Removal of tetramethylammonium hydroxide (TMAH) by cold plasma treatment combined with periodate oxidation: Degradation, kinetics, and toxicity study.

Tetramethylammonium hydroxide (TMAH), which is a chemical used in the electronic industry, is classified as a hazardous material (HAZMAT class 8) that threatens aquatic ecosystems and human health. Consequently, numerous studies have attempted to remove TMAH using various treatment methods, including advanced oxidation processes such as ozone, UV, or Fenton oxidation. However, prior research has indicated a low kinetic rate of TMAH removal. In this context, we proposed an alternative to TMAH degradation by combining a cold plasma (CP) process with periodate oxidation. As for the kinetics of TMAH removal, the kinetic constant was improved by 5 times (0.1661 and 0.0301 for 40.56 and 2.2 W, respectively) as the electric power of a CP system increased from 2.2 to 40.56 W. The kinetic constant of a 40.56 W CP system further increased by 54 times (1.6250) than a 2 W CP system when 4 mM periodate was used simultaneously. As a result, the integrated CP/periodate system represented 2 times higher TMAH removal efficiency (29.5%) than a 2 W CP system (14.4%). This excellent TMAH degradation capability of the integrated CP/periodate system became pronounced at pH 10 and 25 °C. Overall, the integrated CP/periodate system is expected to be a viable management option for effectively controlling hazardous TMAH chemicals.

Benefits of fungal-to-bacterial quorum quenching as anti-biofouling strategy in membrane bioreactors for wastewater treatment and water reuse.

This study addresses membrane biofouling in membrane bioreactors (MBRs) by exploring fungal-to-bacterial quorum quenching (QQ) strategies. While most research has been focused on bacterial-to-bacterial QQ tactics, this study identified fungal strain Vanrija sp. MS1, which is capable of degrading N-acyl-homoserine lactones (signaling molecules of Gram-negative bacteria). To determine the benefits of fungal over bacterial strains, after immobilization on fluidizing spherical beads in an MBR, MS1 significantly reduced the fouling rate by 1.8-fold compared to control MBR, decreased extracellular polymeric substance levels in the biofilm during MBR operation, and favorably changed microbial community and bacterial network, resulting in biofouling mitigation. It is noteworthy that, unlike Rhodococcus sp. BH4, MS1 enhanced QQ activity when switching from neutral to acidic conditions. These results suggest that MS1 has the potential for the effective treatment of acidic industrial wastewater sources such as semiconductor and secondary battery wastewater using MBRs.

Membrane reciprocation and quorum quenching: An innovative combination for fouling control and energy saving in membrane bioreactors.

Membrane bioreactors (MBRs) play a crucial role in wastewater treatment, but they face considerable challenges due to fouling. To tackle this issue, innovative strategies are needed. This study investigated the effectiveness of membrane reciprocation and quorum quenching (QQ) to control fouling in MBRs. The study compared MBRs using membrane reciprocation (30 rpm) and QQ (injecting media containing 100 or 200 mg/L BH4) with conventional MBRs employing different air-scouring intensities. The results demonstrated that combining membrane reciprocation (30 rpm) with QQ (200 mg/L BH4) significantly extended the service time of MBRs, making it approximately six times longer than conventional methods. Moreover, this approach reduced physically reversible resistance. The reduction in signal molecules related to biofouling due to QQ showcased its critical role in controlling biofouling, even under high shear caused by membrane reciprocation. However, the impact of QQ on microbial community structure appeared relatively insignificant when compared to factors such as operation time, aeration intensity, and membrane reciprocation. By combining membrane reciprocation and QQ, the study achieved a remarkable 81 % energy saving compared to extensive aeration (103 s-1 in velocity gradient), in addition to the extended service time. Importantly, this combined antifouling approach did not negatively affect microbial characteristics and wastewater treatment, emphasizing its effectiveness in MBRs. Overall, the findings of this study offer valuable insights for developing synergistic fouling control strategies in MBRs, significantly improving the energy efficiency of the wastewater treatment process.

Inhibiting Biofilm Formation via Simultaneous Application of Nitric Oxide and Quorum Quenching Bacteria.

Membrane biofouling is an inevitable challenge in membrane-based water treatment systems such as membrane bioreactors. Recent studies have shown that biological approaches based on bacterial signaling can effectively control biofilm formation. Quorum quenching (QQ) is known to inhibit biofilm growth by disrupting quorum sensing (QS) signaling, while nitric oxide (NO) signaling helps to disperse biofilms. In this study, batch biofilm experiments were conducted to investigate the impact of simultaneously applying NO signaling and QQ for biofilm control using Pseudomonas aeruginosa PAO1 as a model microorganism. The NO treatment involved the injection of NONOates (NO donor compounds) into mature biofilms, while QQ was implemented by immobilizing QQ bacteria (Escherichia coli TOP10-AiiO or Rhodococcus sp. BH4) in alginate or polyvinyl alcohol/alginate beads to preserve the QQ activity. When QQ beads were applied together with (Z)-1-[N-(3-aminopropyl)-N-(n-propyl) amino]diazen-1-ium-1,2-diolate (PAPA NONOate), they achieved a 39.0% to 71.3% reduction in biofilm formation, which was substantially higher compared to their individual applications (16.0% to 54.4%). These findings highlight the significant potential of combining QQ and NO technologies for effective biofilm control across a variety of processes that require enhanced biofilm inhibition.

Role of quorum sensing and quorum quenching in anaerobic digestion: A scoping review.

Anaerobic digestion (AD) is a biological process that employs anaerobic microorganisms to degrade organic material, yielding biogas and biofertilizers. Understanding quorum sensing (QS) signaling in mixed microbial systems provides valuable insights into microbial behavior and functions. This review aims to examine recent studies on the roles of QS and QQ in the AD processes. A QS signal molecule, N-acyl homoserine lactone (AHL), induce the production of extraceluller polymers, promoting biofilm formation and bacterial aggregation, thereby the efficiency of AD process. QS-assisted granule formation fosters syntrophy between acetogens and methanogens, leading to increased organic removal and methane production. Specific AHLs were shown to be correlated with the abundance of hydrolytic bacteria and acidogens, further benefiting methane production. QQ was shown to effectively control membrane fouling in anaerobic membrane bioreactors, yet its impact on methane productivity remains unclear. This review shed lights on the existing literature gaps regarding the mechanisms of QS and QQ in AD systems, which will play a vital role in advancing AD applications in the future.

Enhancement of biomethane recovery from batch anaerobic digestion by exogenously adding an N-acyl homoserine lactone cocktail.

Biomethane recovered through anaerobic digestion (AD) is a renewable, sustainable, and cost-effective alternative energy source that has the potential to help address rising energy demands. Efficient bioconversion during AD depends on the symbiotic relationship between hydrolytic bacteria and methanogenic archaea. Interactions between microorganisms occur in every biological system via a phenomenon known as quorum sensing (QS), in which signaling molecules are simultaneously transmitted and detected as a mode of cell-to-cell communication. However, there's still a lack of understanding on how QS works in the AD system, where diverse bacteria and archaea interact in a complex manner. In this study, different concentrations (0.5 and 5 µM) of signaling molecules in the form of an N-acyl homoserine lactone cocktail (C6-, C8-, C10-, and 3-oxo-C6-HSL) were prepared and introduced into anaerobic batch reactors to clearly assess how QS affects AD systems. It was observed that the methane yield increased with the addition of AHLs: a 5 µM AHL cocktail improved the methane yield (341.9 mL/g-COD) compared to the control without AHLs addition (285.9 mL/g-COD). Meanwhile, evidence of improved microbial growth and cell aggregation was noticed in AHLs-supplemented systems. Our findings also show that exogenously adding AHLs alters the microbial community structure by increasing the overall bacterial and archaeal population counts while favoring the growth of the methanogenic archaea group, which is essential in biomethane synthesis.

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.

Innovative Biofouling Control for Membrane Bioreactors in Cold Regions by Inducing Environmental Adaptation in Quorum-Quenching Bacteria.

Bacterial quorum quenching (QQ), whose mechanism involves the degradation of quorum-sensing signal molecules, is an effective strategy for controlling biofouling in membrane bioreactors (MBRs). However, MBRs operated at low temperatures, either due to cold climates or seasonal variations, exhibit severe deterioration in QQ efficiency. In this study, a modified culture method for Rhodococcus sp. BH4, a QQ bacterium, was developed to induce environmental adaptation in cold regions. BH4-L, which was prepared by the modified culture method, showed enhancement in QQ efficiency at low temperatures. The higher QQ efficiency obtained by employing BH4-L at 10 °C (compared with that obtained by employing BH4 at 10 °C) was attributed to the higher live/dead cell ratio in the BH4-L-entrapping beads. When BH4-L-entrapping beads were applied to lab-scale MBRs operated at low temperatures, membrane biofouling in MBRs at low temperatures was successfully mitigated because BH4-L could substantially reduce the concentration of signal molecules (N-acyl homoserine lactones) in the biocake. Employing BH4-L in QQ-MBRs could offer a novel solution to the problem of severe membrane biofouling in MBRs in cold regions.

Convection and the Extracellular Matrix Dictate Inter- and Intra-Biofilm Quorum Sensing Communication in Environmental Systems.

The mechanisms and impact of bacterial quorum sensing (QS) for the coordination of population-level behaviors are well studied under laboratory conditions. However, it is unclear how, in otherwise open environmental systems, QS signals accumulate to sufficient concentration to induce QS phenotypes, especially when quorum quenching (QQ) organisms are also present. We explore the impact of QQ activity on QS signaling in spatially organized biofilms in scenarios that mimic open systems of natural and engineered environments. Using a functionally differentiated biofilm system, we show that the extracellular matrix, local flow, and QQ interact to modulate communication. In still aqueous environments, convection facilitates signal dispersal while the matrix absorbs and relays signals to the cells. This process facilitates inter-biofilm communication even at low extracellular signal concentrations. Within the biofilm, the matrix further regulates the transport of the competing QS and QQ molecules, leading to heterogenous QS behavior. Importantly, only extracellular QQ enzymes can effectively control QS signaling, suggesting that the intracellular QQ enzymes may not have evolved to degrade environmental QS signals for competition.

Veterinary drug, 17ß-trenbolone promotes the proliferation of human prostate cancer cell line through the Akt/AR signaling pathway.

Trenbolone acetate (TBA) is a synthetic anabolic steroidal growth factor that is used for rapid muscle development in cattle. The absorbed TBA is hydrolyzed to the active form, 17ß-trenbolone (17 TB; 17ß-hydroxy-estra-4,9,11-trien-3-one) in meat and milk products, which can cause adverse health effects in humans. Similar to 5α-dihydrotestosterone (DHT), 17 TB was reported to exhibit endocrine disrupting effects on animals and humans due to its androgenic effect via binding to the androgen receptor. The purpose of this study is to investigate the molecular mechanism of cell proliferation in prostate cancer (PCa) cells treated with 17 TB. We found that 17 TB induces AR-dependent cell proliferation in the human prostate cancer cell line, 22Rv1 in a concentration dependent manner. Treatment with 17 TB increased the expression of cell cycle regulatory proteins, cyclin D2/CDK-4 and cyclin E/CDK-2, whereas the expression of p27 was down-regulated. Furthermore, phosphorylation of Rb and activation of E2F were also induced, which suggests the activation of cyclin D2/CDK-4 and cyclin E/CDK-2 in the cells. When 22Rv1 cells were exposed to 30 pM of 17 TB, which is the effective concentration (EC50) value required to observe proliferative effects on 22Rv1 cells, the expression levels of the phosphorylated forms of Akt and GSK3ß were increased. This study demonstrates that 17 TB induces AR-dependent proliferation through the modulation of cell cycle-related proteins in the Akt signaling pathway. The present study provides an effective methodology for identifying cell proliferation signaling of veterinary drugs that exert AR agonistic effects.

Nitric Oxide-Mediated Induction of Dispersal in Pseudomonas aeruginosa Biofilms Is Inhibited by Flavohemoglobin Production and Is Enhanced by Imidazole.

The biological signal molecule nitric oxide (NO) was found to induce biofilm dispersal across a range of bacterial species, which led to its consideration for therapeutic strategies to treat biofilms and biofilm-related infections. However, biofilms are often not completely dispersed after exposure to NO. To better understand this phenomenon, we investigated the response of Pseudomonas aeruginosa biofilm cells to successive NO treatments. When biofilms were first pretreated with a low, noneffective dose of NO, a second dose of the signal molecule at a concentration usually capable of inducing dispersal did not have any effect. Amperometric analysis revealed that pretreated P. aeruginosa cells had enhanced NO-scavenging activity, and this effect was associated with the production of the flavohemoglobin Fhp. Further, quantitative real-time reverse transcription-PCR (qRT-PCR) analysis showed that fhp expression increased by over 100-fold in NO-pretreated biofilms compared to untreated biofilms. Biofilms of mutant strains harboring mutations in fhp or fhpR, encoding a NO-responsive regulator of fhp, were not affected in their dispersal response after the initial pretreatment with NO. Overall, these results suggest that FhpR can sense NO to trigger production of the flavohemoglobin Fhp and inhibit subsequent dispersal responses to NO. Finally, the addition of imidazole, which can inhibit the NO dioxygenase activity of flavohemoglobin, attenuated the prevention of dispersal after NO pretreatment and improved the dispersal response in older, starved biofilms. This study clarifies the underlying mechanisms of impaired dispersal induced by repeated NO treatments and offers a new perspective for improving the use of NO in biofilm control strategies.

Assessment of androgen receptor agonistic/antagonistic effects on 25 chemicals in household applicants by OECD in vitro stably transfected transcriptional activation assays.

The aim of this study is to assess the androgen receptor (AR) agonistic/antagonistic effects on various chemicals, which are used in household products including cleaning agents and wetted tissues by in vitro OECD test guideline No. 458 (using AR-EcoScreen™ cell line) and the me-too test method (using 22Rv1cell line), which was adopted as OECD project No. 4.99. All chemicals were not determined as AR agonists. However α-dodecyl-ω-hydroxypoly (oxyethylene) and 3-iodo-2-propynyl butylcarbamate have shown a weak AR antagonistic effects with IC50 values of 2.18 ±â€¯0.12 and 4.26 ±â€¯0.17 µg/ml via binding affinity to AR in only 22Rv1/mouse mammary tumor virus using AR transcriptional activation assay, because of their different cytotoxicity on each applied cell line. This report firstly provides information about agonistic/antagonistic effects against human AR of various chemicals including surfactants and biocides by OECD in vitro stably transfected transcriptional activation assays. However, further in vivo and human model studies are needed to confirm their adverse effects.

Vaccination history in elementary school children enrolled in the varicella epidemic investigations held in Jeju-si, Korea in the first half of 2017.

OBJECTIVES: The reported incidence rate of varicella infection in Jeju-do is higher compared with the national average. This study aimed to examine varicella vaccination history and evaluate clinical manifestation of varicella cases in Jeju-do. METHODS: Based on the guideline suggested by the Korea Centers for Disease Control and Prevention (KCDC), two epidemic investigations for varicella infection were conducted in the first half of 2017. The history of varicella vaccination was confirmed using the Integrated Control System for Diseases and Health operated by the KCDC. RESULTS: Out of a total of 60 elementary school children as the study subjects, all had been previously vaccinated against varicella. Twenty cases (33%) showed mild clinical manifestations and no complications. CONCLUSIONS: As the government of Jeju-do has supplied a single-labeled vaccine since 2011, there is a need to evaluate the type of vaccination failure such as primary or secondary.

Comparison of the effects and distribution of zinc oxide nanoparticles and zinc ions in activated sludge reactors.

Zinc Oxide nanoparticles (ZnO NPs) are being increasingly applied in the industry, which results inevitably in the release of these materials into the hydrosphere. In this study, simulated waste-activated sludge experiments were conducted to investigate the effects of Zinc Oxide NPs and to compare it with its ionic counterpart (as ZnSO4). It was found that even 1 mg/L of ZnO NPs could have a small impact on COD and ammonia removal. Under 1, 10 and 50 mg/L of ZnO NP exposure, the Chemical Oxygen Demand (COD) removal efficiencies decreased from 79.8% to 78.9%, 72.7% and 65.7%, respectively. The corresponding ammonium (NH4+ N) concentration in the effluent significantly (P < 0.05) increased from 11.9 mg/L (control) to 15.3, 20.9 and 28.5 mg/L, respectively. Under equal Zn concentration, zinc ions were more toxic towards microorganisms compared to ZnO NPs. Under 50 mg/L exposure, the effluent Zn level was 5.69 mg/L, implying that ZnO NPs have a strong affinity for activated sludge. The capacity for adsorption of ZnO NPs onto activated sludge was found to be 2.3, 6.3, and 13.9 mg/g MLSS at influent ZnO NP concentrations of 1.0, 10 and 50 mg/L respectively, which were 1.74-, 2.13- and 2.05-fold more than under Zn ion exposure.

Comparison and distribution of copper oxide nanoparticles and copper ions in activated sludge reactors.

Copper oxide nanoparticles (CuO NPs) are being increasingly applied in the industry which results inevitably in the release of these materials into the hydrosphere. In this study, simulated waste-activated sludge experiments were conducted to investigate the effects of Copper Oxide NPs at concentrations of 0.1, 1, 10 and 50 mg/L and to compare it with its ionic counterpart (CuSO4). It was found that 0.1 mg/L of CuO NPs had negligible effects on Chemical Oxygen Demand (COD) and ammonia removal. However, the presence of 1, 10 and 50 mg/L of CuO NPs decreased COD removal from 78.7% to 77%, 52.1% and 39.2%, respectively (P < 0.05). The corresponding effluent ammonium (NH4-N) concentration increased from 14.9 mg/L to 18, 25.1 and 30.8 mg/L, respectively. Under equal Cu concentration, copper ions were more toxic towards microorganisms compared to CuO NPs. CuO NPs were removed effectively (72-93.2%) from wastewater due to a greater biosorption capacity of CuO NPs onto activated sludge, compared to the copper ions (55.1-83.4%). The SEM images clearly showed the accumulation and adsorption of CuO NPs onto activated sludge. The decrease in Live/dead ratio after 5 h of exposure of CuO NPs and Cu2+ indicated the loss of cell viability in sludge flocs.

Quorum quenching bacteria can be used to inhibit the biofouling of reverse osmosis membranes.

Over the last few decades, significant efforts have concentrated on mitigating biofouling in reverse osmosis (RO) systems, with a focus on non-toxic and sustainable strategies. Here, we explored the potential of applying quorum quenching (QQ) bacteria to control biofouling in a laboratory-scale RO system. For these experiments, Pantoea stewartii was used as a model biofilm forming organism because it was previously shown to be a relevant wastewater isolate that also forms biofilms in a quorum sensing (QS) dependent fashion. A recombinant Escherichia coli strain, which can produce a QQ enzyme, was first tested in batch biofilm assays and significantly reduced biofilm formation by P. stewartii. Subsequently, RO membranes were fouled with P. stewartii and the QQ bacterium was introduced into the RO system using two different strategies, direct injection and immobilization within a cartridge microfilter. When the QQ bacterial cells were directly injected into the system, N-acylhomoserine lactone signals were degraded, resulting in the reduction of biofouling. Similarly, the QQ bacteria controlled biofouling when immobilized within a microfilter placed downstream of the RO module to remove QS signals circulating in the system. These results demonstrate the proof-of-principle that QQ can be applied to control biofouling of RO membranes and may be applicable for use in full-scale plants.

Fungal Quorum Quenching: A Paradigm Shift for Energy Savings in Membrane Bioreactor (MBR) for Wastewater Treatment.

In the last 30 years, the use of membrane bioreactors (MBRs) for advanced wastewater treatment and reuse have been expanded continuously, but they still suffer from excessive energy consumption resulting from the intrinsic problem of membrane biofouling. One of the major causes of biofouling in MBRs is bacterial quorum sensing (QS) via N-acylhomoserine lactones (AHLs) and/or autoinducer-2 (AI-2), enabling intra- and interspecies communications, respectively. In this study, we demonstrate that farnesol can substantially mitigate membrane biofouling in a MBR due to its quorum quenching (QQ) activity. When Candida albicans (a farnesol producing fungus) entrapping polymer beads (AEBs) were placed in the MBR, the rate of transmembrane pressure (TMP) rise-up was substantially decreased, even for lower aeration intensities. This finding corresponds to a specific aeration energy savings of approximately 40% (25% through the physical washing effect and a further 15% through the biological QQ effect of AEBs) compared to conventional MBRs without AEBs. A real-time RT-qPCR analysis revealed that farnesol secreted from C. albicans mitigated the biofilm formation in MBRs via the suppression of AI-2 QS. Successful control of biofouling and energy savings through fungal-to-bacterial QQ could be expanded to the plant scale for MBRs in wastewater treatment with economic feasibility.

Effect of the Shape and Size of Quorum-Quenching Media on Biofouling Control in Membrane Bioreactors for Wastewater Treatment.

Recently, spherical beads entrapping quorum quenching (QQ) bacteria have been reported as effective moving QQ-media for biofouling control in MBRs for wastewater treatment owing to their combined effects of biological (i.e., quorum quenching) and physical washing. Taking into account both the mass transfer of signal molecules through the QQ-medium and collision efficiencies of the QQ-medium against the filtration membranes in a bioreactor, a cylindrical medium (QQ-cylinder) was developed as a new shape of moving QQ-medium. The QQ-cylinders were compared with previous QQ-beads in terms of the QQ activity and the physical washing effect under identical loading volumes of each medium in batch tests. It was found that the QQ activity of a QQ-medium was highly dependent on its specific surface area, regardless of the shape of the medium. In contrast, the physical washing effect of a QQ-medium was greatly affected by its geometric structure. The enhanced anti-biofouling property of the QQ-cylinders relative to QQ-beads was confirmed in a continuous laboratory-scale MBR with a flat-sheet membrane module.

Effects of Quorum Quenching on the Microbial Community of Biofilm in an Anoxic/Oxic MBR for Wastewater Treatment.

Recently, bacterial quorum quenching (QQ) has been proven to have potential as an innovative approach for biofouling control in membrane bioreactors (MBRs) for advanced wastewater treatment. Although information regarding the microbial community is crucial for the development of QQ strategies, little information exists on the microbial ecology in QQ-MBRs. In this study, the microbial communities of biofilm were investigated in relation to the effect of QQ on anoxic/oxic MBRs. Two laboratory-scale MBRs were operated with and without QQ-beads (QQ-bacteria entrapped in beads). The transmembrane pressure increase in the QQ-MBRs was delayed by approximately 100-110% compared with conventional- and vacant-MBRs (beads without QQ-bacteria) at 45 kPa. In terms of the microbial community, QQ gradually favored the development of a diverse and even community. QQ had an effect on both the bacterial composition and change rate of the bacterial composition. Proteobacteria and Bacteroidetes were the most dominant phyla in the biofilm, and the average relative composition of Proteobacteria was low in the QQ-MBR. Thiothrix sp. was the dominant bacterium in the biofilm. The relative composition of Thiothrix sp. was low in the QQ-MBR. These findings provide useful information that can inform the development of a new QQ strategy.

More Efficient Media Design for Enhanced Biofouling Control in a Membrane Bioreactor: Quorum Quenching Bacteria Entrapping Hollow Cylinder.

Recently, membrane bioreactors (MBRs) with quorum quenching (QQ) bacteria entrapping beads have been reported as a new paradigm in biofouling control because, unlike conventional post-biofilm control methods, bacterial QQ can inhibit biofilm formation through its combined effects of physical scouring of the membrane and inhibition of quorum sensing (QS). In this study, using a special reporter strain (Escherichia coli JB525), the interaction between QS signal molecules and quorum quenching bacteria entrapping beads (QQ-beads) was elucidated through visualization of the QS signal molecules within a QQ-bead using a fluorescence microscope. As a result, under the conditions considered in this study, the surface area of QQ-media was likely to be a dominant parameter in enhancing QQ activity over total mass of entrapped QQ bacteria because QQ bacteria located near the core of a QQ-bead were unable to display their QQ activities. On the basis of this information, a more efficient QQ-medium, a QQ hollow cylinder (QQ-HC), was designed and prepared. In batch experiments, QQ-HCs showed greater QQ activity than QQ-beads as a result of their higher surface area and enhanced physical washing effect because of their larger impact area against the membrane surface. Furthermore, it was shown that such advantages of QQ-HCs resulted in more effective mitigation of membrane fouling than from QQ-beads in lab-scale continuous MBRs.