A high resolution and wide range valve for micronewton cold gas thrusters.

Numerous scientific satellites require micronewton thrusters for compensating environmental disturbances. The mass flow control proportional valve plays a crucial role in precisely regulating the thrust. To meet the high resolution and wide range requirements of the thrusters, this paper introduces a novel proportional valve with two sets of independently controllable piezoelectric stack. One set of the piezo-stack is used to compensate the stroke loss of the valve core, mainly caused by the deformation of the valve seat. The valve sealing mechanism is carefully analyzed to reduce the stroke loss. Another set of the stack works as the primary actuator, enabling the high mass flow control resolution. Two sets of independently controlled piezoelectric stacks not only expand the range and improve the range ratio but also provide redundancy and enhance reliability. This means that the actuator can still operate at lower ranges even if one piezo-stack is damaged. The piezo-actuators are assembled using U-shaped connectors, creating a compact and space-efficient overall design. Experimental tests have been conducted to verify the performance of the valve, which demonstrated a mass flow range of 0-675 µg/s with a resolution better than 0.1 µg/s and a flow noise below 0.1 µg/s/Hz1/2 at 0.1 mHz-1 Hz.

Insight into the Pseudocapacitive Behavior of Electroactive Biofilms in Response to Dynamic-Controlled Electron Transfer and Metabolism Kinetics for Current Generation in Water Treatment.

Electroactive biofilms (EBs) engage in complex electron transfer and storage processes involving intracellular and extracellular mediators with temporary electron storage capabilities. Consequently, electroactive biofilms exhibit pseudocapacitive behaviors during substrate degradation processes. However, comprehensive systematic research in this area has been lacking. This study demonstrated that the pseudocapacitive property was an intrinsic characteristic of EBs. This property represents dynamic-controlled electron transfer and is critical in current generation, unlike noncapacitive responses. Nontransient charge and discharge experiments revealed a correlation between capacitive charge accumulation and current generation in EBs. Additionally, analysis of substrate degradation suggested that the maximum power density (Pmax) changed with the kinetic constants of COD degradation, with pseudocapacitances of EBs directly proportional to Pmax. The interaction networks of key latent variables were evaluated through partial least-squares path modeling analysis. The results indicated that cytochrome c was closely associated with the formation of pseudocapacitance in EBs. In conclusion, pseudocapacitance can be considered a valuable indicator for assessing the complex electron transfer behavior of EBs. Pseudocapacitive biofilms have the potential to efficiently regulate biological reactions and serve as a promising carbon-neutral and renewable strategy for energy generation and storage. An in-depth understanding of the intrinsic property of pseudocapacitive behavior in EBs can undoubtedly advance the development of this concept in the future.

Vitamin B12 and iron-rich sludge-derived biochar enhanced PFOA biodegradation: Importance of direct inter-species electron transfer and functional microbes.

Owing to the strong C-F bond in nature and the rigidity of the poly-fluoroalkyl chain, perfluorooctanoic acid (PFOA) is difficult to be eliminated by reactive species and microbes in environments, thus posing a serious threat to ecosystems. Vitamin B12 as a cofactor for enzymes, and biochar as the electron providers and conductors, were integrated to enhance PFOA biodegradation. The raw material of biochar was the sludge after dewatering by adding 50 mg/g DS of Fe(III). After pyrolysis under high temperature (800 °C), biochar (SC800) detected high content of Fe(II) (197.64 mg/g) and abundant oxygen-containing functional groups, thus boosting PFOA biodegradation via donating electrons. 99.9% of PFOA could be removed within 60 d as 0.1 g/L SC800 was presented in the microbial systems containing vitamin B12. Moreover, vitamin B12 facilitated the evolution of Sporomusa which behaved the deflorination. Via providing reactive sites and mediating direct inter-species electron transfer (DIET), SC800 boosted PFOA biodegradation. Corresponding novel results in the present study could guide the development of bioremediation technologies for PFOA-polluted sites.

Efficient and selective recovery of iron phosphate from the leachate of incinerated sewage sludge ash by thermally induced precipitation.

Phosphorus recovery from incinerated sewage sludge ash (ISSA) is important but hindered by low selectivity. Here, a novel strategy of acid leaching followed by thermally induced precipitation was proposed for the efficient and selective recovery of FePO4 from ISSA samples. A high phosphorus leaching efficiency of ∼ 99.6% was achieved with 0.2 mol/L H2SO4 and liquid to solid (L/S) ratio of 50 mL/g. Without removing various co-existing ions (Al3+, Ca2+, SO42-, etc.), high-purity FePO4 of ∼ 92.9% could be facilely produced from this highly acidic H2SO4 leachate (pH = 1.2) by simple addition of Fe(III) at a molar ratio of 1:1 to the phosphorus and reacted at 80 °C for thermally induced precipitation. The remained acid leachate could be further reused for five times to continue leaching phosphorus from the ISSA samples and produce the FePO4 precipitates with a high phosphorus recovery efficiency of 81.1 ± 1.8%. The selective recovery of FePO4 from the acid leachate was demonstrated more thermodynamically favorable compared to other precipitates at this acidic pH of 1.2, and elevated temperature of 80 °C towards thermally induced precipitation. The estimated cost of this strategy was ∼$26.9/kg-P and lower than that of other existing technologies. The recovered FePO4 precipitates could be used as a phosphate fertilizer to promote the growth of ryegrass, and also as a precursor to synthesize high-value LiFePO4 battery material, demonstrating the high-value application potential of the phosphorus from the ISSA.

Ultra-High-Speed Accelerator Architecture for Convolutional Neural Network Based on Processing-in-Memory Using Resistive Random Access Memory.

Processing-in-Memory (PIM) based on Resistive Random Access Memory (RRAM) is an emerging acceleration architecture for artificial neural networks. This paper proposes an RRAM PIM accelerator architecture that does not use Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs). Additionally, no additional memory usage is required to avoid the need for a large amount of data transportation in convolution computation. Partial quantization is introduced to reduce the accuracy loss. The proposed architecture can substantially reduce the overall power consumption and accelerate computation. The simulation results show that the image recognition rate for the Convolutional Neural Network (CNN) algorithm can reach 284 frames per second at 50 MHz using this architecture. The accuracy of the partial quantization remains almost unchanged compared to the algorithm without quantization.

Cathodic biofouling control by microbial separators in air-breathing microbial fuel cells.

Microbial fuel cells (MFCs) incorporating air-breathing cathodes have emerged as a promising eco-friendly wastewater treatment technology capable of operating on an energy-free basis. However, the inevitable biofouling of these devices rapidly decreases cathodic catalytic activity and also reduces the stability of MFCs during long-term operation. The present work developed a novel microbial separator for use in air-breathing MFCs that protects cathodic catalytic activity. In these modified devices, microbes preferentially grow on the microbial separator rather than the cathodic surface such that biofouling is prevented. Trials showed that this concept provided low charge transfer and mass diffusion resistance values during the cathodic oxygen reduction reaction of 4.6 ± 1.3 and 17.3 ± 6.8 Ω, respectively, after prolonged operation. The maximum power density was found to be stable at 1.06 ± 0.07 W m-2 throughout a long-term test and the chemical oxygen demand removal efficiency was increased to 92% compared with a value of 83% for MFCs exhibiting serious biofouling. In addition, a cathode combined with a microbial separator demonstrated less cross-cathode diffusion of oxygen to the anolyte. This effect indirectly induced the growth of electroactive bacteria and produced higher currents in air-breathing MFCs. Most importantly, the present microbial separator concept enhances both the lifespan and economics of air-breathing MFCs by removing the need to replace or regenerate the cathode during long-term operation. These results indicate that the installation of a microbial separator is an effective means of stabilizing power generation and ensuring the cost-effective performance of air-breathing MFCs intended for future industrial applications.

Efficient degradation of refractory pollutant in a microbial fuel cell with novel hybrid photocatalytic air-cathode: Intimate coupling of microbial and photocatalytic processes.

A microbial fuel cell-photocatalysis system with a novel photocatalytic air-cathode (MFC-PhotoCat) was proposed for synergistic degradation of 2,4,6-trichlorophenol (TCP) with simultaneous electricity generation. Stable electricity generation of 350 mV was achieved during 130 days of operation. Besides, 50 mg L-1 TCP was completely degraded within 72 h, and the rate constant of 0.050 h-1 was 1.8-fold higher than MFC with air-cathode without N-TiO2 photocatalyst. Degradation pathway was proposed based on the intermediates detected and density functional theory (DFT) calculation, with two open-chain intermediates (2-chloro-4-keto-2-hexenedioic acid and hexanoic acid) detected. Furthermore, hierarchical cluster and PCoA revealed significant shifts of microbial community structures, with enriched exoelectrogen (55.2% of Geobacter) and TCP-degrading microbe (7.1% of Thauera) on the cathode biofilm as well as 61.8% of Pseudomonas in the culture solution. This study provides a promising strategy for synergic degradation of recalcitrant contaminants by intimate-coupling of MFC and photocatalysis.

Simultaneous heavy metal removal and sludge deep dewatering with Fe(II) assisted electrooxidation technology.

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation-reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Integration of electrochemical and calcium hypochlorite oxidation for simultaneous sludge deep dewatering, stabilization and phosphorus fixation.

A hybrid electrochemical process with Ca(ClO)2 addition for simultaneous sludge dewaterability, stabilization and phosphorus fixation was proposed. Under optimal conditions (150 mg/g VS Ca(ClO)2, 15 V), the capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 88% and 92%, respectively. Efficient sludge stabilization with E. coli colonies of less than 1000 MPN/g TS was achieved. Phosphorus of 99% was removed from the filtrate and successfully fixed in the sludge cake and on the electrode surface. The integration of electrochemical and hypochlorite oxidation could effectively degrade the tightly bound extracellular polymeric substances (TB-EPS) structure with a total organic carbon (TOC) reduction of 52%. Besides, the disintegration of microbial cell envelopes was also achieved, with a reduction of living cell fraction of 98%. Furthermore, system pH could be maintained at near neutral (7.45) and the conversion of Fe(II) to Fe(III) was also facilitated with the addition of Ca(ClO)2, resulting in improved electrocoagulation process for enhanced sludge dewatering and phosphorus fixation. The multifunctional effects were achieved with the cooperated extracellular electrooxidation for EPS destruction and the active chlorine for intracellular microbial cell disintegration. This research provides a promising strategy for integrated sludge treatment and recycling for possible land utilization.

Biogas and phosphorus recovery from waste activated sludge with protocatechuic acid enhanced Fenton pretreatment, anaerobic digestion and microbial electrolysis cell.

Biogas and phosphorus recovery from waste activated sludge (WAS) with sequential homogeneous protocatechuic acid (PCA) enhanced Fenton pretreatment, anaerobic digestion (AD) and microbial electrolysis cell (MEC) were investigated. The cumulation of biogas production of WAS-Fenton-AD was 330.4 mL/g VS, which was 2.05-fold of the control without pretreatment (WAS-AD) during anaerobic digestion. Biogas production of 178 mL/L/d from WAS-Fenton-AD-MEC was achieved, which was 5.23-fold of the WAS-MEC, 2.28-fold of WAS-Fenton-MEC and 1.46-fold of WAS-AD-MEC, respectively. Enhanced phosphorus recovery in form of struvite reached 1.72 g/g TS (18.03% of total P) with a purity of 74.4%. Microbial community richness and diversity analysis revealed that the pretreatment process under circumneutral condition improved the diversity of microbial community, which was consisted of Bacteroidetes (33.90%), Proteobacteria (33.14%), and Chloroflexi (10.14%), compared to a majority of Firmicutes (70.81%) in WAS-AD. This study provides a feasible strategy for the recovery of biogas combined with phosphorus from WAS.

Application of Deep Compression Technique in Spiking Neural Network Chip.

In this paper, a reconfigurable and scalable spiking neural network processor, containing 192 neurons and 6144 synapses, is developed. By using deep compression technique in spiking neural network chip, the amount of physical synapses can be reduced to 1/16 of that needed in the original network, while the accuracy is maintained. This compression technique can greatly reduce the number of SRAMs inside the chip as well as the power consumption of the chip. This design achieves throughput per unit area of 1.1 GSOP/([Formula: see text]) at 1.2 V, and energy consumed per SOP of 35 pJ. A 2-layer fully-connected spiking neural network is mapped to the chip, and thus the chip is able to realize handwritten digit recognition on MNIST with an accuracy of 91.2%.

A bio-electro-Fenton system with a facile anti-biofouling air cathode for efficient degradation of landfill leachate.

Bio-electro-Fenton (BEF) system holds great potential for sustainable degradation of refractory organics. Activated carbon (AC) air cathode was modified by co-pyrolyzing of AC with glucose and doping with nano-zero-valent iron (denoted as nZVI@MAC) in order to promote two-electron oxygen reduction reaction (2e- ORR) for enhanced oxidizing performance. Single chamber microbial fuel cells (SCMFCs) with nZVI@MAC cathode was examined to degrade landfill leachate. It was revealed that nZVI@MAC cathode SCMFC showed higher degradation efficiency towards landfill leachate. Six landfill leachate treatment cycles indicated that nZVI@MAC cathode SCMFC exhibited higher COD removal efficiencies over AC and nZVI@AC and greatly enhanced columbic efficiency compared to AC and nZVI@AC cathode. Anti-biofouling effect was found on nZVI@MAC cathode because of the high Fenton oxidation effects at the vicinity of the cathode. Electrochemical characterizations indicated that MAC cathode had superior 2e- ORR capability than AC and nZVI@AC cathode, which was further evidenced by higher H2O2 production from nZVI@MAC cathode in SCMFC. Graphitic structure of MAC was evidenced by High Resolution Transmission Electron Microscopy, and glucose pyrolysis also resulted in nano carbon spheres on the activated carbon skeletons. Raman spectra indicated more defects were generated on MAC during its co-pyrolyzation with glucose.

In situ generation of zero valent iron for enhanced hydroxyl radical oxidation in an electrooxidation system for sewage sludge dewatering.

A hybrid electrochemical conditioning strategy for enhanced sewage sludge dewatering was proposed. A water content of 47.2 wt.% for the dewatered sludge cake was achieved at an applied voltage of 20 V for 30 min, which was significantly lower than previously reported results. The capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 75.6% and 90.9%, respectively. Four simultaneous processes, including electrooxidation, the electro-Fenton process, molecular oxygen activation via zero valent iron (ZVI) and Fe(III) flocculation, had synergetic effects on the degradation of extracellular polymeric substances (EPS) to enhance sludge dewaterability. The in situ generation of ZVI on the cathode electrode facilitated the reduction of Fe(III) to Fe(II) via activation of molecular oxygen. The sludge pH decreased spontaneously and remained acidic due to the competitive reaction of ZVI generation to hydrogen evolution as well as the Fe(III) flocculation process, which further guaranteed the high efficiency of hydroxyl radical generation. Changes in the physiochemical properties of the sludge (particle size distribution, zeta potential, viscosity and EPS characteristics) induced by the hybrid conditioning process were further explored. In addition, the economic potential of the hybrid system was preliminarily assessed (USD$ 127.6/ton dry sludge).