Characterization of stratified EPS and their role in the initial adhesion of anammox consortia

Transcriptional and molecular simulation analysis of the response mechanism of anammox bacteria to 3,4-dimethylpyrazole phosphate stress

Anaerobic ammonium oxidation (anammox) and nitrification are two vital biological pathways for ammonium oxidation, pivotal in microbial nitrogen cycling. 3,4-Dimethylpyrazole phosphate (DMPP) is commonly used as inhibitors in agricultural soils to reduce nitrogen losses from farmland, while whether it affect anammox is an open question. Acute inhibition tests revealed that 53.5 mg·L-1 DMPP caused 50 % reduction in anammox bacteria. After 36 days of prolonged exposure to 5 mg·L-1 DMPP, the ammonium(nitrite) removal rate of endnote decreased from 78.39(94.78) to 13.57(15.28) mgN·gVSS-1·d-1. Additionally, the abundance of Ca. Kuenenia decreased from 36.5 % to 6.06 %. Transcriptomic analysis revealed that the mRNA levels of ammonium transport genes (amt_1 and amt_4), and hydrazine synthase (hzs) were significantly downregulated. Molecular docking simulations indicated that DMPP bound with ammonium transport and hydrazine synthesis. This interaction hindered the transcriptional levels of genes encoding ammonium transporters and hzs. The study has guiding value to reduce the nitrogen loss involved in anammox bacteria in agricultural soils under the application of DMPP.

Response characteristics of the microbial community, metabolic pathways, and anti-resistance genes under high nitrate and sulfamethoxazole stress in a fluidized sulfur autotrophic denitrification process

The adaptability and microbial response mechanism of a sulfur autotrophic denitrification (SADN) biofilm under high nitrate (NO3--N) and sulfamethoxazole (SMX) stress through long-term operation of a fluidized bioreactor was evaluated. The SADN biofilm adapted to nitrate contents of up to 150 mg/L, and at 1 mg/L SMX, the nitrogen removal efficiency and SMX removal efficiency were as high as 85 % and 64 %, respectively. Microbial adaptation was driven by upregulated secretion of acyl-homoserine lactone (AHL) signal molecules, specifically 3OC6-HSL and 3OC8-HSL, which stabilized at concentrations of 575.7 ng/L and 579.9 ng/L, respectively. These molecules dynamically regulated the composition of extracellular polymeric substances, with total EPS content increasing from 113.37 mg/gVSS in the initial phase to 456.85 mg/gVSS under early SMX exposure, ensuring biofilm structural integrity. Under prolonged SMX stress, Simplicispira emerged as a key genus with a relative abundance of 21.20 %, utilizing apoptotic autotrophic denitrifiers and EPS metabolites as carbon sources for heterotrophic denitrification. This genus harbored critical nitrate reductase genes, including NarG, which accounted for 28.5 % of total functional gene abundance. In addition, SMX stress reduced the abundance of total anti-resistance genes (ARGs), with resistance mechanisms dominated by antibiotic efflux pumps, with the contribution increased from 63 % to 67 %. The relevance of this pump continuously increased, which hindered binding of SMX to cells and effectively reduced its toxicity. The results of this study provide scientific evidence for the application of SADN technology in a high-nitrate and antibiotically stressed environment. The results can further guide practical operations and provide technical support for increasing denitrification efficiency and antibiotic removal capacity in the SADN process.

Recent advances in isolation and physiological characterization of planktonic anaerobic ammonia-oxidizing bacteria

Anaerobic ammonia oxidation (anammox) is widely regarded as an efficient biological nitrogen removal technology and is increasingly applied in wastewater treatment processes. However, the long doubling time and sensitivity to environmental pressures of anaerobic ammonia-oxidizing bacteria (AnAOB) often lead to unstable nitrogen removal performance. Various combined processes are being explored to overcome these limitations, providing insights into the ecological, physiological, and biochemical characteristics of AnAOB. Nevertheless, due to the lack of AnAOB pure cultures, the mechanisms of nitrogen metabolism, growth regulation, and cell communication remain unclear. This review highlights the unique physiological structures of AnAOB, current techniques for isolating and enriching planktonic AnAOB, and the associated challenges. A deeper understanding of these aspects offers guidance for improving planktonic AnAOB enrichment and incubation.

A comprehensive review of antibiotics stress on anammox systems: Mechanisms, applications, and challenges

Anaerobic ammonia oxidation (anammox), an energy-efficient technology for treating ammonium-rich wastewater, faces the challenge of antibiotic stress in sewage. This paper systematically evaluated the impact of antibiotics on anammox by considering both inhibitory effects and recovery duration. This review focused on cellular responses, including extracellular polymeric substances (EPS), quorum sensing (QS), and enzymes. Then, the physiological properties of cells and the interactions between nitrogen and carbon metabolism under antibiotic stress were discussed, particularly within the anammoxosome. The microbial community evolution and the development and transfer of antibiotic resistance genes (ARGs) were further analyzed to reveal the resistance mechanisms of anammox. To address the limitations imposed by antibiotics, the development of bio-augmentation and combined processes based on molecular biology techniques, such as bio-electrochemical systems (BES), has been suggested. This review offered new insights into the mechanisms of antibiotic inhibition during the anammox process and aimed to advance their engineering applications.

Effects of degradable and non-degradable microplastics on SPNEDPR-AGS system: Sludge characteristics, nutrient transformation, key enzyme, and microbial community

The environmental risk of microplastics (MPs) in aerobic granular sludge (AGS) system is unclear. This study evaluates the effects of non-biodegradable polyvinyl chloride microplastics (PVC-MPs) and biodegradable polylactic acid microplastics (PLA-MPs) on AGS systems. The results showed that both destroyed the performance of AGS systems, with PVC-MPs achieving this by disrupting the AGS structure, while PLA-MPs mainly by causing the expansion of filamentous bacteria induced through the stimulation by lactic acid metabolite (R0: 5.52 ± 0.49 μg/L; RPLA5: 11.67 ± 0.56 μg/L). Moreover, both MPs inhibited nitrogen removal by disrupting partial nitrification and endogenous denitrification and suppressed key microbes such as Candidatus Competibacter and Nitrosomonas. Metabolic pathway analysis and molecular docking have further confirmed the mechanisms by which MPs affect critical metabolic pathways and key enzymes. Consequently, the hazards of biodegradable MPs to the stable operation of sewage treatment plants should also be of concern.

Matrix matters: How extracellular substances shape biofilm structure and mechanical properties

Biofilms possess unique mechanical properties that are vital to their stability and function. Biofilms are made of extracellular polymeric substances (EPS) secreted by microorganisms and comprise polysaccharides, proteins, extracellular DNA (eDNA), and lipids. EPS is the primary contributor and driver of the biofilm structure and mechanical properties such as stiffness, cohesion, and adhesion. EPS enhances the elasticity and viscosity of biofilms, allowing them to withstand mechanical stresses, shear forces, and deformation. Therefore, biofilms are notoriously difficult to remove and can result in billions of dollars in losses for various industries due to their adverse effects, such as contamination, pressure loss, and corrosion. As a result, it is essential to comprehend the mechanical properties of biofilms to control or remove them in various scenarios. We undertook a fundamental study to determine the relationship between individual EPS components and biofilm mechanical properties. In this study, a CDC biofilm reactor was used to grow pure culture biofilms (Staphylococcus epidermidis) which were treated with six EPS modifier agents (Ca2+, Mg2+, periodic acid, protease K, lipase, and DNAase I) to modify or cleave specific EPS components. The mechanical properties (Young's Modulus) of treated biofilms were subsequently tested using atomic force microscopy (AFM), the biofilm EPS functional groups were measured via the Fourier transform infrared (FTIR) spectroscopy, and biofilm structural characteristics using confocal imaging. The FTIR results showed that EPS modifier agents successfully reduced their target EPS components. Similarly, the confocal microscopic analysis results showed that most of these modifier agents (except lipase) significantly reduced (P-value <0.05) the biovolume and thickness of treated biofilms. Conversely, most of these modifier agents (except protease K) significantly increased (P-value <0.05) the roughness coefficient of the biofilms. Finally, data from AFM showed that biofilm mechanical properties (Young's modulus) significantly (P-value <0.05) changed with their EPS composition. These results have significant ramifications for biofilm management and control in myriad scenarios.

Effects of stratified microbial extracellular polymeric substances on microalgae dominant biofilm formation and nutrients turnover under batch and semi-continuous operation

Extracellular polymeric substances (EPS) are well-acknowledged to accelerate microalgal biofilm formation, yet specific role of stratified EPS is unknown. Bacterial biofilm stratified EPS could enrich phosphorus, whether microalgal biofilm stratified EPS could also realize phosphorus or nitrogen enrichment remains unclarified. This study investigated microalgae dominant biofilm growth characteristics and nutrients removal via inoculating microalgae and stratified bacterial EPS at various microalgae:bacteria ratios. Soluble-EPS favored biofilm establishment and chlorophyll synthesis, while loosely-bound (LB-EPS) and tightly-bound EPS (TB-EPS) improved phosphorus removal, and optimum microalgae:bacteria cell count ratio was 1:0.5. Under semi-continuous operation, stable and efficient nutrients removal was observed at hydraulic retention time (HRT) of 2 days. Both nitrogen and phosphorus enrichment by TB-EPS over LB-EPS (respectively up to 7.9 and 23.8 times) were innovatively discovered, with enhanced nutrients turnover efficiency at higher HRTs. This study provided direct evidences regarding the role of stratified EPS on microalgal biofilm development and nutrients turnover.

The inhibition of anammox system under Cu2 + stress and mechanisms of biochar-mediated recovery

Copper (Cu2+)-containing wastewater has proven difficult to effectively treat using the anammox process. In this study, the nitrogen removal efficiency (NRE), sludge characteristics, microbial community and recovery mechanisms of biochar-mediated anammox under Cu2+ stress were elucidated. At a Cu2+stress of 5 mg/L, a 73.52 % decrease in NRE (from 99 % to 25.48 %) was observed within the control setup (no biochar). The highest average NH4+-N removal for 36.28 % was observed at a reduced Cu2+ concentration of 3 mg/L with biochar addition compared to only 16.63 % in control reactor. The differences in the protein/polysaccharide (PN/PS) content in sludge from different biochar systems under long-term Cu2+ stress was a key factor influencing overall nitrogen removal performance, with the sludge predominantly displaying tightly bound extracellular polymeric substances (TB-EPS). The relative abundance of Candidatus Brocadia increased from 2.61 % to 15.28 % in the nitric acid-modified bamboo biochar group following cessation Cu2+ addition, while the control group only recovered to 0.76 %. The Cu2+ inhibition alleviation effect of biochar, facilitated via enhanced EPS secretion and selective proliferation of key functional microorganisms, has thus been demonstrated.

Metagenomics and metaproteomics reveal the effects of sludge types and inoculation modes on N,N-dimethylformamide degradation pathways and the microbial community involved

This study demonstrated the effects of the sludge type and inoculation method on the N,N-dimethylformamide degradation pathway and associated microbial communities. The sludge type is critical for DMF metabolism, with acclimatized aerobic sludge having a significant advantage in terms of DMF metabolism performance, whereas acclimatized anaerobic sludge has a reduced DMF metabolism capacity. Metagenomic revealed increased abundances of Methanosarcina, Pelomona and Xanthobacter in the adapted anaerobic sludge, suggesting that anaerobic sludge can utilize the methyl products produced by DMF metabolism for growth. Adapted aerobic sludge had high Mycobacterium abundance, significantly boosting DMF hydrolysis. In addition, a large number of dmfA2 genes were found in aerobic sludge, more so in acclimatized sludge, indicating stronger DMF metabolism. Conversely, acclimatized anaerobic sludge showed lower abundance of dmd-tmd and mauA/B, qhpA genes, implying long-term DMF toxicity reduced anaerobic microbial activity. Metaproteomic analysis showed that Methanosarcina and Methanomethylovorans enzymes in anaerobic sludge metabolized dimethylamine and methylamine to methane, aiding DMF degradation. In the aerobic sludge, aminohydrolase proteins, which hydrolyze DMF, were significantly upregulated. These findings provide insights into DMF wastewater treatment.

Comprehensive performance of a new-type hybrid membrane bioreactor applied to mainstream anammox process

The new-type submerged granular sludge membrane bioreactor (S-GSMBR) was constructed by installing a membrane module inside an upflow anaerobic sludge blanket. S-GSMBR achieved the fast start-up (47 d) and long-term stable operation (133 d) of mainstream Anammox process as well as the effective control of membrane fouling. The maximum nitrogen removal rate and efficiency were 0.52 kg N m-3 d-1 and 88.32%. The flow field analysis indicated that the turbulent effects were found around the membrane module and benefited for alleviating the membrane fouling at the special axial flow velocity at the central section of the membrane module (4.89 × 10-7 m s-1 to 1.30 × 10-6 m s-1). On day 133, S-GSMBR achieved sludge granulation with 68.63% of particles larger than 200 μm. Meanwhile, Candidatus Brocadia and Candidatus Kuenenia were typical Anammox bacteria in mature Anammox granular sludge. The relative abundance of Candidatus Brocadia and Candidatus Kuenenia was 21.22% and 0.36%, indicating that Candidatus Brocadia occupied the main niche under mainstream Anammox conditions. The feasibility of application of S-GSMBR in mainstream Anammox process was confirmed and moreover S-GSMBR was proven to be a robust mainstream Anammox reactor. This study lays the important theoretical foundation and technical support for the engineering application of the mainstream Anammox process.

Deciphering the inhibitory mechanisms of didecyldimethylammonium chloride on microalgal removal of fluoxetine: Insights from the alterations in cell surface properties and the physio-biochemical and molecular toxicity

The COVID-19 pandemic has increased the co-occurrence of quaternary ammonium compounds (QACs) and antidepressants in aquatic environments. Microalgae are sustainable and cost-effective candidates for removing emerging pollutants. QACs have a robust ability to adsorb on cell surface and alter membrane permeability, but little is known about the influence of QACs on microalgal bioremediation of co-existing pollutants like antidepressants. In this study, the influence mechanisms of didecyldimethylammonium chloride (DDAC) on the removal of fluoxetine (FLX) by C. pyrenoidosa were explored. The results showed that C. pyrenoidosa exhibited high removal efficiency of single FLX (75.23 %-88.65 %) mainly through biodegradation (57.12 %-67.19 %). However, the coexisting medium and high concentrations of DDAC considerably decreased the biodegradation amount (10.50 %-33.30 %) and removal efficiency (29.47 %-52.89 %) of FLX by C. pyrenoidosa. In contrast, the presence of DDAC increased extracellular and intracellular FLX concentrations due to the enhanced extracellular polymeric substance content, cell surface hydrophobicity, and cell membrane permeability. Meanwhile, DDAC showed synergistic effects with FLX on microalgal growth through exacerbated oxidative damage and photosynthesis inhibition. Moreover, transcriptomics revealed that the dysregulations of key genes involved in the DNA replication and repair, ribosome biogenesis, photosynthesis-antenna proteins, peroxisomes, and glutathione metabolism pathways were important molecular mechanisms underlying the synergistic toxicity. Furthermore, the principal component analysis suggested that the enhancement of extracellular and intracellular FLX concentrations induced by the coexistence of DDAC increased the mixture's toxicity, resulting in the decreased biodegradation amount and ultimately a reduction in the removal efficiency of FLX. Our results highlight the significance of recognizing the influence of QACs on microalgal remediation and ecological risks of antidepressants.

Nano-Fe3O4/FeCO3 modified red soil-based biofilter for simultaneous removal of nitrate, phosphate and heavy metals: Optimization, microbial community and possible mechanism

The pollution of nitrogen, phosphorus and heavy metals in surface water is becoming more and more serious, affecting the safety of water quality. In this study, three biofilters were constructed using iron-modified red soil-based filler carriers (RSC, nano-Fe3O4@RSC, and FeCO3@RSC) combined with strain Zoogloea sp. ZP7 to simultaneously remove nitrate (NO3--N), phosphate (PO43--P), copper (Cu2+), and zinc (Zn2+). The long-term operation results showed that the three groups of biofilters could remove 85.0 %, 90.0 %, and 89.8 % of NO3--N, respectively. Furthermore, the addition of iron compounds enhanced the removal of PO43--P and the resistance to the stress of Cu2+ and Zn2+ in the biofilter. The analysis illustrated that iron modification improved the redox activity and zeta potential of RSC surface. The secondary structure analysis of the protein showed that the microbial secreted proteins were more compact on the surface of the iron-modified RSC, which facilitated the formation of biofilm on the carrier surface. In addition, the iron-modified RSC-based biofilter also showed excellent NO3--N and PO43--P removal efficiency in the treatment of actual surface water. The microbial community analysis results showed that Zoogloea became the dominant species in the biofilter. On the other hand, the presence of iron-reducing bacteria and the expression iron cycle-related genes may contribute to denitrification under low nutrient conditions.

Novel ellipsoid-like granules exhibit enhanced anammox performance compared to sphere-like granules

Anammox granular sludge (AnGS) serves as an important platform for cost-effective nitrogen removal from wastewater. Different to the traditionally sphere-like granules, a novel type of AnGS in a unique ellipsoid-like shape was obtained through enhancing shear force. The ellipsoid-like AnGS significantly exhibited a smaller aspect ratio (-25.1 %) and granular size (-11.8 %), compared to traditional sphere-like AnGS (p < 0.01). Comprehensive comparisons showed that ellipsoid-like AnGS possessed a significantly higher extracellular polymeric substances (EPS) content and strength, as well as an enhanced mass transfer and a higher viable bacteria proportion due to the larger substrate permeable zone (p < 0.01). Additionally, the anammox bacterial abundance (Candidatus Kuenenia) was 12.2 % higher in ellipsoid-like AnGS than in sphere-like AnGS. All these characteristics of ellipsoid-like AnGS jointly increased the specific anammox activity by 29.0 % and nitrogen removal capacity by 22.6 %, compared to sphere-like AnGS. Further fluid field simulation suggested the enhanced flow shear on the side surface of AnGS likely drove the formation of ellipsoid-like AnGS. The higher shear force on the side surface led to an increase of EPS content (especially hydrophobic protein) and elastic modulus, thus constraining lateral expansion. This study sheds light on impacts of granular shape, an overlooked morphological factor, on anammox performance. The ellipsoid-like AnGS presented herein also offers a unique and promising aggregate to enhance anammox performance.

Continuous self-circulating up-flow granular sludge fluidized bed process treating low-strength real municipal wastewater at high hydraulic loads

Conditions conducive to aerobic granular sludge (AGS) growth and maintenance are very difficult to realize in continuous-flow biological treatment processes. This study conducted a continuous-flow self-circulating up-flow granular sludge fluidized bed (Zier process) treating real urban wastewater approximately one year. The substantial self-circulating multiple times (RSCMT, 8-15 times) and up-flow velocity (8-15 m/h) generated by aeration, the only power equipment in Zier process, facilitated pollutant removal, particle granulation and stabilization. With hydraulic retention time of 5 h, RSCMT of 9.3-14.4 times and chemical oxygen demand (COD)/total nitrogen (TN) ratio of 5.9 ± 1.0, the effluent COD, ammonia nitrogen and TN were 28.6 ± 7.7, 1.1 ± 1.2, and 13.3 ± 1.7 mg/L, respectively. The median particle size was 150-250 μm and effluent suspended solids concentration was 33.4 ± 14.5 mg/L. It is unnecessary to set up sludge reflux which simplifies the subsequent mud-water separation facilities. The Zier process provides a new process structure for implementation of continuous-flow AGS process.

Response of anammox to organics with different degradation characteristics and exposure time: Performance, sludge characteristics and bacterial community

The effects of typical organic compounds including easily degradable organic matters sodium acetate, yeast and methanol, and refractory organic matter (ROM) humic acid on anaerobic ammonium oxidation (anammox) systems in short-term and medium-term exposure time were studied. During short-term experiments, nitrogen removal activity (NRA) was inhibited at sodium acetate level of 150 mg L-1 total organic carbon (TOC) and methanol level of 30-150 mg L-1 TOC, but humic acid and yeast (≤150 mg L-1 TOC) enhanced nitrogen removal in anammox systems. The greatest NRA of 30.10 mg TN g-1 VSS h-1 was recorded at yeast level of 90 mg L-1 TOC. In medium-term experiments, organics significantly inhibited the nitrogen removal ability. As a ROM, humic acid enhanced sludge aggregation and biological diversity, but decreased the bioactivity and extracellular polymeric substances levels. Due to the endogenous denitrification, the relative abundance of anammox bacteria (AnAOB) was decreased. Candidatus Kuenenia is still dominant in sludge with methanol and humid acid, but AnAOB are not dominant due to the addition of sodium acetate and yeast. This research would be beneficial for the full-scale application of the anammox process in treating real wastewater with organics and ammonia.

Different nitrogen conditions regulating extracellular polymeric substances and erosion resistance of sewer sediment: Mechanism of microbial metabolism and molecular response

Nitrogen biotransformation plays a vital role in the metabolism of microbial communities in sewers. Extracellular polymeric substances (EPS) secreted by microbial communities can form gel-like sewer sediments, causing clogging of the sewer. However, knowledge on the effects of varying nitrogen conditions on the erosion resistance of sewer sediments and EPS produced by sewer microorganisms is limited. In this study, two typical organic/inorganic nitrogen ratios of sewage were reproduced in simulated sewer reactors, i.e., 3/7 (R1 group) and 7/3 (R2 group). Higher organic nitrogen (ON) concentrations were found to increase the critical erosion shear stress by 26.43%; this was ascribed to increased particle diameter, weakened electrostatic repulsion of sediments and stimulated EPS secretion in the R2 group. The protein and polysaccharide contents of the R2 group were 48.84% and 34.25% higher than those of the R1 group, respectively, which was supported by increased gene abundances for aromatic amino acid synthesis, general secretory pathways of protein, and synthesis of precursors and polysaccharides. Tightly-bound EPS in R2 group exhibited increased contents of hydrophobic protein secondary structures and intermolecular hydrogen bonds, thereby promoting the formation of gel-like sediment structures with enhanced erosion resistance. However, the microbial diversity and the abundance of key genes involved in EPS generation and secretion (e.g., tyrB, yajC, secB, gumF, and gumH) obviously decreased in the R1 group. Moreover, high ON concentrations increased microbial diversity and enhanced microbial glycolysis, tricarboxylic acid cycle and ammonium assimilation. This study reveals the formation mechanisms of EPS in sewer sediments under different nitrogen conditions and their effects on sediment erosion resistance, which contributed to improved sewer system operation and sewer sediment control.

The effects of graphene on low-temperature anammox process: The insights from short-term tests and long-term operation

Effluent quality deterioration caused by seasonal low temperature is a great challenge to the application of anammox technology. Here, the effects of different graphene materials on anammox process were investigated under both optimal temperature and low-temperature. The batch tests showed that at 30 °C, 300 mg/L of reduced graphene oxide‑sodium alginate gel (RGOSA) had the most significant promoting effect, reaching nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of 95 % and 8.88 mgN/L/d, respectively. The changes of EPS secretion patterns and increasing of key enzymes activity might contribute to the enhanced anammox activity. During the long-term operation of anammox reactor, the NRE and NRR of the reactor decreased when the temperature dropped to 15 °C, showing an NRE of 50 %-57 % with the addition of 200 mg/L of reduced graphene oxide (RGO) and 40 %-45 % with the addition of 20 mg/L of RGO. Furthermore, specific anammox activity (SAA) of the RGO200 reactor at 15 °C increased by 57.1 % compared to the UASB reactor without graphene addition. Additionally, 16S rRNA and metagenomic analysis results revealed anammox bacteria Ca. Kuenenia was the dominant bacteria. Moreover, the RGO can significantly increase the relative abundance of N-converting functional genes. This study demonstrates the graphene materials can help anammox process adapting to low temperatures, providing a possible solution for the application of anammox technology.

Force mechanism analysis of composite microbial dust suppressants based on extracellular polymeric substances (EPS) mode components

As an important potential dust suppression method, the slow onset time is one of the key factors that restrict the effect of microbial dust suppressant. In the early stage, we have confirmed that extracellular polymeric substances (EPS) can improve the dust suppression effect by wetting coal dust and increasing Ca2+ nucleation sites. Therefore, in this study, chitosan (CTS) and bovine serum albumin (BSA) in different ratios (CTS: BSA = 1:1, 1:2, 2:1) as model molecules of EPS were combined with Bacillus subtilis to prepare efficient and fast microbial dust suppressants. Furthermore, the interaction forces were analyzed through molecular dynamics simulation. Results showed that adding CTS and BSA would improve the dust suppression effect, and the dust suppression effect was the best when the ratio of CTS: BSA was 1:2. In addition, the contact angle decreased as the BSA content increased. The Fourier transform infrared spectroscopy (FTIR) results showed that when the ratio of CTS to BSA was 1:2, the dust suppressants were easier to interact with coal dust by the key functional groups and form calcite type CaCO3. The molecular dynamics simulation results showed that the main interaction was Van der Waals force. In addition, the interaction force was strongest when CTS: BSA was 1:2, increasing by 137% compared with the microbial dust suppressants without CTS or BSA. This study provides theoretical support for the development of efficient and rapid microbial dust suppressants.

Insights into the carbon and nitrogen metabolism pathways in mixed-autotrophy/heterotrophy anammox consortia in response to temperature reduction

While the multi-coupled anammox system boasts a substantial research foundation, the specific characteristics of its synergistic metabolic response to decreased temperatures, particularly within the range of 13-15 °C, remained elusive. In this study, we delve into the intricate carbon and nitrogen metabolism pathways of mixed-autotrophy/heterotrophy anammox consortia under conditions of temperature reduction. Our macrogenomic analyses reveal a compelling phenomenon: the stimulation of functional genes responsible for complete denitrification, suggesting an enhancement of this process during temperature reduction. This adaptation likely contributes to maintaining system performance amidst environmental challenges. Further metabolic functional recombination analyses highlight a dramatic shift in microbial community composition, with denitrifying MAGs (metagenome-assembled genomes) experiencing a substantial increase in abundance (up to 200 times) compared to autotrophic MAGs. This proliferation underscores the strong stimulatory effect of temperature reduction on denitrifying species. Notably, autotrophic MAGs play a pivotal role in supporting the glycolytic processes of denitrifying MAGs, underscoring the intricate interdependencies within the consortia. Moreover, metabolic variations in amino acid composition among core MAGs emerge as a crucial adaptation mechanism. These differences facilitate the preservation of enzyme activity and enhance the consortia's resilience to low temperatures. Together, these findings offer a comprehensive understanding of the microbial synergistic metabolism within mixed-autotrophy/heterotrophy anammox consortia under temperature reduction, shedding light on their metabolic flexibility and resilience in dynamic environments.

Monitoring the Biochemical Activity of Single Anammox Granules with Microbarometers

Granule-based anaerobic ammonium oxidation (Anammox) is a promising biotechnology for wastewater treatments with extraordinary performance in nitrogen removal. However, traditional analytical methods often delivered an average activity of a bulk sample consisting of millions and even billions of Anammox granules with distinct sizes and components. Here, we developed a novel technique to monitor the biochemical activity of individual Anammox granules in real-time by recording the production rate of nitrogen gas with a microbarometer in a sealed chamber containing only one granule. It was found that the specific activity of a single Anammox granule not only varied by tens of folds among different individuals with similar sizes (activity heterogeneity) but also revealed significant breath-like dynamics over time (temporal fluctuation). Statistical analysis on tens of individuals further revealed two subpopulations with distinct color and specific activity, which were subsequently attributed to the different expression levels of heme c content and hydrazine dehydrogenase activity. This study not only provides a general methodology for various kinds of gas-producing microbial processes but also establishes a bottom-up strategy for exploring the structural-activity relationship at a single sludge granule level, with implications for developing a better Anammox process.

Sulfide addition accelerates anammox sludge granulation and promotes microbial cooperation

The granular anaerobic ammonium oxidation (anammox) system has attractive advantages in tolerance to environmental-stress and enhancement of nitrogen removal capacity. Sulfide addition can improve nitrogen removals in anammox systems via inducing sulfur denitrification, yet its function in the improvement of the property of anammox granular sludge remains unclear. Herein, we investigated the variations in the morphological and microbial properties of the anammox sludge response to different sulfide concentrations (Na2S: 10-100 mg/L) through a long-term experiment. By comparing the sludge diameter and heme c content, it comes that a relatively low sulfide (S/N [nitrate] molar ratio of 0.18-0.50) significantly promoted the average diameter and heme c concentration of sludge by 25-175 % and 75-95 %, respectively, compared to that of both without sulfide addition and a high sulfide addition (S/N > 0.85). This enhancement is primarily because a low amount of sulfide had stimulated the secretion of extracellular polymeric substance, induced slight biogenic sulfur accumulation as microbial nuclei, and facilitated the appropriate amount of filamentous bacteria proliferation. Microbial metabolism functions analyses revealed a robust granular anammox coupled with sulfur denitrification in the sulfide-mediated anammox reactor, and the assembled granules exhibited exceptional tolerance to environmental stress. Significantly, the anammox bacteria (Candidatus_Brocadia) dominating the granules displayed satisfactory anammox activity (21.8 ± 2.1 mg N/g VSS h), and their produced nitrate was efficiently removed by the sulfur-oxidizing bacteria (Thiobacillus) that predominantly occurred in the flocs. This collaboration ensured an efficient sulfide-mediated anammox granules system, achieving nitrogen removal efficiency exceeding 95 %. These results highlight the function of sulfide in improving the morphological property of anammox sludge as well as the creation of a favorable ecological niche for the functional microorganism, which is important to maintain the efficiency and robustness of the anammox process in treating wastewater.

Removal of sulfamethoxazole in an algal-bacterial membrane aerated biofilm reactor: Microbial responses and antibiotic resistance genes

Antibiotics are frequently detected in wastewater, but often are poorly removed in conventional wastewater treatment processes. Combining microalgal and nitrifying bacterial processes may provide synergistic removal of antibiotics and ammonium. In this research, we studied the removal of the antibiotic sulfamethoxazole (SMX) in two different reactors: a conventional nitrifying bacterial membrane aerated biofilm reactor (bMABR) and algal-bacterial membrane aerated biofilm reactor (abMABR) systems. We investigated the synergistic removal of antibiotics and ammonium, antioxidant activity, microbial communities, antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and their potential hosts. Our findings show that the abMABR maintained a high sulfamethoxazole (SMX) removal efficiency, with a minimum of 44.6 % and a maximum of 75.8 %, despite SMX inhibition, it maintained a consistent 25.0 % ammonium removal efficiency compared to the bMABR. Through a production of extracellular polymeric substances (EPS) with increased proteins/polysaccharides (PN/PS), the abMABR possibly allowed the microalgae-bacteria consortium to protect the bacteria from SMX inactivation. The activity of antioxidant enzymes caused by SMX was reduced by 62.1-98.5 % in the abMABR compared to the bMABR. Metagenomic analysis revealed that the relative abundance of Methylophilus, Pseudoxanthomonas, and Acidovorax in the abMABR exhibited a significant positive correlation with SMX exposure and reduced nitrate concentrations and SMX removal. Sulfonamide ARGs (sul1 and sul2) appeared to be primarily responsible for defense against SMX stress, and Hyphomicrobium and Nitrosomonas were the key carriers of ARGs. This study demonstrated that the abMABR system has great potential for removing SMX and reducing the environmental risks of ARGs.

How Does Triclocarban Affect Sulfur Transformation in Anaerobic Systems?

Triclocarban (TCC), as a typical antimicrobial agent, accumulates at substantial levels in natural environments and engineered systems. This work investigated the impact of TCC on anaerobic sulfur transformation, especially toxic H2S production. Experimental findings revealed that TCC facilitated sulfur flow from the sludge solid phase to liquid phase, promoted sulfate reduction and sulfur-containing amino acid degradation, and largely improved anaerobic H2S production, i.e., 50-600 mg/kg total suspended solids (TSS) TCC increased the cumulative H2S yields by 24.76-478.12%. Although TCC can be partially biodegraded in anaerobic systems, the increase in H2S production can be mainly attributed to the effect of TCC rather than its degradation products. TCC was spontaneously adsorbed by protein-like substances contained in microbe extracellular polymers (EPSs), and the adsorbed TCC increased the direct electron transfer ability of EPSs, possibly due to the increase in the content of electroactive polymer protein in EPSs, the polarization of the amide group C═O bond, and the increase of the α-helical peptide dipole moment, which might be one important reason for promoting sulfur bioconversion processes. Microbial analysis showed that the presence of TCC enriched the organic substrate-degrading bacteria and sulfate-reducing bacteria and increased the abundances of functional genes encoding sulfate transport and dissimilatory sulfate reduction.

Typical Heterotrophic and Autotrophic Nitrogen Removal Process Coupled with Membrane Bioreactor: Comparison of Fouling Behavior and Characterization

There is limited research on the relationship between membrane fouling and microbial metabolites in the nitrogen removal process coupled with membrane bioreactors (MBRs). In this study, we compared anoxic-oxic (AO) and partial nitritation-anammox (PNA), which were selected as representative heterotrophic and autotrophic biological nitrogen removal-coupled MBR processes for their fouling behavior. At the same nitrogen loading rate of 100 mg/L and mixed liquor suspended solids (MLSS) concentration of 4000 mg/L, PNA-MBR exhibited more severe membrane fouling compared to AO-MBR, as evidenced by monitoring changes in transmembrane pressure (TMP). In the autotrophic nitrogen removal process, without added organic carbon, the supernatant of PNA-MBR had higher concentrations of protein, polysaccharides, and low-molecular-weight humic substances, leading to a rapid flux decline. Extracellular polymeric substances (EPS) extracted from suspended sludge and cake sludge in PNA-MBR also contributed to more severe membrane fouling than in AO-MBR. The EPS subfractions of PNA-MBR exhibited looser secondary structures in protein and stronger surface hydrophobicity, particularly in the cake sludge, which contained higher contents of humic substances with lower molecular weights. The higher abundances of Candidatus Brocadia and Chloroflexi in PNA-MBR could lead to the production of more hydrophobic organics and humic substances. Hydrophobic metabolism products as well as anammox bacteria were deposited on the hydrophobic membrane surface and formed serious fouling. Therefore, hydrophilic membrane modification is more urgently needed to mitigate membrane fouling when running PNA-MBR than AO-MBR.

Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances

Microplastics (MPs) and nanoplastics (NPs) present in wastewater can pose a negative impact to aerobic granular sludge (AGS). Herein, this study found that MPs and NPs (20 mg/L) deteriorated the sludge settleability and granule integrity, resulting in a 15.7 % and 21.9 % decrease in the total nitrogen removal efficiency of the AGS system, respectively. This was possibly due to the reduction of the extracellular polymeric substances (EPS) content. The subsequent analysis revealed that tyrosine, tryptophan, and humic acid-like substances in EPS exhibited a higher propensity for chemisorption and inhomogeneous multilayer adsorption onto NPs compared to MPs. The binding of EPS onto the surface of plastic particles increased the electronegativity of the MPs, but facilitated the aggregation of NPs through reducing the electrostatic repulsion, thereby mitigating the adverse effects of MPs/NPs on the AGS stability. Additionally, comprehensive analysis of the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the suppressed aggregation of microorganisms was the internal mechanisms contributing to the inadequate stability of AGS induced by MPs/NPs. This study provides novel insights into the detrimental mechanisms of MPs/NPs on the AGS stability, highlighting the key role of EPS in maintaining the structural stability of AGS when exposed to MPs/NPs.

Response of nitrifiers to gradually increasing pH conditions in a membrane nitrification bioreactor: Microbial dynamics and alkali-resistant mechanism

Nitrification and nitrifiers are pH-sensitive especially under the alkaline environment in the activated sludge system. However, it is unclear how nitrifiers and nitrification respond to long-term alkaline environment. This study employed a continuous flow membrane nitrification bioreactor to investigate the dynamics of nitrification efficiency and microbial community adaptation under a 320-day alkaline operation. Results showed that activated sludge adapted remarkably to a progressive increase in pH from 7.5 to 10.0, achieving robust nitrification with average ammonia removal efficiencies of 96.6 ± 2.2%. Subsequently, an integrated alkali-resistant mechanism of nitrifiers was proposed. Specifically, under the long-term operation of pH 10.0, certain bacteria secreted enhanced extracellular acidic polysaccharides (i.e., up to 10.95 ± 0.27 mg·g-1 MLVSS in soluble extracellular polymeric substances (EPS)) and acidic organic compounds (e.g., humic acids increased by 1.47-fold in tightly bounded EPS) to neutralize external alkalinity. Moreover, significant enrichments in both the ammonia oxidizing bacteria Nitrosomonas (by 1.3%) and the nitrite oxidizing bacteria Nitrospira (by 5.4%) were observed in a 170-day operation of pH 10.0 condition. Meanwhile, norank_f__JG30-KF-CM45 (2.0%) and Rhodobacter (0.9%) also contributed to ammonia removal at pH 10.0. On the cellular-level, bacteria enabled to maintain intracellular pH stabilization primarily through cation/proton antiporters, evidenced by significant increases in NhaA, TrkA and KefB activities by 98.0%, 151.7% and 115.2%, respectively. A 43.1% increase in carbonic anhydrase activity also facilitated consumption of aqueous OH- ions through biomineralization, leading to CaCO3 deposition on microbial surface. These findings further enhanced understandings of physiological adaptation of nitrifiers in the long-term alkaline activated sludge system.

Illuminating the role of powder carrier materials in shaping sludge aggregation in wastewater treatment: Insights from extended operation performance to microbial response mechanism

This study uncovered the response of novel micro-granule wastewater treatment technology to different powder carrier materials. Characteristics and distinctions among different systems were assessed based on process performance, sludge aggregation capacity, and microbial metabolism. Zeolite carrier system exhibited remarkable nitrogen removal efficiency of 89.6 ± 0.9 %, while diatomite carriers, in conjunction with intermittent aeration, enhanced simultaneous nitrification and denitrification from 2.6 % to 27.1 %. Iron-based carriers demonstrated efficient phosphorus removal (94.7 ± 1.2 %) through both chemical and microbial pathways. Specific surface area, pore structure and biocompatibility of powder carriers determined the formation and size of micro-granules. Tryptophan-like substances, C-(C/H), and Npr in extracellular polymeric substances strongly correlated with sludge hydrophobicity and granulation. Significant enrichment in norank_Comamonadaceae and Nitrosomonas in zeolite powder carrier system promoted partial nitrification and endogenous denitrification. Differences in metabolic pathways elucidated the up-regulation of amino acid synthesis, energy metabolism, and membrane transport as potential mechanisms driving micro-granule formation and efficient treatment performance.

Deciphering retention effect of extracellular polymeric substances to typical heavy metals and their interaction with key inner enzymes of Candidatus Kuenenia

This study employed spectroscopy, metagenomics, and molecular simulation to investigate the inhibitory effects of Cd(II) and Cu(II) on the anammox system, examining both intracellular and extracellular effects. At concentrations of 5 mg/L, Cd(II) and Cu(II) significantly reduced nitrogen removal efficiency by 41.46 % and 62.03 %, respectively. Additionally, elevated metal concentrations were correlated with decreased extracellular polymeric substances (EPS), thereby reducing their capacity to absorb heavy metals, particularly Cu(II), which decreased from 76.47 % to 14.67 %. Spectral analysis revealed alterations in the secondary structures of EPS induced by Cd(II) and Cu(II), decreasing the ratio of extracellular protein α-helix to (β-sheet + random coil), which resulted in looser extracellular protein configurations. The results of the metagenomics study showed that the abundance of Candidatus Kuenenia and its genes encoding nitrogen removal-related enzymes was reduced. The abundance of hzs-γ was reduced by 35.09 % at a concentration of 5 mg/L Cu(II). Conversely, genes associated with metal efflux enzymes, like czcR, increased by 54.86 % at 2 mg/L Cd(II). Molecular docking revealed robust bindings of Cd(II) to HZS-α (-342.299 ± 218.165 kJ/mol) and Cu(II) to HZS-γ (-880.934 ± 55.526 kJ/mol). This study elucidated the inhibitory mechanisms of Cd(II) and Cu(II) on the anammox system, providing insights into the resistance of anammox bacteria to heavy metals.

Natural defence mechanisms of electrochemically active biofilms: From the perspective of microbial adaptation, survival strategies and antibiotic resistance

Electrochemically active biofilms (EABs) play an ever-growingly critical role in the biological treatment of wastewater due to its low carbon footprint and sustainability. However, how the multispecies biofilms adapt, survive and become tolerant under acute and chronic toxicity such as antibiotic stress still remains well un-recognized. Here, the stress responses of EABs to tetracycline concentrations (CTC) and different operation schemes were comprehensively investigated. Results show that EABs can quickly adapt (start-up time is barely affected) to low CTC (≤ 5 μM) exposure while the adaptation time of EABs increases and the bioelectrocatalytic activity decreases at CTC ≥ 10 μM. EABs exhibit a good resilience and high anti-shocking capacity under chronic and acute TC stress, respectively. But chronic effects negatively affect the metabolic activity and extracellular electron transfer, and simultaneously change the spatial morphology and microbial community structure of EABs. Particularly, the typical exoelectrogens Geobacter anodireducens can be selectively enriched under chronic TC stress with relative abundance increasing from 45.11% to 85.96%, showing stronger TC tolerance than methanogens. This may be attributed to the effective survival strategies of EABs in response to TC stress, including antibiotic efflux regulated by tet(C) at the molecular level and the secretion of more extracellular proteins in the macro scale, as the C=O bond in amide I of aromatic amino acids plays a critical role in alleviating the damage of TC to cells. Overall, this study highlights the versatile defences of EABs in terms of microbial adaptation, survival strategies, and antibiotic resistance, and deepens the understanding of microbial communities' evolution of EABs in response to acute and chronic TC stress.

Fate of antibiotic resistance genes and EPS defence mechanisms during simultaneous denitrification and methanogenesis, coupled with the biodegradation of multiple antibiotics under zinc stress

High-strength nitrogen and antibiotics-containing wastewater can be efficiently eliminated by simultaneous denitrification and methanogenesis (SDM). Heavy metals and antibiotics are two critical factors that can lead to horizontal transfer of antibiotic resistance genes (ARGs), which can be simultaneously detected in wastewater. Unfortunately, the impacts of heavy metals on SDM and antibiotic biodegradation have not been fully elucidated. Herein, the effects of SDM and multiple antibiotics biodegradation, extracellular polymeric substances (EPSs) and protein response mechanisms, and ARG fate under Zn(II) stress were comprehensively evaluated. The results indicated that a high level of Zn(II) (≥5 mg/L) stress significantly decreased the degradation rate of multiple antibiotics and suppressed denitrification and methanogenesis. In addition, Zn(II) exposure prompted the liberation of proteins from microbes into the EPSs, and the combination of EPSs with small molecules quenched the original fluorescent components and destroyed the protein structure. The dominant proteins can bind to both Zn(II) and multiple antibiotics through several types of chemical interactions, including metallic and hydrogen bonds, hydrophobic interactions, and salt bridges, relieving the toxicity of harmful substances. Moreover, metagenomic sequencing revealed that the abundance of zinc resistance genes (Zn-RGs), ARGs (mainly tetracyclines), and mobile genetic elements (MGEs) increased under Zn(II) stress. Mantel test illustrated that the ARGs mecD, tetT, and tetB(60) were most affected by MGEs. Moreover, molecular network analysis revealed that several MGEs can bridge metal resistance genes (MRGs) and ARGs, facilitating the horizontal transfer of ARGs. This study provides theoretical guidance for the environmental risk control of antibiotics-containing wastewater treated by an SDM system.

Mechanistic insight into microbial interaction and metabolic pattern of anammox consortia on surface-modified biofilm carrier with extracellular polymeric substances

The extremely slow growth rate of anaerobic ammonia oxidation (anammox) bacteria limits full-scale application of anammox process worldwide. In this study, extracellular polymeric substances (EPS)-coated polypropylene (PP) carriers were prepared for biofilm formation. The biomass adhesion rate of EPS-PP carrier was 12 times that of PP carrier, and EPS-PP achieved significant enrichment of E. coli BY63. The 120-day continuous flow experiment showed that the EPS-PP carrier accelerated the formation of anammox biofilm, and the nitrogen removal efficiency increased by 10.5 %. In addition, the abundance of Candidatus Kuenenia in EPS-PP biofilm was 27.1%. Simultaneously, amino acids with high synthesis cost and the metabolites of glycerophospholipids related to biofilm formation on EPS-PP biofilm were significantly up-regulated. Therefore, EPS-PP carriers facilitated the rapid formation of anammox biofilm and promoted the metabolic activity of functional bacteria, which further contributed to the environmental and economic sustainability of anammox process.

Removal of dibutyl phthalate (DBP) by bacterial extracellular polymeric substances (EPS) via enzyme catalysis and electron transmission

Phthalic acid esters (PAEs) showed high environmental risk due to the widely existence and toxicity. Microbial-excreted extracellular polymeric substances (EPS) showed potential of degrading organic compounds. In this study, the degradation ability and the mechanisms of EPS from two bacteria (PAEs degrader Gordonia sihwensis; electrochemically active strain Shewanella oneidensis MR-1) were investigated. Results showed that EPS of the two bacteria had different composition of C-type cytochromes, flavins, catalase, and α-glucosidase. The removal of dibutyl phthalate (DBP) by total EPS were 68% of G. sihwensis and 72% for S. oneidensis. For both bacteria, the degradation rates k of EPS were as TB-EPS > LB-EPS > S-EPS. The degradation mechanisms of EPS from the two bacteria showed difference with electrochemical active components mediated electron transmission for S. oneidensis MR-1 and enzymes catalysis for G. sihwensis. Results of this study illustrated the variation of the contribution of active components of EPS to degradation.

Characterization of EPS subfractions from a mixed culture predominated by partial-denitrification functional bacteria

Extracellular polymeric substances (EPS) play a crucial role in the aggregation of partial denitrification (PD) consortia, as EPS is closely linked to bioreactor performance. However, the structural and compositional properties of EPS from PD consortia have not yet been investigated. In this study, photometric measurements indicated that PD consortia contained significantly more EPS (168.81 ± 2.10 mg/g VSS) compared to conventional activated sludge (79.79 mg/g VSS). The EPS of PD consortia exhibited a significant predominance of proteins over polysaccharides, with a protein/polysaccharide ratio of 1.43 ± 0.10. FTIR analysis revealed that the EPS of PD consortia contained fewer hydrophilic functional groups, particularly carboxyl and carbonyl groups, indicating a high aggregation potential. The content comparison of EPS and functional groups across three stratified EPS subfractions from PD consortia consistently followed the sequence: TB-EPS > LB-EPS > S-EPS. XPS results corroborated the FTIR findings and the protein/polysaccharide ratio determined by photometric measurements, all of which suggested that the EPS of PD consortia exhibited a higher abundance of hydrophobic functional groups. However, the higher α-helix/(β-sheet + random coil) ratio (0.99) suggested that the proteins in PD consortia had a compact structure, making inner hydrophobic groups difficult to expose. This compact protein structure could limit aggregation among bacterial cells, indicating the need for process optimization to enhance sludge aggregation in PD-related processes. Overall, understanding the aggregation characteristics of PD consortia could improve the application of PD-based processes.

Molecular spectra and docking simulations investigated the binding mechanisms of tetracycline onto E. coli extracellular polymeric substances

Extracellular polymeric substances (EPS), which were an important fraction of natural organic matter (NOM), played an important role in various environmental processes. However, the heterogeneity, complexity, and dynamics of EPS make their interactions with antibiotics elusive. Using advanced multispectral technology, this study examined how EPS interacts with different concentrations of tetracycline (TC) in the soil system. Our results demonstrated that protein-like (C1), fulvic-like (C2), and humic-like (C3) fractions were identified from EPS. Two-dimensional synchronous correlation spectroscopy (2D-SF-COS) indicated that the protein-like fraction gave faster responses than the fulvic-like fraction during the TC binding process. The sequence of structural changes in EPS due to TC binding was revealed by two-dimensional Fourier Transformation Infrared correlation spectroscopy (2D-FTIR-COS) as follows: 1550 > 1660 > 1395 > 1240 > 1087 cm-1. It is noteworthy that the sensitivity of the amide group to TC has been preserved, with its intensity gradually increasing to become the primary binding site for TC. The integration of hetero-2DCOS maps with moving window 2D correlation spectroscopy (MW2DCOS) provided a unique insight into understanding the correlation between EPS fractions and functional groups during the TC binding process. Moreover, molecular docking (MD) discovered that the extracellular proteins would provide plenty of binding sites with TC through salt bridges, hydrogen bonds, and π-π base-stacking forces. With these results, systematic investigations of the dynamic changes in EPS components under different concentrations of antibiotic exposure demonstrated the advanced capabilities of multispectral technology in examining intricate interactions with EPS in the soil environment.

Engineered Probiotic Bio-Heterojunction with Robust Antibiofilm Modality via "Eating" Extracellular Polymeric Substances for Wound Regeneration

The compact three-dimensional (3D) structure of extracellular polymeric substances (EPS) within biofilms significantly hinders the penetration of antimicrobial agents, making biofilm eradication challenging and resulting in persistent biofilm-associated infections. To address this challenge, a solution is proposed: a probiotic bio-heterojunction (P-bioHJ) combining Lactobacillus rhamnosus with MXene (Ti3C2) quantum dots (MQDs)/FeS heterojunction. This innovation aims to break down the saccharides in EPS, enabling effective combat against biofilm-associated infections. Initially, the P-bioHJ targets saccharides through metabolic processes, causing the collapse of EPS and allowing infiltration into bacterial colonies. Simultaneously, upon exposure to near-infrared (NIR) irradiation, the P-bioHJ produces reactive oxygen species (ROS) and thermal energy, deploying physical mechanisms to combat bacterial biofilms effectively. Following antibiofilm treatment, the P-bioHJ adjusts the oxidative environment, reduces wound inflammation by scavenging ROS, boosts antioxidant enzyme activity, and mitigates the NF-κB inflammatory pathway, thereby accelerating wound healing. In vitro and in vivo experiments confirm the exceptional antibiofilm, antioxidant/anti-inflammatory, and wound-regeneration properties of P-bioHJ. In conclusion, this study provides a promising approach for treating biofilm-related infections.

Bibliometric analysis of research trends in biogranulation technology for wastewater treatment

Inadequate management and treatment of wastewater pose significant threats, including environmental pollution, degradation of water quality, depletion of global water resources, and detrimental effects on human well-being. Biogranulation technology has gained increasing traction for treating both domestic and industrial wastewater, garnering interest from researchers and industrial stakeholders alike. However, the literature lacks comprehensive bibliometric analyses that examine and illuminate research hotspots and trends in this field. This study aims to elucidate the global research trajectory of scientific output in biogranulation technology from 1992 to 2022. Utilizing data from the Scopus database, we conducted an extensive analysis, employing VOSviewer and the R-studio package to visualize and map connections and collaborations among authors, countries, and keywords. Our analysis revealed a total of 1703 journal articles published in English. Notably, China emerged as the leading country, Jin Rencun as the foremost author, Bioresource Technology as the dominant journal, and Environmental Science as the prominent subject area, with the Harbin Institute of Technology leading in institutional contributions. The most prominent author keyword identified through VOSviewer analysis was "aerobic granular sludge," with "sequencing batch reactor" emerging as the dominant research term. Furthermore, our examination using R Studio highlighted "wastewater treatment" and "sewage" as notable research terms within the field. These findings underscore a diverse research landscape encompassing fundamental aspects of granule formation, reactor design, and practical applications. This study offers valuable insights into biogranulation potential for efficient wastewater treatment and environmental remediation, contributing to a sustainable and cleaner future.

A review of microplastics on anammox: Influences and mechanisms

Microplastics (MPs) are prevalent in diverse environmental settings, posing a threat to plants and animals in the water and soil and even human health, and eventually converged in wastewater treatment plants (WWTPs), threatening the stable operation of anaerobic ammonium oxidation (anammox). Consequently, a comprehensive summary of their impacts on anammox and the underlying mechanisms must be provided. This article reviews the sources and removal efficiency of MPs in WWTPs, as well as the influencing factors and mechanisms on anammox systems. Numerous studies have demonstrated that MPs in the environment can enter WWTPs via domestic wastewater, rainwater, and industrial wastewater discharges. More than 90% of these MPs are found to accumulate in the sludge following their passage through the treatment units of the WWTPs, affecting the characteristics of the sludge and the efficiency of the microorganisms treating the wastewater. The key parameters of MPs, encompassing concentration, particle size, and type, exert a notable influence on the nitrogen removal efficiency, physicochemical characteristics of sludge, and microbial community structure in anammox systems. It is noteworthy that extracellular polymer secretion (EPS) and reactive oxygen stress (ROS) are important impact mechanisms by which MPs exposure affects anammox systems. In addition, the influence of MPs exposure on the microbial community structure of anammox cells represents a crucial mechanism that demands attention. Future research endeavors will delve into additional crucial parameters of MPs, such as shape and aging, to investigate their effects and mechanisms on anammox. Furthermore, the effective mitigation strategies will also be developed. The paper provides a fresh insight to reveal the influences of MPs exposure on the anammox process and its influence mechanisms, and lays the groundwork for further exploration into the influence of MPs on anammox and potential mitigation strategies.

The superiority of hydrophilic polyurethane in comammox-dominant ammonia oxidation during low-strength wastewater treatment

Carriers have been extensively employed to enhance nitrification performance during low-strength wastewater treatment by retaining slow-growing ammonia oxidizing microorganisms (AOMs). Still, there is a dearth of systematic understanding of biofilm properties and microbial community structure formed on different carriers. In this study, hydrophilic polyurethane foam (PUF) carriers were prepared and compared with five widely used commercial carriers, namely Kaldness 3, Biochip, activated carbon, volcanic rock, and zeolite. The results indicated that the biofilms formed on carriers enhanced microbial ammonia oxidation activity. Additionally, the biofilm developed on the PUF demonstrated the most superior performance among all selected carriers, not only exhibiting the highest abundant and the most active AOMs, with amoA gene abundance of 1.41 × 1013 copies/m3 and specific ammonia oxidation rate of 9.84 g NH4+-N/(m3 × h), but also possessing a compact structure, with 3.41 kg VSS/m3 and 46.83 mg extracellular polymeric substances/g VSS. The high-throughput sequencing analysis revealed that the comammox (CMX) Nitrospira dominated on biofilm due to the intrinsically low apparent half-saturation constant for substrate. A unique ecological community structure was established on PUF, characterized by low species diversity and high homogeneity in alignment with community characteristics of CMX. The biofilms on PUF contributed to the proliferation of CMX Nitrospira dominated by Nitrospira nitrosa, achieving the highest proportion among colonial three AOMs at 86.58 %. The appropriate average pore size, superior hydrophilicity, and large specific surface area of PUF carriers provided a robust foundation for the exceptional ammonia oxidation performance of the formed biofilms.

Metabolomic reveals the responses of sludge properties and microbial communities to high nitrite stress in denitrifying phosphorus removal systems

Nitrite, as an electron acceptor, plays a good role in denitrifying phosphorus removal (DPR); however, high nitrite concentration has adverse affects on sludge performance. We investigated the precise mechanisms of responses of sludge to high nitrite stress, including surface characteristics, intracellular and extracellular components, microbial and metabolic responses. When the nitrite stress reached 90 mg/L, the sludge settling performance was improved, but the activated sludge was aging. FTIR and XPS analysis revealed a significant increase in the hydrophobicity of the sludge, resulting in improve settling performance. However, the intracellular carbon sources synthesis was inhibited. In addition, the components in the tightly bound extracellular polymeric substances (TB-EPS) of sludge were significantly reduced and indicated the disturb of metabolism. Notably, Exiguobacterium emerged as a new genus when face high nitrite stress that could maintaining survival in hostile environments. Moreover, metabolomic analysis demonstrated strong biological response to nitrite stress further supported above results that include the inhibited of carbohydrate and amino acid metabolism. More importantly, some lipids (PS, PA, LysoPA, LysoPC and LysoPE) were significantly upregulated that related enhanced membrane lipid remodeling. The comprehensive analyses provide novel insights into the high nitrite stress responses mechanisms in activated sludge systems.

The mystery of rich human gut antibiotic resistome in the Yellow River with hyper-concentrated sediment-laden flow

Human gut antibiotic resistome widely occur in anoxic environments characterized by high density of bacterial cells and frequent transmission of antibiotic resistance genes (ARGs). Such resistome is greatly diluted, degraded, and restrained in the aerobic habitats within most natural rivers (regarded as "terrestrial guts") connecting continents and the oceans. Here we implemented a large-scale monitoring campaign extending 5,200 km along the Yellow River, and provide the first integral biogeographic pattern for both ARGs and their hosts. We identified plentiful ARGs (24 types and 809 subtypes) and their hosts (24 phyla and 757 MAGs) in three media (water, suspended particulate matter (SPM), and sediment). Unexpectedly, we found diverse human gut bacteria (HGB) acting as supercarriers of ARGs in this oxygen-rich river. We further discovered that numerous microhabitats were created within stratified biofilms that surround SPMs, particularly regarding the aggregation of anaerobic HGB. These microhabitats provide numerous ideal sinks for anaerobic bacteria and facilitate horizontal transfer of ARGs within the stratified biofilms, Furthermore, the stratification of biofilms surrounding SPMs has facilitated synergy between human gut flora and denitrifiers for propagation of ARGs in the anoxic atmospheres, leading to high occurrence of human gut antibiotic resistome. SPMs play active roles in the dynamic interactions of river water and sediment, thus accelerating the evolution of riverine resistome and transmission of human gut antibiotic resistome. This study revealed the special contribution of SPMs to the propagation of ARGs, and highlighted the necessity of making alternative strategies for sustainable management of large rivers with hyper-concentrated sediment-laden flows.

Deciphering the role of extracellular polymeric substances in the adsorption and biotransformation of organic micropollutants during anaerobic wastewater treatment

Extracellular polymeric substances (EPS) participate in the removal of organic micropollutants (OMPs), but the primary pathways of removal and detailed mechanisms remain elusive. We evaluated the effect of EPS on removal for 16 distinct chemical classes of OMPs during anaerobic digestion (AD). The results showed that hydrophobic OMPs (HBOMPs) could not be removed by EPS, while hydrophilic OMPs (HLOMPs) were amenable to removal via adsorption and biotransformation of EPS. The adsorption and biotransformation of HLOMPs by EPS accounted up to 19.4 ± 0.9 % and 6.0 ± 0.8 % of total removal, respectively. Further investigations into the adsorption and biotransformation mechanisms of HLOMPs by EPS were conducted utilizing spectral, molecular dynamics simulation, and electrochemical analysis. The results suggested that EPS provided abundant binding sites for the adsorption of HLOMPs. The binding of HLOMPs to tryptophan-like proteins in EPS formed nonfluorescent complexes. Hydrogen bonds, hydrophobic interactions and water bridges were key to the binding processes and helped stabilize the complexes. The biotransformation of HLOMPs by EPS may be attributed to the presence of extracellular redox active components (c-type cytochromes (c-Cyts), c-Cyts-bound flavins). This study enhanced the comprehension for the role of EPS on the OMPs removal in anaerobic wastewater treatment.

Identification of extracellular polymeric substances layer barrier in chloroquine phosphate-disturbed anammox consortia and mechanism dissection on cytotoxic behavior by computational chemistry

The over-dosing use of chloroquine phosphate (CQ) poses severe threats to human beings and ecosystem due to the high persistence and biotoxicity. The discharge of CQ into wastewater would affect the biomass activity and process stability during the biological processes, e.g., anammox. However, the response mechanism of anammox consortia to CQ remain unknown. In this study, the accurate role of extracellular polymeric substances barrier in attenuating the negative effects of CQ, and the mechanism on cytotoxic behavior were dissected by molecular spectroscopy and computational chemistry. Low concentrations (≤6.0 mg/L) of CQ hardly affected the nitrogen removal performance due to the adaptive evolution of EPS barrier and anammox bacteria. Compact protein of EPS barrier can bind more CQ (0.24 mg) by hydrogen bond and van der Waals force, among which O-H and amide II region respond CQ binding preferentially. Importantly, EPS contributes to the microbiota reshape with selectively enriching Candidatus_Kuenenia for self-protection. Furthermore, the macroscopical cytotoxic behavior was dissected at a molecular level by CQ fate/distribution and computational chemistry, suggesting that the toxicity was ascribed to attack of CQ on functional proteins of anammox bacteria with atom N17 (f-=0.1209) and C2 (f+=0.1034) as the most active electrophilic and nucleophilic sites. This work would shed the light on the fate and risk of non-antibiotics in anammox process.

The fate of pharmaceuticals and personal care products (PPCPs) in sewer sediments:Adsorption triggering resistance gene proliferation

In recent years, large quantities of pharmaceuticals and personal care products (PPCPs) have been discharged into sewers, while the mechanisms of PPCPs enrichment in sewer sediments have rarely been revealed. In this study, three PPCPs (tetracycline, sulfamethoxazole, and triclocarban) were added consecutively over a 90-day experimental period to reveal the mechanisms of PPCPs enrichment and the transmission of resistance genes in sewer sediments. The results showed that tetracycline (TC) and triclocarban (TCC) have higher adsorption concentration in sediments compared to sulfamethoxazole (SMX). The absolute abundance of Tets and suls genes increased in sediments under PPCPs pressure. The increase in secretion of extracellular polymeric substances (EPS) and the loosening of the structure exposed a large number of hydrophobic functional groups, which promoted the adsorption of PPCPs. The absolute abundance of antibiotic resistance genes (ARGs), EPS and the content of PPCPs in sediments exhibited significant correlations. The enrichment of PPCPs in sediments was attributed to the accumulation of EPS, which led to the proliferation of ARGs. These findings contributed to further understanding of the fate of PPCPs in sewer sediments and opened a new perspective for consideration of controlling the proliferation of resistance genes.

Novel insights into intrinsic mechanisms of magnetic field on long-term performance of anaerobic ammonium oxidation process

The performance of an anaerobic ammonium oxidation (anammox) reactor with the magnetic field of 40 mT was systematically investigated. The total nitrogen removal rate was enhanced by 16% compared with that of the control group. The enhancing mechanism was elucidated from the improved mass transfer efficiency, the complicated symbiotic interspecific relationship and the improved levels of functional genes. The magnetic field promoted formation of the loose anammox granular sludge and the homogeneous and well-connected porous structure to enhance the mass transfer. Consequently, Candidatus Brocadia predominated in the sludge with an increase in abundance of 13%. Network analysis showed that the positive interactions between Candidatus Brocadia and heterotrophic bacteria were strengthened, which established a more complicated stable microbial community. Moreover, the magnetic field increased the levels of hdh by 26% and hzs by 35% to promote the nitrogen metabolic process. These results provided novel insights into the magnetic field-enhanced anammox process.

Sustainable biochar application in anammox process: Unveiling novel pathways for enhanced nitrogen removal and efficient start-up at low temperature

This study explored the use of biochar to accelerate the establishment of anaerobic ammonium oxidation (anammox) reactors operating at 15 ± 1℃. Incorporating 10 g/L bamboo charcoal in S1 accelerated the start-up of anammox in 87 days, which was significantly shorter than 103 days in S0 (without biochar). After 140 days, S1 exhibited a 10.9 % increase in nitrogen removal efficiency due to a 28.9 % elevation in extracellular polymeric substances, bolstering anammox bacterial resilience. Predominant anammox bacteria (Cadidatus Brocadia and Cadidatus Jettenia) showed relative abundances of 3.19 % and 0.38 % in S1, respectively, which were significantly higher than 0.40 % and 0.05 % in S0. Biochar provides favorable habitats for the enrichment of anammox bacteria and accelerates the establishment of anammox at low temperatures. This finding holds promise for enhancing the efficiency of anammox in cold climates and advancing sustainable wastewater nitrogen removal.

Enhancing anammox process with granular activated carbon: A study on Microbial Extracellular Secretions (MESs)

Granular activated carbon (GAC), a porous carbon-based material, provides increased attachment space for functional microorganisms and enhances nitrogen removal by facilitating extracellular electron transfer in the anammox process. This study investigates the effects of GAC on the biosynthesis of microbial extracellular secretions (MESs) and explores the roles of these secretions in anammox activities. Four lab-scale reactors were operated: two downstream UASB reactors (D1 and D2) receiving effluents from the upstream UASB reactors (U1: no-GAC, U2: yes-GAC). Our results indicate that MESs were enhanced with the addition of GAC. The effluent from U2 exhibited a 59.62 % higher amino acid content than that from U1. These secretions contributed to an increase in the nitrogen loading rate (NLR) in the downstream reactors. Specifically, NLR in D1 increased from 130.5 to 142.7 g N/m3/day, and in D2, it escalated from 137.5 to 202.8 g N/m3/day, likely through acting as cross-feeding substrates or vital nutrients. D2 also showed increased anammox bacterial activity, enriched Ca. Brocadia population and hao gene abundance. Furthermore, this study revealed that D2 sludge has significantly higher extracellular polymeric substances (EPS) (48.71 mg/g VSS) and a larger average granule size (1.201 ± 0.119 mm) compared to D1 sludge. Overall, GAC-stimulated MESs may have contributed to the enhanced performance of the anammox process.

Non-filamentous bulking of activated sludge induced by graphene oxide: Insights from extracellular polymeric substances

Widespread use of nanomaterials raises concerns. The underlying mechanism by which graphene oxide (GO) nanoparticles causes poor settleability of activated sludge remains unclear. To explore this mechanism, three reactors with different GO concentrations were established. Extended Derjaguin-Landau-Verwey-Overbeek theory indicated that GO destroyed the property of extracellular polymeric substances (EPS), increasing the energy barrier between bacteria. Low levels of uronic acid and hydrogen bonding in exopolysaccharide weakened the EPS gelation increasing aggregation repulsion. Lager amounts of hydrophilic amino acid and looser structure of extracellular proteins for exposing inner hydrophilic groups significantly contributed to the hydrophilicity of EPS. Both changes implied deterioration in EPS structure under GO stress. Metagenome demonstrated a decrease in genes responsible for capsular polysaccharide colonization and genes regulated the translocation of loose proteins were increased, which increased repulsion between bacteria. This study elucidated that changes in EPS secretion under GO exposure are the underlying causes of poor settleability.

Mechanistic insight into the aggregation ability of anammox microorganisms: Roles of polarity, composition and molecular structure of extracellular polymeric substances

The chemical characteristics of extracellular polymeric substances (EPS) of anammox bacteria (AnAOB) play a crucial role in the rapid enrichment of AnAOB and the stable operation of wastewater anammox processes. To clarify the influential mechanisms of sludge EPS on AnAOB aggregation, multiple parameters, including the polarity distribution, composition, and molecular structure of EPS, were selected, and their quantitative relationship with AnAOB aggregation was analyzed. Compared to typical anaerobic sludge (anaerobic floc and granular sludge), the anammox sludge EPS exhibited higher levels of tryptophan-like substances (44.82-56.52 % vs. 2.57-39.81 %), polysaccharides (40.02-53.49 mg/g VSS vs. 30.22-41.69 mg/g VSS), and protein structural units including α-helices (20.70-23.98 % vs. 16.48-19.32 %), β-sheets (37.43-42.98 % vs. 25.78-36.72 %), and protonated nitrogen (Npr) (0.065-0.122 vs. 0.017-0.061). In contrast, it had lower contents of β-turns (20.95-27.39 % vs. 28.17-39.04 %). These biopolymers were found to originate from different genera of AnAOB. Specifically, the α-helix-rich proteins were mainly derived from Candidatus Kuenenia, whereas the extracellular proteins related to tryptophan and Npr were closely associated with Candidatus Brocadia. Critically, these EPS components could drive anammox aggregation through interactions. Substantial amounts of tryptophan-like substances facilitated the formation of β-sheet structures and the exposure of internal hydrophobic clusters, which benefited the anammox aggregation. Meanwhile, extracellular proteins with high Npr content played a pivotal role in the formation of mixed protein-polysaccharide gel networks with the electronegative regions of polysaccharides, which could be regarded as the key component in the maintenance of anammox sludge stability. These findings provide a comprehensive understanding of the multifaceted roles of EPS in driving anammox aggregation and offer valuable insights into the development of EPS regulation strategies aimed at optimizing the anammox process.

Anammox process in anaerobic baffled biofilm reactors with columnar packings: Characteristics of flow field and microbial community

The enrichment of anammox bacteria is a key issue in the application of anammox processes. A new type of reactor － anaerobic baffle biofilm reactor (ABBR) developed from anaerobic baffle reactor (ABR) was filled with columnar packings and established for effective enrichment of anammox bacteria. The flow field analysis showed that, compared with ABR, ABBR narrowed the dead zone so as to improve the substrate transferring performances. Two ABBRs with different types of columnar packings (Packings 1 and Packings 2) were constructed to culture anammox biofilms. Packings 1 consisted of the single-form honeycomb carriers while Packings 2 was modular composite packings consisting of non-woven fabric and honeycomb carriers. The effects of different types of columnar packings on microbial community and nitrogen removal were studied. The ABBR filled with Packings 2 had a higher retention rate of biomass than the ABBR filled with Packings 1, making the anammox start-up period be shortened by 21.28%. The enrichment of anammox bacteria were achieved and the dominant anammox bacteria were Candidatus Brocadia in both R1 and R2. However, there were four genera of anammox bacteria in R2 and one genus of anammox bacteria in R1, and the cell density of anammox bacteria in R2 was 95% higher than that in R1. R2 has the advantage of maintaining excellent and stable nitrogen removal performance at high nitrogen loading rate. The results revealed that the packings composed of two types of carriers may have a better enrichment effect on anammox bacteria. This study is of great significance for the rapid enrichment of anammox bacteria and the technical promotion of anammox process.

Effect of biochar on the SPNA system at ambient temperatures

Biochar has been extensively studied in wastewater treatment systems. However, the role of biochar in the single-stage partial nitritation anammox (SPNA) system remains not fully understood. This study explored the impact of biochar on the SPNA at ambient temperatures (20 °C and 15 °C). The nitrogen removal rate of the system raised from 0.43 to 0.50 g N/(L·d) as the biochar addition was raised from 2 to 4 g/L. Metagenomic analysis revealed that gene abundances of amino sugar metabolism and nucleotide sugar metabolism, amino acid metabolism, and quorum sensing were decreased after the addition of biochar. However, the gene abundance of enzymes synthesizing NADH and trehalose increased, indicating that biochar could stimulate electron transfer reactions in microbial metabolism and assist microorganisms in maintaining a steady state at lower temperatures. The findings of this study provide valuable insights into the mechanism behind the improved nitrogen removal facilitated by biochar in the single-stage partial nitritation anammox system.