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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] • 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]

• 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]

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]

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]

[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]

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]

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]

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]

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]

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]

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]

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]

• 150 mgN/L of nitrate photolysis improved SCFAs production from WAS. • Nitrate increase (150∼375 mgN/L) has no significant promotion on SCFAs in photolysis. • ROS contributed more than RNS on WAS solubilization, hydrolysis and acidification. • Both AFB and NRB enriched for the high SCFAs production and complete denitrification. • Genes related to glycolysis, amino acid, acetate and nitrogen metabolism were enhanced. Nitrate photolysis has become an efficient, low-cost and promising technology for emerging contaminants removal, while its performance and mechanism for waste activated sludge (WAS) treatment is still unknown. This study innovatively introduced nitrate photolysis for WAS disintegration, and investigated the effect of nitrate addition (150–375 mg N/L) for short-chain fatty acids (SCFAs) production during anaerobic fermentation (AF). The results showed that nitrate photolysis significantly promoted the SCFAs production from WAS, and peaked at 280.7 mg/g VSS with 7-d fermentation with 150 mg N/L addition (150N-UV), which increased by 8.8–35.0 % and 10.7–23.3 % compared with other photolysis groups and sole nitrate groups. Effective release of the soluble organics was observed in the nitrate photolysis groups during AF, especially soluble proteins, reaching 1505.4 mg COD/L at 9 d in 150N-UV group, promoted by 7.0∼15.7 % than nitrate/nitrate photolysis groups. The model compounds simulation experiment further demonstrated the positive effect of nitrate photolysis on organics hydrolysis and SCFAs accumulation. The result of the radical capture and quenching verified the reactive oxygen species contributed more compared with reactive nitrogen species. Functional group analysis confirmed the effective bioconversion of the macromolecular organics during the fermentation. Moreover, the nitrate photolysis enhanced the enrichment of the functional consortia, including anaerobic fermentation bacteria (AFB), e.g., Fnoticella, Romboutsia, Gracilibacter and Sedimentibacter , and nitrate reducing bacteria (NRB), e.g., Acinerobacter and Ahniella. The macrogenetic analysis further revealed that glycolysis, amino acid metabolism, acetate metabolism and nitrogen metabolism were the dominating metabolic pathways during fermentation, and the abundance of the relevant genes were enhanced in 150N-UV group. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The Na+ + Lysozyme pretreatment increased the yield of SCFAs in WAS by 7.6 times. • A synergistic effect was occurred between Na+ and lysozyme in promoting cell lysis. • Na+ + Lysozyme pretreatment significantly shortened the hydrolysis and acidification reaction times. • 87% of the carbon source recovery in the liquid phase can be achieved after PAC conditioning. Augmentation of the anaerobic treatment efficiency of waste activated sludge (WAS) to achieve better resource utilization is an effective approach for reducing carbon emissions and minimizing solid waste generation. However, resource recovery from WAS is often limited by the insufficient release and hydrolysis of organic matters within microbial cells. To overcome these issues, a novel Na+ and lysozyme co-pretreatment method has been used in this study to accelerate the production of short-chain fatty acids (SCFAs) by promoting cell lysis. Experimental results have revealed that the maximal SCFAs production of 302.8 ± 47.8 mg COD/g VSS is achieved with 10 % w/w lysozyme and 0.34 mol/L Na+ co-pretreatment on day 2, which is 7.6-fold higher than that of the control. Mechanism exploration has also exposed that Na+ and lysozyme exhibit a pronounced synergistic effect in cell lysis, where 1 + 1 > 2. The maximum sludge disintegration degree (DD M) and SCFAs conversion efficiency have been achieved by combined pretreatment, reaching 68.5 % and 74 %, respectively. The structure of extracellular polymeric substance (EPS) including protein content and looseness are also modified by Na+ or Na+ + Lysozyme pretreatment, which further confirm the impact of Na+ on the permeability of EPS. The carbon sources generated through Na+ and lysozyme pretreated WAS can be efficiently recovered through PAC conditioning, with a high recovery rate of 87 %. The Na+ and lysozyme reagents implemented in the present study are all non-toxic and cost-effective, thereby promising a green and efficient solution for the carbon recovery and separation from the WAS. [ABSTRACT FROM AUTHOR]

Biochar produced from bio-wastes has been widely used to promote the performance of anaerobic digestion. Waste activated sludge (WAS) is considered as a kind of popular precursor for biochar preparation, but the abundant resources in WAS were neglected previously. In this study, the roles of biochar prepared from raw, pretreated, and fermented sludge on anaerobic digestion were investigated. That is, parts of carbon sources and nutrients like polysaccharides, proteins, and phosphorus were firstly recovered after sludge pretreatment or fermentation, and then the sludge residuals were used as raw material to prepare biochar. The methane yield improved by 22.1% with adding the biochar (AK-BC) prepared by sludge residual obtained from alkaline pretreatment. Mechanism study suggested that the characteristics of AK-BC like specific surface area and defect levels were updated. Then, the conversion performance of intermediate metabolites and electro-activities of extracellular polymeric substances were up-regulated. As a result, the activity of electron transfer was increased with the presence of AK-BC, with increase ratio of 21.4%. In addition, the electroactive microorganisms like Anaerolineaceae and Methanosaeta were enriched with the presence of AK-BC, and the potential direct interspecies electron transfer was possibly established. Moreover, both aceticlastic and CO 2 -reducing methanogenesis pathways were improved by up-regulating related enzymes. Therefore, the proposed strategy can not only obtain preferred biochar but also recover abundant resources like carbon source, nutrients, and bioenergy. [Display omitted] • Biochar from raw, pretreated, and fermented sludge residuals were optimized. • Methane yield increased by 22.1% with biochar from alkaline pretreated sludge. • Alkaline pretreated sludge biochar increased electron transport activity by 21.4%. • Both aceticlastic and CO 2 -reducing methanogenesis pathways were improved. • A green and sustainable strategy for final disposal of sludge was proposed. [ABSTRACT FROM AUTHOR]

Electro-fermentation (EF) has been extensively studied for recovering hydrogen and phosphorus from waste activated sludge (WAS), while was limited for the further application due to the low hydrogen yield and phosphorus recovery efficiency. This study proposed an efficient strategy for hydrogen and vivianite recovery from the simulated sludge fermentation liquid by sacrificial iron anode in EF. The optimum hydrogen productivity and the utilization efficiency of short chain fatty acids (SCFAs) reached 45.2 mmol/g COD and 77.6% at 5 d in pH 8. Phosphate removal efficiency achieved at 90.8% at 2 d and the high crystallinity and weight percentage of vivianite (84.8%) was obtained. The functional microbes, i.e., anaerobic fermentative bacteria, electrochemical active bacteria, homo-acetogens and iron-reducing bacteria were highly enriched and the inherent interaction between the microbial consortia and environmental variables was thoroughly explored. This work may provide a theoretical basis for energy/resource recovery from WAS in the further implementation. [Display omitted] • Enhanced hydrogen and vivianite recovery were realized in pH 8 via Fe mediated EF. • Appropriate iron release led to the higher crystallinity of vivianite in pH 8 group. • EAB, AFB and homo-acetogens preferred to enrich in pH 8 than other pH conditions. • The mutual symbiosis of microbes and environmental factors was the main mechanism in EF. [ABSTRACT FROM AUTHOR]

[Display omitted] • Specific colonization pattern of key symbionts in MES was firstly investigated. • Co-colonization of EAB and CSB promoted caproate biosynthesis in MES. • CSB and EAB mutually interacted in metabolic activity and enhanced electron transfer. • Ecological mechanism was revealed in terms of MEN analysis and Mantel test. • Economic benefit and carbon emission were preferable via co-colonization. As promising and value-added platform chemicals, the biosynthesis of medium-chain fatty acids (MCFAs, C6-C12) via chain elongation (CE) in microbial electrosynthesis systems (MES) has recently garnered significant attentions due to the unique bioelectrocatalytic behaviors and the reduction of exogenous electron donors (EDs). Caproate-synthesizing bacteria (CSB) played a crucial role in the generation of acetyl-CoA, which subsequently underwent reverse β oxidation to synthesize MCFAs. However, the presence of electrochemically active bacteria (EAB) was also pivotal for MES as they generated hydrogen in the cathodic electron transfer pathways, the specific colonization patterns of key symbionts remained unknown. The aim of this study was to investigate the selective colonization of EAB and CSB on the performance of caproate production in MES. The reactors colonized EAB and CSB achieved the maximum caproate concentration of 5332.5 mg COD/L, which was 7.9 and 1.3 times higher compared to that inoculated with either sole EAB or CSB, respectively. Moreover, the reactors colonized with mixed culture exhibited a clear redox peak and preferable electron transfer efficiency. CSB and EAB mutually interacted in metabolic activities, thereby resulting in increased substrate utilization and caproate production. The findings of this study provide a new strategy and insights for value-added chemicals recovery in microbial electrosynthesis platform. [ABSTRACT FROM AUTHOR]

A huge production of waste activated sludge (WAS) has been a burden for wastewater treatment plants (WWTPs) with high disposal cost and little benefit back to wastewater purification. The short-chain fatty acids (SCFAs) produced by a short-term acidogenic fermentation of WAS before methane production have been proven to be a high-quality carbon source available for microbial denitrification process. The dual purpose of full recovery of fermentation liquid products and facilitating disposal of residual solid waste necessitate an efficient solid-liquid separation process of short-term fermentation liquid. The transformation and loss of various soluble carbon sources between solid and liquid are very important issues for carbon recovery efficiency when combining short-term fermentation and sludge dewatering in WWTPs. Here we testified the three conventional preconditioning coagulants, Polyferric Sulfate (PFS), Poly Aluminum Chloride (PAC) and Polyacrylamide (PAM), to improve the efficiency of subsequent solid-liquid separation. The results show that conversion yield of SCFAs in the liquid phase of sludge after short-term fermentation was 195 mg COD/g VSS, when using the coagulants PFS, PAC, and PAM for recovery, the recovery ratio was 79.5%, 82.0%, and 85.9%, respectively, while the dewaterability could be improved after preconditioning short-term fermentation sludge. The complexation of Al3+/Fe3+ in metal coagulants with carboxyl groups of SCFA demonstrated by Density Functional Theory calculation led to small part of soluble carbons co-migration to the solid phase, mainly a loss of high molecular weight organic compounds (carbohydrate, proteins, humic acids), while the application of PAM had little impact on carbon recovery. Economic calculations further showed PAM preconditioning short-term fermentation liquid of WAS could achieve higher recovery benefits. [Display omitted] • Soluble carbon recovery for denitrification is carried out from waste activated sludge. • The technology is optimized by combining short-term fermentation and sludge dewatering in WWTPs. • Conventional coagulants were applied for carbon source recovery. • The transformation and loss of various soluble carbon sources were evaluated. • Potential mechanism of the loss of Short-chain fatty acids was revealed. [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]

Methane recovery from bio-wastes is one promising renewable energy to relieve the energy crisis faced around the world. Zeolite is one of attractive exogenous additives for promoting methane production from anaerobic digestion due to its potentials in regulating microorganism enrichment and anaerobic environment. However, the poor electron mediated ability limited its positive effects. Hence, this study hypothesized that the electron mediated ability of zeolite would be improved by loading magnetite, thereby generating more positive impacts on the performance of sludge anaerobic digestion. Compared to control group, magnetite modified zeolite (MZ) effectively improved methane yield by 37.4%. The reason was that the electron mediated ability and adsorption capacity of zeolite were improved by loading magnetite, facilitating the degradation of refractory organics and the conversion of volatile fatty acids. Moreover, the activities of cytochrome c and F420 increased by 33.3% and 29.8% with MZ additive, contributing to stimulating efficient electron transfer process. In addition, the electro-active genera were enriched, such as Bacteroidetes_vadinHA17 , Methanobacterium , and Methanosaeta , and the direct interspecies electron transfer was possibly established for methanogenesis with the help of MZ. This study will provide valuable references for the application of zeolite in anaerobic digestion. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Immobilized CB and NF electrode can increase methane yield by 38%-94%. • Applying no voltage to the electrodes is more conducive to methane production. • Syntrophic methane production was enhanced by immobilized electrode. • Voltage weakens anode methanogenesis but strengthens cathode DIET/IHT methanogenesis. Introduction of voltage or conductive materials have been proven to be effective strategies for enhancing the stability and efficiency of sludge digestion for methane recovery. This experiment simulated a two-phase anaerobic system, consisting of an acid-producing phase with alkali pretreatment and a methane-producing phase with immobilized electrodes and voltage enhancement. Various effective and comparative experiments were conducted to investigate the crucial roles of immobilized electrodes like carbon brush (CB) and nickel foam (NF), electroactive biofilm and voltage during the sludge methane-producing phase. The experimental results indicate that directly application of immobilized CB and NF electrode to promote sludge anaerobic digestion achieves better performance than additional voltage supply. The electrodes can increase methane production by 38% to 94%, whereas under additional voltage supply, methane production only increases by 22%–53% compared to the control. Through the analysis of key transformations in organic substrates and changes in microbial community structure, the inherent advantages of electrode materials in promoting the syntrophic methanogenesis processes are confirmed. Compared to suspended sludge, the types and relative abundance of typical syntrophic methane-producing microorganisms, Methanosarcina , and acetogenic bacteria, Syntrophomonas on the electrode surface significantly increase by 8.5% and 1.7%. This process is notably superior to the methane generation process dominated by hydrogenotrophic methanogensis after applying voltage. The results indicate that CB and NF are suitable conductive materials to promote anaerobic methane recovery, and their effectiveness surpasses that of applying voltage. These research outcomes provide new insights for the development of novel anaerobic digestion enhancement systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bioelectrochemical system-anaerobic digestion (BES-AD) coupling for resource gain. • Algal BES-AD supports carbon capture and nutrient recovery make it sustainable. • Intricacy of BES-AD increases the upscaling challenges for field applications. • BES-AD with high energy efficacy and negative economics demands performance boost. • Future market demands industrial trials and boost in yield before commercial use. With advancements in research and the necessity of improving the performance of bioelectrochemical system (BES), coupling anaerobic digestion (AD) with BES is crucial for energy gain from wastewater and bioremediation. Hybridization of BES-AD concept opens new avenues for pollutant degradation, carbon capture and nutrient-resource recovery from wastewater. The strength of merging BES-AD lies in synergy, and this approach was employed to differentiate fads from strategies with the potential for full-scale implementation and making it an energy-positive system. The integration of BES and AD system increases the overall performance and complexity of combined system and the cost of operation. From a technical standpoint, the primary determinants of BES-AD feasibility for field applications are the scalability and economic viability. High potential market for such integrated system attract industrial partners for more industrial trials and investment before commercialization. However, BES-AD with high energy efficacy and negative economics demands performance boost. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pd nanoparticles promoted the generation and stabilization of atomic H*. • An atomic H* mediated electrochemical reduction method was applied for removal contaminants from wastewater. • Atomic H* was proved by electrochemical characterizations, HRMS and DFT. • Quantification of transient atomic H* was achieved by double integration of the ESR signal. Electro-generated atomic hydrogen (H*) plays a crucial role in the electrochemical reduction process, serving as the key species that mediates the electrocatalytic hydrogenation reduction of stubborn contaminants in wastewater treatment. However, precisely identifying and quantifying transient atomic H* presents a significant challenge due to its limited lifespan and its existence solely within the boundary layer at the electrode/solution interface. Herein, we developed the electrodeposition of palladium nanoparticles onto carbon cloth and assessed its effectiveness as a cathode for generating and stabilizing atomic H*. The environmental application of atomic H* was validated through the dechlorination of 2, 4-dichlorophenol wastewater and the reduction of antimonite wastewater. Additionally, the identification of atomic H* was verified by electrochemical measurements, high-resolution mass spectra, and density functional theory. Moreover, introducing an excess of a spin trapping agent (5,5-dimethyl-1-pyrroline-N-oxide) and fast in-situ spin trapping facilitated creating favorable conditions for efficient trapping of atomic H* and subsequent electron spin resonance (ESR) spectroscopy quantification analysis. Subsequently, the quantification of atomic H* was achieved by double integration of the ESR signal of spin adduct and comparison with the external standard agent (4-hydroxy-2,2,6,6-tetramethyl-1-piperidine 1-oxyl). This study introduces a novel method for in-situ spin trapping and quantification of atomic H*, facilitating the advancement of electrochemical reduction technology and its application in wastewater treatment. [ABSTRACT FROM AUTHOR]