Coupling of membrane-based bubbleless micro-aeration for 2,4-dinitrophenol degradation in a hydrolysis acidification reactor

Effect of carbon source on the migration and transformation of sulfate and rare earth elements in wastewater by sulfate-reducing anaerobic digestion

The rare earth extraction wastewater containing trace amounts of rare earth elements (REE3+), posed significant environmental risks and complicated recovery efforts. Sulfate-reduced anaerobic digestion (SRAD) offered promising treatment for the wastewater. However, the influence of carbon source on the collaborative transformation of sulfate and REE3+ within SRAD remained inadequately explored. Thus, this study explored the transformation of sulfate and REE3+ under different carbon source conditions. The results demonstrated that, despite the advantage of ethanol in electron donation, it was less effective than a mixed carbon source in removing REE3+. This was attributed to several factors: (1) Mixed carbon sources not only enhances the production of S2- but also promotes the stable forms of REE3+ through preferential formation of organically bound fraction/residual fraction coordination complexes; (2) Microorganisms cultivated with mixed carbon sources secreted more tryptophan-like proteins capable of adsorbing REE3+; and (3) CO-SRB (complete oxidizers-sulfate-reducing bacteria) enriched by mixed carbon sources exhibited stronger adaptability to REE3+ and more robust interspecies interactions. Moreover, the COD/SO42- ratio of 1.5 was found to be optimal, achieving approximately 90 % removal of REE3+ and 69.38 ± 4.63 % removal of SO42-. This study provides theoretical guidance for carbon source dosing strategies aimed at the simultaneous removal of sulfate and REE3+ from rare earth wastewater.

Biodegradation of p-nitrophenol by Rhodococcus sp. 21391 unveils a two-component p-nitrophenol monooxygenase with broad substrate specificity

BACKGROUND

Bioremediation relying on highly efficient degrading bacteria constitutes a promising and sustainable avenue for controlling and reducing nitrophenol contamination in the environment. A thorough understanding of the bacterial degradation mechanism of nitrophenol is of paramount importance for supporting the development of efficient microbial remediation technology.

RESULTS

In this study, a new bacterium, Rhodococcus sp. 21391, endowed with superior p-nitrophenol (PNP) degradation ability was obtained. Genomic and comparative proteomic analyses revealed that it utilizes the 1,2,4-benzenetriol (BT) pathway for PNP degradation. The catalytic properties of the two-component p-nitrophenol monooxygenase RsNcpAB from the strain were investigated in vitro. The enzyme exhibited a broad substrate selectivity, catalyzing the oxidation of various nitrophenols and halogenated phenols, with significant potential for further research and development. Additionally, the crystal structure of the oxidative component of p-nitrophenol monooxygenase, RsNcpA, was determined. Structural analysis and site-directed mutagenesis revealed that residues Arg100 and His293 in the active site play a crucial role in enzyme catalysis, and a catalytic mechanism model was subsequently proposed.

CONCLUSIONS

This study reports a high-performance nitrophenol-degrading bacterium and enzyme, and reveals their mechanisms at the molecular level. These findings increase the understanding of the bacterial degradation of nitrophenol, thereby providing a crucial foundation for the development of efficient bioremediation technologies.

Roles of nitrite in facilitating nitrogen and sulfur conversion in the hybrid bioreactor of Sulfate-reduced ammonium oxidation and anaerobic ammonium oxidation

The hybrid bioreactor combining sulfate-reducing ammonium oxidation (Sulfammox) and Anammox offered potential for simultaneous nitrogen and sulfur removal, but the removal efficiency and microbial mechanism remain unclear. This study demonstrated that in the hybrid bioreactor, the ammonium utilization rate (AUR) of Sulfammox increased by 5.42 times. The promotion of NO2- on nitrogen and sulfur conversion in Sulfammox could be attributed to: 1) Increasing extracellular polymers substance (EPS) accelerated the stratification of granule sludge; 2) Increasing the relative abundance of Candidatus Brocadia by 29.55 times and Candidatus Anammoxoglobus by 3.17 times; 3) Upregulating the expression of nitrification (amo, hao and nxr) and sulfur metabolism (sat, aprAB dsr and sox) genes, associated with the pathways NH4+→NH2OH → NO2-→NO3- and SO42-→S2-→SO42-. Moreover, Candida Brocadia sapporoensis emerged as a potential specie of Sulfammox, mediating nitrification by hao and nxr, and sulfate reduction by sat and aprAB, thereby enabling electron transfer between nitrogen and sulfur.

Microbiome regulation for sustainable wastewater treatment

Sustainable wastewater treatment is essential for attaining clean water and sanitation, aligning with UN Sustainable Development Goals. Wastewater treatment plants (WWTPs) have utilized environmental microbiomes in biological treatment processes in this effort for over a century. However, the inherent complexity and redundancy of microbial communities, and emerging chemical and biological contaminants, challenge the biotechnology applications. Over the past decades, understanding and utilization of microbial energy metabolism and interaction relationships have revolutionized the biological system. In this review, we discuss how microbiome regulation strategies are being used to generate actionable performance for low-carbon pollutant removal and resource recovery in WWTPs. The engineering application cases also highlight the real feasibility and promising prospects of the microbiome regulation approaches. In conclusion, we recommend identifying environmental risks associated with chemical and biological contaminants transformation as a prerequisite. We propose the integration of gene editing and enzyme design to precisely regulate microbiomes for the synergistic control of both chemical and biological risks. Additionally, the development of integrated technologies and engineering equipment is crucial in addressing the ongoing water crisis. This review advocates for the innovation of conventional wastewater treatment biotechnology to ensure sustainable wastewater treatment.

Molecular-level insights into dissolved organic matter and its variations of the full-scale processes in a typical petrochemical wastewater treatment plant

Petrochemical wastewater (PCWW) treatment poses challenges due to its unique and complex dissolved organic matter (DOM) composition, originating from various industrial processes. Despite the addition of advanced treatment units in PCWW treatment plants to meet discharge standards, the mechanisms of molecular-level sights into DOM reactivity of the upgraded full-scale processes including multiple biological treatments and advanced treatment remain unclear. Herein, we employ water quality indexes, spectra, molecular weight (MW) distribution, and Fourier transform ion cyclotron resonance mass spectrometry to systematically characterize DOM in a typical PCWW treatment plant including influent, micro-oxygen hydrolysis acidification (MOHA), anaerobic/oxic (AO), and micro-flocculation sand filtration-catalytic ozonation (MFSF-CO). Influent DOM is dominated by tryptophan-like and soluble microbial products with MW fractions 〈 1 kDa and 〉 100 kDa, and CHO with lignin and aliphatic/protein structures. MOHA effectively degrades macromolecular CHO (10.86 %) and CHON (5.24 %) compounds via deamination and nitrogen reduction, while AO removes CHOS compounds with MW < 10 kDa by desulfurization, revealing distinct DOM conversion mechanisms. MFSF-CO transforms unsaturated components to less aromatic and more saturated DOM through oxygen addition reactions and shows high CHOS and CHONS reactivity via desulfurization and deamination reactions, respectively. Moreover, the correlation among multiple parameters suggests UV254 combined with AImod as a simple monitoring indicator of DOM to access the chemical composition. The study provides molecular-level insights into DOM for the contribution to the improvement and optimization of the upgraded processes in PCWW.

Optimizing intermittent micro-aeration as a strategy for enhancing aniline anaerobic biodegradation: kinetic, ecotoxicity, and microbial community dynamics analyses

Groundwater and soil contamination by aromatic amines (AAs), used in the production of polymers, plastics, and pesticides, often results from improper waste disposal and accidental leaks. These compounds are resistant to anaerobic degradation; however, micro-aeration can enhance this process by promoting microbial interactions. In batch assays, anaerobic degradation of aniline (0.14 mM), a model AA, was tested under three micro-aeration conditions: T30, T15, and T10 (30, 15, and 10 min of micro-aeration every 2 h, respectively). Aniline degradation occurred in all conditions, producing both aerobic (catechol) and anaerobic (benzoic acid) byproducts. The main genera involved in T30 and T15 were Comamonas, Clostridium, Longilinea, Petrimonas, Phenylobacterium, Pseudoxanthomonas, and Thiobacillus. In contrast, in T10 were Pseudomonas, Delftia, Leucobacter, and Thermomonas. While T30 and T15 promoted microbial cooperation for anaerobic degradation and facultative respiration, T10 resulted in a competitive environment due to dominance and oxygen scarcity. Despite aniline degradation in 9.4 h under T10, this condition was toxic to Allium cepa seeds and exhibited cytogenotoxic effects. Therefore, T15 emerged as the optimal condition, effectively promoting anaerobic degradation without accumulating toxic byproducts. Intermittent micro-aeration emerges as a promising strategy for enhancing the anaerobic degradation of AA-contaminated effluents.

Achieving high nitrogen and antibiotics removal efficiency by nZVI-C in partial nitritation/anammox system with a single-stage membrane-aerated biofilm reactor

This study innovated constructed an activated carbon-loaded nano-zero-valent iron (nZVI-C) enhanced membrane aerated biofilm reactor (MABR) coupled partial nitritation/anammox (PN/A) system for optimizing nitrogen and antibiotics removal. Results showed that nitrogen and antibiotic removal efficiencies of 88.45 ± 0.14% and 89.90 ± 3.07% were obtained by nZVI-C, respectively. nZVI-C hastened Nitrosomonas enrichment (relative abundance raised from 2.85% to 12.28%) by increasing tryptophan content in EPS. Furthermore, nZVI-C proliferated amo gene by 3.92 times and directly generated electrons, stimulating Ammonia monooxygenase (AMO) co-metabolism activity. Concurrently, via antibiotic resistance genes (ARGs) horizontal transfer, Nitrosomonas synergized with Arenimonas and Comamonadaceae for efficient antibiotic removal. Moreover, nZVI-C mitigated antibiotics inhibition of electron transfer by proliferating genes for PN and anammox electron production (hao, hdh) and utilization (amo, hzs, nir). That facilitated electron transfer and synergistic substrate conversion between ammonia oxidizing bacteria (AOB) and anaerobic ammonia oxidizing bacteria (AnAOB). Finally, the high nitrogen removal efficiency of the MABR-PN/A system was achieved.

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

Enhanced anaerobic digestion performance and sludge filterability by membrane microaeration for anaerobic membrane bioreactor application

Slow dissolution/hydrolysis of insoluble/macromolecular organics and poor sludge filterability restrict the application potential of anaerobic membrane bioreactor (AnMBR). Bubble-free membrane microaeration was firstly proposed to overcome these obstacles in this study. The batch anaerobic digestion tests feeding insoluble starch and soluble peptone with and without microaeration showed that microaeration led to a 65.7-144.8% increase in methane production and increased critical flux of microfiltration membrane via driving the formation of large sludge flocs and the resultant improvement of sludge settleability. The metagenomic and bioinformatic analyses showed that microaeration significantly enriched the functional genes and bacteria for polysaccharide and protein hydrolysis, microaeration showed little negative effects on the functional genes involved in anaerobic metabolisms, and substrate transfer from starch to peptone significantly affected the functional genes and microbial community. This study demonstrates the dual synergism of microaeration to enhance the dissolution/hydrolysis/acidification of insoluble/macromolecular organics and sludge filterability for AnMBR application.

The synergistic role of ozonation and hydrolysis acidification on the enhanced pre-treatment of high-strength refractory 2-butenal manufacture wastewater: Performance, metabolism, and mechanisms

Targeted removal of three key refractory toxic organic compounds (TOMs) in 2-butenal manufacturing wastewater (2-BMW) is critical for enhancing pre-treatment by hydrolysis acidification (HA). We investigated the pre-treatment of 2-BMW with HA, coupled with ozonation in this study. Our results indicated that the removal rate of these key TOMs and the detoxification rate reached almost 100% and 46.3%, respectively, by ozonation under only 0.099 mg O3/mg chemical oxygen demand (COD). The organic load rate (OLR) reached 10.25 ± 0.43 kg COD/m3·d, and the acidification degree (AD) and detoxification efficiency reached 56.0% and 98.3%, respectively, with enhancements of 35.1% and 55.2%, respectively, compared with HA alone. The removal rate of the three key TOMs was improved by > 75%. The degradation pathways of these key TOMs were ring cleavage and ester formation by ozonation, followed by fermentation and acid production by HA. Ultimately, the synergistic role of ozonation and HA was revealed. The preferential cleavage of these key TOMs by ozonation was achieved because of their high electron cloud density and multiple reaction sites, which generated more fermentation-friendly products. The fermentation and acid production reactions may be directly involved in these products. Functional bacteria and key metabolic pathways were also enhanced by ozonation.

Effects of Fe/Fe-Mn oxides loaded biochar on anaerobic degradation of typical phenolic compounds in coal gasification wastewater: Performance and mechanism

In this study, two kinds of magnetic biochar (BC) were synthesized by loading Fe (FeBC) and Fe-Mn oxides (FMBC) and their effects on anaerobic phenolics degradation were investigated. Compared with BC/FMBC, FeBC addition achieved the superior phenolics biodegradation even for 3,5-xylenol. Compared with control, FeBC addition enhanced CH4 production by 100.1 % with the lag time shortened from 9.5 days to 6.6 days while it increased to 11.2 days with FMBC addition. FeBC addition activated adsorption-biodegradation and Fe (III) reduction with the improved electron transfer activity, adenosine triphosphate and cytochrome C concentrations. Abundant phenol degrading bacteria, electroactive bacteria, syntrophic partners could be enriched by FeBC addition, contributing to the enhanced benzoyl-CoA and methanogenesis pathways. However, this enhancement was inhibited by FMBC addition owing to the accumulation of reactive oxygen species. This study provided novel insights into the application of magnetic BC to enhanced anaerobic treatment of phenolic wastewater.

High-rate nitrogen removal by partial nitritation/anammox with a single-stage membrane-aerated biofilm reactor

In this study, a membrane aerated biofilm reactor (MABR) coupled partial nitritation/anammox (PN/A) system was established for high-rate nitrogen removal. Results showed that the nitrogen removal efficiency of 90.34% was finally obtained when influent ammonia increased from 150 mg L-1 to 300 mg L-1. Based on the fluorescence spectroscopy technology, the raised hydrophobicity tryptophan in extracellular polymeric substances (EPS) promoted biofilm formation and bacteria aggregation. 16S rRNA gene amplicon sequencing revealed that the relative abundance of AOB and AnAOB was also enhanced by ammonia (Nitrosomonas and Candidatus Brocadia increased by 6.02 % and 10.06 % in biofilm, respectively), which further facilitated nitrogen removal efficiency. Furthermore, the key functional genes involved in partial nitritation and anammox, especially hao and nirK, up-regulated by 1.31 and 1.26 times, respectively, accelerating the electron generation and consumption. Therefore, raising influent ammonia content intensified microbial electron transfer behavior and high-rate nitrogen metabolism.

Enhanced Mass Transfer of Ozone and Emerging Pollutants through a Gas-Solid-Liquid Reaction Interface for Efficient Water Decontamination

Ozone (O3), as an environmentally friendly oxidant, is widely used to remove emerging pollutants and ensure the safety of the water supply, whereas the restricted accessibility of O3 and limited collision frequency between pollutants and O3 will inevitably reduce the ozonation efficiency. To promote the chemical reactions between O3 and target pollutants, here we developed a novel gas-solid-liquid reaction interface dominated triphase ozonation system using a functional hydrophobic membrane with an adsorption layer as the O3 distributor and place where chemical reactions occurred. In the triphase system, the functional hydrophobic membrane simultaneously improved the interface adsorption performance of emerging pollutants and the access pathway of O3, leading to a marked enhancement of interfacial pollutant concentration and O3 levels. These synergistic qualities result in high ciprofloxacin (CIP) removal efficiency (94.39%) and fast apparent reaction rate constant (kapp, 2.75 × 10-2 min-1) versus a traditional O3 process (41.82% and 0.48 × 10-2 min-1, respectively). In addition, this triphase system was an advanced oxidation process involving radical participation and showed excellent degradation performance of multiple emerging pollutants. Our findings highlight the importance of gas-solid-liquid triphase reaction interface design and provide new insight into the efficient removal of emerging pollutants by the ozonation process.

The response of nitrifying activated sludge to chlorophenols: Insights from metabolism and redox homeostasis

The specialized wastewater treatment plants for the chemical industry are rapidly developed in China and many other countries. But there is a common bottleneck in that the toxic pollutants in chemical wastewater often cause shock impacts on biological nitrogen removal systems, which directly affects the stability and cost of operation. As the research on nitrification inhibition characteristics is not sufficient till now, there is a great lack of theoretical guidance on the control of the inhibition. This study investigated the response of nitrifying activated sludge to chlorophenols (CPs) inhibition in terms of metabolism disorder and oxidative stress. At the initial stage of reaction (i.e., 1 h), reactive oxygen species (ROS)-induced membrane damage which might account for declining nitrification performance. Simultaneously excessive extracellular polymeric substances (EPS) were secreted to alleviate oxidative stress injury and protected microorganisms to some extent. In particular tyrosine-like substances in LB-EPS with a Fmax increase of 242.30% were confirmed to efficiently resist phenols inhibition. Thus, as the inhibition proceeded, metabolism disorder replaced oxidative stress as the main cause of nitrification inhibition. The affected metabolic processes include weakened enzyme catalysis, restricted electron transport and lessened energy generation. At 4 h, nitrifying production of sludge amended with 5 mg/L chlorophenols was 89.27 ± 9.51%-98.15 ± 9.60% lower than blank, the inhibition could be attributed to comprehensively affected metabolism. The structural equation modeling indicated that phenols restricted nitrification enzymes and bacterial electron transport efficiency which was critical to nitrification performance. Moreover, the lessened energy generation weakens enzyme activity to further suppress nitrification. These findings enriched our knowledge of nitrifiers' responses to CPs inhibition and provided the basis for addressing nitrification inhibition.

Micro-aeration and leachate recirculation for the acceleration of landfill stabilization: Enhanced hydrolytic acidification by facultative bacteria

The long duration of landfill stabilization is one of the challenges faced by municipalities. In this paper, a combination of micro-aeration and leachate recirculation is used to achieve rapid degradation of organic matter in landfill waste. The results showed that the content of volatile fatty acids (VFAs) in the hydrolysis phase increased significantly and could enter the methanogenic phase quickly. Until the end of the landfill, the removal rates of chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen (NH4+-N) by micro-aeration and leachate recirculation reached 80.17 %, 48.30 % and 48.56 %, respectively, and the organic matter degradation rate reached 50 %. Micro-aeration and leachate recirculation enhanced the abundance of facultative hydrolytic bacteria such as Rummeliibacillus and Bacillus and the oxygen tolerance of Methanobrevibacter and Methanoculleus. Micro-aeration and leachate recirculation improved the organic matter degradation efficiency of landfill waste by promoting the growth of functional microorganisms.

Sustainable disposal of Fenton sludge and enhanced organics degradation based on dissimilatory iron reduction in the hydrolytic acidification process

Fenton sludge generated in the flocculation stage of the Fenton oxidation process contains significant amounts of ferric iron and organic pollutants, which require proper treatment. Previous studies have demonstrated that adding Fenton sludge to an anaerobic digester can decompose some of the organic pollutants in the Fenton sludge to lower its environmental risk, but iron gradually accumulates in the reactor, which weakens the sustainability of the method. In this study, Fenton sludge was introduced into a hydrolytic acidification reactor with a weak acid environment to relieve the iron accumulation as well as improve the degradation of organic matter. The results showed that the added Fenton sludge acted as an extracellular electron acceptor to induce dissimilatory iron reduction, which increased chemical oxygen demand (COD) removal and acidification efficiency by 16.1% and 19.8%, respectively, compared to the group without Fenton sludge. Along with the operation, more than 90% of the Fe(III) in Fenton sludge was reduced to Fe(II), and part of them was released to the effluent. Moreover, the Fe(II) in the effluent could be used as flocculants and Fenton reagents to further decrease the effluent COD by 29.8% and 44.5%, respectively. It provided a sustainable strategy to reuse Fenton sludge to enhance organic degradation based on the iron cycle.

Anaerobic hydrolysis of recalcitrant tetramethylammonium from semiconductor wastewater: Performance and mechanisms

The treatment of tetramethylammonium hydroxide (TMAH)-bearing wastewater, generated in the electronic and semiconductor industries, raises significant concerns due to the neurotoxic, recalcitrant, and bio-inhibiting effects of TMAH. In this study, we proposed the use of an anaerobic hydrolysis bioreactor (AHBR) for TMAH removal, achieving a high removal efficiency of approximately 85%, which greatly surpassed the performance of widely-used advanced oxidation processes (AOPs). Density functional theory calculations indicated that the unexpectedly poor efficiency (5.8-8.0%) of selected AOPs can be attributed to the electrostatic repulsion between oxidants and the tightly bound electrons of TMAH. Metagenomic analyses of the AHBR revealed that Proteobacteria and Euryarchaeota played a dominant role in the transformation of TMAH through processes such as methyl transfer, methanogenesis, and acetyl-coenzyme A synthesis, utilizing methyl-tetrahydromethanopterin as a substrate. Moreover, several potential functional genes (e.g., mprF, basS, bcrB, sugE) related to TMAH resistance have been identified. Molecular docking studies between five selected proteins and tetramethylammonium further provided evidence supporting the roles of these potential functional genes. This study demonstrates the superiority of AHBR as a pretreatment technology compared to several widely-researched AOPs, paving the way for the proper design of treatment processes to abate TMAH in semiconductor wastewater.

Bubbleless aerated-biological activated carbon as a superior process for drinking water treatment in rural areas

Drinking water supply in rural areas remains a substantial challenge due to complex natural, technical and economic conditions. To provide safe and affordable drinking water to all, as targeted in the UN Sustainable Development Goals (2030 Agenda), low-cost, efficient water treatment processes suitable for rural areas need to be developed. In this study, a bubbleless aeration BAC (termed ABAC) process is proposed and evaluated, involving the incorporation of a hollow fiber membrane (HFM) assembly within a slow-rate BAC filter, to provide dissolved oxygen (DO) throughout the BAC filter and an increased DOM removal efficiency. The results showed that after a 210-day period of operation, the ABAC increased the DOC removal by 54%, and decreased the disinfection byproduct formation potential (DBPFP) by 41%, compared to a comparable BAC filter without aeration (termed NBAC). The elevated DO (> 4 mg/L) not only reduced secreted extracellular polymer, but also modified the microbial community with a stronger degradation ability. The HFM-based aeration showed comparable performance to 3 mg/L pre-ozonation, and the DOC removal efficiency was four times greater than that of a conventional coagulation process. The proposed ABAC treatment, with its various advantages (e.g., high stability, avoidance of chemicals, ease of operation and maintenance), is well-suited to be integrated as a prefabricated device, for decentralized drinking water systems in rural areas.

Bubbleless Air Shapes Biofilms and Facilitates Natural Organic Matter Transformation in Biological Activated Carbon

The biodegradation in the middle and downstream of slow-rate biological activated carbon (BAC) is limited by insufficient dissolved oxygen (DO) concentrations. In this study, a bubbleless aerated BAC (termed ABAC) process was developed by installing a hollow fiber membrane (HFM) module within a BAC filter to continuously provide aeration throughout the BAC system. The BAC filter without an HFM was termed NBAC. The laboratory-scale ABAC and NBAC systems operated continuously for 426 days using secondary sewage effluent as an influent. The DO concentrations for NBAC and ABAC were 0.78 ± 0.27 and 4.31 ± 0.44 mg/L, respectively, with the latter providing the ABAC with greater electron acceptors for biodegradation and a microbial community with better biodegradation and metabolism capacity. The biofilms in ABAC secreted 47.3% less EPS and exhibited greater electron transfer capacity than those in NBAC, resulting in enhanced contaminant degradation efficiency and long-term stability. The extra organic matter removed by ABAC included refractory substances with a low elemental ratio of oxygen to carbon (O/C) and a high elemental ratio of hydrogen to carbon (H/C). The proposed ABAC filter provides a valuable, practical example of how to modify the BAC technology to shape the microbial community, and its activity, by optimizing the ambient atmosphere.

The microbial synergy and response mechanisms of hydrolysis-acidification combined microbial electrolysis cell system with stainless-steel cathode for textile-dyeing wastewater treatment

Microbial electrolysis cell (MEC) has been existing problems such as poor applicability to real wastewater and lack of cost-effective electrode materials in the practical application of refractory wastewater. A hydrolysis-acidification combined MEC system (HAR-MECs) with four inexpensive stainless-steel and conventional carbon cloth cathodes for the treatment of real textile-dyeing wastewater, which was fully evaluated the technical feasibility in terms of parameter optimization, spectral analysis, succession and cooperative/competition effect of microbial. Results showed that the optimum performance was achieved with a 12 h hydraulic retention time (HRT) and an applied voltage of 0.7 V in the HAR-MEC system with a 100 μm aperture stainless-steel mesh cathode (SSM-100 μm), and the associated optimum BOD₅/COD improvement efficiency (74.75 ± 4.32 %) and current density (5.94 ± 0.03 A·m^-2) were increased by 30.36 % and 22.36 % compared to a conventional carbon cloth cathode. The optimal system had effective removal of refractory organics and produced small molecules by electrical stimulation. The HAR segment could greatly alleviate the imbalance between electron donors and electron acceptors in the real refractory wastewater and reduce the treatment difficulty of the MEC segment, while the MEC system improved wastewater biodegradability, amplified the positive and specific interactions between degraders, fermenters and electroactive bacteria due to the substrate complexity. The SSM-100 μm-based system constructed by phylogenetic molecular ecological network (pMEN) exhibited moderate complexity and significantly strong positive correlation between electroactive bacteria and fermenters. It is highly feasible to use HAR-MEC with inexpensive stainless-steel cathode for textile-dyeing wastewater treatment.

Revealing mechanism of micro-aeration for enhancing volatile fatty acids production from swine manure

Micro-aeration is considered a new strategy for improving volatile fatty acids (VFAs) production of agricultural waste. This study investigated the effect and mechanism of micro-aeration of air and oxygen (O₂) on VFAs production from swine manure. The results showed that Air-micro-aeration had the most significant improvement effect, with the highest VFAs of 8.21 g/L, which was increased by 22.4%. Moreover, the mixing effects of different micro-aeration were limited, and the microbial communities significantly varied. Firmicutes and Bacteroidota were the dominant hydrolytic and acidogenic bacteria, and Air-micro-aeration preferentially promoted electron transfer activity and energy generation. Methanosarcina, Methanocorpusculum, and Methanobrevibacter can adapt to environmental changes according to their different oxygen tolerance, and the consumption and conversion of VFAs by methanogens were slow under Air-micro-aeration condition. This study revealed mechanism of micro-aeration for improving VFAs production from swine manure, providing a theoretical basis for micro-aeration regulation optimization.

Micro-aeration: an attractive strategy to facilitate anaerobic digestion

Micro-aeration can facilitate anaerobic digestion (AD) by regulating microbial communities and promoting the growth of facultative taxa, thereby increasing methane yield and stabilizing the AD process. Additionally, micro-aeration contributes to hydrogen sulfide stripping by oxidization to produce molecular sulfur or sulfuric acid. Although micro-aeration can positively affect AD, it must be strictly regulated to maintain an overall anaerobic environment that permits anaerobic microorganisms to thrive. Even so, obligate anaerobes, especially methanogens, could suffer from oxidative stress during micro-aeration. This review describes the applications of micro-aeration in AD and examines the cutting-edge advances in how methanogens survive under oxygen stress. Moreover, barriers and corresponding solutions are proposed to move micro-aeration technology closer to application at scale.

Structural characteristics and microbial function of biofilm in membrane-aerated biofilm reactor for the biodegradation of volatile pyridine

In order to avoid the serious air pollution caused by the volatilization of high recalcitrant pyridine, membrane-aerated biofilm reactor (MABR) with bubble-free aeration was used in this study, with the structural characteristics and microbial function of biofilm emphasized. The results showed that as high as 0.6 kg·m^-3·d^-1 pyridine could be completely removed in MABR. High pyridine loading thickened the biofilm, but without obvious detachment observed. The distinct stratification of microbes and extracellular polymeric substances were shaped by elevated pyridine load, enhancing the structural heterogeneity of biofilm. The increased tryptophan-like substances as well as α-helix and β-sheet proportion in proteins stabilized the biofilm structure against high influent loading. Based on the identified intermediates, possible pyridine biodegradation pathways were proposed. Multi-omics analyses revealed that the metabolic pathways with initial hydroxylation and reduction reaction was enhanced at high pyridine loading. The functional genes were mainly associated with Pseudomonas and Delftia, might responsible for pyridine biodegradation. The results shed light on the effective treatment of wastewater containing recalcitrant pollutants such as pyridine via MABR.