Effect of EPS production on the performance of membrane-based biofilm reactors

Rapid formation of partial denitrification biofilm using gas-liquid separation membrane as carrier: Performance and mechanism

Partial denitrification (PD) can ensure stable supply of electron acceptors for anaerobic ammonia oxidation, and biofilm is an effective method to prevent biomass loss, which are crucial for stable operation of PD. In this study, hydrophobic hollow-fiber gas-liquid separation membranes were placed in a denitrification sequencing batch reactor, and dense biofilms were formed within just 3 days. Confocal laser microscopy showed the preferential attachment of the protein (PN) content in extracellular polymeric substances (EPS) to the membrane surface, followed by exopolysaccharides. Further analyses showed the decrease in the types of signal molecules from six to two (i.e., C4-HSL, C6-HSL) due to negative pressure operation. Importantly, the concentration of C4-HSL increased dramatically with the increase in PN concentration, suggesting that negative pressure promoted the synthesis of C4-HSL signal molecules, which further mediated the secretion of PN for biofilm formation. In addition, biofilm formation was accompanied by nitrite accumulation, leading to successful achievement of PD. Furthermore, 60 % of nitrate-to-nitrite transformation ratio was obtained even when COD/N was increased from 4.5 to 5.0 and influent nitrate concentration was reduced to 25 mg/L. This confirmed the stability of PD, which was mainly attributed to a change in the microbial community and a decrease in nitrite reductase (Nir) activity, with microorganisms enriched through the gas-liquid separation operation exhibiting low Nir activity. This study provides a new method for rapid formation of biofilm for wastewater treatment and stable operation of PD.

Tolerant and highly-permeable membrane aerated biofilm reactor enabled by selective armored membrane

Membrane aerated biofilm reactor (MABR) is a promising technology for dramatically reducing aeration energy consumption in wastewater treatment. However, the crucial membranes, including microporous hydrophobic membranes and dense membranes, are intolerant to fouling and possess high oxygen transfer resistance respectively, hindering their application potential. Herein, we developed a tolerant and highly-permeable membrane aerated biofilm reactor (THMABR) with a selective armor layer on the membrane to support the biofilm. The selective permeability of the selective armor layer enabled oxygen transfer efficiently and prevented interference by water, surfactant and microbial extracellular polymers. Besides, the composite of the 5 μm selective armor layer and microporous support significantly shortened the distance for solution-diffusion, reducing the transmembrane energy barrier of oxygen molecules. The THMABR's excellent and stable oxygen permeability solved the oxygen substrate concentration's limitation on oxidation rate, enabling functional bacteria to possess a higher oxidation potential and more abundant ecological niche. Based on the novel design, oxygen selective armor membrane (OSAM) performed notably higher oxygen transfer rates (9.61 gO2·m-2d-1) compared to the fouled microporous hydrophobic membrane (3.31 gO2·m-2d-1) and the dense membrane (4.04 gO2·m-2d-1). Besides, the OSAM exhibited more stable fouling resistance to water infiltration and pollutant intrusion compared to the microporous hydrophobic membrane after surfactant pretreatment. Municipal wastewater treatment tests further confirmed that the novel membrane support-selective armored layer-biofilm structure of THMABR can high-efficiently remove nitrogen. The structural characteristics, mechanisms of fouling resistance and oxygen transfer, as well as wastewater treatment performance of the THMABR and OSAM are discussed in detail. This work introduces a new design concept to overcome the bottleneck of traditional MABRs involving the disunity of tolerance and permeability, being expected to support the low-carbon and stable operation of wastewater biological treatment.

Photoimmunologic Therapy of Stubborn Biofilm via Inhibiting Bacteria Revival and Preventing Reinfection

Stubborn biofilm infections pose serious threats to public health. Clinical practices highly rely on mechanical debridement and antibiotics, which often fail and lead to persistent and recurrent infections. The main culprits are 1) persistent bacteria reviving, colonizing, and rejuvenating biofilms, and 2) secondary pathogen exposure, particularly in individuals with chronic diseases. Addressing how to inhibit persistent bacteria revival and prevent reinfection simultaneously is still a major challenge. Herein, an oligo-ethylene glycol-modified lipophilic cationic photosensitizer (PS), TBTCP-PEG7, is developed. It effectively eradicates Methicillin-Resistant Staphylococcus aureus (MRSA) under light irradiation. Furthermore, TBTCP-PEG7-mediated photodynamic therapy (PDT) not only conquers stubborn biofilm infections by downregulating the two-component system (TCS), quorum sensing (QS), and virulence factors, thereby reducing intercellular communication, inhibiting persistent bacterial regrowth and biofilm remodeling but also prevents reinfection by upregulating heat shock protein-related genes to induce immunogenetic cell death (ICD) and establish immune memory. In vivo, TBTCP-PEG7 efficiently eradicates MRSA biofilm adhered to medical catheters, stimulates angiogenesis, reduces inflammatory factor expression, and accelerates wound healing. Furthermore, ICD promotes short-term immune and long-term immunological memory for coping with secondary infections. This two-pronged strategy not only effectively overcomes stubborn, persistent and recurrent biofilm infection, but also provides theoretical guidance for designing the next generation of antibacterial materials.

Microbial extracellular polymeric substances in the environment, technology and medicine

Microbial biofilms exhibit a self-produced matrix of extracellular polymeric substances (EPS), including polysaccharides, proteins, extracellular DNA and lipids. EPS promote interactions of the biofilm with other cells and sorption of organics, metals and chemical pollutants, and they facilitate cell adhesion at interfaces and ensure matrix cohesion. EPS have roles in various natural environments, such as soils, sediments and marine habitats. In addition, EPS are relevant in technical environments, such as wastewater and drinking water treatment facilities, and water distribution systems, and they contribute to biofouling and microbially influenced corrosion. In medicine, EPS protect pathogens within the biofilm against the host immune system and antimicrobials, and emerging evidence suggests that EPS can represent potential virulence factors. By contrast, EPS yield a wide range of valuable products that include their role in self-repairing concrete. In this Review, we aim to explore EPS as a functional unit of biofilms in the environment, in technology and in medicine.

Sulfamethoxazole removal in nitrifying membrane aerated biofilms: Physiological responses and antibiotic resistance genes

Efficient removal of ammonia nitrogen and sulfamethoxazole (SMX) from wastewater has become increasingly critical due to their detrimental effects on aquatic ecosystems and public health. This study aimed to investigate the nitrogen transformation and SMX removal in a membrane aerated biofilm reactor (MABR) under different SMX concentrations (0-200 μg L-1) with a nitrifying membrane bioreactor (MBR) as a control. Results suggested that SMX removal in MABR was better than that of MBR with SMX addition (50-200 μg L-1). Membrane aerated biofilms tended to secrete more extracellular polymeric substances (EPS) and generate less antioxidant enzymes in response to SMX stress when compared with nitrifying sludge in MBR. Metagenomic analysis indicated that distinct succession of microbial community was observed in both systems after SMX addition, and the relative abundance of nitrifying bacteria (Nitrosomonas, Nitrospira, and Nitrobacter) evidently decreased under SMX concentration of 200 μg L-1. The proliferation of predominant antibiotic resistance gene (ARG) sul2 was suppressed more obviously in MABR than that in MBR. Thus, this study provided extensive insights into the advantages of nitrifying MABR in simultaneous removal of ammonium and antibiotics with less risk of associated ARGs spread.

Revealing synergistic mechanisms of biochar-assisted microbial electrolysis cells in enhancing the anaerobic digestion performance of waste activated sludge: Extracellular polymeric substances characterization, enzyme activity assay, and multi-omics analysis

Although biochar (BC)-assisted microbial electrolysis cells (MEC) has been shown to improve anaerobic digestion (AD) performance of waste activated sludge (WAS), the underlying mechanisms remain unclear. This study conducted an in-depth investigation into the mechanism based on analyses of extracellular polymeric substances (EPS) characteristics, enzyme activities and multi-omics. The results showed that compared with the control group, methane production improved by 16.73 %, 21.32 %, and 29.37 % in the BC, MEC, and BC-assisted MEC (BC-MEC) groups, respectively. The reconfiguration of the protein secondary structure increased the hydrophobicity of the EPS, thereby promoting microbial aggregation. In addition, partial least-squares path modeling (PLS-PM) and mantel test based on the enzyme activity and multi-omics analyses revealed that the promotional effect of MEC on the hydrolysis of WAS was superior to that of BC, while BC was more advantageous in promoting electron transfer and biofilm formation regulated by quorum sensing. The synergistic effects of BC and MEC were exemplified in the BC-MEC group. g_norank_Aminicenantales responsible for the hydrolysis of WAS was enriched (29.6 %), and the activities of hydrolytic enzymes including α-glucosidases and proteases were increased by 29.1 % and 43.6 %, respectively. Further, the expressions of genes related to acyl homoserine lactones (AHLs) and diffusible signal factor (DSF) in quorum sensing systems, as well as the genes related to hydrogenase involved in electron transfer (mbhJKL, hyfB-JR, hypA-F, and hoxFHUY), were up-regulated in the BC-MEC group. This facilitated electron transfer and microbial communication, consequently enhancing methane production. This research significantly advances the understanding of the mechanism by which BC-assisted MEC enhances AD performance and provides valuable insights into strategies for improving energy recovery from WAS.

Biodegradation of organosulfur with extra carbon source: Insights into biofilm formation and bacterial metabolic processes

Organosulfur compounds are prevalent in wastewater, presenting challenges for biodegradation, particularly in low-carbon environments. Supplementing additional carbon sources not only provides essential nutrients for microbial growth but also serves as regulators, influencing adaptive changes in biofilm and enhancing the survival of microorganisms in organosulfur-induced stress bioreactors. This study aims to elucidate the biodegradation of organosulfur under varying carbon source levels, placing specific emphasis on functional bacteria and metabolic processes. It has been observed that higher levels of carbon supplementation led to significantly improved total sulfur (TS) removal efficiencies, exceeding 83 %, and achieve a high organosulfur CH3SH removal efficiency of ~100 %. However, in the reactor with no external carbon source added, the oxidation end-product SO42- accumulated significantly, surpassing 120 mEq/m2-day. Furthermore, the TB-EPS concentration consistently increasedwith the ascending glucose concentration. The analysis of bacterial community reveals the enrichment of functional bacteria involved in sulfur metabolism and biofilm formation (e.g. Ferruginibacter, Rhodopeudomonas, Gordonia, and Thiobacillus). Correspondingly, the gene expressions related to the pathway of organosulfur to SO42- were notably enhanced (e.g. MTO increased by 27.7 %). In contrast, extra carbon source facilitated the transfer of organosulfur into amino acids in sulfur metabolism and promoted assimilation. These metabolic insights, coupled with kinetic transformation results, further validate distinct sulfur pathways under different carbon source conditions. The intricate interplay between bacteria growth regulation, pollutant biodegradation, and microbial metabolites underscores a complex network relationship that significantly contributes to efficient operation of bioreactors.

Effects of a novel sawdust-modified carrier on performance, bioaccumulation and microbial community of sequencing batch reactor

The impact of a novel sawdust-modified carrier on the performance of aerobic sequencing batch reactor (SBR) was examined. Compared with the conventional polyethylene (PE) carrier, the sawdust-modified carrier had coarse surface and porous side wall, which was beneficial for the rapid formation of biofilm. The biomass of sawdust-modified carrier was 3.4 ± 0.7 times more than those of PE carrier at the end of this study. The biofilm gotten from suspended carrier had higher extracellular polymeric substances (EPS) concentrations than activated sludge (AS). The EPS from biofilm contained higher proportions of polysaccharides compared to those from AS. The SBR with addition of sawdust-modified carrier exhibited higher ammonia nitrogen removal efficiency (84.8%) than the one with addition of conventional PE carrier (73.1%) in a typical cycle at 12 h. The volumetric nitrification rates of modified carrier were higher than those of conventional PE carrier. High throughput sequencing revealed that sawdust-modified carriers exhibited greater microbial richness and diversity compared with traditional PE carriers. Saccharimonadales was the most predominant genus that removed organic matter under aerobic condition, whereas Nitrospira was the dominant nitrifying genus. The present study verifies the advantage of sawdust-modified carrier, which has the potential for the full-scale application in the future.

Bacteriophage-mediated approaches for biofilm control

Biofilms are complex microbial communities in which planktonic and dormant bacteria are enveloped in extracellular polymeric substances (EPS) such as exopolysaccharides, proteins, lipids, and DNA. These multicellular structures present resistance to conventional antimicrobial treatments, including antibiotics. The formation of biofilms raises considerable concern in healthcare settings, biofilms can exacerbate infections in patients and compromise the integrity of medical devices employed during treatment. Similarly, certain bacterial species contribute to bulking, foaming, and biofilm development in water environments such as wastewater treatment plants, water reservoirs, and aquaculture facilities. Additionally, food production facilities provide ideal conditions for establishing bacterial biofilms, which can serve as reservoirs for foodborne pathogens. Efforts to combat antibiotic resistance involve exploring various strategies, including bacteriophage therapy. Research has been conducted on the effects of phages and their individual proteins to assess their potential for biofilm removal. However, challenges persist, prompting the examination of refined approaches such as drug-phage combination therapies, phage cocktails, and genetically modified phages for clinical applications. This review aims to highlight the progress regarding bacteriophage-based approaches for biofilm eradication in different settings.

Simultaneous carbon, nitrogen and phosphorus removal in sequencing batch membrane aerated biofilm reactor with biofilm thickness control via air scouring aided by computational fluid dynamics

Membrane aerated biofilm reactor (MABR) is challenged by biofilm thickness control and phosphorus removal. Air scouring aided by computational fluid dynamics (CFD) was employed to detach outer biofilm in sequencing batch MABR treating low C/N wastewater. Biofilm with 177-285 µm thickness in cycle 5-15 achieved over 85 % chemical oxygen demand (COD) and total inorganic nitrogen (TIN) removals at loading rate of 13.2 gCOD/m2/d and 2.64 gNH4+-N/m2/d. Biofilm rheology measurements in cycle 10-25 showed yield stress against detachment of 2.8-7.4 Pa, which were equal to CFD calculated shear stresses under air scouring flowrate of 3-9 L/min. Air scouring reduced effluent NH4+-N by 10 % and biofilm thickness by 78 µm. Intermittent aeration (4h off, 19.5h on) and air scouring (3 L/min, 30 s before settling) in one cycle achieved COD removal over 90 %, TIN and PO43--P removals over 80 %, showing great potential for simultaneous carbon, nitrogen and phosphorus removals.

Insights into the removal of antibiotics from livestock and aquaculture wastewater by algae-bacteria symbiosis systems

With the burgeoning growth of the livestock and aquaculture industries, antibiotic residues in treated wastewater have become a serious ecological threat. Traditional biological wastewater treatment technologies-while effective for removing conventional pollutants, such as organic carbon, ammonia and phosphate-struggle to eliminate emerging contaminants, notably antibiotics. Recently, the use of microalgae has emerged as a sustainable and promising approach for the removal of antibiotics due to their non-target status, rapid growth and carbon recovery capabilities. This review aims to analyse the current state of antibiotic removal from wastewater using algae-bacteria symbiosis systems and provide valuable recommendations for the development of livestock/aquaculture wastewater treatment technologies. It (1) summarises the biological removal mechanisms of typical antibiotics, including bioadsorption, bioaccumulation, biodegradation and co-metabolism; (2) discusses the roles of intracellular regulation, involving extracellular polymeric substances, pigments, antioxidant enzyme systems, signalling molecules and metabolic pathways; (3) analyses the role of treatment facilities in facilitating algae-bacteria symbiosis, such as sequencing batch reactors, stabilisation ponds, membrane bioreactors and bioelectrochemical systems; and (4) provides insights into bottlenecks and potential solutions. This review offers valuable information on the mechanisms and strategies involved in the removal of antibiotics from livestock/aquaculture wastewater through the symbiosis of microalgae and bacteria.

Biofilm growth characteristic and footprint identification in gravity-driven ceramic membrane bioreactor with electro-coagulation under extreme conditions for roofing rainwater purification

The identification of biofilm growth footprints influencing on the biofilm detachment and breakup can advance research into how biofilms form. Thus, a gravity-driven ceramic membrane bioreactor (GDCMBR) was used to investigate the growth, detachment and breakup of biofilm using rainwater pretreated by electrocoagulation under 70-days continuous operation. The in-situ ultrasonic time-domain reflectometry (UTDR) technique was applied to non-invasively determine the biofilm thickness. Initially, the biofilm was slowly thickening, but it would collapse and became thinner after accumulating to a certain level, and then it thickened again in a later period, following a cyclic pattern of 'thickening - collapsing - thickening'. This is because the biofilm growth is related with the accumulation of flocs, however, excessive floc formation results in the biofilm being overweight till reaching the thickness limit and thus collapsing. Subsequently, the biofilm gradually thickens again due to the floc production and continuous deposition. Although the biofilm was dynamically changing, the water quality of treatment of the biofilm always remained stable. Ammonia nitrogen and total phosphorus have been almost completely removed, while CODMn removal efficiency was around 25%. And total bacteria amount in the membrane concentrate was obviously higher than that in the influent with the greater microbial activity, demonstrating the remarkable enrichment effect on bacteria. The understanding of biofilm growth characteristic and footprint identification enables us to develop rational approaches to control biofilm structure for efficient GDCMBR performance and operation lifespan.

Spectral fusion-based machine learning classifiers for discriminating membrane breakage in multiple scenarios

Membrane breakage can lead to filtration failure, which allows harmful substances to enter the effluent, posing potential hazards to human health and the environment. This study is an innovative combination of fluorescence and ultraviolet-visible (UV-Vis) spectroscopy to identify membrane breakage. It aims to unravel more comprehensive information, improve detection sensitivity and selectivity, and enable real-time monitoring capabilities. Fluorescence and UV-Vis data are extracted through variance partitioning analysis (VPA) and integrated through a decision tree algorithm to form a superior system with enhanced discrimination capabilities. VPA improves discrimination efficiency by extracting key information from spectral data and eliminating redundancy. The decision tree algorithm, on the other hand, can process large amounts of data simultaneously. In addition, the method has a wide range of applications and can be used in various scenarios accurately. The scenarios include domestic sewage, micropollutant water, aquaculture wastewater, and secondary treated sewage. The experimental results validate the application of machine learning classifiers in membrane breakage detection with an accuracy rate of 96.8 % to 97.4 %.

Lumen air pressure regulated multifunctional microbiotas in membrane-aerated biofilm reactors for simultaneous nitrogen removal and antibiotic elimination from aquaculture wastewater

In this study, two membrane-aerated biofilm reactors (MABRs) were constructed: one solely utilizing biofilm and another hybrid MABR (HMABR) incorporating both suspended-sludge and biofilm to treat low C/N aquaculture wastewater under varying lumen air pressure (LAP). Both HMABR and MABR demonstrated superior nitrogen removal than conventional aeration reactors. Reducing LAP from 10 kPa to 2 kPa could enhance denitrification processes without severely compromising nitrification, resulting in an increase in total inorganic nitrogen (TIN) removal from 50.2±3.1 % to 71.6±1.0 %. The HMABR exhibited better denitrification efficacy than MABR, underscoring its potential for advanced nitrogen removal applications. A decline in LAP led to decreased extracellular polymeric substance (EPS) production, which could potentially augment reactor performance by minimizing mass transfer resistance while maintaining microbial matrix stability and function. Gene-centric metagenomics analysis revealed decreasing LAP impacted nitrogen metabolic potentials and electron flow pathways. The enrichment of napAB at higher LAP and the presence of complete ammonia oxidation (Comammox) Nitrospira at lower LAP indicated aerobic denitrification and Comammox processes in nitrogen removal. Multifunctional microbial communities developed under LAP regulation, diversifying the mechanisms for simultaneous nitrification-denitrification. Increased denitrifying gene pool (narGHI, nirK, norB) and enzymatic activity at a low LAP can amplify denitrification by promoting denitrifying genes and electron flow towards denitrifying enzymes. Sulfamethoxazole (SMX) was simultaneously removed with efficiency up to 80.2 ± 3.7 %, mainly via biodegradation, while antibiotic resistome and mobilome were propagated. Collectively, these findings could improve our understanding of nitrogen and antibiotic removal mechanisms under LAP regulation, offering valuable insights for the effective design and operation of MABR systems in aquaculture wastewater treatment.

Response of antibiotic resistance genes expression and distribution on extracellular polymeric substances and microbial community in membrane biofilm during greywater treatment

This study evaluated how organic loading affects antibiotic resistance genes (ARGs) expression and distribution in the membrane biofilm. Organic surface loading rate of 4.65 g chemical oxygen demand (COD)/m2·d achieved the maximum biofilm thickness, concentration and linear alkylbenzene sulfonate (LAS) removal ratio of 136.9 ± 4.7 μm, 5.4 ± 0.1 g VSS/m2 and 99.4 %, respectively. Extracellular polymeric substances (EPS), EPS-attached LAS, and ARGs gradually increased in the membrane air inlet, middle and air outlet. AGRs and Intl1 were abundant in biofilm. LAS promoted EPS secretion, biofilm growth and ARGs proliferation. EPS, protein and carbohydrate were significantly correlated with most of biofilm ARGs, but not corrected with liquid-based ARGs. Microbial community structure impacted ARGs proliferation and transfer in the system. The findings indicated that EPS and microbial community play a crucial role in ARGs proliferation, spread and distribution, which lay the foundation for front-end control of ARGs during biofilm-based wastewater treatment.

Copper(II)-infused porphyrin MOF: maximum scavenging GSH for enhanced photodynamic disruption of bacterial biofilm

Bacterial biofilm infection is a serious obstacle to clinical therapeutics. Photodynamic therapy (PDT) plays a dynamic role in combating biofilm infection by utilizing reactive oxygen species (ROS)-induced bacterial oxidation injury, showing advantages of mild side effects, spatiotemporal controllability and little drug resistance. However, superfluous glutathione (GSH) present in biofilm and bacteria corporately reduces ROS levels and seriously affects PDT efficiency. Herein, we have constructed a Cu2+-infused porphyrin metal-organic framework (MOF@Cu2+) for the enhanced photodynamic combating of biofilm infection by the maximum depletion of GSH. Our results show that the released Cu2+ from porphyrin MOF@Cu2+ could not only oxidize GSH in biofilm but also consume GSH leaked from ROS-destroyed bacteria, thus greatly weakening the antioxidant system in biofilm and bacteria and dramatically improving the ROS levels. As expected, our dual-enhanced PDT nanoplatform exhibits a strong biofilm eradication ability both in vitro and in an in vivo biofilm-infected mouse model. In addition, Cu2+ can promote biofilm-infected wound closing by provoking cell immigration, collagen sediment and angiogenesis. Besides, no apparent toxicity was detected after treatment with MOF@Cu2+. Overall, our design offers a new paradigm for photodynamic combating biofilm infection.