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[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]

• 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]

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]