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•The effect of external load in MFCs along with anodic biofilm response was studied.•Dynamic control of external load based on internal resistance aided the performance.•Mass and ...charge transfer limitations were determined by the external load.•Geobacter and co-existing species affected the stability and performance of MFCs.
The performance and behavior of microbial fuel cells (MFCs) are influenced by among others the external load (Rext). In this study, the anode-surface biofilm formation in MFCs operated under different Rext selection/tracking-strategies was assessed. MFCs were characterized by electrochemical (voltage/current generation, polarization tests, EIS), molecular biological (microbial consortium analysis) and bioinformatics (principal component analysis) tools. The results indicated that the MFC with dynamic Rext adjustment (as a function of the actual MFC internal resistance) achieved notably higher performance but relatively lower operational stability, mainly due to the acidification of the biofilm. The opposite (lower performance, increased stability) could be observed with the static (low or high) Rext application (or OCV) strategies, where adaptive microbial processes were assumed. These possible adaptation phenomena were outlined by a theoretical framework and the significant impact of Rext on the anode colonization process and energy recovery with MFCs was concluded.
Anaerobic digestion (AD) for biogas production is affected by many factors that includes organic loading rate (OLR). This OLR appears to be closely linked to various other factors and understanding ...these linkages would therefore allow the sole use of OLR for process performance monitoring, control, as well as reactor design. This review's objective is to collate the various AD factor specific studies, then relate these factors' role in OLR fluctuations. By further analyzing the influence of OLR on the AD performance, it would then be possible, once all the other factors have been determined and fixed, to manage an AD plant by monitoring and controlling OLR only. Decisions on reactor design, process kinetics, biogas yield and process stability can then be made much more quickly and with minimal troubleshooting steps.
Iron- and steelmaking cause ∼7% of the global CO2 emissions, due to the use of carbon for the reduction of iron ores. Replacing carbon by hydrogen as the reductant offers a pathway to massively ...reduce these emissions. However, the production of hydrogen using renewable energy will remain as one of the bottlenecks at least during the next two decades, because making the gigantic annual crude steel production of 1.8 billion tons sustainable requires a minimum stoichiometric amount of ∼97 million tons of green hydrogen per year. Another fundamental aspect to render the ironmaking sector more sustainable lies in an optimal utilization of green hydrogen and energy, thus reducing efforts for costly in-process hydrogen recycling. We therefore demonstrate here how the efficiency in hydrogen and energy consumption during iron ore reduction can be dramatically improved by the knowledge-based combination of two technologies: partially reducing the ore at low temperature via solid-state direct reduction (DR) to a kinetically defined degree, and subsequently melting and completely transforming it to iron under a reducing plasma (i.e. via hydrogen plasma reduction, HPR). Results suggest that an optimal transition point between these two technologies occurs where their efficiency in hydrogen utilization is equal. We found that the reduction of hematite through magnetite into wüstite via DR is clean and efficient, but it gets sluggish and inefficient when iron forms at the outermost layers of the iron ore pellets. Conversely, HPR starts violent and unstable with arc delocalization, but proceeds smoothly and efficiently when processing semi-reduced oxides, an effect which might be related to the material's high electrical conductivity. We performed hybrid reduction experiments by partially reducing hematite pellets via DR at 700 °C to 38% global reduction (using a standard thermogravimetry system) and subsequently transferring them to HPR, conducted with a lean gas mixture of Ar-10%H2 in an arc-melting furnace, to achieve full conversion into liquid iron. This hybrid approach allows to exploit the specific characteristics and kinetically favourable regimes of both technologies, while simultaneously showing the potential to keep the consumption of energy and hydrogen low and improve both, process stability and furnace longevity by limiting its overexposure to plasma radiation.
•Performing modification, calibration and validation of ADM1 by real operating data.•Employing biowaste, manure and grease as co-substrates beside sludge (future plan)•Estimating biogas and power ...generation, and waste minimization of co-substrates.•Average value of power output (0.9 MWel) increased to 2.5 MWel with no instability.•Manure was not a suitable co-substrate for co-digestion with sewage sludge.
Anaerobic digesters of Tehran waste water treatment plant (WWTP) working in mono-digestion operation are investigated for not only methane augmentation but also for waste minimization by the use of co-digestion process. Three types of co-substrate wastes including slaughterhouse flotation greases, biowaste, and cattle manure were selected because they were available in large amounts. A model was required to predict the volume flow rates of feeding co-substrate wastes into digesters during operation time for providing sufficient biogas in order to generate maximum gas engine power output. Thus, Anaerobic Digestion Model Number 1 (ADM1) for mono-substrate is modified so that it could be used with characterization of primary sludge, secondary sludge, and several co-substrate waste inputs into digesters. Then, appropriate coefficients (hydrolysis coefficient and bio-degradability factor) in this model were determined by the use of sludge biochemical methane potential (BMP) tests. After complete modification, calibration and validation of ADM1 method with experimental values of primary and secondary sludge for anaerobic digestion (which is the current reality in Tehran WWTP), the developed model is integrated with a co-substrate feeding strategy for estimation of required feed flow rates of co-substrate wastes. Results indicated that feeding grease, biowaste and manure increased the average generated biogas from 10524 m3/day (62.1% CH4) to 29161 m3/day (61.5% CH4), 30183 m3/day (59.5% CH4), and 32531 m3/day (53.8% CH4), respectively. Also, the gas engine power output increased from an average value of 906 kW to about 2.5 MW (during the studied operation time period). Low hydrolysis coefficient and low degradability of manure caused high bio-degradable feed flow rate of this co-substrate waste to about 58,200 kgCODb/day in average. This value for biowaste and grease was 38,800 and 36,100 kgCODb/day, respectively. Feeding grease and biowaste into digesters increased COD removal efficiency from 37% to 58% and 54%, respectively, while feeding manure dropped it to 31%. Furthermore, values of pH and VFA/Alk indicators showed stable conditions in digesters. Moreover, it was found that all three co-digestion processes did not impose a new load on other WWTP equipment for reducing nitrogen in the effluent stream of WWTP. Finally, it was concluded that biowaste is an appropriate co-substrate for our case study.
Anaerobic digestion has received significant attention in recent years due to dual benefits of waste diversion from landfill and bioenergy recovery. Among various temperature regimes, digesters ...operated under thermophilic (50–70 °C) condition has potential to provide several advantages over mesophilic (30–45 °C) and psychrophilic (<20 °C) conditions, which include faster degradation of organics and higher energy recovery. However, the operation of thermophilic digesters requires closer monitoring and control due to an additional risk of ammonia inhibition and irreversible acidification through the accumulation of volatile fatty acids. Conventional strategies to alleviate instabilities in thermophilic anaerobic digestion process have been focused primarily on the development of robust microbiome and co-digestion of complementary substrates. On the other hand, emerging strategies include the integration of digesters with microbial electrochemical systems and amendment of conductive additives. This review provides a critical overview of these strategies and summarizes research gaps to guide researchers and practitioners in the future research.
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•Process instabilities due to ammonia inhibition and acidification are reviewed.•Methods for improving process stability in thermophilic digesters are summarized.•Research gaps associated with the implementation of these methods are identified.
In milling of thin-walled workpieces, like aero engine blades, the reduction of vibrations is of central importance to reach a more economical and reliable process as well as an improved workpiece ...surface quality. However, the dynamic behavior of the workpiece continuously varies due to changes in workpiece stiffness and mass, caused by the moving position of the excitation force as well as the material removal. In this paper, the simulation of the changing workpiece dynamics for a simplified blade geometry using FE-modal analysis is demonstrated. All extracted workpiece dynamic states are combined in a reduced LPV-model (Linear Parameter-Varying model). The LPV-model is able to describe the varying process dynamic behavior and makes the selection of advantageous spindle speeds possible.
Organic loading rate (OLR) disturbances were introduced into a mesophilic anaerobic digester treating food waste (FW) to induce stable and deteriorative phases. The microbial community of each phase ...was investigated using 454-pyrosequencing. Results show that the relative abundance of acid-producing bacteria and syntrophic volatile fatty acid (VFA) oxidizers increased dramatically at deteriorative phase, while the dominant methanogens did not shift from acetoclastic to hydrogenotrophic groups. The mismatching between bacteria and methanogens may partially be responsible for the process deterioration. Moreover, the succession of predominant hydrogenotrophic methanogens reduced the consumption efficiency of hydrogen; meanwhile, the dominant Methanosaeta with low acetate degradation rate, and the increase of inhibitors concentrations further decreased its activity, which may be the other causes for the process failure. These results improve the understanding of the microbial mechanisms of process instability, and provide theoretical basis for the efficient and stable operation of anaerobic digester treating FW.
To reveal the effects of welding speed on welding process stability, microstructure, and mechanical performance of SUS304 weldments fabricated by local dry underwater pulsed metal inert-gas welding ...(LDU-PMIG), the electrical signals and droplet transfer behaviours of welding process, phase morphologies and distributions, grain sizes and grain boundary characteristics, microhardness, and tensile strength of these weldments were investigated in this work. The results indicated that with the increase of welding speed from 9.0 mm/s to 16.2 mm/s, the welding process stability first improved and then deteriorated. The more rapid water cooling rate caused by the increase of welding speed led to the δ-ferrite morphological evolution from skeletal to lath, which promoted the transformation from brittleness to ductility in the weld mechanical performance. Furthermore, the proportions of small-size grains (less than 10 μm) and low-angle grain boundaries (2–15°) first increased and then decreased, which determined the same variation trend in the comprehensive mechanical performance of weldments. The weldment obtained at 12.6 mm/s exhibited the highest microhardness, tensile strength and elongation, which achieved 70.0 %, 92.3 %, and 61.6 % of base metal. These results are conducive to enhance the SUS304 LDU-PMIG weldment quality and facilitate its application in marine equipment field.
•Thick plate laser-arc hybrid welding stability was observed with high speed imaging.•Laser-arc interaction is described for a wide range of parameters.•Pulsed arc mode can maintain stable processing ...speeds than the CMT+P mode.•Arc setup affects droplet trajectories, which for a leading arc can cause porosity.
Thick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.
This brief develops an innovative robust iterative learning control law using the repetitive process setting. The new design is experimentally validated through a comprehensive set of experiments ...highlighting the capabilities for the position tracking control of a permanent magnet synchronous motor subject to load disturbances in the presence of uncertainties in selected parameters.
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