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In this study, a microbial fuel cell (MFC) with granular activated carbon packed anode (GAC-MFC) is developed and compared with a MFC with granular graphite packed anode (GG-MFC), to evaluate the adsorptive effect of the granular activated carbon anode on MFC’s performance. The current output of GAC-MFC (11.1 mA, 18.1 mA and 21.6 mA) is much higher than that of GG-MFC (4.87 mA, 12.5 mA and 17.9 mA) at low substrate COD concentrations (∼50, ∼100 and ∼200 mg/L) when a low external resistance (20 Ω) and high circulation flow rate (20 mL/min) are applied. The half-saturation constant ( K s ) of GAC-MFC is about half as much as that of GG-MFC, suggesting that GAC-MFC has more affinity for anode substrate and deliver better kinetic performance than GG-MFC. Internal resistance distribution shows that mass diffusion resistance of GAC-MFC is at least 50% lower than that of GG-MFC when the substrate COD is ∼50 mg/L, indicating that the adsorptive effect of granular activated carbon packed anode helps to effectively facilitate mass transfer at low COD concentrations. Otherwise, the substrates adsorbed on GAC surface also serve to buffer the impact of COD concentration plummeting in bulk solution. [ABSTRACT FROM AUTHOR]

A novel anode is fabricated by electrodepositing manganese dioxide (MnO 2 ) on carbon felt to promote MFC's power production. Compared to the bare carbon felt anode, when the electrodeposition time increases to 60 min, the anode capacitance improves 46 times. The maximum power density of the MFC with the MnO 2 -coated anode reaches 3580 ± 130 mW m −2 , 24.7% higher than that with the bare carbon felt anode (2870 mW m −2 ). MnO 2 is believed to facilitate extracellular electron transfer and accordingly improve the power output. Three anode substrate circulation modes, i.e., flow-through, side-flow, and no-flow, are applied. Electrochemical impedance spectroscopy (EIS) tests reveal that flow-through mode decreases the anode mass transfer resistance by 41.4% compared to the no-flow mode and contributes to the MFC's power production improvement. [ABSTRACT FROM AUTHOR]

[Display omitted] • A compromise volume fraction of the added magnetizable particles was 0.40. • Preferred magnetizable particles made admixture MFB within magnetic stabilization. • The more stable the obtained magnetic stabilization, the better the intensification. • Mass transfer intensification depended on hydrodynamics in resulting admixture MFB. This work aimed to explore the property effects of added magnetizable particles on the magnetic intensification of mass transfer between the fluidizing gas and Geldart-B nonmagnetizable particles. A compromise volume fraction (x vM) of magnetizable particles in the resulting binary admixture was 0.40 to transmit the stabilizing effect of magnetic field to the nonmagnetizable particles and save the bed volume. When x vM was maintained the same (=0.40), the added magnetizable particles had an optimal size/density to maximize the magnetic intensification. When the gas velocity was three times the minimum fluidization velocity of the nonmagnetizable particles, the optimum size and density ratios between the added magnetizable particles and the nonmagnetizable particles were 0.41 and 2.99, respectively. When the mass fraction was kept constant (=0.77), the lighter magnetizable particles were preferred to transmit the magnetic stabilization. The property effects of added magnetizable particles on the magnetic intensification of mass transfer depended on its effects on the hydrodynamics in the resulting admixture MFB. Provided the added magnetizable particles could make the obtained admixture MFB locate in the magnetic stabilization flow regime, the mass transfer could be significantly intensified. The more stable the obtained magnetic stabilization, the better the magnetic intensification of the mass transfer. [ABSTRACT FROM AUTHOR]

High sensitivity is essential for the application of bioelectrochemical system-based sensor (BES sensor) in water quality early-warning, where the electroactive biofilm is of vital importance as it delivers a responsive electric signal to toxic substances. This study artificially designed the morphology of a naturally formed biofilm by employing a serrated knife to scrape the biofilm and thus obtained a reduced thickness and roughness. Then it was further cut by half to halve the biomass. BES sensors equipped with control and processed biofilms were operated under constant anode potential (CAP) and tested at different Cu(II) concentrations to study their sensitivities. Results revealed that the scraped biofilms delivered much increased sensitivity towards Cu(II) shock, which was attributed to a reduced thickness as illustrated by macroscopic and microscopic morphology analysis. Another finding was that biomass per unit interfacial area, rather than the biomass, also affected the sensitivity. To further describe how the inner biofilm responded the toxicity after morphology design, a one-dimension mass transfer model was developed to simulate the mass transfer of Cu(II) in the biofilms with different thicknesses. The relative threshold value of inlet Cu(II) concentration was employed to fit the modeling and experimental results, indicating that decreased biofilm thickness was beneficial for improving the sensitivity. Unlabelled Image • Biofilm's morphology design leads to reduced thickness and roughness. • Scraping the biofilm raises the sensitivity by 34%. • Biofilm's thickness is recognized essential factor on sensitivity. • Biomass per unit interfacial area affects the sensitivity. • One-dimension model simulates the Cu(II) transfer in biofilm. [ABSTRACT FROM AUTHOR]

• A pilot-scale bubbling fluidized bed adsorption device was designed and operated. • Bubbling fluidized bed is suitable to recovery the industrial VOCs. • Diffusion is the rate-determining factor of adsorption. • The adsorption rate of the bubbling fluidized bed is significantly high. • The optimized conditions of bed height is 40 mm for the bubbling fluidized bed. Adsorption is one of the most efficient inexpensive strategies for the removal of volatile organic compounds (VOCs). However, adsorption of VOCs by fixed beds has certain limitations, such as considerable energy consumption and high operating costs. To treat VOCs with high volume and low concentration, a pilot-scale multistage bubbling fluidized bed adsorber was developed herein and was used to conduct the adsorption experiments. Experimental investigation of ethanol adsorption on the adsorbent under static and dynamic conditions revealed that ethanol adsorption on the adsorbent followed the Langmuir adsorption model. The adsorption kinetics followed a linear driving force (LDF) model, which showed that diffusion was the rate-determining factor. Moreover, the effects of operating conditions, such as bed height, superficial gas velocity, inlet concentration, and desorption temperature, on adsorption were investigated. The results showed that adsorption efficiency in the bubbling fluidized bed varied from 85.7% to 94.5%. The findings of this study could provide the basic data for the design and development of a bubbling fluidized bed for application in the recovery of low-to-medium concentrations of industrial VOCs. [ABSTRACT FROM AUTHOR]

For lack of relevant investigation in the context of large-scale membrane bioreactors (MBRs), evaluation of the oxygen mass transfer parameters is important for the optimized design of the aeration system in an MBR process. In this study, we sampled the actual sludge from several large-scale MBRs (>10,000 m 3 /d) for the oxygen transfer tests. It was found that specific surface area of bubbles, aeration intensity, and diffuser submerged depth had positive effect on the oxygen transfer coefficient ( k L a ), while some mixed liquor characteristics such as the mixed liquor suspended solids (MLSS) concentration and apparent viscosity exerted negative function on it. We further proposed quantitative expressions to predict the alpha-factor ( α -factor) under typical aeration conditions. The α -factor was found to be above 0.6 when MLSS was roughly less than 12 g/L, which was generally higher than the α -factor predicted in the previous literature, such that overestimation of aeration demand in large-scale MBRs might be avoided. [ABSTRACT FROM AUTHOR]

• Conductivity is a comparable metric to characterize EET. • Nanowires and microbial aggregates have substantially different conductivity levels. • Several factors can cause a large variability in the measured conductivity. • Calculating the EET flux in microbial aggregates from conductivity measurement. Microbial extracellular electron transfer (EET) plays a crucial role in bioenergy production and resource recovery from wastewater. Interdisciplinary efforts have been made to unveil EET processes at various spatial scales, from nanowires to microbial aggregates. Electrical conductivity has been frequently measured as an indicator of EET efficiency. In this review, the conductivity of nanowires, biofilms, and granular sludge was summarized, and factors including subjects, measurement methods, and conducting conditions that affect the conductivity difference were discussed in detail. The high conductivity of nanowires does not necessarily result in efficient EET in microbial aggregates due to the existence of non-conductive substances and contact resistance. Improving the conductivity measurement of microbial aggregates is important because it enables the calculation of an EET flux from conductivity and a comparison of the flux with mass transfer coefficients. This review provides new insight into the significance, characterization, and optimization of EET in microbial aggregates during a wastewater treatment process. [ABSTRACT FROM AUTHOR]

In this study, nitrogen-doped carbon nanotube (N-CNT) membrane compared with Pt-coated CNT (Pt-CNT) membrane and pristine CNT membrane were utilized as air cathode as well as filtration material of microbial fuel cells (MFCs). The MFCs were continuously operated for 39 days to investigate their power generation, organics removal, proton transfer, and fouling behavior under various influent concentrations and hydraulic retention times (HRTs). During operation, the N-CNT filtration MFC achieved the best effluent quality and power generation, with efficient removal of total organic carbon (TOC) (95.2%) and NH 4 + -N (97.7%), and maximum power density and current density of 408 mW/m 2 and 2.36 A/m 2 respectively. The excellent performance of the N-CNT MFC was mainly attributed to its special morphology and rich N-functional groups. The N-CNT membrane has a nanotube diameter of 37 ± 4 nm, pore size of 95 ± 33 nm, and porosity of 79.9%, which was even better than traditional microfiltration membrane as a filtration material for pollutant removal. The high nitrogen content (2.12 at%) and high specific surface area (93.5 m 2 /g) due to its network structure also enhanced O 2 reduction. In addition to the excellent performance of N-CNT cathode, the filtration operation enhanced cathode O 2 reduction by increasing mass transfer in cathode micro-pore and improving proton transfer with water flowing from anode to cathode. Moreover, a separate experiment also demonstrated that the cathode fouling could be mitigated under high current operation. [ABSTRACT FROM AUTHOR]

Researchers believe that adding conductive mediums in electrochemically active biofilms (EABs) would improve the sensitivity of EAB-based biosensor for real-time water quality early-warning through facilitating the extracellular electron transfer (EET), which has been hardly evidenced mostly because naturally formed EABs employed in previous biosensor studies were recognized distinct and incapable of delivering comparable electrical signals. By preparing artificial EABs where Shewanella oneidensis MR-1 was encapsulated in sodium alginate (SA), this study solved how polypyrrole (PPy) as conductive medium would affect the sensitivity of EAB-based biosensor, as well as mass transfer of toxicant during this process. Different mass ratios (0.125:1, 0.25:1 and 1:1) of PPy over SA were tested, and the sensitivity promoted by 20%, 15% and 6%, respectively. Results indicated that a small amount of PPy addition (PPy: SA = 0.125: 1 in mass ratio) was more effective to increase the biosensor's sensitivity compared to larger amount of PPy employed in EAB. This was when improved conductivity introduced by PPy would dominate in affecting the sensitivity over contrarily weakened mass transfer in the meantime. • Artificial electroactive biofilms containing polypyrrole were prepared. • Polypyrrole increases conductivity as well as decreases mass transfer. • Small amount of polypyrrole better increased biosensor's sensitivity. [ABSTRACT FROM AUTHOR]

• Biohythane production from MEC led to positive energy recovery • Dual-chamber MEC could stabilize biohythane generation and composition • Methanogen in single-chamber MEC consumed hydrogen to unbalance composition • CEM was key part to maintain hydrogen production for stable biohythane composition • Geobacter and methanogens were key species to affect biohythane composition Biohythane is alternative fuel to replace fossil fuel for car combustion, and biohythane generation could be potential pathway for energy recovery from wastewater treatment. Microbial electrolysis cell (MEC) is electrochemical technique to convert waste to methane and hydrogen gas for biohythane generation, but the feasibility and stability of MEC needs further investigation to assure sustainable energy recovery. System configuration is paramount factor for electrochemical reaction and mass transfer, and this study was to investigate the configuration impact (single vs dual chamber) of MEC for biohythane generation rate and stability. This study showed that dual-chamber MEC could separate methane and hydrogen gas production in the anode and cathode, and combined both together to produce biohythane. To reduce ohmic resistance for higher current, cation exchange membrane (CEM) was removed from dual-chamber to single-chamber MEC. However, free hydrogen diffusion was allowed in the single chamber since CEM was removed. The diffused hydrogen and substrate towards the cathode would favor the methanogen growth, and thus the hydrogen was consumed to reduce the biohythane generation and energy recovery efficiency (i.e., 7.5 × 10−3 reduced to 5.7 × 10−3 kWh kg−1 degraded COD day−1 after converting dual-chamber to single-chamber MEC). Absolute abundance of methanogen in single-chamber MEC was greatly boosted, as Methanosarcina and Methanobacteriale on the anode surface, increased by 132% and 243%, respectively, while the original dual-chamber MEC could maintain Geobacter growth for high current generation. This is the keystone study to demonstrate the importance of dual-chamber MEC for the feasibility and stability for the biohythane generation, building up the foundation to use electrochemical device to convert the organic waste to the alternative biohythane. [Display omitted] [ABSTRACT FROM AUTHOR]

• Artificial EAB shortens startup time of biosensor. • High repeatability of biosensor can be obtained by using artificial EAB. • Low concentration of electroactive bacteria improves biosensor's sensitivity. • 1% of sodium alginate was optimum for sensitivity of artificial EAB. • Artificial EAB realizes real-time online water quality early-warning. A major challenge for devising an electrochemically active biofilm (EAB)-based biosensor for real-time water quality early-warning is the formation of EAB that requires several days to weeks. Besides the onerous and time-consuming preparation process, the naturally formed EABs are intensively concerned as they can hardly deliver repeatable electrical signals even at identical experimental conditions. To address these concerns, this study employed sodium alginate as immobilization agent to encapsulate Shewanella oneidensis MR-1 and prepared EAB for devising a biosensor in a short period of less than 1 h. The artificial EAB were found capable of delivering highly consistent electrical signals with each other when fed with the same samples. Morphology and bioelectrochemical properties of the artificial EAB were investigated to provide interpretations for these findings. Different concentrations of bacteria and alginate in forming the EAB were investigated for their effects on the biosensor's sensitivity. Results suggested that lower concentration of bacteria would be beneficial until it increased to 0.06 (OD 660). Concentration of sodium alginate affected the sensitivity as well and 1% was found an optimum amount to serve in the formation of EAB. A long-term operation of the biosensor with artificial EAB for 110 h was performed. Clear warning signals for incoming toxicants were observed over random signal fluctuations. All results suggested that the artificial EAB electrode would support a rapid devised and highly sensitivity biosensor. [Display omitted] [ABSTRACT FROM AUTHOR]

• Electrospun rGO@TiF membranes have advanced photocatalytic degradation capability. • Filtration-enhanced degradation is 2.15 times as much as that without filtration. • Filtration-induced improvement could be attributed to enhanced mass transfer. • Filtration might inhibit electron–hole recombination thus more effective radicals. • rGO@TiF membrane performs stably over ten degradation cycles. Novel membranes with advanced oxidation functions are urgently required for degradation of organic micropollutants. This study proposed a novel electrospun rGO@TiO 2 nanofibrous (rGO@TiF) membrane fabricated with a successive electrospinning–calcination method. The optimized rGO-2@TiF_450 membrane achieved 100% removal of propranolol within 60 min. Systematic degradation experiments in different operational modes were conducted to reveal the enhancing mechanism of filtration on photocatalysis. The resulted degradation efficiency with filtration is up to 2.15 times as much as that without filtration. This filtration-induced improvement could be probably attributed to the enhanced mass transfer of the reactants and inhibited electron–hole recombination that resulted in more practically active oxidative radicals. The proportion of the improved degradation in membrane interior due to filtration was determined to be ∼35%. Additionally, the degradation performance of the rGO@TiF membrane is highly stable over 10 degradation cycles and the removal rate was 2–10 times higher than other studies. [ABSTRACT FROM AUTHOR]