Impact and application of electron shuttles on the redox (bio)transformation of contaminants : a review

During the last two decades, extensive research has explored the catalytic effects of different organic molecules with redox mediating properties on the anaerobic (bio)transformation of a wide variety of organic and inorganic compounds. The accumulated evidence points at a major role of electron shuttles in the redox conversion of several distinct contaminants, both by chemical and biological mechanisms. Many microorganisms are capable of reducing redox mediators linked to the anaerobic oxidation of organic and inorganic substrates. Electron shuttles can also be chemically reduced by electron donors commonly found in anaerobic environments (e.g. sulfide and ferrous iron). Reduced electron shuttles can transfer electrons to several distinct electron-withdrawing compounds, such as azo dyes, polyhalogenated compounds, nitroaromatics and oxidized metalloids, among others. Moreover, reduced molecules with redox properties can support the microbial reduction of electron acceptors, such as nitrate, arsenate and perchlorate. The aim of this review paper is to summarize the results of reductive (bio)transformation processes catalyzed by electron shuttles and to indicate which aspects should be further investigated to enhance the applicability of redox mediators on the (bio)transformation of contaminants.F.P. van der Zee thanks the Portuguese Fundaicao para a Ciencia e a Tecnologia for financial support (Grant SFRH/BPD/39086/2007). F. J. Cervantes greatly acknowledges a grant from Council of Science and Technology of Mexico (Grant SEP-CONACYT-C02-55045)

Discontinuities without discontinuity: The Weakly-enforced Slip Method

Tectonic faults are commonly modelled as Volterra or Somigliana dislocations in an elastic medium. Various solution methods exist for this problem. However, the methods used in practice are often limiting, motivated by reasons of computational efficiency rather than geophysical accuracy. A typical geophysical application involves inverse problems for which many different fault configurations need to be examined, each adding to the computational load. In practice, this precludes conventional finite-element methods, which suffer a large computational overhead on account of geometric changes. This paper presents a new non-conforming finite-element method based on weak imposition of the displacement discontinuity. The weak imposition of the discontinuity enables the application of approximation spaces that are independent of the dislocation geometry, thus enabling optimal reuse of computational components. Such reuse of computational components renders finite-element modeling a viable option for inverse problems in geophysical applications. A detailed analysis of the approximation properties of the new formulation is provided. The analysis is supported by numerical experiments in 2D and 3D.Comment: Submitted for publication in CMAM

Fate of aniline and sulfanilic acid under denitrifying conditions

Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BDP/1874

A High-Efficiency 4x45W Car Audio Power Amplifier using Load Current Sharing

A 4x45W (EIAJ) monolithic car audio power amplifier is presented that achieves a power dissipation decrease of nearly 2x over standard class AB operation by sharing load currents between loudspeakers. Output signals are conditioned using a common-mode control loop to allow switch placement between loads with minimal THD increase. A prototype is realized in a SOI bipolar-CMOS-DMOS process with 0.5μm feature size. Die area is 7.5x4.6mm2. THD+N @(1kHz,10W) is 0.05%

Explaining Student Behavior at Scale: The Influence of Video Complexity on Student Dwelling Time

Understanding why and how students interact with educational videos is essential to further improve the quality of MOOCs. In this paper, we look at the complexity of videos to explain two related aspects of student behavior: the dwelling time (how much time students spend watching a video) and the dwelling rate (how much of the video they actually see). Building on a strong tradition of psycholinguistics, we formalize a definition for information complexity in videos. Furthermore, building on recent advancements in time-on-task measures we formalize dwelling time and dwelling rate based on click-stream trace data. The resulting computational model of video complexity explains 22.44% of the variance in the dwelling rate for students that finish watching a paragraph of a video. Video complexity and student dwelling show a polynomial relationship, where both low and high complexity increases dwelling. These results indicate why students spend more time watching (and possibly contemplating about) a video. Furthermore, they show that even fairly straightforward proxies of student behavior such as dwelling can already have multiple interpretations; illustrating the challenge of sense-making from learning analytics.Centre for Innovatio

Fate of aniline and sulfanilic acid in UASB bioreactors under denitrifying conditions

Two upflow anaerobic sludge blanket (UASB) reactors were operated to investigate the fate of aromatic amines under denitrifying conditions. The feed consisted of synthetic wastewater containing aniline and/or sulfanilic acid and a mixture of volatile fatty acids (VFA) as the primary electron donors. Reactor 1 (R1) contained a stoichiometric concentration of nitrate and Reactor 2 (R2) a stoichiometric nitrate and nitrite mixture as terminal electron acceptors. The R1 results demonstrated that aniline could be degraded under denitrifying conditions while sulfanilic acid remains. The presence of nitrite in the influent of R2, caused a chemical reaction that led to immediate disappearance of both aromatic amines and the formation of an intense yellow coloured solution. HPLC analysis of the influent solution, revealed the emergence of three product peaks: the major one at retention time (Rt) 14.3 min and two minor at Rt 17.2 and 21.5 min. In the effluent, the intensity of the peaks at Rt 14.3 and 17.2 min was very low and of that at Rt 21.5 min increased (~3-fold). Based on the mass spectrometry analysis, we propose the structures of some possible products, mainly azo compounds. Denitrification activity tests suggest that biomass needed to adapt to the new coloured compounds, but after a 3 days lag phase, activity is recovered and the final (N2 + N2O) is even higher than that of the control.Fundação para a Ciência e a Tecnologia (FCT

Lab-scale bioreactors for aromatic amines reduction under denitrification conditions

Under anaerobic conditions, azo dyes are readily decolourised as a result of the reductive transformation of the azo group leading to the formation of aromatic amines which are known to be even more toxic than the original dyes. A logical concept for the removal of azo dyes in biological wastewater treatment systems is based on the combination of anaerobic/aerobic treatment, for the degradation of also aromatic amines. A drawback of aerobic treatment is that many aromatic amines are prone to autoxidation. Nitrate/Nitrite are powerful electron acceptors as alternative to oxygen, avoiding the autoxidation. Our research consisted of operating two bioreactors with the objective to investigate the fate of aromatic amines under denitrifying conditions. The reactors were fed with synthetic wastewater contained aniline and/or sulfanilic acid and a mixture of volatile fatty acids as the primary electron donors. Reactor 1 (R1) contained a stoichiometric concentration of nitrate and Reactor 2 (R2) a mixture of nitrate and nitrite as terminal electron acceptors. The R1 results demonstrated that aniline could be degraded under denitrifying conditions while sulfanilic acid remains. The presence of nitrite in the effluent of R2, at low pH, caused a chemical reaction that led to immediate disappearance of both aromatic amines and the formation of an orange colour solution. HPLC analysis revealed the presence of phenol as a product of aniline. Other compounds were detected by LC_MS. The overall COD removal was always higher in R1 than in R2, suggesting toxicity of nitrite and/or the formed products. Whereas a replacement of amino-groups by hydroxyl-groups holds promise for biodegradability, the results indicate that the chemical reaction is more complex, resulting in the formation of compounds that were not mineralized during the course of the experiment