Evaluation of a novel quorum quenching strain for MBR biofouling mitigation

Study on efficiency and mechanism of ultrasonic controlling membrane fouling in ceramic membrane bioreactors

In recent years, ceramic membranes have been increasingly used in membrane bioreactors (MBRs). However, membrane fouling was still the core issue restricting the large-scale engineering application of ceramic MBRs. As a novel and alternative technology, ultrasonic could be used to control membrane fouling. This research focused on the efficiency and mechanism of ultrasonic controlling membrane fouling in ceramic MBRs. The results showed that ultrasonic reduced the sludge concentration in MBR, and the average particle size of sludge was always in a high range. The sludge activity of the system was stable at 6-9 (mg O2·(g MLSS·h)-1), indicating that ultrasonic did not destroy the activity of microorganisms in the system. The extracellular polymer substance (EPS) of the ultrasonic group was slightly higher than that of the control group, while the soluble microbial product (SMP) content was relatively stable. The ceramic membrane of the ultrasonic group has a partial retention effect on the organic components. The application of ultrasonic slowed down the decrease of the hydrophilicity of the ceramic membrane. The main pollutants on the membrane surface exist in the form of aromatic and heteroaromatic rings, alkynes, and so forth. Ultrasonic removes the amide substances from the membrane surface. Membrane fouling resistance is mainly due to membrane pore blockage, accounting for 75.53%. PRACTITIONER POINTS: Enrich the research on the mechanism of ultrasonic technology in membrane fouling control. The MBR can still operate normally with ultrasonic applied. The time for the ceramic membrane to reach the fouling end point is 2.4 times that without ultrasonic. The main cause of membrane fouling was pore blocking, accounting for 75.53%.

Regulation of extracellular polymers based on quorum sensing in wastewater biological treatment from mechanisms to applications: A critical review

Extracellular polymeric substances (EPS) regulated by quorum sensing (QS) could directly mediate adhesion between microorganisms and form tight microbial aggregates. Besides, EPS have redox properties, which can facilitate electron transfer for promoting electroactive bacteria. Currently, the applications research on improving wastewater biological treatment performance based on QS regulated EPS have been widely reported, but reviews on the level of QS regulated EPS to enhance EPS function in microbial systems are still lacking. This work proposes the potential mechanisms of EPS synthesis by QS regulation from the viewpoint of material metabolism and energy metabolism, and summarizes the effects of QS on EPS synthesis. By synthesizing the role of QS in EPS regulation, we further point out the applications of QS-regulated EPS in wastewater biological treatment, which involve a series of aspects such as strengthening microbial colonization, mitigating membrane biofouling, improving the shock resistance of microbial metabolic systems, and strengthening the electron transfer capacity of microbial metabolic systems. According to this comprehensive review, future research on QS-regulated EPS should focus on the exploration of the micro-mechanisms, and economic regulation strategies for QS-regulated EPS should be developed, while the stability of QS-regulated EPS in long-term production experimental research should be further demonstrated.

Isolation and application of Bacillus thuringiensis LZX01: Efficient membrane biofouling mitigation function and anti-toxicity potential

Significant progress has been made in mitigating membrane biofouling by microbial quorum quenching (QQ). More efficient and survivable QQ strains need to be discovered. A new strain named Bacillus thuringiensis LZX01 was isolated in this study using a low carbon source concentration "starving" method from a membrane bioreactor (MBR). LZX01 secreted intracellular lactonase to enable QQ behavior and was capable of degrading 90 % of C8-HSL (200 ng/mL) within 30 min, which effectively delayed biofouling by inhibiting the growth of bacteria associated with biofouling and improving the hydrophilicity of bound extracellular polymeric substances. As a result, the membrane biofouling rate of MBR adding LZX01 was four times slower than that of the control MBR. Importantly, LZX01 maintains its QQ activity even in environments contaminated with typical toxic pollutants. Therefore, with high efficiency, toxicity resistance, and easy culture, LZX01 holds great potential and significant promise for biofouling control applications.

New Strategies for Biocontrol of Bacterial Toxins and Virulence: Focusing on Quorum-Sensing Interference and Biofilm Inhibition

The overuse of antibiotics and the emergence of multiple-antibiotic-resistant pathogens are becoming a serious threat to health security and the economy. Reducing antimicrobial resistance requires replacing antibiotic consumption with more biocontrol strategies to improve the immunity of animals and humans. Probiotics and medicinal plants have been used as alternative treatments or preventative therapies for a variety of diseases caused by bacterial infections. Therefore, we reviewed some of the anti-virulence and bacterial toxin-inhibiting strategies that are currently being developed; this review covers strategies focused on quenching pathogen quorum sensing (QS) systems, the disruption of biofilm formation and bacterial toxin neutralization. It highlights the probable mechanism of action for probiotics and medicinal plants. Although further research is needed before a definitive statement can be made on the efficacy of any of these interventions, the current literature offers new hope and a new tool in the arsenal in the fight against bacterial virulence factors and bacterial toxins.

Biofouling in Membrane Bioreactors-Mitigation and Current Status: a Review

Biological fouling as termed biofouling is caused by varied living organisms and is difficult to eliminate from the environment thus becoming a major issue during membrane bioreactors. Biofouling in membrane bioreactors (MBRs) is a crucial problem in increasing liquid pressure due to reduced pore diameter, clogging of the membrane pores, and alteration of the chemical composition of the water which greatly limits the growth of MBRs. Thus, membrane biofouling and/or microbial biofilms is a hot research topic to improve the market competitiveness of the MBR technology. Though several antibiofouling strategies (addition of bioflocculant or sponge into MBRs) came to light, biological approaches are sustainable and more practicable. Among the biological approaches, quorum sensing-based biofouling control (so-called quorum quenching) is an interesting and promising tool in combating biofouling issues in the MBRs. Several review articles have been published in the area of membrane biofouling and mitigation approaches. However, there is no single source of information about biofouling and/or biofilm formation in different environmental settings and respective problems, antibiofilm strategies and current status, quorum quenching, and its futurity. Thus, the objectives of the present review were to provide latest insights on mechanism of membrane biofouling, quorum sensing molecules, biofilm-associated problems in different environmental setting and antibiofilm strategies, special emphasis on quorum quenching, and its futurity in the biofilm/biofouling control. We believe that these insights greatly help in the better understanding of biofouling and aid in the development of sustainable antibiofouling strategies.

Scavenging of reactive oxygen species effectively reduces Pseudomonas aeruginosa biofilms through disrupting policing

Biofilm formation is likely to contribute greatly to antibiotic resistance in bacteria and therefore the efficient removal of bacterial biofilms needs addressing urgently. Here, we reported that the supplement of non-inhibitory concentration of N-acetyl-L-cysteine (NAC), a common reactive oxygen species (ROS) scavenger, can significantly reduce the biomass of mature Pseudomonas aeruginosa biofilms (corroborated by crystal violet assay and laser scanning confocal microscopy). 1 mM NAC increased the cheater (ΔlasR mutant) frequency to 89.4 ± 1.5% in the evolved PAO1 after the 15-day treatment. Scavenging of ROS by NAC induced the collapse of P. aeruginosa biofilms, but it did not alter quorum sensing-regulated genes expression (e.g., hcnC and cioAB) and hydrogen cyanide production. The replenishment of public good protease contributed to the recovery of biofilm biomass, indicating the role of disrupting policing in biofilm inhibition. Furthermore, 7 typical ROS scavengers (e.g., superoxide dismutase, catalase and peroxidase, etc.) also effectively inhibited mature P. aeruginosa biofilms. This study demonstrates that scavenging of ROS can promote the selective control of P. aeruginosa biofilms through policing disruption as a targeted biofilm control strategy in complex water environments.

Application of Encapsulated Quorum Quenching Strain Acinetobacter pittii HITSZ001 to a Membrane Bioreactor for Biofouling Control

Quorum quenching (QQ) is a novel anti-biofouling strategy for membrane bioreactors (MBRs) used in wastewater treatment. However, actual operation of QQ-MBR systems for wastewater treatment needs to be systematically studied to evaluate the comprehensive effects of QQ on wastewater treatment engineering applications. In this study, a novel QQ strain, Acinetobacter pittii HITSZ001, was encapsulated and applied to a MBR system to evaluate the effects of this organism on real wastewater treatment. To verify the effectiveness of immobilized QQ beads in the MBR system, we examined the MBR effluent quality and sludge characteristics. We also measured the extracellular polymeric substances (EPS) and soluble microbial products (SMP) in the system to determine the effects of the organism on membrane biofouling inhibition. Additionally, changes in microbial communities in the system were analyzed by high-throughput sequencing. The results indicated that Acinetobacter pittii HITSZ001 is a promising strain for biofouling reduction in MBRs treating real wastewater, and that immobilization does not affect the biofouling control potential of QQ bacteria.

Quorum-Sensing Inhibitors from Probiotics as a Strategy to Combat Bacterial Cell-to-Cell Communication Involved in Food Spoilage and Food Safety

Experience-based knowledge has shown that bacteria can communicate with each other through a cell-density-dependent mechanism called quorum sensing (QS). QS controls specific bacterial phenotypes, such as sporulation, virulence and pathogenesis, the production of degrading enzymes, bioluminescence, swarming motility, and biofilm formation. The expression of these phenotypes in food spoiling and pathogenic bacteria, which may occur in food, can have dramatic consequences on food production, the economy, and health. Due to the many reports showing that the use of conventional methods (i.e., antibiotics and sanitizers) to inhibit bacterial growth leads to the emergence of antibiotic resistance, it is necessary to research and exploit new strategies. Several studies have already demonstrated positive results in this direction by inhibiting autoinducers (low-molecular-weight signaling compounds controlling QS) and by other means, leading to QS inhibition via a mechanism called quorum quenching (QQ). Thus far, several QS inhibitors (QSIs) have been isolated from various sources, such as plants, some animals from aqueous ecosystems, fungi, and bacteria. The present study aims to discuss the involvement of QS in food spoilage and to review the potential role of probiotics as QSIs.

Biodiesel production potential of microalgae, cultivated in acid mine drainage and livestock wastewater

The adaptability and biofuel production potential of two strains of microalgae isolated and cultivated in livestock wastewater effluent (LWE) with acid mine drainage (AMD) were investigated. The isolated strains of microalgae from samples obtained from LWE and AMD, two microalgal strains (Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17) were selected based on their growth rate and lipid productivity. The dry cell weight of Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17 after 20 days of cultivation in AMD increased from 0.05 to 0.59 g/L and from 0.05 to 0.55 g/L, respectively. These findings revealed a significant accumulation of fatty acids with increasing AMD content. Nephroselmis sp. KGE2 in LWE with 5% AMD demonstrated a higher growth rate (0.59 ± 0.03 g/L) and fatty acid production (401.5 ± 47.3 mg/L) than Autodesmus obliquus KGE17 with 5% AMD. Additionally, Nephroselmis sp. KGE2 had C16-C18 fatty acid content (92.4%) in LWE with AMD. Biodiesel produced from Nephroselmis sp. KGE2 had a higher cetane number (52.31) and iodine value (88.26 g I₂/100 g oil). Consequently, Nephroselmis sp. KGE2 can be considered a potential candidate for biodiesel production using AMD as an iron source.

Role of initial bacterial community in the aerobic sludge granulation and performance

The structure of bacterial community was greatly varied from different seed sludge sources, which affected the sludge characteristics. To explore the role of different functional bacteria in AGS granulation and pollutant degradation, three different resources of seed sludge obtained from pharmaceutical wastewater (R1), livestock (R2), and municipal sludge (R3) were employed in this study. Results showed that the initial bacterial community had important significance for AGS formation and pollutants removal. Seed sludge taken from R3 granulated faster than those from R1 and R2. A large number of mature granules were formed after 20 days of operation in R3. In addition, the final mixed liquor suspended solids (MLSS) reached 6853 mg L^-1, with 48 mL g^-1 sludge volume index (SVI) in R3, indicating that it had better settling performance and granulation. In the stable stage of R3, the removal rates of COD, NH₄⁺-N, and TN reached 99.2%, 98.5%, and 97.6%, respectively. The α-diversity analysis showed that the bacterial community of seed sludge greatly determined the microbial composition of AGS. Firmicutes, Gracilibacteria, and Spirochaetes were abundant in R3, which maintained the structures and functions of aerobic granules. This study might provide approaches and insights for AGS culture from different sludge sources.

Quorum quenching bacteria isolated from industrial wastewater sludge to control membrane biofouling

N-acylhomoserine lactone (AHL)-based bacterial communication through quorum sensing (QS) is one of the main causes of biofouling. Although quorum quenching (QQ) has proven to be an effective strategy against biofouling in membrane bioreactors (MBRs) for municipal wastewater treatment, its applicability for industrial wastewater treatment has rarely been studied. This is the first study to isolate QQ strains from the activated sludge used to treat industrial wastewater containing toxic tetramethylammonium hydroxide (TMAH) and 1-methyl-2-pyrrolidinone. The two QQ strains from genus Bacillus (SDC-U1 and SDC-A8) survived and effectively degraded QS signals in the presence of TMAH. They also showed resistance to toxic byproducts of TMAH degradation such as ammonium and formaldehyde. They effectively reduced the biofilm formation of Pseudomonas aeruginosa PAO1 and mixed community of activated sludge. The strains isolated in this study thus have the potential to be employed to reduce membrane biofouling in MBRs during the treatment of TMAH-containing wastewater.

Quorum-Sensing Inhibition by Gram-Positive Bacteria

The modern paradigm assumes that interspecies communication of microorganisms occurs through precise regulatory mechanisms. In particular, antagonism between bacteria or bacteria and fungi can be achieved by direct destruction of the targeted cells through the regulated production of antimicrobial metabolites or by controlling their adaptive mechanisms, such as the formation of biofilms. The quorum-quenching phenomenon provides such a countermeasure strategy. This review discusses quorum-sensing suppression by Gram-positive microorganisms, the underlying mechanisms of this process, and its molecular intermediates. The main focus will be on Gram-positive bacteria that have practical applications, such as starter cultures for food fermentation, probiotics, and other microorganisms of biotechnological importance. The possible evolutionary role of quorum-quenching mechanisms during the development of interspecies interactions of bacteria is also considered. In addition, the review provides possible practical applications for these mechanisms, such as the control of pathogens, improving the efficiency of probiotics, and plant protection.

Nitric oxide-secreting probiotics as sustainable bio-cleaners for reverse osmosis membrane systems

Membrane biofouling in water purification plants is a serious issue of worldwide concern. Various chemical, physical, and biochemical processes are practised for membrane clean-up. A high-dosage treatment adversely affects the life expectancy of the membrane, and minimum dosage seems unable to deteriorate the biofilms on the membrane. It is reported that quorum quenchers like nitric oxide (NO) disrupt biofilm signals through metabolic rewiring, and also NO is known to be secreted by probiotics (good bacteria). In the present review, it is hypothesized that if probiotic biofilms secreting NO are used, other microbes that aggregate on the filtration membrane could be mitigated. The concept of probiotic administration on filtration membrane seeks to be encouraged because probiotic bacteria will not be hazardous, even if released during filtration. The fundamental motive to present probiotics as a resource for sequestering NO may serve as multifunctional bioweapons for membrane remediation, which will virtually guarantee their long-term sustainability and green approach.

Efficient biostimulants for bacterial quorum quenching to control fouling in MBR

Quorum quenching (QQ), which disrupts bacterial communication and biofilm formation, could alleviate biofouling in MBR. QQ bio-stimulus possessing similar conserved moiety as the signal molecule could promote indigenous QQ bacteria, and thus successfully alleviate biofouling in MBR. However, efficient biostimulant has been barely explored for QQ enhancement in activated sludge system. This study extensively enumerated the potential QQ bio-stimuli, and examined their efficacy on QQ promotion for activated sludge. Moreover, the effect of the QQ consortia on fouling mitigation was also investigated. The results indicated that gamma-caprolactone (GCL), d-xylonic acid-1,4-lactone (XAL), gamma-heptalactone (GHL), urea, and acetamide proved effective in promoting AHLs inactivating activity of activated sludge. GCL, XAL, and GHL intensified the lactonase activity, while urea and acetamide augmented acylase activity. While coupled with beads entrapment, GCL consortia beads, XAL consortia beads, and urea consortia beads effectively disrupted quorum sensing (QS) and controlled membrane fouling in MBR. This work found out several optional bio-stimuli valid for tuning QQ in activated sludge system, and provided easily available and economical alternatives for QQ biostimulation, meanwhile the proposed QQ-MBR approach through QQ biostimulation and consortia entrapment also proved effective and practical.

Acylase enzymes disrupting quorum sensing alter the transcriptome and phenotype of Pseudomonas aeruginosa, and the composition of bacterial biofilms from wastewater treatment plants

Biofilms represent an essential way of life and colonization of new environments for microorganisms. This feature is regulated by quorum sensing (QS), a microbial communication system based on autoinducer molecules, such as N-acyl-homoserine lactones (AHLs) in Gram negative bacteria. In artificial ecosystems, like Wastewater Treatment Plants (WWTPs), biofilm attachment in filtration membranes produces biofouling. In this environment, the microbial communities are mostly composed of Gram-negative phyla. Thus, we used two AHLs-degrading enzymes, obtained from Actinoplanes utahensis (namely AuAAC and AuAHLA) to determine the effects of degradation of QS signals in the biofilm formation, among other virulence factors, of a Pseudomonas aeruginosa strain isolated from a WWTP, assessing molecular mechanisms through transcriptomics. Besides, we studied the possible effects on community composition in biofilms from activated sludge samples. Although the studied enzymes only degraded the AHLs involved in one of the four QS systems of P. aeruginosa, these activities produced the deregulation of the complete QS network. In fact, AuAAC -the enzyme with higher catalytic efficiency- deregulated all the four QS systems. However, both enzymes reduced the biofilm formation and pyocyanin and protease production. The transcriptomic response of P. aeruginosa affected QS related genes, moreover, transcriptomic response to AuAAC affected mainly to QS related genes. Regarding community composition of biofilms, as expected, the abundance of Gram-negative phyla was significantly decreased after enzymatic treatment. These results support the potential use of such AHLs-degrading enzymes as a method to reduce biofilm formation in WWTP membranes and ameliorate bacterial virulence.

Photochemical Behavior of Microbial Extracellular Polymeric Substances in the Aquatic Environment

Microbially derived extracellular polymeric substances (EPSs) occupy a large portion of dissolved organic matter (DOM) in surface waters, but the understanding of the photochemical behaviors of EPS is still very limited. In this study, the photochemical characteristics of EPS from different microbial sources (Shewanella oneidensis, Escherichia coli, and sewage sludge flocs) were investigated in terms of the production of reactive species (RS), such as triplet intermediates (³EPS*), hydroxyl radicals (^•OH), and singlet oxygen (¹O₂). The steady-state concentrations of ^•OH, ³EPS*, and ¹O₂ varied in the ranges of 2.55-8.73 × 10^-17, 3.01-4.56 × 10^-15, and 2.08-2.66 × 10^-13 M, respectively, which were within the range reported for DOM from other sources. The steady-state concentrations of RS varied among different EPS isolates due to the diversity of their composition. A strong photochemical degradation of the protein-like components in EPS isolates was identified by excitation emission matrix fluorescence with parallel factor analysis, but relatively, humic-like components remained stable. Fourier-transform ion cyclotron resonance mass spectrometry further revealed that the aliphatic portion of EPS was resistant to irradiation, while other portions with lower H/C ratios and higher O/C ratios were more susceptible to photolysis, leading to the phototransformation of EPS to higher saturation and lower aromaticity. With the phototransformation of EPS, the RS derived from EPS could effectively promote the degradation of antibiotic tetracycline. The findings of this study provide new insights into the photoinduced self-evolution of EPS and the interrelated photochemical fate of contaminants in the aquatic environment.

Mitigation of membrane biofouling in membrane bioreactor treating sewage by novel quorum quenching strain of Acinetobacter originating from a full-scale membrane bioreactor

A novel quorum quenching (QQ) strain, Acinetobacter guillouiae ST01, was isolated from a full-scale membrane bioreactor (MBR) and characterized for its QQ activities. Batch reactor studies at lab-scale showed that A. guillouiae ST01 exhibited higher QQ activity against acyl homoserine lactones (AHLs) with an oxo group compared to those without an oxo group. The organism was then inoculated (10%) in an MBR (Q-MBR) treating sewage over 48 days and was found to reduce quorum sensing (QS) activity by reducing AHL concentrations in the sludge and the biofilm of the Q-MBR. The concentration of polysaccharides was reduced up to 30% in both the biofilm and sludge relative to the control, whereas protein concentrations were reduced by 40% and 47% in the sludge and biofilm, respectively. The Q-MBR fouling rates were halved. These results indicate that A. guillouiae ST01 is a promising strain for biofouling reduction in MBR treating real wastewater.

Membrane Fouling Controlled by Adjustment of Biological Treatment Parameters in Step-Aerating MBR

A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the direction of improvement of the membrane filtration. In this work, these parameters were investigated in a step-aerating pilot MBR that treated municipal wastewater, in order to control the filamentous population. When F/M loading in the first aeration tank (AT₁) was ≤0.65 ± 0.2 g COD/g MLSS/d at 20 ± 3 °C, DO = 2.5 ± 0.1 mg/L and HRT = 1.6 h, the filamentous bacteria were controlled effectively at a moderate filament index of 1.5-3. The moderate population of filamentous bacteria improved the membrane performance, leading to low transmembrane pressure (TMP) at values ≤ 2 kPa for a great period, while at the control MBR the TMP gradually increased reaching 14 kPa. Soluble microbial products (SMP), were also maintained at low concentrations, contributing additionally to the reduction of ΤΜP. Finally, the step-aerating MBR process and the selected imposed operating conditions of HRT, F/M and DO improved the MBR performance in terms of fouling control, facilitating its future wider application.

Investigation into the Novel Microalgae Membrane Bioreactor with Internal Circulating Fluidized Bed for Marine Aquaculture Wastewater Treatment

A microalgae membrane bioreactor (MMBR) with internal circulating fluidized bed (ICFB) was constructed at room temperature to study the removal efficiency of marine aquaculture wastewater pollutants and continuously monitor the biomass of microalgae. Within 40 days of operation, the removal efficiency of NO₃⁻–N and NH₄⁺–N in the ICFB-MMBR reached 52% and 85%, respectively, and the removal amount of total nitrogen (TN) reached 16.2 mg/(L·d). In addition, the reactor demonstrated a strong phosphorus removal capacity. The removal efficiency of PO₄³⁻–P reached 80%. With the strengthening of internal circulation, the microalgae could be distributed evenly and enriched quickly. The maximum growth rate and biomass concentration reached 60 mg/(L·d) and 1.4 g/L, respectively. The harvesting of microalgae did not significantly affect the nitrogen and phosphorus removal efficiency of ICFB-MMBR. The membrane fouling of the reactor was investigated by monitoring transmembrane pressure difference (TMP). Overall, the membrane fouling cycle of ICFB-MMBR system was more than 40 days.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Effect of quorum quenching on EPS and size-fractioned particles and organics in anaerobic membrane bioreactor for domestic wastewater treatment

Quorum quenching (QQ) has been applied as a promising membrane fouling control strategy for anaerobic membrane bioreactors (AnMBRs). Nevertheless, long-term operation of AnMBRs for real domestic wastewater (DWW) treatment needs to be systematically studied to evaluate comprehensive membrane fouling mechanisms and bioprocess performance. In this study, the impact of QQ on membrane fouling was investigated using a quorum quenching AnMBR (QQAnMBR) deploying a bead-entrapped facultative quorum quenching consortium (FQQ) to treat DWW. FQQ was shown to prolong membrane filtration operation by an average of 75%. Reduced proteins (p < 0.005) and carbohydrates (p < 0.005) in the extracellular polymeric substances (EPS) of mixed liquor (ML) were key differentiators that led to lower cake layer (CL) formation. Additionally, reduced biopolymers production (p < 0.05) in EPS improved sludge dewaterability. The findings suggested that QQ could alter fluorescent microbial metabolites of both EPS and CL as unveiled by excitation-emission matrix spectra pattern. Furthermore, colloidal particles (i.e., particles with size larger than 0.45 μm in ML supernatants) production was retarded by QQ, thereafter, also contributed to the reduced CL formation. Pore blockage was slightly increased by QQ, which might be attributed to pore blockage by large (∼230 nm) and small organic compounds (∼51 nm) in soluble microbial products (SMP). However, QQ had no significant impact on organic concentration of SMP, and QQ was not associated with particle size distribution of biomass. QQ performance was further affirmed through suppressed production of C4-HSL, 3-OXO-C6-HSL, and C6-HSL. The overall AHLs degradability of FQQ was well-maintained even after five membrane service cycles (total operation of 70 d). Moreover, QQ had no compromised impact on treatment performance (i.e., chemical oxygen demand (COD) removal and methane yield). Collectively, this study bridged the knowledge gap to bring forward QQ technology in AnMBR for widespread domestic wastewater treatment application.

Combined Effect of Colloids and SMP on Membrane Fouling in MBRs

Membrane fouling investigations in membrane bioreactors (MBRs) are a top research issue. The aim of this work is to study the combined effect of colloids and soluble microbial products (SMPs) on membrane fouling. Two lab-pilot MBRs were investigated for treating two types of wastewater (wwt), synthetic and domestic. Transmembrane pressure (TMP), SMP, particle size distribution and treatment efficiency were evaluated. Chemical Oxygen Demand (COD) removal and nitrification were successful for both kinds of sewage reaching up to 95–97% and 100%, respectively. Domestic wwt presented 5.5 times more SMP proteins and 11 times more SMP carbohydrates compared to the synthetic one. In contrast, synthetic wwt had around 20% more colloids in the mixed liquor with a size lower than membrane pore size (<400 nm) than domestic. Finally, the TMP at 36 days reached 16 kPa for synthetic wwt and 11 kPa for domestic. Therefore, synthetic wwt, despite its low concentration of SMPs, caused severe membrane fouling compared to domestic, a result that is attributed to the increased concentration of colloids. Consequently, the quantity of colloids and possibly their special characteristics play decisive and more important roles in membrane fouling compared to the SMP—a novel conclusion that can be used to mitigate membranes fouling.

Investigating the influences of quorum quenching and nutrient conditions on activated sludge flocs at a short-time scale

Quorum sensing signals regulate various functions within activated sludge processes such as formation of microbial aggregates. Disturbance of this signaling system, known as quorum quenching (QQ), provides opportunities for eliminating some problems related to biological wastewater treatment (e.g., biofouling and excess sludge production). However, it is poorly understood how and to what extent QQ systems can affect the microbial aggregation processes and the following floc formation. In particular, an in-depth structural characterization at the scale of microbial aggregate while considering nutrient conditions in the reactor is still largely disregarded. Here, we evaluated the QQ effects at the short-term time scale (i.e., after 4 h for the exogenous period and 19 h for exogenous/endogenous period), by combining advanced techniques for microbial characterization (flow cytometry, CARD-FISH, and confocal laser scanning microscopy) and conventional physical-chemical assessments. The results indicated that by implementing QQ agents (immobilized Acylase I enzyme in porous alginate beads) the abundance of single cells and suspended microbial aggregates in the supernatant did not show significant changes during the exogenous period. Conversely, at the end of the exogenous/endogenous period a significant increase of single prokaryotic cells, small and large microbial aggregates favored the growth of grazers, including free-living nanoflagellates and ciliates. Flocs became looser and thinner than those in the control reactor, thus affecting the sludge settling behavior. Inability of microbial community in degradation of soluble protein during the endogenous period confirmed that the QQ agents are likely to inhibit the secretion of protease enzyme within microbial communities of activated sludge.

Biofouling and me: My Stockholm syndrome with biofilms

Biofouling is the undesired deposition and growth of microorganisms on surfaces, forming biofilms. The definition is subjective and operational: not every biofilm causes biofouling - only if a given a subjective "threshold of interference" is exceeded, biofilms cause technical or medical problems. These range from the formation of slime layers on ship hulls or in pipelines, which increase friction resistance, to separation membranes, on which biofilms increase hydraulic resistance, to heat exchangers where they interfere with heat transport to contamination of treated water by eroded biofilm cells which may comprise hygienically relevant microorganisms, and, most dangerous, to biofilms on implants and catheters which can cause persistent infections. The largest fraction of anti-fouling research, usually in short-term experiments, is focused on prevention or limiting primary microbial adhesion. Intuitively, this appears only logical, but turns out mostly hopeless. This is because in technical systems with open access for microorganisms, all surfaces are colonized sooner or later which explains the very limited success of that research. As a result, the use of biocides remains the major tool to fight persistent biofilms. However, this is costly in terms of biocides, it stresses working materials, causes off-time and environmental damage and it usually leaves large parts of biofilms in place, ready for regrowth. In order to really solve biofouling problems, it is necessary to learn how to live with biofilms and mitigate their detrimental effects. This requires rather an integrated strategy than aiming to invent "one-shot" solutions. In this context, it helps to understand the biofilm way of life as a natural phenomenon. Biofilms are the oldest, most successful and most widely distributed form of life on earth, existing even in extreme environments and being highly resilient. Microorganisms in biofilms live in a self-produced matrix of extracellular polymeric substances (EPS) which allows them to develop emerging properties such as enhanced nutrient acquisition, synergistic microconsortia, enhanced tolerance to biocides and antibiotics, intense intercellular communication and cooperation. Transiently immobilized, biofilm organisms turn their matrix into an external digestion system by retaining complexed exoenzymes in the matrix. Biofilms grow even on traces of any biodegradable material, therefore, an effective anti-fouling strategy comprises to keep the system low in nutrients (good housekeeping), employing low-fouling, easy-to-clean surfaces, monitoring of biofilm development, allowing for early intervention, and acknowledging that cleaning can be more important than trying to kill biofilms, because cleaning does not cut the nutrient supply of survivors and dead biomass serves as an additional carbon source for "cannibalizing" survivors, supporting rapid after growth. An integrated concept is presented as the result of a long journey of the author through biofouling problems.

Role of soluble microbial product as an intermediate electron station linking C/N and nitrogen removal performance in sequencing batch reactor

The C/N ratio in wastewater differs in place and time and affects the nitrogen removal performance of wastewater treatment. However, studies have focused only on the direct relationship between C/N and nitrogen removal efficiency but disregarded the significant role of soluble microbial products (SMPs) as an intermediate electron station. In this work, the contribution of SMPs to TN removal for treating wastewater with different C/N in a sequencing batch reactor (SBR) was investigated to extend relevance from C/N-TN removal to C/N-SMP-TN removal. TN removal efficiency was improved by increasing the influent C/N. The relative contribution of SMPs increased from 15% (C/N = 2) to 54% (C/N = 8), including 25.5% via utilization-associated product (UAP)-dependent denitrification and 28.5% via biomass-associated product (BAP)-dependent denitrification. The direct contribution of influent organic substrates dramatically decreased from 85.1% to 46%. In addition, providing an anoxic phase effectively enhanced BAP-dependent denitrification and achieved an increment of the SMP absolute contribution from 20.3% to 43% at C/N = 8 with 6.7 mg/L of TN additionally removed. This work clarified the significant contribution of SMPs to the nitrogen removal process, particularly in treating wastewater with high C/N. It also presented a new strategy for improving nitrogen removal performance via SMP reclamation.

Conditional quorum-sensing induction of a cyanide-insensitive terminal oxidase stabilizes cooperating populations of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic pathogen of humans, uses quorum sensing (QS) to regulate the production of extracellular products that can benefit all members of the population. P. aeruginosa can police QS-deficient cheaters by producing hydrogen cyanide, which is also QS regulated; however, the mechanism by which cooperators selectively protect themselves from the toxicity of cyanide remained unresolved. Here, we show that a cyanide-insensitive terminal oxidase encoded by cioAB provides resistance to cyanide, but only in QS-proficient strains. QS-deficient cheaters do not activate cioAB transcription. QS-mediated regulation of cioAB expression depends on production of both cyanide by cooperators (which is QS regulated) and reactive oxygen species (ROS) from cheaters (which is not QS regulated). This type of regulatory system allows cooperating populations to respond, via ROS, to the presence of cheaters, and might allow them to defer the substantial metabolic cost of policing until cheaters are present in the population.

Quorum sensing (QS) regulates production of ‘public goods’ by Pseudomonas aeruginosa, which releases toxic hydrogen cyanide to constrain QS-deficient cheaters. Here, Yan et al. show that QS-proficient strains protect themselves by producing a cyanide-insensitive enzyme in response to reactive oxygen species released by cheaters.

Control of indigenous quorum quenching bacteria on membrane biofouling in a short-period MBR

In this paper, the immobilized quorum quenching (QQ) bacteria - microbial bag was added to a short-period membrane bioreactor (MBR) and its antifouling ability and mechanism were studied by monitoring the changes in transmembrane pressure (TMP), along with the production of N-acyl-homoserine lactones (AHLs), extracellular polymeric substance (EPS) and soluble microbial products (SMP). The QQ bacteria showed efficient mitigation of TMP increase in different membrane fouling stages. In the control MBR group, the TMP reached 43 kPa on the 4th day, while in the experimental group, TMP of QQ-MBR was only 18 kPa at the same time. The detection result of EPS and SMP content of protein and polysaccharide in MBRs showed that QQ bacteria had significant inhibitory effects on EPS and SMP. Also, the QQ bacterial exhibited excellent AHLs degradation rate in MBR reaction tank.

Bacterial assembly in the bio-cake of membrane bioreactors: Stochastic vs. deterministic processes

Much about assembly processes dictating bio-cake microbiota remains uncertain, leading to poor understanding of membrane biofouling in membrane bioreactors (MBRs). This work aimed to reveal the underlying mechanisms driving bio-cake community during the biofouling process under different flux conditions. On the basis of 16S rRNA sequences, the results showed that bacterial diversity decreased with increasing fouling. Additionally, low-flux bio-cake (8 LMH) communities harbored much lower diversity than high-flux (16 LMH) bio-cake microbiomes. Ecological null model analyses and phylogenetic molecular ecological networks (pMENs) revealed that environmental filtering deterministically governed low-flux bio-cake communities. In contrast, high-flux bio-cake communities were mainly shaped in a stochastic manner. This is likely due to the higher stochastic deposition of bacterial taxa from bulk sludge because of the presence of a stronger drag force. Moreover, by lowering the flux, the interactions between bacterial lineages were enhanced; this is evidenced by the greater number of links, the higher average degree, and the higher average clustering coefficients within the pMENs in low-flux bio-cakes than those in high-flux bio-cakes. Most keystone fouling-related taxa in low-flux bio-cakes were motile and involved in nitrate reduction and polysaccharide/protein metabolism. This corroborated the important role of environmental filtering in the assembly process dictating low-flux bio-cake formation. Some low-abundance taxa were observed to be key fouling-related bacteria under both flux conditions, indicating that a few populations play paramount ecological roles in triggering biofouling. In summary, our findings clearly indicate distinct bio-cake community assembly patterns under different operational conditions and highlight the importance of developing specialized strategies for fouling control in individual MBR systems.

Tracing membrane biofouling to the microbial community structure and its metabolic products: An investigation on the three-stage MBR combined with worm reactor process

The biofouling characteristics of an MBR (S-MBR) combined with the worm reactor and a conventional MBR (C-MBR) were analyzed, respectively, over the three-stage (fast-slow-fast) process. Whether it was in the C-MBR or the S-MBR, the species of the active sludge (AS) were similar to that of the cake sludge (CS) in stage 1 (before day 1), the bacterial adsorption and the metabolites attachment contributed to this transmembrane pressure (TMP) rise. In the stage 2, the TMP increasing rate of the C-MBR was eight times more than that of the S-MBR. During this period, a characteristic community colonized the AS and CS of the S-MBR with the microbes, ie Flavobacteria, Firmicutes and Chloroflexi which were responsible for the degradation of extracellular polymeric substances (EPS) and soluble microbial products (SMP). These dominant species caused the slower accumulation of biofouling metabolites in the CS, resulting in the slow rise-related in TMP. Meanwhile, the enrichment of β-proteobacterium and the absence of Mycobacterium and Propionibacterium in AS and CS of the C-MBR were deemed as the main biological factors bringing about the rise-associated in TMP. In the stage 3, the biofilm was matured, and the cake layer was more compacted, which resulted in an abrupt rise in TMP and severe membrane fouling. Additionally, the statistical analysis revealed that a highly correlation between the TMP increasing rate and the content of carbonhydrates in SMP (SMP_c). When the SMP_c content increased slowly, there was a relatively slow biofouling. But, when the SMP_c increasing rate was greater, it led to a more serious membrane fouling with the sudden TMP jump. Additionally, there was also a highly significant correlation coefficient for the TMP rise and the content of carbonhydrates in EPS (EPS_c) and the protein in SMP (SMP_p), rather than the protein in EPS (EPS_p). The cluster analysis showed that the microbes contributing to membrane fouling were more abundant in the C-MBR, while the microbes related to organic compounds degradation were more abundant in the S-MBR. There was significant correlation between the microbes and their metabolites. The SMP_c in conjunction with EPS_c and SMP_p were the main factors accelerating the membrane fouling. It was concluded that a quick rise in SMP_c triggered an abrupt increase in TMP, while the EPS_c and SMP_p caused the sustained increase in TMP.

Fouling in membrane bioreactors: An updated review

The goal of the current article is to update new findings in membrane fouling and emerging fouling mitigation strategies reported in recent years (post 2010) as a follow-up to our previous review published in Water Research (2009). According to a systematic review of the literature, membrane bioreactors (MBRs) are still actively investigated in the field of wastewater treatment. Notably, membrane fouling remains the most challenging issue in MBR operation and attracts considerable attention in MBR studies. In this review, we summarized the updated information on foulants composition and characteristics in MBRs, which greatly improves our understanding of fouling mechanisms. Furthermore, the emerging fouling control strategies (e.g., mechanically assisted aeration scouring, in-situ chemical cleaning, enzymatic and bacterial degradation of foulants, electrically assisted fouling mitigation, and nanomaterial-based membranes) are comprehensively reviewed. As a result, it is found that the fundamental understanding of dynamic changes in membrane foulants during a long-term operation is essential for the development and implementation of fouling control methods. Recently developed strategies for membrane fouling control denoted that the improvement of membrane performance is not our ultimate and only goal, less energy consumption and more green/sustainable fouling control ways are more promising to be developed and thus applied in the future. Overall, such a literature review not only demonstrates current challenges and research needs for scientists working in the area of MBR technologies, but also can provide more useful recommendations for industrial communities based on the related application cases.