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A large amount of chemical energy in wastewater is highly valuable in resource utilization, and nitrogen is one of the key nutrients and contaminants in diverse wastewater. Traditional wastewater treatment technologies focus on removing nitrogen from wastewater, which s not sustainable and consumes a lot of resources and energy. Microbial electrochemical technologies (METs) have been invested to transform conventional energy-intensive wastewater treatment into a resource recovery process for reclaiming valuable nitrogen products. Nevertheless, the engineering application of METs from different real wastewater is still in its infancy due to the complex characteristics of different waste streams. This review broadly concludes the present METs-assisted nitrogen recovery systems and the ammonium recovery performance of different wastewater streams. Additionally, the environmental impact and economic analysis of different METs and end products are presented to demonstrate their application potential. The results show that the microbial electrolysis cell (MEC) has better engineering application compared to microbial fuel cell (MFC), which could reduce the overall environmental burden and infrastructure costs. And coupling the MEC with stripping technology can be a preferable option for ammonia recovery.. Finally, present challenges and prospects in the field of METs-assisted nitrogen recovery are discussed, including scaling up bioreactors, enhancing strategies, and conducting life cycle assessment of the entire recovery process. [Display omitted] [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]

Rapid hydrolysis of waste activated sludge (WAS) can be achieved by improving activities of extracellular enzymes under proper temperature conditions. As short-chain fatty acids (SCFAs) accumulation is always consumed by methanogens under anaerobic conditions, and considering that the micro-aerobic condition can inhibit the activities of methanogens, in this study, effects of temperature (55–75°C) on thermophilic micro-aerobic fermentation of WAS were investigated. Results showed that the highest soluble chemical oxygen demand (SCOD) yield was obtained at 60°C (4,407 ± 80 mg/L, 36 h), 2.0 times higher than that obtained at 75°C (2,180 ± 40 mg/L, 36 h), the corresponding hydrolysis rate was 0.6689 d−1. The highest SCFAs yield was 2,928 ± 12 mg COD/L at 60°C and 36 h, 4.9 times higher than that obtained at 75°C (594 ± 10 mg COD/L, 36 h). The analysis of SCFAs composition showed that acetic acid (HAc) accounted for the most percentage (>40%), followed by n-valeric (n-HVa) (20–25%), and propionic acids (HPr) (10–15%). Total suspended solids removal efficiency reached 18.7% after 192-h fermentation at 60°C. These results suggested that the optimal thermophilic micro-aerobic conditions for WAS hydrolysis and SCFAs accumulation from WAS were 60°C and 36-h fermentation time. [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]

To recover resource from waste activated sludge (WAS) presents great roles on developing carbon-neutral operation of wastewater treatment plants. This study was conducted to evaluate SCFAs production potential from anaerobic fermentation of WAS by a novel strategy, i.e., low temperature assisting potassium ferrate (PF) treatment. Results showed that the maximal SCFAs production reached 217 mg chemical oxygen demand (COD)/g volatile suspended solids (VSS) with the shortened fermentation time of six days, and the sum of acetic and propionic acids reached 128 mg COD/g VSS. Meanwhile, the potentially recovered carbon source, in terms of SCFAs, soluble polysaccharides and proteins, reached 437 mg COD/g VSS. The mechanism study indicated that both solubilization and hydrolysis steps were accelerated, supporting by the highest accumulations of soluble organics and ammonia nitrogen, while methanogenesis step was inhibited, supporting by the lowest methane production. In addition, it is noted that low temperature treatment facilitated organics release from extracellular polymeric substance (EPSs), with the removal efficiencies of 51.1% for polysaccharides and 44.3% for proteins, while PF facilitated cell lysis. Interestingly, compared with low temperature followed by PF treatment, PF followed by low temperature treatment performed better on facilitating disintegration of both cells and EPSs, with the highest soluble polysaccharides and proteins of 439 and 1845 mg COD/L. Also, the acid-producing bacteria was greatly enriched, with total percentage of 29.5%. The findings of this study may provide some potential solutions for SCFAs production enhancement from WAS. [Display omitted] • PF followed by low temperature treatment improved SCFAs production from WAS. • The potentially recovered carbon source increased to 437 mg COD/g VSS. • Low temperature treatment promoted EPSs removal while PF facilitated cell lysis. • PF-T enhanced solubilization and hydrolysis steps but inhibited methanogenesis. • PF-T treatment facilitated the enrichment of acid-producing bacteria. [ABSTRACT FROM AUTHOR]

Wastewater, as the used water, carries huge energy that is frequently ignored and unexploited. Microbes, as bioelectrocatalysts in microbial electrochemical systems (MESs), can convert chemical energy stored in biodegradable matrixes from wastewater to bioelectricity and chemicals. However, due to sluggish wastewater treatment rates and bioenergy production, wider applications have been hampered. Currently, photo-assisted MESs, combined electrochemical/photochemical driving force with microbial catalysis, have emerged as a sustainable platform to enhance pollutants degradation and bioenergy recovery from wastewater with the aid of solar light, accompanied by reasonable energy investment and minimal environmental disturbance. Nevertheless, the development of photo-assisted MESs is still in its infancy. This work broadly concludes present photo-assisted MESs wastewater treatment technologies and their overall limitations in terms of performance and the future advancements that will be necessary to make them more widely applicable. Herein, crucial factors influencing the performance of these photo-assisted MESs, such as the reactor types (bioanode-photocathode, photoanode-biocathode, photomicrobial electrode, and photosynthetic bacteria/algae MESs), the bandgap of semiconductor and microbe species are discussed. Furthermore, prominent research accomplishments of photo-assisted MESs with an emphasis on eliminating contaminants (initial concentration, removal efficiency, and removal rate) and recovering bioenergy (product types, production rate, and current density) from various wastewaters are systematically summarized. Finally, present challenges and prospects in the field of photo-assisted MESs technology are discussed, mainly including the optimization of electrode materials, screening and culture of microorganisms, scale-up of bioreactors, intermittency of solar energy, and other complications overarchingly shared with photo-assisted microbial electrochemical wastewater treatment and bioenergy recovery. Graphical Abstract [Display omitted] [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]

[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]

[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]