs. standard hydrogen electrode). These results show that exoelectrogens are present in these extreme environments and can be used to startup MEC under thermophilic and hypersaline conditions. Bacteroides was enriched on the anode of the Valdivia MEC, but it was not detected in the open circuit voltage reactor seeded with the Valdivia brine pool.Apr 2017Recent estimates suggest that approximately 40% of global electricity demands can be met by capturing the potential energy contained in the mixing of seawater and freshwater at coasts. Several technologies are currently being explored to capture this energy and maximize the achievable electrical power density. Here we report a new method to capture this energy that yielded a peak power density of 12.6 ± 0.5 W m??-membrane area (average = 3.8 ± 0.1 W m??), which is the highest value reported to date for salinity gradient technologies being fed with synthetic seawater (30 g L?? NaCl) and freshwater (1 g L?? NaCl). This unprecedented high power density was achieved in a concentration flow cell containing non-toxic copper hexacyanoferrate electrodes that developed electrode potentials based on Na? activities and an anion-exchange membrane that developed a Donnan potential based on Cl? activities. The peak power density increased to 26.3 ± 1.3 W m?? (average = 9.4 ± 0.9 W m??) when using a highly saline synthetic brine (300 g L?? NaCl) and freshwater (1 g L?? NaCl). Stacking two flow cells in series doubled the total power while maintaining the same power per membrane area. Combining electrode and Donnan potentials in a concentration flow cell offers a new means to harvest salinity gradient energy that may lead to an economically viable technology.Feb 2017[...]Supporting Information for &Improved electrical power production of thermally regenerative batteries using a poly(phenylene oxide) based anion exchange membrane&.Feb 2017Metal–organic framework (MOF) on activated carbon (AC) enhanced the performance of cathodes but longevity needs to be considered in the presence of metal chelators or ligands, such as phosphate, present in wastewaters. MOF catalysts on AC initially produced 2.78±0.08 W m–2, but power decreased by 26% after eight weeks in microbial fuel cells using a 50 mM phosphate buffer (PBS) and acetate due to decreased cathode performance. However, power was still 41% larger than that of the control AC (no MOF). Power generation using domestic wastewater was initially 0.73 ± 0.01 W m–2, and decreased by 21% over time, with power 53% larger than previous reports, although changes in wastewater composition were a factor in performance. Adding phosphate salts to the wastewater did not affect the catalyst performance over time. While MOF catalysts are therefore initially adversely affected by chelators, performance remains enhanced compared to plain AC.Jan 2017[...]Microbial fuel cells (MFCs) need to have a compact architecture, but power generation using low strength domestic wastewater is unstable for closely-spaced electrode designs using thin anodes (flat mesh or small diameter graphite fiber brushes) due to oxygen crossover from the cathode. A composite anode configuration was developed to improve performance, by joining the mesh and brushes together, with the mesh used to block oxygen crossover to the brushes, and the brushes used to stabilize mesh potentials. In small, fed-batch MFCs (28 mL), the composite anode produced 20% higher power densities than MFCs using only brushes, and 150% power densities compared to carbon mesh anodes. In continuous flow tests at short hydraulic retention times (HRTs, 2 or 4 h) using larger MFCs (100 mL), composite anodes had stable performance, while brush anode MFCs exhibited power overshoot in polarization tests. Both configurations exhibited power overshoot at a longer HRT of 8 h due to lower effluent CODs. The use of composite anodes reduced biomass growth on the cathode (1.9 ± 0.2 mg) compared to only brushes (3.1 ± 0.3 mg), and increased coulombic efficiencies, demonstrating that they successfully reduced oxygen contamination of the anode and the bio-fouling of cathode.Jan 2017The CO2 concentration difference between ambient air and exhaust gases created by combusting fossil fuels is an untapped energy source for producing electricity. One method to capture this energy is to dissolve CO2 gas into water, then convert the produced chemical potential energy into electrical power using an electrochemical system. Previous efforts using this method found that electricity can be generated, but electrical power densities were low and expensive ion-exchange membranes were needed. Here, we overcame these challenges by developing a new approach to capture electrical power from CO2 dissolved in water: the pH-gradient flow cell. In this approach, two identical supercapacitive manganese oxide electrodes were separated by a non-selective membrane and exposed to an aqueous buffer solution sparged with either CO2 gas or air. This pH-gradient flow cell produced an average power density of 0.82 W/m?, which was nearly 200 times higher than values reported using previous approaches.Jan 2017[...]h i g h l i g h t s g r a p h i c a l a b s t r a c t A battery based on ammonia and copper salts was used to produce electricity. Quaternary ammonium-based poly(-phenylene oxide) membranes were tested. The synthesized membranes had different ion exchange capacities and thicknesses. The power density of the BTMA membrane (40% DF, 50 mm thick) was 106 ± 7 W m ?2. Energy recovery was estimated to reach 7.0% relative to the Carnot efficiency. a b s t r a c t Thermally regenerative ammonia-based batteries (TRABs) can be used to harvest low-grade waste heat as electrical power. To improve TRAB performance, a series of benzyltrimethyl quaternary ammonium-functionalized poly(phenylene oxide) anion exchange membranes (BTMA-AEMs) were examined for their impact on performance relative to a commercial AEM (Selemion AMV). The synthesized AEMs had different degrees of functionalization (DF; 25% and 40%), and thicknesses (50, 100 and 150 mm). Power and energy densities were shown to be a function of both DF and membrane thickness. The power density of TRAB increased by 31% using a BTMA-AEM (40% DF, 50 106 ± 7 W m ?2) compared to the Selemion (81 ± 5 W m ?2). Moreover, the energy density increased by 13% when using a BTMA-based membrane (25% DF, 150 350 Wh m ?3) compared to the Selemion membrane (311 Wh m ?3). The thermal-electric conversion efficiency improved to 0.97% with the new membrane compared to 0.86% for the Selemion. This energy recovery was 7.0% relative to the Carnot efficiency, which was 1.8 Journal of Power Sources 342 (3 times greater than the highest previously reported value of a system used to capture low-grade waste heat as electricity.Dec 2016[...]Dec 2016Dec 2016Anode potential has been shown to be a critical factor in the rate of acetate removal in microbial electrolysis cells (MECs), but studies with fermentable substrates and set potentials are lacking. Here, we examined the impact of three different set anode potentials (SAPs; -0.25, 0, and 0.25 V vs. standard hydrogen electrode) on the electrochemical performance, electron flux to various sinks, and anodic microbial community structure in two-chambered MECs fed with propionate. Electrical current (49–71%) and CH4 (22.9–41%) were the largest electron sinks regardless of the potentials tested. Among the three SAPs tested, 0 V showed the highest electron flux to electrical current (71 ± 5%) and the lowest flux to CH4 (22.9 ± 1.2%). In contrast, the SAP of -0.25 V had the lowest electron flux to current (49 ± 6%) and the highest flux to CH4 (41.1 ± 2%). The most dominant genera detected on the anode of all three SAPs based on 16S rRNA gene sequencing were Geobacter, Smithella and Syntrophobacter, but their relative abundance varied among the tested SAPs. Microbial community analysis implies that complete degradation of propionate in all the tested SAPs was facilitated by syntrophic interactions between fermenters and Geobacter at the anode and ferementers and hydrogenotrophic methanogens in suspension.Dec 2016Treatment of low strength wastewaters using microbial fuel cells (MFCs) has been effective at hydraulic retention times (HRTs) similar to aerobic processes, but treatment of high strength wastewaters can require longer HRTs. The use of two air-cathode MFCs hydraulically connected in series was examined to continuously treat high strength swine wastewater (7–8 g/L of chemical oxygen demand) at an HRT of 16.7 h. The maximum power density of 750 ± 70 mW/m? was produced after 12 days of operation. However, power decreased by 85% after 185 d of operation due to serious cathode fouling. COD removal was improved by using a lower external resistance, and COD removal rates were substantially higher than those previously reported for a low strength wastewater. However, removal rates were inconsistent with first order kinetics as the calculated rate constant was an order of magnitude lower than rate constant for the low strength wastewater.Dec 2016[...]Salinity gradient energy can be directly converted to electrical power using reverse electrodialysis (RED) and other technologies, but reported power densities have been too low for practical applications. Here, the RED stack performance was improved by using 2,6-dihydroxyanthraquinone and ferrocyanide as redox couples. These electrolytes were then used in a flow battery, to produce an integrated RED stack and flow battery (RED-FB) system capable of capturing, storing, and discharging salinity gradient energy. Energy captured from the RED stack was discharged in the flow battery at a maximum power density of 3.0 kW/m2-anode, which was similar to the flow batteries charged by electrical power and could be used for practical application. Salinity gradient energy captured from the RED stack was recovered from the electrolytes as electricity with a 30% efficiency, and the maximum energy density of the system was 2.4 kWh/m3-anolyte. The combined RED-FB system overcomes many limitations of previous approaches to capture, store, and use salinity gradient energy from natural or engineered sources.Dec 2016Understanding how current densities affect electrogenic biofilm activity is important for wastewater treatment as current densities can substantially decrease at COD concentrations greater than those suitable for discharge to the environment. We examined the biofilm’s response, in terms of viability and enzymatic activity, to different current densities using microbial electrolysis cells with a lower (0.7 V) or higher (0.9 V) added voltage to alter current production. Viability was assessed using florescent dyes, with dead cells identified on the basis of dye penetration due to a compromised cell outer-membrane (red), and live cells (intact membrane) fluorescing green. Biofilms operated with 0.7 V produced 2.4 ± 0.2 A m??, and had an inactive layer near the electrode and a viable layer at the biofilm-solution interface. The lack of cell activity near the electrode surface was confirmed by using an additional dye that fluoresces only with enzymatic activity. Adding 0.9 V increased the current by 61%, and resulted in a single, more homogeneous and active biofilm layer. Switching biofilms between these two voltages produced outcomes associated with the new current rather than the previous biofilm conditions. These findings suggest that maintaining higher current densities will be needed to ensure long-term viability electrogenic biofilms.Nov 2016[...]Large differences between the water and air pressure in microbial fuel cells (MFCs) can deform and damage cathodes. To avoid deformation, the cathode air pressure was controlled to balance pressure differences between the air and water. Raising the air pressures from 0 to 10 kPa at a set cathode potential of -0.3 V (versus Ag/AgCl) enhanced cathode performance by 17%, but pressures ≥25 kPa decreased current and resulted in air leakage into the solution. Matching the air pressure with the water pressure avoided cathode deformation and improved performance. The maximum power density increased by 15%, from 1070 ± 20 to 1230 ± 70 mW m??, with balanced air and water pressures of 10–25 kPa. Oxygen partial pressures ≥12.5 kPa in the cathode compartment maintained the oxygen reduction rate to be within 92 ± 1% of that in ambient air. The use of pressurized air flow through the cathode compartments can enable closer spacing of the cathodes compared to passive gas transfer systems, which could make the reactor design more compact. The energy cost of pressurizing the cathodes was estimated to be smaller than the increase in power that resulted from the use of pressurized cathodes.Nov 2016[...]Anaerobic fluidized bed membrane bioreactors (AFMBRs) use granular activated carbon (GAC) particles suspended by recirculation to effectively treat low strength wastewaters (~100-200 mg L??, chemical oxygen demand, COD), but the effluent can contain dissolved methane. An aerobic fluidized bed membrane bioreactor (AOFMBR) was developed to avoid methane production and the need for wastewater recirculation by using rising air bubbles to suspend GAC particles. The performance of the AOFMBR was compared to an AFMBR and a conventional aerobic membrane bioreactor (AeMBR) for domestic wastewater treatment over 130 d at ambient temperatures (fixed hydraulic retention time of 1.3 h). The effluent of the AOFMBR had a COD of 20 ± 8 mg L??, and a turbidity of &0.2 NTU, for low-COD influent (153 ± 19 and 214 ± 27 mg L??), similar to the AeMBR and AFMBR. For the high-COD influent (299 ± 24 mg L??), higher effluent CODs were obtained for the AeMBR (38 ± 9 mg L??) and AFMBR (51 ± 11 mg L??) than the AOFMBR (26 ± 6 mg L??). Transmembrane pressure of the AOFMBR increased at 0.04 kPa d??, which was 20% less than the AeMBR and 57% less than the AFMBR, at the low influent COD. Scanning electron microscopy (SEM) analysis indicated a more uniform biofilm on the membrane in AOFMBR than that from the AeMBR biofilm, and no evidence of membrane damage. High similarity was found between communities in the suspended sludge in the AOFMBR and AeMBR (square-root transformed Bray-Curtis similarity, SRBCS, 0.69). Communities on the GAC and suspended sludge were dissimilar in the AOFMBR (SRBCS, 0.52), but clustered in the AFMBR (SRBCS, 0.63).Nov 2016[...]An anaerobic fluidized bed membrane bioreactor (AFMBR) is a new and effective method for energy-efficient treatment of low strength wastewater, but the factors that affect performance are not well known. Different inocula and acclimation methods of the granular activated carbon (GAC) used in the reactor were examined here to determine their impact on chemical oxygen demand (COD) removal and microbial community composition of domestic wastewater-fed AFMBRs. AFMBRs inoculated with anaerobic digester sludge (D) or domestic wastewater (W) and fed domestic wastewater, or inoculated with a microbiologically diverse anaerobic bog sediment and acclimated using methanol (M), all produced the same COD removal of 63 ± 12% using a diluted wastewater feed (100 ± 21 mg L?? COD). However, an AFMBR with GAC inoculated with anaerobic digester sludge and acclimated using acetate (A) showed significantly increased wastewater COD removal to 84 ± 6%. In addition, feeding the AFMBR with the M-acclimated GAC with an acetate medium for one week subsequently increased COD removal to 70 ± 6%. Microbial communities enriched on the GAC included Geobacter, sulfur-reducing bacteria, Syntrophaceae, and Chlorobiaceae, with reactor A having the highest relative abundance of Geobacter. These results showed that acetate was the most useful substrate for acclimation of GAC communities, and GAC harbors unique communities relative to those in the AFMBR influent and recirculated solution.Nov 2016[...]A new three-electrode electrocoagulation reactor was investigated to increase the rate of removal of phosphate from domestic wastewater. Initially, two electrodes (graphite plate and air cathode) were connected with 0.5 V of voltage applied for a short charging time (~10 s). The direction of the electric field was then reversed, by switching the power supply lead from the anode to the cathode, and connecting the other lead to a sacrificial aluminum mesh anode for removal of phosphate by electrocoagulation. The performance of this process, called a reverse–electric field, air–cathode electrocoagulation (REAEC) reactor, was tested using domestic wastewater as a function of charging time and electrocoagulation time. REAEC wastewater treatment removed up to 98% of phosphate in 15 min (inert electrode working time of 10 s, current density of 1 mA/cm2, and 15 min total electrocoagulation time), which was 6% higher than that the control (no inert electrode). The energy demand varied from 0.05 kWh/m3 for 85% removal in 5 min, to 0.14 kwh/m3 for 98% removal in 15 min. These results indicate that the REAEC can reduce the energy demands and treatment times compared to conventional electrocoagulation processes for phosphate removal from wastewater.Oct 2016[...]A thermally regenerative ammonia battery (TRAB) recently developed for electricity generation using waste heat was adapted and used here as a treatment process for solutions containing high concentrations of copper ions. Copper removal reached a maximum of 77% at an initial copper concentration (Ci) of 0.05 M, with a maximum power density (P) of 31 W m??-electrode area. Lowering the initial copper concentration decreased the percentage of copper removal from 51% (Ci = 0.01 M, P = 13 W m??) to 2% (Ci = 0.002 M, P = 2 W m??). Although the final solution may require additional treatment, the adapted TRAB process removed much of the copper while producing electrical power that could be used in later treatment stages. These results show that the adapted TRAB can be a promising technology for removing copper ions and producing electricity by using waste heat as a highly available and free source of energy at many industrial sites.Sep 2016[...]Sep 2016[...]A larger (6.1 L) MFC stack made in a scalable configuration was constructed with four anode modules and three (two-sided) cathode modules, and tested at a wastewater treatment plant for performance in terms of chemical oxygen demand (COD) removal and power generation. Domestic wastewater was fed either in parallel (raw wastewater to each individual anode module) or series (sequentially through the chambers), with the flow direction either alternated every one or two days or kept fixed in a single direction over time. The largest impact on performance was the wastewater COD concentration, which greatly impacted power production, but did not affect the percentage of COD removal. With higher COD concentrations (~500 mg L??) and alternating flow conditions, power generation was primarily limited by the cathode specific area. In alternating flow operation, anode modules connected to two cathodes produced an average maximum power density of 6.0 ± 0.4 W m??, which was 1.9 ± 0.2 times that obtained for anodes connected to a single cathode. In fixed flow operation, a large subsequent decrease in COD influent concentration greatly reduced power production independent of reactor operation in parallel or serial flow modes. Anode modules connected to two cathodes did not consistently produce more power than the anodes connected to a single cathode, indicating power production became limited by restricted anode performance at low CODs. Cyclic voltammetry and electrochemical impedance spectroscopy data supported restricted anode performance with low COD. These results demonstrate that maintaining power production of MFC stack requires higher influent and effluent COD concentrations. However, overall performance of the MFC in terms of COD removal was not affected.Sep 2016Microbial fuel cell (MFC) cathodes must have high performance and be resistant to water leakage. Hydrophobic poly(vinylidene fluoride) (PVDF) membranes have shown great advantages in providing a waterproof diffusion layer for MFCs and reducing the cathode costs. However, previous approaches have lacked a method to integrate the diffusion layer into the cathode structure. Here, a hot pressing was used to bind the PVDF diffusion layer onto the air side of the activated carbon cathode, and additional catalyst layers were added to improve performance. Cathodes pressed at 60 °C produced a 16% higher maximum power density of 1630 ± 10 mW m?? than non-pressed controls (1400 ± 7 mW m??). Cathode performance was further increased to 1850 ± 90 mW m?? by catalyst stacking, through the addition of an extra catalyst layer (CL), which better utilized the available surface area of the stainless steel mesh (SS) current collector. The use of one stainless steel current collector and two catalyst layers (SS/2CLs) produced more positive cathode potentials compared to other designs (SS/CL or 2SS/2CL). Low material costs and high power production for MFCs using these cathodes could enable more cost effective power production using MFCs.Sep 2016Microbial electrolysis cells (MECs) can generate methane by fixing carbon dioxide without using expensive catalysts, but the impact of acclimation procedures on subsequent performance has not been investigated. Granular activated carbon (GAC) was used to pre-enrich electrotrophic methanogenic communities, as GAC has been shown to stimulate direct transfer of electrons between different microbial species. MEC startup times using pre-acclimated GAC were improved compared to controls (without pre-acclimation or without GAC), and after three fed batch cycles methane generation rates were similar (P & 0.4) for GAC acclimated to hydrogen (22 ± 9.3 nmol cm- 3 d- 1), methanol (25 ± 9.7 nmol cm- 3 d- 1), and a volatile fatty acid (VFA) mix (22 ± 11 nmol cm- 3 d- 1). However, MECs started with GAC but no pre-acclimation had lower methane generation rates (13 ± 4.1 nmol cm- 3 d- 1), and MECs without GAC had the lowest rates (0.7 ± 0.8 nmol cm- 3 d- 1 after cycle 2). Microbes previously found in methanogenic MECs, or previously shown to be capable of exocellular electron transfer, were enriched on the GAC. Pre-acclimation using GAC is therefore a simple approach to enrich electroactive communities, improve methane generation rates, and decrease startup times in MECs.Sep 2016[...]Tim-Patrick FellingerThe Cover picture shows a concept of using a carbon aerogel as catalyst in air cathodes for microbial fuel cells. This nitrogen-doped ionothermal carbon aerogel (NDC) has a high surface area, large pore volume, and hierarchical porosity. The NDC shows excellent electrocatalytic performance for oxygen reduction at neutral pH. Microbial fuel cells using NDC air cathodes achieve a high maximum power density, higher than most of the state-of-the-art catalysts used as air cathodes, and allow simultaneous wastewater treatment. More details can be found in the Full Paper by Zhang et al. (DOI: 10.1002/cssc.).Sep 2016[...]Tim-Patrick FellingerInvited for this month's Cover are the groups at Tsinghua University, Max-Planck Institute of Colloids and Interfaces, and Penn State University, and their collaborators at Harbin Institute of Technology and Stanford University. They present a new nitrogen-doped ionothermal carbon aerogel (NDC) air cathode for use in microbial fuel cells, allowing high power generation and simultaneous wastewater treatment. The Full Paper itself is available at 10.1002/cssc..Aug 2016[...]Aug 2016Salinity-gradient energy (SGE) technologies produce carbon-neutral and renewable electricity from salinity differences between seawater and freshwater. Capacitive mixing (CapMix) is a promising class of SGE technologies that captures energy using capacitive or battery electrodes, but CapMix devices have produced relatively low power densities and often require expensive materials. Here, we combined existing CapMix approaches to develop a concentration flow cell that can overcome these limitations. In this system, two identical battery (i.e., faradaic) electrodes composed of copper hexacyanoferrate (CuHCF) were simultaneously exposed to either high (0.513 M) or low (0.017 M) concentration NaCl solutions in channels separated by a filtration membrane. The average power density produced was 411±14 mW m–2 (normalized to membrane area), which was twice as high as previously reported values for CapMix devices. Power production was continuous (i.e., it did not require a charging period and did not vary during each step of a cycle) and was stable for 20 cycles of switching the solutions in each channel. The concentration flow cell only used inexpensive materials and did not require ion-selective membranes or precious metals. The results demonstrate that the concentration flow cell is a promising approach for efficiently harvesting energy from salinity differences.Aug 2016[...]Tim-Patrick FellingerMicrobial fuel cells (MFCs) can generate electricity from the oxidation of organic substrates using anodic exoelectrogenic bacteria and have great potential for harvesting electric energy from wastewater. Improving oxygen reduction reaction (ORR) performance at a neutral pH is needed for efficient energy production. Here we show a nitrogen doped (≈4 wt%) ionothermal carbon aerogel (NDC) with a high surface area, large pore volume, and hierarchical porosity, with good electrocatalytic properties for ORR in MFCs. The MFCs using NDC air cathodes achieved a high maximum power density of 2300 mW m-2, which was 1.7 times higher than the most commonly used Pt/C air cathodes and also higher than most state-of-the-art ORR catalyst air cathodes. Rotating disk electrode measurements verified the superior electrocatalytic activity of NDC with an efficient four-electron transfer pathway (n=3.9). These findings highlight NDC as a better-performing and cost-efficient catalyst compared with Pt/C, making it highly viable for MFC applications.Jul 2016Applications of microbial fuel cells (MFCs) are limited in part by low power densities mainly due to cathode performance. Successful immobilization of an Fe-N-C co-catalyst on activated carbon (Fe-N-C/AC) improved the oxygen reduction reaction to nearly a four-electron transfer, compared to a twoelectron transfer achieved using AC. With acetate as the fuel, the maximum power density was 4.7±0.2 W m(-2) , which is higher than any previous report for an air-cathode MFC. With domestic wastewater as a fuel, MFCs with the Fe-N-C/AC cathode produced up to 0.8±0.03 W m(-2) , which was twice that obtained with a Pt-catalyzed cathode. The use of this Fe-N-C/AC catalyst can therefore substantially increase power production, and enable broader applications of MFCs for renewable electricity generation using waste materials.Jul 2016Long-term operation of microbial fuel cells (MFCs) can result in substantial degradation of activated carbon (AC) air-cathode performance. To examine a possible role in fouling from organic matter in water, cathodes were exposed to high concentrations of humic acids (HA). Cathodes treated with 100 mg L-1 HA exhibited no significant change in performance. Exposure to 1000 mg L-1 HA decreased the maximum power density by 14% (from 1310 ± 30 mW m-2 to 1130 ± 30 mW m-2). Pore blocking was the main mechanism as the total surface area of the AC decreased by 12%. Minimization of external mass transfer resistances using a rotating disk electrode exhibited only a 5% reduction in current, indicating about half the impact of HA adsorption was associated with external mass transfer resistance and the remainder was due to internal resistances. Rinsing the cathodes with deionized water did not restore cathode performance. These results demonstrated that HA could contribute to cathode fouling, but the extent of power reduction was relatively small in comparison to large mass of humics adsorbed. Other factors, such as bio-polymer attachment, or salt precipitation, are therefore likely more important contributors to long term fouling of MFC cathodes.Jun 2016May 2016Research developments in environmental electrochemistry and its potential to contribute to a cleaner environment are reviewed here for wastewater treatment applications. Most environmental pollutants can be successfully eliminated or converted to non-toxic materials by one or more processes, including electrochemical oxidation, electrochemical reduction, electrocoagulation and electrocoagulation/flotation, electrodialysis, and electrochemical advanced oxidation processes. Specific examples of applications for pollutant removal and reclamation of the wastewater are given for the different processes, along with research needs and improvements for commercial application of these electrochemical processes.Apr 2016Mar 2016Mixing entropy batteries (MEBs) are a new approach to generate electricity from salinity differences between two aqueous solutions. To date, MEBs have only been prepared from solutions containing chloride salts, owing to their relevance in natural salinity gradients created from seawater and freshwater. We hypothesized that MEBs could capture energy using ammonium bicarbonate (AmB), a thermolytic salt that can be used to convert waste heat into salinity gradients. We examined six battery electrode materials. Several of the electrodes were unstable in AmB solutions or failed to produce expected voltages. Of the electrode materials tested, a cell containing a manganese oxide electrode and a metallic lead electrode produced the highest power density (6.3 mW m(-2) ). However, this power density is still low relative to previously reported NaCl-based MEBs and heat recovery systems. This proof-of-concept study demonstrated that MEBs could indeed be used to generate electricity from AmB salinity gradients.Mar 2016[...]Mar 2016[...]Microbial electrolysis cells (MECs) provide a viable approach for bioenergy generation from fermentable substrates such as propionate. However, the paths of electron flow during propionate oxidation in the anode of MECs are unknown. Here, the paths of electron flow involved in propionate oxidation in the anode of two-chambered MECs were examined at low (4.5 mM) and high (36 mM) propionate concentrations. Electron mass balances and microbial community analysis revealed that multiple paths of electron flow (via acetate/H2 or acetate/formate) to current could occur simultaneously during propionate oxidation regardless of the concentration tested. Current (57–96 %) was the largest electron sink and methane (0–2.3 %) production was relatively unimportant at both concentrations based on electron balances. At a low propionate concentration, reactors supplemented with 2-bromoethanesulfonate had slightly higher coulombic efficiencies than reactors lacking this methanogenesis inhibitor. However, an opposite trend was observed at high propionate concentration, where reactors supplemented with 2-bromoethanesulfonate had a low}