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Fe-containing sludge can be converted to functional biochar as a promising resource recycle pathway. However, activating properties of Fe sludge-based biochar are always limited by low specific surface area and weak carbon center for persistent free radical(PFRs). In the current study, waste expandable polystyrene particles were simultaneously used to improve the biochar catalytic performance. The co-prepared biochar achieved a high micromesoporous ratio(98.4%) with specific surface area (345.3 m²/g), improved by 20.1% and 105.2% than unimproved biochar. The improved micromesoporous properties performed better iron active sites and oxygen-containing functional groups for PFRs functioning in wastewater. The co-prepared biochar showed an efficient catalytic degradation through persulfate activating multiple free radicals of 1O 2 , O 2 ˙ˉ, ˙OH and SO 4 ˙ˉ, which removed 95.4% sulfamethoxazole with mineralizing ratio of 74% within 60 min. The recycling of waste iron sludge and waste polystyrene foam material can achieve functional biochar to apply in deep treatment of refractory organic wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Chelation with Al3+ enhances the intrinsic fluorescence emission of tetracycline. • The emission exhibits far superior sensitivity than the absorption signal. • Molecular motion restriction contributes to an increased quantum yield. • The monitoring capability of optical signal is expanded via this simple strategy. Rapid on-site detection of antibiotics such as tetracycline (TC) is crucial for understanding their elusive environmental fate. Fluorescence-based strategies are promising owing to their sensitivity and ease of use. This study demonstrates that Al3+–TC coordination significantly enhances the intrinsic fluorescence of TC at excitation/emission wavelengths of 395/490 and 270/490 nm. The fluorescence emission intensity is proportional to the TC concentration between 0.005 and 7.5 μmol/L TC, which increases the detection sensitivity by 40 times compared with the commonly used absorption signals. Density functional theory calculations, when combined with the independent gradient model, indicate that the six-membered chelate ring in the octahedral Al3+–TC complex restricts molecular motion, along with two intramolecular hydrogen bonds formed between TC and water ligands. These factors lead to a narrowing of the energy gap between the highest occupied and lowest unoccupied molecular orbitals upon complexation with Al3+. Consequently, the enhanced molecular rigidity and facilitated electron transfer result in a significant increase in the fluorescence quantum yield. This captivating fluorescence response significantly enhances the proficiency of optical signals in detecting TC, thereby enriching future environmental monitoring systems with greater diversity and adaptability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of PFS, PAC, and PAM conditioning on recycling CS for denitrification were evaluated. • PFS-conditioned fermentation liquor showed higher denitrification efficiency for woolen wastewater. • PFS-conditioned fermentation liquor enhanced carbon-ferrous-sulfur hybrid denitrification. • Microbial mechanisms for carbon-ferrous-sulfur mixotrophic denitrification were analyzed. Reducing pollution and carbon emissions synergistically in wastewater treatment is an important part of carbon neutralization. Recycling carbon sources (CSs) in sludge to refeed denitrification has been considered a promising sustainable pathway, but it is limited by CSs purification and recovery. This study evaluated the effects of polyferric sulfate (PFS), polyaluminum chloride (PAC), and polyacrylamide (PAM) conditioning on fermentation CSs recovery and denitrification efficiency. Results indicated PFS-conditioned recovered fermentation liquor showed higher denitrification efficiency for woolen wastewater. CSs recovery test showed that PFS conditioning improved the purity of high-bioavailability CSs by depleting fewer short-chain fatty acids (SCFAs) and removing more total nitrogen (TN), total phosphorus (TP), and humic acids. Under the 0.05 g/gTSS PFS conditioning and recovery, the preservation of soluble chemical oxygen demand (SCOD) and SCFAs were 71.00 % and 84.36 %, respectively, and the nitrate degradation rate achieved 3.19 mgNO 3 −·h−1·gVSS−1. Importantly, Fe(III) dissociated from PFS oxidized the S2− from woolen wastewater, and generated Fe(II) and S0, which composed a synergistic electron donor system together with SCFAs. They constituted a mixotrophic denitrification dominated by heterotrophic denitrification and reinforced by ferrous and sulfur-autotrophic denitrifications, which contributed 69.56, 17.72, and 12.72 % to nitrogen removal, respectively. In addition, the refeeding of PFS-conditioned recovered fermentation liquor promoted the proliferation of microorganisms involved in iron/sulfur autotrophic denitrification and the abundance of denitrification functional genes, especially the napA , nirS , cnorB , qnorB , and nosZ , forming an efficient Carbon-Ferrous-Sulfur hybrid denitrifiers community to enhanced nitrogen removal from woolen wastewater. [ABSTRACT FROM AUTHOR]

High overpotential and soaring prices of the cathode electrode are the bottlenecks for the development of microbial electrolysis technology for hydrogen production. In this study, a novel one-step electrodeposition method has been attempted to fabricate electrodeposited cathodes in situ growth of Ni–Co–S, Ni–S, Co–S catalyst on nickel foam (NF) to reduce the overpotential of electrodes. Finally, a uniform nanosheet with a high specific surface area and more active sites is formed on the NF surface, resulting in a lower overpotential than plain NF. At 0.8 V, the Co–S/NF cathode produces a favorable 42% increase in hydrogen yield (0.68 m3·m−3·d−1), 40% upsurge in current density (10.6 mA/cm3) and 39% rise of cathodic recovery rate (58.0 ± 3.2%) than bare NF, followed by Ni–Co–S/NF and Ni–S/NF cathode. All the electrodeposited electrodes demonstrate enhanced current density and reduced electron losses, thereby achieving efficient hydrogen production. These innovative varieties of electrodes are highly advantageous as they are relatively inexpensive and easy to manufacture with great potential in reducing costs and further real time application in large scale. • The overpotential of nickel foam is greatly reduced by Ni/Co/S electrodeposition. • High hydrogen yield is achieved by Co–S/NF electrode in neutral condition. • Electrodeposited electrodes show high current density and low electron losses in MEC. [ABSTRACT FROM AUTHOR]

The corrosive issues are comprehensively caused in oilfield rejection system, in which sulfide is one of (bio-)chemical factors leading to high corrosive rate and blocking problem. Generally, aerobic treatment is a well-established and cost-effective unit for sulfide removal before oilfield wastewater reinjection. However, the residual dissolved oxygen (DO), which causes chemical, biological and electrochemical corrosion to water injection pipeline equipment, is still high after multi-stage filtration of DO removal. Here, a novel system to achieve quick and efficient DO removal through a three-electrode (cathode-anode-cathode)-upflow bioelectrochemical reactor (R CAC) was constructed before wastewater reinjection. Bioelectrodes were well established by utilizing organic matters of oilfield wastewater and conducted extracellular electron transport to achieve a steady DO removal from ∼5 mg/L to 0.01 mg/L (HRT 6 h), the DO removal efficiency reached approximately 100%, and the downside biocathode made the largest contribution for DO removal. In the treated wastewater, the corrosion rate of stainless steel N80 ultimately declined over 30 days testing. As a result of DO removal and ammonia conversion to nitrate by bioelectrodes, the corrosive microorganisms were substantially changed. Especially, sulfate-reducing bacteria (SRB) on the surface of N80 immersed in treated wastewater were decreased in abundance; while nitrate-reducing bacteria (NRB) enriched more, which can compete with SRB to prevent biological corrosion. Image 1 • A three-electrode bioelectrochemical reactor was constructed for dissolved oxygen removal. • Removal efficiency of dissolved oxygen can reach ca.100%. • The biocathodes made the most contribution of dissolved oxygen removal. • Corrosion rate of N80 stainless steel declined in the treated effluent during 30 days. • Sulfate-reducing bacteria on pipeline surface were decreased when immerged in treated effluent. [ABSTRACT FROM AUTHOR]

Rhamnolipid (RL), a biosurfactant produced by bacteria, is investigated to alter the physical characteristics of extracellular polymeric substance (EPS) of waste-activated sludge (WAS), and subsequently promotes hydrolysis and acidogenesis during anaerobic digestion for short chain fatty acids (SCFAs) production. The results revealed that RL could decrease the adhesion force of EPS from 13.46 nN to 1.08 nN, resulting in EPS disintegration layer by layer, decreasing the median particle size by 31.57 μm and releasing abundant soluble organic matter. The cell number of living bacteria remained stable after RL pretreatment (2.59 × 109 vs. 2.66 × 109), indicating that RL has a minimal impact on microbial cells (only ~2% bacterial lysis was observed). The kinetic studies of ammonia nitrogen release and SCFA production suggested that, in the RL-pretreated WAS, the reaction rate constants for hydrolysis and acidogenesis were respectively 2-fold and 1.5-fold higher than those of the control group. Unlabelled Image • Rhamnolipid changes the physical properties of extracellular polymeric substance. • Rhamnolipid decreased adhesion force of extracellular polymeric substances. • The efficiency of hydrolysis and acidification were highly promoted by rhamnolipid. [ABSTRACT FROM AUTHOR]

Abstract The underlying dynamics of microbial (bacteria and archaea) communities ecologically responding to an applied potential are critical to achieving the goal of enhancing bioenergy recovery but are not sufficiently understood. We built a MEC-AD mode that increased methane production rate by several times (max. 3.8 times) during the startup period compared to control AD, changed the absence or presence of external voltage to provide the pre-, dur-, and post- samples for microbial analysis. From a time and spatially dependent community analysis of electrode-respiring bacteria and methanogens, the corresponding Geobacter developed under the influence of external voltage, pairing with methanogens in the anodic and cathodic biofilm to generate methane. Additionally, at the cathode, the Alkaliphilus (basophilic bacteria) also correspondingly shifted alongside the change of external voltage. The mcrA sequencing confirmed a change in the dominant microbe from acetoclastic (mostly Methanosarcina mazei LYC) to hydrogenotrophic methanogens (mostly basophilic Methanobacterium alcaliphilum) at the cathode with 0.8 V voltage. Overall, the external voltage not only enriched the functional microbes including electrogens and methanogens but also indirectly shifted the composition of the bacterial and archaeal community via disturbing the pH condition. The predictive functional profiling indicated that the cathodic methanogenesis principally followed the metabolism pathway of the hydrogenotrophic methanogens, suggesting the F420 co-enzyme could be the key mediate for electron transfer. All data suggested that the electric stimulation would change and maintain the micro-environmental conditions to shift the bacterial/archaeal community. Graphical abstract Unlabelled Image Highlights • Electricity-driven induced a core-shell structure of microbial communities. • Hydrogenotrophs and acetoclastic methanogens enriched at cathodic community. • Basophilic Alkaliphilus and Methanobacterium alcaliphilum were influenced by electricity. [ABSTRACT FROM AUTHOR]

Cathodic methanogenesis is a promising method for accelerating and stabilising bioenergy recovery in anaerobic processes. The change in composition of microbial (especially methanogenic) communities in response to an applied potential—and especially the associated pH gradient—is critical for achieving this goal, but is not well understood in cathodic biofilms. We found here that the pH-polarised region in the 2 mm surrounding the cathode ranged from 6.9 to 10.1, as determined using a pH microsensor; this substantially affected methane production rate as well as microbial community structure. Miseq sequencing data of a highly conserved region of the mcrA gene revealed a dramatic variation in alpha diversity of methanogens concentrated in electrode biofilms under the applied potential, and confirmed that the dominant microbes at the cathode were hydrogenotrophic methanogens (mostly basophilic Methanobacterium alcaliphilum ). These results indicate that regional pH variation in the microenvironment surrounding the electrode is an ecological niche enriched with Methanobacterium . [ABSTRACT FROM AUTHOR]

Due to the crucial role of the cathodic catalyst in the electron-transfer rate and hydrogen recovery in bioelectrochemical systems, coupling nickel and earth-abundant transition metal phosphides with high catalysis efficiency and low cost could provide a promising alternative to Pt/C catalysts. Herein, we fabricated a three-dimensional (3D) biphasic Ni 5 P 4 -NiP 2 nanosheet matrix to act as a cathodic tunnel for electron transfer for hydrogen coupled with a microbially catalyzed bioanode. Benefiting from the “ensemble effect” of P, the Tafel slope obtained from voltammetry reflected the improved catalytic performance (83.9 mV/dec vs. 113.6 mV/dec) and contributed to a higher hydrogen production rate of 9.78 ± 0.38 mL d −1  cm −2 that was 1.5 times faster than that of NF, which was even faster than that reported for commercial Pt/C. The impedance resistance obtained using electrochemical impedance spectroscopy (EIS) showed that the NF-P simultaneously exhibited <10% electron loss, corresponding to a 2.5-fold improvement over the ∼25% electron loss of NF. The long-term durability of the new material was verified through long-term operation with high performance in practice. It is proved that a good catalytic property of cathode was well maintained, even with microorganism attachment on NF-P cathode. [ABSTRACT FROM AUTHOR]

Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (R CC ) and open-circuit (R OC ) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups R CC and R OC during the start-up stage. The experiment results showed significantly greater methane production in R CC than R OC , the average methane production of R CC was 0.131 m 3 /m 3 /d, which was 1.4 times higher than that of R OC (0.055 m 3 /m 3 /d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in R OC without applied voltage, which was 20% higher than that in R CC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in R CC was 6% higher than that in R OC . The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in R CC . Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, R CC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors. [ABSTRACT FROM AUTHOR]

A cheap but efficient electrode material is required to explore and apply to microbial electrolysis cell (MEC) with high hydrogen evolution reaction (HER) efficiency and low over-potential loss. Pt coating carbon cloth (Pt/CC) was one of the most efficient catalyst for hydrogen production in current lab research, but it is difficult to be applied in practice because of expensive cost and week strength from the base material (carbon cloth). Thus a cheap and effective supporting base material is worth to evaluate on hydrogen recovery and loss to methane for the MEC future application. In this study, nickel foam (NF) was used as an alternative to expensive carbon cloth, and NF coated with Pt (Pt/NF) was applied and evaluated through catalytic performance, hydrogen production efficiency and economic assessment in comparison with Pt/CC. The Pt/NF showed a competitive HER performance to Pt/CC. The highest hydrogen yield was reached 0.71 ± 0.03 m 3 /m 3 ·d by Pt/NF under 0.8 V, which exceeded 6%, 10% over Pt/CC and NF, respectively. The energy efficiency relative to the electrical energy input was 127% for Pt/NF and 123%, 110% for Pt/CC and NF, respectively. For fifteen cycles, the methane content of Pt/NF got the lowest due to its higher hydrogen evolution activity. The economic analysis showed a 56% reduction when using Pt/NF as supporting base in place of carbon cloth to achieve similar performance. The linear sweep voltammetry (LSV) showed the possibility to further reduce input voltage in a long term operation. [ABSTRACT FROM AUTHOR]

• The two-step digestion pre-treatment was developed and optimised to efficiently extract MPs. • The identification of aged nonbiodegradable MPs was not affected after digestion. • MLSS and MLVSS interfere most with MPs extraction. • WWTPs in Shenzhen had higher concentrations of MPs. • Rayon, polyester and PP were the most frequently detected MPs in the effluent. As the gathering place of urban wastewater, wastewater treatment plants (WWTPs) are indispensable for removing microplastics (MPs), one of the emerging contaminants of great concern, from cities into the natural environment. A reliable and efficient extraction method for MPs, especially in organic-rich matrices, such as sludge samples, is the basis for studying MPs contamination, while it is still lacking. The digestion process, which requires further optimisation, is the most important step during extraction. In this study, we developed and optimised a two-step digestion process to extract MPs and proposed a recommended dosage of digestion reagents based on the mixed liquid volatile suspended solids (MLVSS) level of the sample. Successive addition of 30% H 2 O 2 + 1 M HNO 3 (v: v = 1:1, T = 60 °C, t = 5 h + 5 h) could efficiently extract MPs from sludge samples (over 90%), and the recommended dosage of digestion reagent was 100 ml 30% H 2 O 2 +100 ml 1 M HNO 3 with the sample MLVSS lower than approximately 0.43 g. This new method was also applied to examine the characteristics of MPs in two typical WWTPs (anaerobic-anoxic-oxic and biofilter processes) in Shenzhen. The concentrations of MPs in the influent, effluent and dewatered sludge were approximately 114.00 n/L, 6.00 n/L, and 126.00 n/g (dry weight) in WWTP A, whereas 404.00 n/L, 22.00 n/L, and 204.00 n/g (dry weight) in WWTP B, respectively. Rayon and polyester were the dominant polymers in both the WWTPs. Fibers accounted for the largest proportion of the influent and effluent. Sizes between 0.20–0.50 mm were most detected. This study provides a new and efficient reference method to extract MPs from WWTPs samples, especially sludge sample, with less MPs loss and more beneficial to subsequent identification. [Display omitted] [ABSTRACT FROM AUTHOR]

In comparison to precious metal catalyst especially Platinum (Pt), nickel foam (NF) owned cheap cost and unique three-dimensional (3D) structure, however, it was scarcely applied as cathode material in microbial electrolysis cell (MEC) as the intrinsic laggard electrochemical activity for hydrogen recovery. In this study, a self-assembly 3D nickel foam-graphene (NF-G) cathode was fabricated by facile hydrothermal approach for hydrogen evolution in MECs. Electrochemical analysis (linear scan voltammetry and electrochemical impedance spectroscopy) revealed the improved electrochemical activity and effective mass diffusion after coating with graphene. NF-G as cathode in MEC showed a significant enhancement in hydrogen production rate compared with nickel foam at a variety of biases. Noticeably, NF-G showed a comparable averaged hydrogen production rate (1.31±0.07 mL H 2 mL −1 reactor d −1 ) to Platinum/carbon (Pt/C) (1.32±0.07 mL H 2 mL −1 reactor d −1 ) at 0.8 V. Profitable energy recovery could be achieved by NF-G cathode at higher applied voltage, which performed the best hydrogen yield of 3.27±0.16 mol H 2 mol −1 acetate at 0.8 V and highest energy efficiency of 185.92±6.48% at 0.6 V. [ABSTRACT FROM AUTHOR]

Methane production rate (MPR) in waste activated sludge (WAS) digestion processes is typically limited by the initial steps of complex organic matter degradation, leading to a limited MPR due to sludge fermentation speed of solid particles. In this study, a novel microbial electrolysis AD reactor (ME-AD) was used to accelerate methane production for energy recovery from WAS. Carbon bioconversion was accelerated by ME producing H 2 at the cathode. MPR was enhanced to 91.8 gCH 4 /m 3 reactor/d in the microbial electrolysis ME-AD reactor, thus improving the rate by 3 times compared to control conditions (30.6 gCH 4 /m 3 reactor/d in AD). The methane production yield reached 116.2 mg/g VSS in the ME-AD reactor. According to balance calculation on electron transfer and methane yield, the increased methane production was mostly dependent on electron contribution through the ME system. Thus, the use of the novel ME-AD reactor allowed to significantly enhance carbon degradation and methane production from WAS. [ABSTRACT FROM AUTHOR]

• A thorough overview of a microbial electrochemistry with anaerobic digestion is summarized. • Principles, configurations, and influential factors for the emerging technology are concluded. • Electron flows of electroactive bacteria and methanogens in CH 4 yield are disclosed. • Community interactions effectively regulated by electrodes are analyzed. • Microbial ecology is well understood, and more efforts are expected before the field application. Biomethane as a sustainable, alternative, and carbon-neutral renewable energy source to fossil fuels is highly needed to alleviate the global energy crisis and climate change. The conventional anaerobic digestion (AD) process for biomethane production from waste(water) streams has been widely employed while struggling with a low production rate, low biogas qualities, and frequent instability. The electric-biologically hybrid microbial electrochemical anaerobic digestion system (MEC-AD) prospects more stable and robust biomethane generation, which facilitates complex organic substrates degradation and mediates functional microbial populations by giving a small input power (commonly voltages < 1.0 V), mainly enhancing the communication between electroactive microorganisms and (electro)methanogens. Despite numerous bioreactor tests and studies that have been conducted, based on the MEC-AD systems, the integrated microbial fingerprints, and cooperation, accelerating substrate degradation, and biomethane production, have not been fully summarized. Herein, we present a comprehensive review of this novel developing biotechnology, beginning with the principles of MEC-AD. First, we examine the fundamentals, configurations, classifications, and influential factors of the whole system's performances (reactor types, applied voltages, temperatures, conductive materials, etc.,). Second, extracellular electron transfer either between diverse microbes or between microbes and electrodes for enhanced biomethane production are analyzed. Third, we further conclude (electro)methanogenesis, and microbial interactions, and construct ecological networks of microbial consortia in MEC-AD. Finally, future development and perspectives on MEC-AD for biomethane production are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

The effects of three widely-used surfactants on waste activated sludge (WAS) fermentation and microbial community structures were investigated. Rhamnolipid bio-surfactants (RL) showed more positive effects on WAS hydrolysis and acidification compared to chemosynthetic surfactants, such as sodium dodecylsulphate (SDS) and sodium dodecyl benzene sulfonate (SDBS). The highest SCOD and VFAs concentrations obtained with RL were 1.15-fold and 1.16-fold that of SDS, and up to 1.73 and 3.63 times higher than those obtained with SDBS. Pyrosequencing analysis showed that an evident reduction in bacterial diversity in surfactant-treated WAS. Moreover, acid-producing bacteria (such as Megasphaera and Oscillibacter ), detected with RL, were (6.8% and 6.4% in proportion) more abundant than with SDS, and were rarely found in SDBS and the control. The results also revealed that RL allowed efficient hydrolysis enhancement and was favorable to functional microorganisms for further acidification during WAS fermentation. [ABSTRACT FROM AUTHOR]

Quorum sensing (QS) has been extensively studied as a cell–cell communication system, where small chemical signal molecules (acylhomoserine lactones, AHLs) can regulate the bacterial communications in bioelectrochemical systems via chemical signaling and electric signaling. In this study, electrochemical activity of bio-anode is substantially promoted by adding two kinds of AHLs with different chain length at the stage of community formation in microbial electrolysis cells (MECs). Hydrogen yield increase is observed by adding of two chain length AHLs, 3-oxo-hexanoyl-homoserine lactone (3OC6-HSL) and 3-oxo-dodecanoyl homoserine lactone (3OC12-HSL). A higher MEC current is acquired with addition of 3OC6-HSL than 3OC12-HSL at a fixed voltage of 0.8 V (vs. SHE). The highest yield is up to 3.8 ± 0.2 mol H 2 mol −1 acetate at 10 μM 3OC6-HSL, which is increased 29% over control MECs. Evaluated on applied voltage, energy efficiency is increased to 171.6 ± 21.3% with short chain AHL, however, no significant improvement is performed on energy efficiency and coulombic efficiency with long-chain AHL. The study shows that bioelectrochemical characteristics of MECs varied on the chain length of AHL signal molecules and short-chain AHLs have a more positive effect on electron transfer and energy recovery in MECs. [ABSTRACT FROM AUTHOR]

A novel pretreatment method combining freezing/thawing with Geobacillus sp. G1 was employed to pretreat waste activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent short-chain fatty acids (SCFAs) production. Results showed that freezing/thawing combined with Geobacillus sp. G1 pretreatment achieved the maximal concentrations of soluble protein from 40 ± 6 mg COD/L (non-pretreated) to 1226 ± 24 mg COD/L (pretreated), and accumulated SCFAs concentration increased from 248 ± 81 mg COD/L to 3032 ± 53 mg COD/L. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, which was the dominant fluorescent organic matters, indicating the synergistic effect of freezing/thawing and Geobacillus sp. G1 pretreatment on organics hydrolysis. High-throughput pyrosequencing analysis investigated that the abundance of bacteria responsible for WAS hydrolysis (such as Clostridium and Caloramator ) and SCFAs production (such as Parabacteroides and Bacterodies ) was greatly enhanced due to the novel pretreatment method used. [ABSTRACT FROM AUTHOR]

Abstract: The short-chain fatty acids (SCFAs) accumulated in waste activated sludge (WAS) fermentation was adopted as an alternative extra carbon source for biohydrogen production in microbial electrolysis cells (MECs). WAS was pretreated by bi-frequency ultrasonic and the highest SCFAs were accumulated at 3rd day. Three groups of tests were conducted in single chamber MECs for H2 production under different SCOD concentrations. SCOD removals were up to 60% at diluted influent, but reduced to 50% at original concentration. Highest H2 yield was 1.2 mL H2/mg COD at 2-fold dilution with 155% energy efficiency. Results showed that >90% of acetate and ∼90% of propionate were effectively converted to hydrogen, and next were n-butyrate and n-valerate (at dilutions), but <20% of iso-butyrate and iso-valerate were converted. The overall biohydrogen recovery in this study was 120 ml H2/g VSS/d. This work shows a possibility of cascade utilization of WAS fermentation liquid and H2 generation in MEC. [Copyright &y& Elsevier]

Abstract: GeoChip (II) and single strand conformation polymorphism (SSCP) were used to characterize anode microbial communities of a microbial electrolysis cell (MEC). Biofilm communities, enriched in a two-chamber MEC (R1, 0.6V applied) having a coulombic efficiency (CE) of 35±4% and a hydrogen yield of 31±3%, were used as the inoculum for a new reactor (R2). After three months R2 achieved stable performance with CE=38±4% and Few changes in the predominant populations were observed from R1 to R2. Unlike sludge inoculation process in R1 in the beginning, little further elimination was aroused by community competitions in anode biofilm reformation in R2. Functional genes detection of biofilm indicated that cytochrome genes enriched soon in new reactor R2, and four genera (Desulfovibrio, Rhodopseudomonas, Shewanella and Geobacter) were likely to contribute to exoelectrogenic activity. This work also implied that symbiosis of microbial communities (exoelectrogens and others) contribute to system performance and stability. [Copyright &y& Elsevier]

Abstract: With limited external applied voltage, the microbial electrolysis cell (MEC) could produce hydrogen by exoelectrogenic microorganisms. The present study revealed that a cubiod-shaped chamber effectively reduces the distance between electrodes and thereby reduces the internal resistance of the entire cell. With 0.6V of applied voltage, the cuboid MEC had a columbic efficiency of 33.7%, much higher than that achieved in the H-shaped MEC test (ca. 15%) of comparable size. Filling the anode chamber with granular activated carbon further enhanced the columbic efficiency to 45%. The corresponding hydrogen conversion rate could reach 35%. [ABSTRACT FROM AUTHOR]

Abstract: In order to optimize operations of microbial electrolysis cell (MEC) for hydrogen production, microbial anode potential (MAP) was analyzed as a function of factors in biofilm anode system, including pH, substrate and applied voltage. The results in “H” shape reactor showed that MAP reflected the information when any factor became limiting for hydrogen production. Commonly, hydrogen generation started around anode potential of −250 mV to −300 mV. While, higher current density and higher hydrogen rate were obtained when MAP went down to −400 mV or even lower in this study. Biofilm anode could work normally between pH 6.5 and 7.0, while the lowest anode potential appeared around 6.8–7.0. However, when pH was lower 6.0 or substrate concentration was less than 50 mg L−1 in anode chamber, MAP went up to −300 mV or above, leading to hydrogen reduction. Applied voltage did not affect MAP much during the process of hydrogen production. Anode potential analysis also showed that planktonic bacteria in suspended solution presented positive effects on biofilm anode system and they contributed to enhance electron transfer by reducing internal resistance and lowering minimum voltage needed for hydrogen production to some extent. [ABSTRACT FROM AUTHOR]

Abstract: Methane production occurs during hydrogen gas generation in microbial electrolysis cells (MECs), particularly when single chamber systems are used which do not keep gases, generated at the cathode, separate from the anode. Few studies have examined the factors contributing to methane gas generation or the main pathway in MECs. It is shown here that methane generation is primarily associated with current generation and hydrogenotrophic methanogenesis and not substrate (acetate). Little methane gas was generated in the initial reaction time (<12h) in a fed batch MEC when acetate concentrations were high. Most methane was produced at the end of a batch cycle when hydrogen and carbon dioxide gases were present at the greatest concentrations. Increasing the cycle time from 24 to 72h resulted in complete consumption of hydrogen gas in the headspace (applied voltage of 0.7V) with methane production. High applied voltages reduced methane production. Little methane (<4%) accumulated in the gas phase at an applied voltage of 0.6–0.9V over a typical 24h cycle. However, when the applied voltage was decreased to 0.4V, there was a greater production of methane than hydrogen gas due to low current densities and long cycle times. The lack of significant hydrogen production from acetate was also supported by Coulombic efficiencies that were all around 90%, indicating electron flow was not altered by changes in methane production. These results demonstrate that methane production in single chamber MECs is primarily associated with current generation and hydrogen gas production, and not acetoclastic methanogenesis. Methane generation will therefore be difficult to control in mixed culture MECs that produce high concentrations of hydrogen gas. By keeping cycle times short, and using higher applied voltages (≥0.6V), it is possible to reduce methane gas concentrations (<4%) but not eliminate methanogenesis in MECs. [Copyright &y& Elsevier]

[Display omitted] • Solar intermittent-powered electromethanogenesis achieved efficient CO 2 reduction. • Higher bicarbonate loading promoted the redox activity of electrode biofilms. • Increased HCO 3 − facilitated electron transfer and lowered charge transfer resistance. • More functional mcrA genes were upregulated with elevated bicarbonates. • Basophilic Methanobacterium alcaliphilum occupied predominated at the biocathode. Microbial electromethanogenesis (EM), as a sustainable bioderived carbon-neutrality catalyzing platform, can be accelerated and regulated by weak power input for carbon fixation into value-added bioenergy. Solar electricity as a day-night intermittent renewable resource has been verified to effectively drive microbes to capture carbon dioxide (CO 2). However, understanding the influence mechanisms of higher CO 2 loading on EM is of intrinsic significance yet lacking. Herein, natural solar-powered bioelectrocatalytic CO 2 reduction to methane (CH 4) under increasing bicarbonate concentrations was investigated. CH 4 recovery for the long-term measurement showed that CH 4 production rate positively responded to improved bicarbonate concentrations from 2.5 to 10.0 g HCO 3 −·L−1, exhibiting a robust and potent competence in CH 4 yield compared to reported EM. Whereas exceed bicarbonate mainly contributed to raised pH in the solution resulting in the proton limitation despite the intermittent driven-mode could mitigate pH shock. Electrochemistry results demonstrated that higher bicarbonate concentrations promoted the redox activity of electrode biofilm and lowered the system resistances, especially the charge transfer resistance. Adequately improving CO 2 loading can dynamically optimize the structure of anodic electroactive microorganisms and facilitate electron transfer. Furthermore, more functional cathodic mcrA genes were upregulated with elevated bicarbonates and the species of basophilic Methanobacterium alcaliphilum occupied predominated at the cathode. These findings open up a perspective avenue to carbon reduction using natural solar intermittent-powered EM. [ABSTRACT FROM AUTHOR]

Sludge lysate is an unavoidable and refractory liquid produced from the waste activated sludge hydrothermal pyrolysis, which contains plenty of hazardous refractory organic compounds and value-added organic resources. Here, the proof of concept for an integrated strategy that couples technically compatible pretreatment to microbial electrolysis assisted AD (ME-AD) system is investigated for sludge lysate treatment and resource recovery. The pretreatment process shows a positive effectiveness on the ME-AD by reducing the organic load and inhibitory matters, which promote the residual refractory organic compounds (Maillard reaction products and humic acid-like substances) and carbon sources further biodegradation and bio-transformation. Combining membrane separation with ME-AD increased not only both the yield and purity of methane to 268.76 mL CH 4 /g COD and 98%, respectively, but also the recovery of 70.0~82.4% crude proteins (9.1 ± 0.5 g/L) from sludge lysate. Alternatively, the alkaline precipitation combined with ME-AD enhanced the recovery efficiency of short-chain fatty acids (SCFAs). The visible decreasing in the unpleasant color of the effluents was observed, implying that the degradation of harmful refractory organic was almost eliminated in sludge lysate. This strategy is worthy to be developed in WWTP for sludge lysate treatment with considerable bio-resources recovery and refractory organics removal. [Display omitted] • Sludge lysate was treated for resource recovery, including crude proteins and biogas. • Pretreatment showed a positive effect on the subsequent ME-AD process. • Maillard reaction products were effectively degraded in the ME-AD process. • Methane production rate of 268.76 mL/gCOD was achieved by membrane separation with ME-AD. [ABSTRACT FROM AUTHOR]

Waste sludge lysate was produced by dehydration after pyrolysis of waste activated sludge. In addition to dominant components such as protein, polysaccharide, and volatile fatty acids (VFAs), it also contained melanoidins, which produced from Maillard reaction. The inclusion of melanoidins will lead to poor biological degradation in conventional anaerobic digestion (AD). While microbial electrolysis cell (MEC) was proved an enhanced degradation of complex organic matter for hydrogen production. The results showed that under high concentration conditions, conventional AD caused the accumulation of propionic acid and slowed down the use of acetic acid, but MEC overcame the defects and increased the chemical oxygen demand (COD) removal efficiency by 40.33%, and achieved average hydrogen production rate (0.15 ± 0.05 L L−1 day−1), which was 79 times that of AD system (0.0019 ± 0.0009 L L−1 day−1). Therefore, MEC can enhanced biodegradation of the waste sludge lysate for high hydrogen production. Unlabelled Image • MEC achieved higher COD removal than AD in high concentration sludge lysate. • MEC overcame the limit of AD on VFAs utilization to degrade sludge lysate. • H 2 production was enhanced significantly in MEC than AD. [ABSTRACT FROM AUTHOR]

• The simulation results of the dynamic distribution of tracer were compared with the results of the RTD experiment, to verify the reliability of the model settings, especially the Non-rigid carbon brush.. • Cathode space ratio based on hydrodynamics character affected electrogenesis capacity. • Electron balance was analyzed on different electrode assembly. • The considerable organic removal, methane recovery, and hydrodynamics characteristics were linked to cathode space ratio. Compared with common anaerobic digestion, microbial electrolysis has been proven feasibly to accelerate biodegradation and methanogenesis with the advantages of effective electron flow regulation. However, its actual application and scale-up required a full understanding and further investigation on electrode size and distribution. For making full use of the space of the integrated reactor and improve methane recovery, an effective interior configuration was significant. In this work, three types of reactors with different cathode spatial distributions, that is, different cathode space ratios (ratio of cathode surface area to reaction region volume), were studied to form a good flow pattern for obtaining high methane production. Tracer experiments and numerical simulation were employed simultaneously for understanding the hydrodynamics characters of the interior flow field. The results showed that by increasing the cathode space ratio to 1.33 cm2/cm3 and 2 cm2/cm3, respectively, better flow patterns with the residence time of 1.336 times and 1.363 times of theoretical hydraulic retention time could be obtained. The stacked structure of nickel meshes was beneficial to prolong the contact time of contaminant and improve the mass transfer. Increasing the cathode space ratio could also enhance the electrochemical performance. Considering the organic removal, methane recovery, electrons generation, and material consumption, the recommended cathode space ratio was 1.33 cm2/cm3. With this structure, COD removal efficiency reached 93.2 ± 1.9% and 94.1 ± 1.5%, methane production rate reached 332.0 and 334.8 mL CH 4 /L reactor/day, and methane yield was 171.3 and 246.4 mL CH 4 /g COD under the HRT of 24 h and 36 h, respectively. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Higher CH 4 yield and economic revenue achieved with intermittent electrostimulations. • Intermittent electro field regulated interspecies electron transfer in bulk solution. • Suspended microbes made considerable contributions to methane recovery. • More complex interactions in extracellular electron transfer bacteria with periodic on/off electrical field. Lately, extracellular electron transfer (EET) is widely disclosed on the surface of the bioelectrodes, and conductive (bio)carriers involved in anaerobic biodegradation/biosynthesis. By electrostimulation, microbial consortia colonize the electrodes and accelerate substrate (waste/wastewater) metabolization on the bioanode or biosynthesize value-added products (methane, acetate, etc.) on the biocathode. However, the connections and contributions of planktonic microbial communities have not been effectually understood. Herein, electromethanogenesis were comprehensively investigated in response to different driving-force modes: intermittent electric field applied by manual on-off or natural solar power and continuous electrical field. Intermittent modes implied preferable electron transfer efficiency, higher methane yield and energy recovery efficiencies from wastewater by the microbes in the bulk solutions. Microbial community analysis revealed that less electroactive microorganisms and acetotrophic methanogens in the bulk solutions were accommodated under the intermittent modes than the continuous electrical field, whereas more fermentative bacteria and hydrogenotrophic methanogens evolved in the intermittent driving modes, implying that the interspecies electron transfer both on and away from the electrodes were favorably regulated. Redundancy and network analysis proved that more complicated ecological interactions were shown in the bulk solutions with the periodic on/off of electrical field. These results hinted that the electrostimulation effectively regulated EET bacteria, even in the bulk solutions, while more efficient electron flow to methane through interspecies electron transfer was developed during the intermittent driving regulation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Electroactive microorganisms (EAMs) can act as pseudocapacitor to store energy and discharge electrons on need, while electromethanogens acting as receptor are able to utilize electrons, protons and carbon dioxide for methanization. However, external energy is required to overcome thermodynamical barriers for electromethanogenesis. Herein, electro-driving power by solar light was established to accelerate conversion of waste organics to bioenergy. The intermittent power supply modes were elucidated for favourable performances (e.g., current density, methane production rate, energy recovery efficiencies and economic evaluation), compared with the control driven by continuous applied voltage. It was found that natural intermittent solar-powered mode was more beneficial for microorganisms involved in electron transfer and energy recovery than manual sharp on-off mode. Electrochemistry analysis unrevealed that a higher redox current and lower resistance were exhibited under the solar-powered mode. A high charge storage capacity and electron mobility were found through cytochrome c content and live cells ratio in the solar-power assisted bioreactor. The intermittent power driving modes can regulate electron transfer proteins with capacitive storage behavior in biomass, which helps to understand the responses of functional communities on the stress of intermittent electric field. These findings indicate a promising perspective of microbial biotechnology driven by solar power to boost bioenergy recovery from waste/wastewater. Image 1 • A solar-powered bioelectrochemical system was established for CH 4 recovery. • Organic removal from wastewater was improved in the solar electro-driving mode. • Cytochrome c was higher expressed under the solar intermittent electro-driving mode. • Capacitive storage behavior was involved in electron transfer proteins. [ABSTRACT FROM AUTHOR]

[Display omitted] • HA contributed a limited TC binding through intermolecular weak interactions. • Unique fluorescence induced by Al3+–TC coordination tracked TC migration. • Coordination with Al3+/Fe3+ immobilized over 90 % TC on HA flocs. • High binding energy from coordination drove superior interfacial binding. In environmental matrices, the migration and distribution of contaminants at water–solid interfaces play a crucial role in their capture or dissemination. Scientists working in environmental remediation and wastewater treatment are increasingly aware of metal–contaminant coordination; however, interfacial behaviors remain underexplored. Here, we show that trivalent metal ions (e.g. Al3+ and Fe3+) mediate the migration of pollutant ligands (e.g. tetracycline (TC) and ofloxacin) to the organic solid interface. In the absence of Al3+, humic acid (HA) colloids (50 mg/L) capture 26.1 % of the TC in water (initial concentration: 10 mg/L) via weak intermolecular interactions (binding energy: −5.71 kcal/mol). Adding Al3+ (2.5 mg/L) significantly enhances the binding of TC to an impressive 94.2 % via Al3+ mediated coordination (binding energy: −84.89 kcal/mol). The significant increase in binding energy results in superior interfacial immobilization. However, excess free Al3+ competes for TC binding via direct binary coordination, as confirmed based on the unique fluorescence of Al3+–TC complexes. Density functional theory calculations reveal the intricate process of HA–Al3+ binding via carboxyl and phenolic hydroxyl sites. The HA–Al3+ flocs then leverage the remaining coordination capacity of Al3+ to chelate with TC. As well as providing insights into the pivotal role of metal ion on the self-purification of natural water bodies, our findings on the interfacial behavior of metal–contaminant coordination will propel coagulation technology to the capture of microscale pollutants. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a promising and efficient biological nitrogen removal process, which can economically treat wastewater without organic supplement and aeration. However, to date, the insufficient nitrite in wastewater is the foremost problem encountered in anammox process. This restriction hinders full-scale application of anammox worldwide. Nitrite can be provided by innovative processes such as autotrophic denitrification and denitrifying anaerobic methane oxidation (DAMO). Therefore, the synergy between them and anammox is feasible means to solve the bottleneck. This review unravels the advantages and operating strategies of autotrophic denitrification, DAMO and their coupled processes with anammox. Besides, different electron donors such as reductive sulfur, iron, hydrogen, manganese and methane are analyzed in the two processes. The characteristics of microbial populations and their synergies in microbial communities are deciphered, and nitrogen removal contributions through different microbes are also highlighted. Still, nitrogen conversion pathways are clarified in the processes with different electron donors, and metabolic mechanisms of both autotrophic denitrifiers and DAMO microbes are revealed. Finally, the challenges to be focused in autotrophic denitrification and DAMO processes are proposed, and future perspectives on their coupled process with anammox are also put forward. [ABSTRACT FROM AUTHOR]

The loss and negative impacts of nitrogen from fertilized soils remain a global challenge in agricultural field. Ammonium nitrogen (NH 4 +-N) and nitrate nitrogen (NO 3 −-N) leaching, together with volatile ammonia loss are the main pathways of nitrogen loss. To improve nitrogen availability, alkaline biochar with improved adsorption capacities is a promising soil amendment. This study was objected to investigate the effects of alkaline biochar (ABC, pH 8.68) on nitrogen mitigation, the effects on nitrogen loss, and the interactions among the mixed soils (biochar, nitrogen fertilizer, and soil) under both pot and field experiments. From pot experiments, ABC addition resulted in the poor reservation of NH 4 +-N which converted to volatile NH 3 under higher alkaline environments, mainly occurring in the first 3 days. But after, NO 3 −-N could be largely retained in surface soil by ABC addition. The reservation of NO 3 −-N by ABC offsets the loss of volatile NH 3 , and ABC ultimately showed positive reservations of nitrogen with fertilization. In the field experiment, the addition of urea inhibitor (UI) addition could inhibit the volatile NH 3 loss caused by ABC mainly in the first week. The long-term operation demonstrated that ABC supported persistent effectiveness in reducing N loss, while UI treatment temporarily delayed the N loss through inhibition of fertilizer hydrolysis. Therefore, the addition of both ABC and UI contributed to reserve soil N in layers (0–50 cm) suitable for crop growth thus improving crops growth. • Alkalinity of soil increased the amount of NH 3 volatilization of fertilization. • The cumulative leaching of NO 3 −-N decreased with alkaline biochar compared to fertilization alone. • N can be greatly reserved in 0–60 cm depth of soil by cooperated 3% of alkaline biochar with urease inhibitor. • Alkaline biochar supported persistent effectiveness on reducing nitrogen losses. [ABSTRACT FROM AUTHOR]

Microbial catalysed electrochemical systems are intensively used in basic and applied research as a sustainable platform for harnessing energy and generating value added bio-products. Recently more emphasis is being laid on enhancement of AD (Anaerobic Digestion) by integrating ME (Microbial Electrolysis) with it to convert CO 2 (Carbon dioxide) directly to CH 4 (Methane). This research attempts to shed light on the effects of electrode positioning and arrangement along with hydraulic retention time (HRT), on CH 4 generation, and organic removal in novel microbial electrolysis coupled anaerobic digestion (ME-AD) reactors. However, the positioning and placement of electrodes in a ME-AD reactor have not yet been evaluated. Four reactors (S1, S2, S3 and S4) are designed with different electrode arrangements and run in four different HRTs (12, 18, 24 and 36 h) with beer brewery wastewater as the substrate for treatment. The reactors with electrodes arranged at the bottom are better in performance than the reactors with electrodes placed at the top. They have maximum COD, TOC and Carbohydrate removal efficiencies of 92.1%, 64.2% and 98.9% respectively, high methane production rate (MPR) and methane yield (MY) with 304.5 mLCH 4 /Lreactor/day and 275.8 mL/gCOD respectively and a maximum current generation of 10 mA, all at 36 h HRT. Electrode placement also has crucial roles to play in microbial community prevalence on the electrode biofilm of the reactors. Methanogens and electrogens are well enriched on the electrode biofilms of the reactors with bottom positioned electrodes, revealing the basis behind their maximum organic removal, methane production efficiencies and current generation. This study demonstrates that the optimization of appropriate electrode position and placement in ME-AD reactors is crucial for their performance and development. [ABSTRACT FROM AUTHOR]

The sludge dewaterability is essential for waste activated sludge (WAS) treatment and disposal in wastewater treatment plants (WWTPs). The biological enzyme conditioning process is a promising method to enhance the dewaterability of WAS. In this study, the optimal conditions in terms of pH, temperature, bio-enzyme dosage, and treatment time for five kinds of biological enzymes (α-amylase, cellulase, acidic protease, neutral protease, and alkaline protease) were investigated. Among them, α-amylase and neutral protease showed good performance in conditional optimization experiments. After biological enzyme conditioning, the sludge supernatant of proteins, polysaccharides, and SCOD contents increased. The sludge water content (Wc) decreased, while the capillary suction time (CST) increased. The optimal conditions for α-amylase were pH 6, 45 ℃ of temperature, 30 mg/g TSS of dosage, and 3 h of treatment time, under which the lowest Wc can reach 68.67%. The optimal conditions for neutral protease were pH 6.5, 40 ℃ of temperature, 30 mg/g TSS of dosage, and 2 h of treatment time, under which the lowest Wc can reach 69.82%. Using biological enzymes is an environmentally friendly conditioning process for efficient WAS dewatering. The optimization of operating conditions in the biological enzymes conditioning process may be beneficial to WAS dewatering and further disposal in actual WWTPs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The performance of anodic ammonium oxidation at varying potentials was investigated. • Anode potential regulation effectively directed ammonium transformation in bioanodes. • Bioelectrorespiration-driven nitritation for nitrite supply in Anammox was proposed. • Metagenomic sequencing revealed the anode microbiome for nitrogen transformation. • Regulatory mechanisms of anode potential on ammonium metabolism were deciphered. Understanding how potential regulation affects ammonium transformation in bioanodes is crucial for promoting their application. This study explored the performance, electrochemical properties, electromicrobiome of bioanodes across potentials from 0.0 V to 0.4 V vs. standard hydrogen electrode (SHE). Higher anode potentials enhanced the performance of electroactive biofilms and ammonium removal but suppressed nitrite oxidation while favoring dissimilatory nitrate reduction (DNRA), leading to increased nitrite accumulation. A reduction in nitrite-oxidizing bacteria (NOB) and an increase in DNRA-related genes resulted in an optimal nitrite-to-ammonium ratio of 1.32 for the Anammox process. Higher anodic potentials (0.3 and 0.4 V) were less effective for TN removal than lower potentials (0, 0.1, and 0.2 V), likely due to increased NOB and denitrification genes at lower potentials enhancing nitrite oxidation and denitrification. These findings indicate that regulating anodic potential effectively directs ammonium transformation in bioanodes, optimizing its conversion to N 2 or nitrite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Caproate was successfully bio-synthesized via EF from prefermented sludge. • Caproate biosynthesis was promoted by symbionts of fermenters, CSB and homo-acetogen. • Ecological mechanism was revealed in terms of MEN analysis and Mantel test. • Economic benefit of caproate biosynthesis in EF_CE process increased by $1.69/m3. • LCA was performed to evaluate environmental impact of EF_CE. Electro-fermentation (EF) has emerged as a promising method to produce value-added medium chain fatty acids (MCFAs) via chain elongation (CE). The biorefinery of waste activated sludge (WAS) to MCFAs has been attracting increasing attention. However, so far anaerobic_CE process was commonly employed, while the contribution and mechanism of EF_CE still remain unclear. In the present study, a comprehensive analysis of caproate biosynthesis from prefermented WAS via EF_CE was performed. The reduction in substrates resulted in an increase in caproate production, yielding the maximum caproate (299.8 mg COD/g volatile suspended solid) in the minimum substrate concentration (25 % prefermented WAS, EF13 group). The highest utilization rate (78.76 %) of soluble proteins was also achieved in EF13. Significant positive correlation among caproate yield, electrochemically active bacteria, caproate-synthesizing consortium and homo-acetogen was revealed by molecular ecological network and Mantel test. Further analysis of the metabolic pathways revealed that EF13 demonstrated more key enzymes participated in the production of acetyl-CoA via the Wood-Ljungdahl pathway and the conversation of acetyl-CoA to caproate via the reverse β-oxidation pathway. Moreover, compared to the anaerobic_CE process, the economic benefits of the EF_CE process significantly increased, and the environmental impacts were greatly reduced. The life cycle assessment and economic benefits analysis identified the strengths of EF_CE and proposed a sustainable strategy to facilitate the commercialization of electro-fermentation assisted biorefinery technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of antibiotics on AD of WAS are type- and dose-dependent. • Acetoclastic methanogens are more sensitive to antibiotics than other microbes. • The control of iARGs is the key to promoting ARGs removal in AD of WAS. • Synergistic advances on AD performance and pollutant removal are needed. • Ecological risk for long-term effects of antibiotics and ARGs should be quantified. Anaerobic digestion (AD) of waste activated sludge (WAS) is considered as a promising alternative to realize sludge stabilization and bioenergy recovery, thereby driving carbon neutrality in wastewater treatment plants. However, most of antibiotics are adsorbed by sludge flocs rather than bio-degraded in wastewater treatment process. Regarding that the accumulation of antibiotics in WAS can not only affect performance of AD but also induce the production of antibiotic resistance genes (ARGs), presenting great ecological risks, this review systematically highlighted the recent progress on the fates and roles of antibiotics in AD of WAS, the production and spread of ARGs related to antibiotics and co-contaminants, and the reduction and control strategies of antibiotics and ARGs. The effects of antibiotics on AD stages like solubilization, hydrolysis, acidogenesis, and methanogenesis are type- and dose-dependent. The co-existence of antibiotics and other contaminants enhances the spread of ARGs via enriching potential antibiotic resistance bacteria and promoting horizontal gene transfer, and the control of intracellular ARGs is the key to improve ARGs removal in AD. To mitigate the ecological risks posed by antibiotics and ARGs, the enhanced strategies like pretreatment, conductive materials, anaerobic co-digestion, and microbial electrolysis cell-assisted anaerobic digestion have been explored. In the future study, the interaction mechanisms between the transfer of ARGs and key metabolic genes in microorganisms responded to co-pollutants should be verified to reveal the potential relationships among co-pollutants, ARGs transfer, and bacterial metabolism. After that, the green and economical strategies for simultaneous resource recovery and pollutants removal enhancement should be explored. Moreover, machine learning technique are urgently needed to quantitatively assess the ecological and human health risks caused by residual antibiotics and ARGs. [ABSTRACT FROM AUTHOR]

Promoting methane production performance from waste activated sludge is of great significance for energy self-sufficiency operation of wastewater treatment plants. This study evaluated the methane production enhancement strategies of biochar and quorum-sensing molecules like N-acylated homoserine lactone (AHL) in single-stage and two-stage anaerobic digestion systems. The methane yield increased to 134.9 mL/g volatile suspended solids in single-stage digestion system, which was 41.7 % higher than that of control group, while it in two-stage digestion system was not only lower than that obtained in single-stage digestion system but also less than that observed in groups adding AHL either at the beginning or on the third day of experiment period. The mechanism studies indicated that the single-stage digestion strategy promoted solubilization, hydrolysis, acetogenesis, and methanogenesis stages and improved the conversion and utilization of organic matters with the enhanced syntrophic metabolisms between microorganisms. In addition, the electron transfer activity between microorganisms was promoted, with an increase ratio of 54.7 %, meanwhile, the syntrophic relationships between methanogens such as Methanosarcina and electroactive bacteria such as norank_f__Bacteroidetes_vadinHA17 were promoted. As a result, both acetotrophic and hydrogenotrophic methanogenesis pathways were improved. This study provided some novel approaches for promoting anaerobic digestion performance while using biochar as the additive. [Display omitted] [ABSTRACT FROM AUTHOR]

As a reliable source for methane production, the major goal of our research was to design and testify a novel microbial electrolysis assisted upflow anaerobic (Upflow-MEC) reactor for beer wastewater treatment and simultaneous methane production. Three reactors with different cathode materials were constructed and the reactor with Ni cathode had a maximum COD removal of 85%, methane yield of 142.8 mL/gCOD, TOC removal of 83%, Carbohydrate removal of 97%, Protein removal of 62% and current production of 8.6 mA, under 0.8 V applied voltage at HRT of 24 h. It was an application-oriented, membrane-free, continuous reactor and shortening the reaction time and increasing organic content conversion to methane were the key developing targets. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cells (MECs) use exoelectrogenic microorganisms to convert organic matter into H2, although yields can vary significantly with environmental conditions, likely due to variations in microbial communities. This study was undertaken to better understand how microbial communities affect reactor function. Using wastewater as inoculum, 15 MEC reactors were operated for >50 days and subsequently five reactors were selected for further analysis. Solution (26 mL) was collected every 3–4 days for DNA extraction. DNA was hybridized to GeoChip, a comprehensive functional gene array, to examine differences in the reactor microbial communities. A large variety of microbial functional genes were observed in all reactors. Performances ranged from poor (0.1 ± 0.1 mL) to high (12.2 ± 1.0 mL) H2 production, with a maximum yield of 5.01 ± 0.43 mol H2/molglucose. The best performance was associated with higher cytochrome c genes, considerably higher exoelectrogenic bacteria (such as Shewanella, Geobacter), less methanogens and less hydrogen-utilizing bacteria. The results confirmed the possibility to obtain an effective community for hydrogen production using wastewater as inoculum. Not like fermentation, hydrogen production was significantly controlled by electron transporting process in MECs. GeoChip findings suggested that biofilm formation can be highly stochastic and that presence of dissimilatory metal-reducing bacteria and antagonistic methanogens is critical for efficient hydrogen production in MEC reactors. [ABSTRACT FROM AUTHOR]

To recover methane from waste activated sludge through anaerobic digestion (AD) is one promising alternative to achieve carbon neutrality for wastewater treatment plants. However, humic acids (HAs) are one of the major compositions in waste activated sludge, and their accumulation performs inhibition effects on AD. This study investigated the potentials of biochar (BC) in alleviating inhibition effects of HAs on AD. Results showed that although the accumulated HAs reduced methane yield by 9.37% compared to control, the highest methane yield, 132.6 mL CH 4 /g VSS, was obtained after adding BC, which was 45.9% higher than that in HA group. Mechanism analysis showed that BC promoted the activities of hydrolase such as protease and α-glucosidase, which were 69.7% and 29.7% higher than those in HA group, respectively. The conversion of short-chain fatty acids was accelerated. In addition, the evolutions of electroactive microorganisms like Clostridium_sensu_stricto_13 and Methanosaeta were consistent with the activitiies of electron transfer and the contents of cytochrome c. Furthermore, parts of HAs rather than all of them were adsorbed by BC, and the remaining free HAs and BC formed synergistic effects on methanogenesis, then both CO 2 reduction and acetoclastic methanogenesis pathways were improved. The findings may provide some solutions to alleviate inhibition effects of HAs on AD. [Display omitted] • The methane yield increased by 45.9% after adding biochar to AD inhibited by HAs. • Biochar alleviated the inhibition effects of HAs on the activities of hydrolase. • Biochar improved electron transfer efficiency and increased cytochrome C content. • Both CO 2 reduction and acetoclastic methanogenesis pathways were improved. • The remaining free HAs and BC formed synergistic effects on methanogenesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Feasibility of nitrate photolysis on enhancing sludge fermentation was explored. • Nitrate photolysis accelerates organics release by generating reactive radicals. • Nitrate photolysis achieves the significant promotion of short chain fatty acids. • Microbes related to fermentation and nitrate reduction are selectively enriched. • Gene expression of the key metabolic pathway is enhanced by nitrate photolysis. • Nitrate photolysis inhibits methanogenesis during anaerobic fermentation. Seeking for the eco-friendly and low-cost pretreatment technology has become the prerequisite for the efficient release of the embedded organics in waste activated sludge (WAS), further for the higher production of short chain fatty acids (SCFAs) via anaerobic fermentation. Nitrate, which can produce reactive oxygen species (ROS) and reactive nitrogen species (RNS) during photolysis, may have the positive effect on WAS disintegration and organics degradation, while its performance and mechanism for WAS treatment is still unknown. This study investigated the feasibility of the nitrate photolysis on WAS disintegration and SCFAs production, and elucidated the underlying mechanism. Results showed that the highest acidification rate (26.6 h−1) and short-chain fatty acid (SCFAs) production (5370.6 mg COD/L) were achieved at 8 d in the nitrate photolysis group (Nitrate-UV) during the anaerobic fermentation, significantly promoted by 2.3 and 12.7 folds than that of Control (raw WAS). Acetic acid (HAc) and propionic acid (HPr) accounted for 89.1 % and 90.1 % in Nitrate-UV and Nitrate group (sole nitrate addition), which were much higher than that obtained in UV and Control. HO• and O 2 •− were the main contributors compared with NO 2 •, ONOO– and NO• on the release and bioconversion of the soluble organics. Microbial community and metagenomics revealed the promotion of nitrate photolysis on anaerobic fermentation bacteria (AFB) and nitrate reducing bacteria (NRB), as well as the gene abundance related to the metabolic pathways of glycolysis, amino acid, acetate and nitrogen metabolism, which jointly devoted to the SCFAs enhancement during the anaerobic fermentation. [ABSTRACT FROM AUTHOR]

Biochar has been used to enhance methane generation from anaerobic digestion through establishing direct interspecific electron transfer between microorganisms. However, the microbial communication is still inadequate, thereby limiting further methane production improvement contributed by biochar. This study investigated the roles of quorum-sensing molecules, acylated homoserine lactone (AHL), in anaerobic digestion of waste activated sludge aided by biochar. Results showed that the co-addition of separated biochar and AHL achieved best methane production performance, with the maximal methane yield of 154.7 mL/g volatile suspended solids, which increased by 51.9%, 47.2%, 17.9%, and 39.4% respectively compared to that of control, AHL-loaded biochar, sole AHL, and sole biochar groups. The reason was that the co-addition of separated biochar and AHL promoted the stages of hydrolysis and acidification, promoting the conversion of organic matters and short-chain fatty acids, and optimizing the accumulation of acetate acid. Moreover, the methanogenesis stage also performed best among experimental groups. Correspondingly, the highest activities of electron transfer and coenzyme F420 were obtained, with increase ratios of 33.2% and 27.2% respectively compared to that of control. Furthermore, biochar did more significant effects on the evolution of microbial communities than AHL, and the direct interspecific electron transfer between fermentative bacteria and methanogens were possibly promoted. [Display omitted] • The strategies of biochar and AHL regulating anaerobic digestion were optimized. • The co-addition of separated biochar and AHL increased methane yield by 51.9%. • AHL-loaded biochar obtained less methane yield than either sole AHL or biochar. • The activities of electron transfer were the highest with addition of biochar and AHL. • Methanogenic communities shifted to mixotrophic methanogens like Methanosarcina. [ABSTRACT FROM AUTHOR]

Persulfate oxidation (PS) is widely employed as a promising alternative for waste activated sludge pretreatment due to the capability of generating free radicals. The product differences and microbiological mechanisms by which PS activation triggers WAS digestion through multiple modes need to be further investigated. This study comprehensively investigated the effects of persulfate oxidation activated through multiple modes, i.e., ferrous, zero-valent iron (ZVI), ultraviolet (UV) and heat, on the performance of sludge digestion. Results showed that PS_ZVI significantly accelerated the methane production rate to 12.02 mL/g VSS. By contrast, PS_Heat promoted the sludge acidification and gained the maximum short-chain fatty acids (SCFAs) yield (277.11 ± 7.81 mg COD/g VSS), which was 3.41-fold compared to that in PS_ZVI. Moreover, ferrous and ZVI activated PS achieved the oriented conversion of acetate, the proportions of which took 73% and 78%, respectively. MiSeq sequencing results revealed that PS_Heat and PS_UV evidently enriched anaerobic fermentation bacteria (AFB) (i.e., Macellibacteroides and Clostridium XlVa). However, PS_Ferrous and PS_ZVI facilitated the enrichment of Woesearchaeota and methanogens. Furthermore, molecular ecological network and mantel test revealed the intrinsic interactions among the multiple functional microbes and environmental variables. The homo-acetogens and sulfate-reducing bacterial had potential cooperative and symbiotic relationships with AFB, while the nitrate-reducing bacteria displayed distinguishing ecological niches. Suitable activation modes for PS pretreatments resulted in an upregulation of genes expression responsible for digestion. This study established a scientific foundation for the application of sulfate radical-based oxidation on energy or high value-added chemicals recovery from waste residues. [Display omitted] • Effect of multiple activated persulfate oxidation on sludge digestion was studied. • Heat and UV activated persulfate effectively promoted the accumulation of SCFAs. • ZVI and Ferrous activated persulfate were beneficial for methane production. • Microbial community structures were altered by multiple persulfate activation modes. • Suitable activation modes for persulfate upregulated the critical genes expression. [ABSTRACT FROM AUTHOR]