Quorum Quenching in Membrane Bioreactors for Fouling Retardation: Complexity Provides Opportunities.

The occurrence of biofouling restricts the widespread application of membrane bioreactors (MBRs) in wastewater treatment. Regulation of quorum sensing (QS) is a promising approach to control biofouling in MBRs, yet the underlying mechanisms are complex and remain to be illustrated. A fundamental understanding of the relationship between QS and membrane biofouling in MBRs is lacking, which hampers the development and application of quorum quenching (QQ) techniques in MBRs (QQMBRs). While many QQ microorganisms have been isolated thus far, critical criteria for selecting desirable QQ microorganisms are still missing. Furthermore, there are inconsistent results regarding the QQ lifecycle and the effects of QQ on the physicochemical characteristics and microbial communities of the mixed liquor and biofouling assemblages in QQMBRs, which might result in unreliable and inefficient QQ applications. This review aims to comprehensively summarize timely QQ research and highlight the important yet often ignored perspectives of QQ for biofouling control in MBRs. We consider what this "information" can and cannot tell us and explore its values in addressing specific and important questions in QQMBRs. Herein, we first examine current analytical methods of QS signals and discuss the critical roles of QS in fouling-forming microorganisms in MBRs, which are the cornerstones for the development of QQ technologies. To achieve targeting QQ strategies in MBRs, we propose the substrate specificity and degradation capability of isolated QQ microorganisms and the surface area and pore structures of QQ media as the critical criteria to select desirable functional microbes and media, respectively. To validate the biofouling retardation efficiency, we further specify the QQ effects on the physicochemical properties, microbial community composition, and succession of mixed liquor and biofouling assemblages in MBRs. Finally, we provide scale-up considerations of QQMBRs in terms of the debated QQ lifecycle, practical synergistic strategies, and the potential cost savings of MBRs. This review presents the limitations of classic QS/QQ hypotheses in MBRs, advances the understanding of the role of QS/QQ in biofouling development/retardation in MBRs, and builds a bridge between the fundamental understandings and practical applications of QQ technology.

Integrating artificial intelligence modeling and membrane technologies for advanced wastewater treatment: Research progress and future perspectives.

Membrane technologies have become proficient alternatives for advanced wastewater treatment, ensuring high contaminant removal and sustainable resource recovery. Despite significant progress, ongoing research efforts aim to further optimize treatment performance. Among the challenges faced, membrane fouling persists as a relevant obstacle in membrane technologies, necessitating the development of more effective mitigation strategies. Mathematical models, widely employed for predicting treatment performance, generally exhibit low accuracy and suffer from uncertainties due to the complex and variable nature of wastewater. To overcome these limitations, numerous studies have proposed artificial intelligence (AI) modeling to accurately predict membrane technologies' performance and fouling mechanisms. This approach aims to provide advanced simulations and predictions, thereby enhancing process control, optimization, and intensification. This literature review explores recent advancements in modeling membrane-based wastewater treatment processes through AI models. The analysis highlights the enormous potential of this research field in enhancing the efficiency of membrane technologies. The role of AI modeling in defining optimal operating conditions, developing effective strategies for membrane fouling mitigation, enhancing the performance of novel membrane-based technologies, and improving membrane fabrication techniques is discussed. These enhanced process optimization and control strategies driven by AI modeling ensure improved effluent quality, optimized resource consumption, and minimized operating costs. The potential contribution of this cutting-edge approach to a paradigm shift toward sustainable wastewater treatment is examined. Finally, this review outlines future perspectives, emphasizing the research challenges that require attention to overcome the current limitations hindering the integration of AI modeling in wastewater treatment plants.

Micro(nano)plastics from synthetic oligomers persisting in Mediterranean seawater: Comprehensive NMR analysis, concerns and origins.

The presence in seawater of low-molecular-weight polyethylene (PE) and polydimethylsiloxane (PDMS), synthetic polymers with high chemical resistance, has been demonstrated in this study for the first time by developing a novel methodology for their recovery and quantification from surface seawater. These synthetic polymer debris (SPD) with very low molecular weights and sizes in the nano- and micro-metre range have escaped conventional analytical methods. SPD have been easily recovered from water samples (2 L) through filtration with a nitrocellulose membrane filter with a pore size of 0.45 µm. Dissolving the filter in acetone allowed the isolation of the particulates by centrifugation followed by drying. The isolated SPD were analysed by 1H nuclear magnetic resonance spectroscopy (1H NMR), identifying PE and PDMS. These polymers are thus persisting on seawater because of their low density and the ponderal concentrations were quantified in mg/m3. This method was used in an actual case study in which 120 surface seawater samples were collected during two sampling campaigns in the Mediterranean Sea (from the Gulf of Salerno to the Gulf of Policastro in South Italy). The developed analytical protocol allowed achieving unprecedented simplicity, rapidity and sensitivity. The 1H and 13C NMR structural analysis of the PE debris indicates the presence of oxidised polymer chains with very low molecular weights. Additionally, the origin of those low molecular weight polymers was investigated by analysing influents and effluents from a wastewater treatment plant (WWTP) in Salerno as a hot spot for the release of SPD: the analysis indicates the presence of low molecular weight polymers compatible with wax-PE, widely used for coating applications, food industry, cosmetics and detergents. Moreover, the origin of PDMS debris found in surface seawater can be ascribed to silicone-based antifoamers and emulsifiers.

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.

Electro living membrane bioreactor for highly efficient wastewater treatment and fouling mitigation: Influence of current density on process performances.

The next generation of the self-forming dynamic membrane, referred to in this study as the "Living Membrane (LM)", is a new patented technology based on an encapsulated biological layer that self-forms on a designed coarse-pore size support material during wastewater treatment and acts as a natural membrane filter. Integrating electrochemical processes with wastewater treatment using the LM approach has also been recently studied (the reactor is referred to as the Electro-Living Membrane Bioreactor or e-LMBR). This study investigated the effects of varying current densities, i.e., 0.3, 0.5, and 0.9 mA/cm2, on the performance of an e-LMBR. The results were also compared with those of the Living Membrane Bioreactor or LMBR (without applied current density). Higher pollutant removals were observed in the presence of the electric field. However, the effect of varying applied current densities on the COD (98-99 %), NH3-N (97-99 %), and PO43-P (100 %) removals was not statistically significant. The more prominent differences (p < 0.05) were observed in the decrease of NO3--N concentrations from mixed liquor to effluent, with increasing current density resulting in lower mean NO3--N effluent concentrations (0.3 mA/cm2: 6.13 mg/L; 0.5 mA/cm2: 4.38 mg/L; 0.9 mA/cm2: 3.70 mg/L). The reduction of NO3--N concentrations as wastewater permeated through the LM layer also confirmed its role in removing nitrogen-containing compounds. Higher current densities resulted in lower concentrations of fouling substances, particularly those of microbial extracellular polymeric substances (EPS) and transparent exopolymer particles (TEPs). The average values of the temporal variation of transmembrane pressure (d(TMP)/d(t)) in the e-LMBR were extremely low, in the range of 0.013-0.041 kPa/day, throughout the operation period. The highest (d(TMP)/d(t)) was observed for the highest current density. However, the TMP values remained below 2 kPa in all the e-LMBR runs even after the initial LM formation stage.

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.

Does quorum quenching matter to microbial community dynamics in long-term membrane bioreactor operation?

Quorum quenching (QQ) has effectively prevented biofouling in membrane bioreactors (MBRs) employing isolated QQ bacterial strains. However, the influence of QQ on the microbial population still needs to be fully understood. This research aims to analyze the microbial population in MBRs over an extended period (>250 days) under different conditions, such as varying aeration intensities and doses of QQ bacteria, QQ media, and types of feed. Results show that no significant changes occurred in the structure and diversity of the microbial community in the mixed liquor and biofilm due to QQ treatment. Canonical correspondence analysis did reveal that the microbial communities were strongly influenced by feed types and phases. The microbial community composition varied between bacterial habitats (i.e., mixed liquor and biofilm), showing the two dominant phyla Proteobacteria and Bacteroidota in the former and Proteobacteria and Chloroflexi in the latter. The co-occurrence network analysis indicated that the biofilm (with 163 edges) in the MBR fed with real wastewater exhibited a more intricate network than the biofilm (with 53 edges) in the MBR fed with synthetic wastewater. With QQ, the biofilm exhibited more positive edges than negative ones. The phylogenetic investigation of communities showed that QQ barely affects functional gene-related quorum sensing (e.g., bacterial chemotaxis, motility proteins, and secretion) in mixed liquor but in biofilms at relatively large QQ doses (> 75 mg/L BH4). This research sheds light on the bacterial QQ's role in reducing MBR biofouling and provides crucial insights into its underlying mechanisms.

The relationship between quorum sensing dynamics and biological performances during anaerobic membrane bioreactor treatment.

Anaerobic membrane bioreactors (AnMBRs) enhance carbon neutrality with biomethane recovery from wastewater; however, microbial signaling, which may affect biological performances, was poorly understood. Here, we thus evaluate quorum sensing (QS) dynamics while monitoring acyl-homoserine lactones (AHLs) and autoinducer-2 (AI-2) levels during long-term AnMBR operations after sludge inoculation. Significant organic removal and methane production were achieved with the reactor startup. Signal molecule levels varied with transient organic loading rates, depending on their types. A starving condition may cause an increase in short- and medium-chain AHLs and AI-2. Biopolymers, biosolids, volatile fatty acids, and alkalinity levels had positive correlations with short- and medium-chain AHLs and AI-2, whereas methane production had positive correlations with long-chain AHLs. The principal component analysis of QS signal composition and biological performance data explains their interconnectivity. The findings of this study help to understand that QS signals regulate metabolic pathways in addition to microbial group behaviors.

Layered Antibiofouling Composite Membrane for Quenching Bacterial Signaling.

Bacterial quorum quenching (QQ) media with various structures (e.g., bead, cylinder, hollow cylinder, and sheet), which impart biofouling mitigation in membrane bioreactors (MBRs), have been reported. However, there has been a continuous demand for membranes with QQ capability. Thus, herein, we report a novel double-layered membrane comprising an outer layer containing a QQ bacterium (BH4 strain) on the polysulfone hollow fiber membrane. The double-layered composite membrane significantly inhibits biofilm formation (i.e., the biofilm density decreases by ~58%), biopolymer accumulation (e.g., polysaccharide), and signal molecule concentration (which decreases by ~38%) on the membrane surface. The transmembrane pressure buildup to 50 kPa of the BH4-embedded membrane (17.8 h ± 1.1) is delayed by more than thrice (p < 0.05) of the control with no BH4 in the membrane's outer layer (5.5 h ± 0.8). This finding provides new insight into fabricating antibiofouling membranes with a self-regulating property against biofilm growth.

Photolytic quorum quenching effects on the microbial communities and functional gene expressions in membrane bioreactors.

Photolytic quorum quenching by ultraviolet A (UVA) irradiation is an effective strategy for controlling membrane bioreactor (MBR) biofouling; however, its effects on MBR microbial communities and functional genes have not yet been explored. Here, we report on the effects of the UVA irradiation, which mitigates membrane biofouling, on the microbial community structures, alpha and beta diversities, and functional gene expressions in the MBR mixed liquor and biocake (membrane fouling layer) for the first time. The results show that the microbial communities become less diversified when alternating UVA is applied to the MBRs. The changes in the community structure are highly influenced by spatiotemporal factors, such as microbial habitats (mixed liquor and biocake) and reactor operation time, although UVA irradiation also has some impacts on the community. The relative abundance of the Sphingomonadaceae family, which can decompose the furan ring of autoinducer-2 (AI-2) signal molecules, becomes greater with continuous UVA irradiation. Xanthomonadaceae, which produces biofilm-degrading enzymes, is also more abundant with UVA photolysis than without it. Copies of monooxygenase and hydroxylase enzyme-related genes increase in the MBR with longer UVA exposures (i.e., continuous UVA). These enzymes seem to be inducible by UVA, enhancing the AI-2 inactivation. In conclusion, UVA irradiation alters the microbial community and the metabolism in the MBR, contributing to the membrane biofouling mitigation.

Wastewater treatment and fouling control in an electro algae-activated sludge membrane bioreactor.

The effect of addition of algae to activated sludge as active biomass in membrane bioreactors (MBRs) and electro-MBRs (e-MBRs) for wastewater remediation was examined in this study. The performances of Algae-Activated Sludge Membrane Bioreactor (AAS-MBR) and electro Algae-Activated Sludge Membrane Bioreactor (e-AAS-MBR) were compared to those observed in conventional MBR and e-MBR, which were previously reported and utilized activated sludge as biomass. The effect of application of electric field was also examined by the comparison of performances of e-AAS-MBR and AAS-MBR. Similar chemical oxygen demand (COD) reduction efficiencies of AAS-MBR, e-AAS-MBR, MBR, and e-MBR (98.35 ± 0.35%, 99.12 ± 0.08%, 97.70 ± 1.10%, and 98.10 ± 1.70%, respectively) were observed. The effect of the algae-activated sludge system was significantly higher in the nutrient removals. Ammoniacal nitrogen (NH3-N) removal efficiencies of AAS-MBR and e-AAS-MBR were higher by 43.89% and 26.61% than in the conventional MBR and e-MBR, respectively. Phosphate phosphorous (PO43--P) removals were also higher in AAS-MBR and e-AAS-MBR by 6.43% and 2.66% than those in conventional MBR and e-MBR. Membrane fouling rates in AAS-MBR and e-AAS-MBR were lower by 57.30% and 61.95% than in MBR and e-MBR, respectively. Lower concentrations of fouling substances were also observed in the reactors containing algae-activated sludge biomass. Results revealed that addition of algae improved nutrient removal and membrane fouling mitigation. The study also highlighted that the application of electric field in the e-AAS-MBR enhanced organic contaminants and nutrients removal, and fouling rate reduction.

Nitrosamine removal: Pilot-scale comparison of advanced oxidation, nanofiltration, and biological activated carbon processes.

Removal of nitrosamines from water intended for consumption is an important topic due to the carcinogenic risks they pose to human health. In this study, we measure and compare nitrosamine removal by four individuals and three combinations of water treatments applied in situ as a pilot study and in the laboratory. Of the two advanced oxidation processes tested, UV irradiation at a wavelength of 254 nm was more effective in nitrosamine removal than ozonation; however, the efficacy of UV photolysis required a high dose (>635 mJ/cm2) for sufficient (>90%) removal of the contaminants. The biological activated carbon (BAC) process was also effective at removing nitrosamines, most of which were adsorbed onto the carbon. A small fraction (<10%) of nitrosamines were removed through biodegradation. Nanofiltration membranes were limited in removing nitrosamines, particularly N-nitrosodimethylamine, which is hydrophilic. Employing either UV or BAC treatments can warrant a high degree of elimination of nitrosamines; however, desorption of nitrosamines from BAC can occur due to variations in the quality of source water and the types of carbon filters used. Combined treatments using both UV and BAC processes offer promising alternative strategies for removing nitrosamines when treating water for human consumption.

Coronavirus in water media: Analysis, fate, disinfection and epidemiological applications.

Considerable attention has been recently given to possible transmission of SARS-CoV-2 via water media. This review addresses this issue and examines the fate of coronaviruses (CoVs) in water systems, with particular attention to the recently available information on the novel SARS-CoV-2. The methods for the determination of viable virus particles and quantification of CoVs and, in particular, of SARS-CoV-2 in water and wastewater are discussed with particular regard to the methods of concentration and to the emerging methods of detection. The analysis of the environmental stability of CoVs, with particular regard of SARS-CoV-2, and the efficacy of the disinfection methods are extensively reviewed as well. This information provides a broad view of the state-of-the-art for researchers involved in the investigation of CoVs in aquatic systems, and poses the basis for further analyses and discussions on the risk associated to the presence of SARS-CoV-2 in water media. The examined data indicates that detection of the virus in wastewater and natural water bodies provides a potentially powerful tool for quantitative microbiological risk assessment (QMRA) and for wastewater-based epidemiology (WBE) for the evaluation of the level of circulation of the virus in a population. Assays of the viable virions in water media provide information on the integrity, capability of replication (in suitable host species) and on the potential infectivity. Challenges and critical issues relevant to the detection of coronaviruses in different water matrixes with both direct and surrogate methods as well as in the implementation of epidemiological tools are presented and critically discussed.

Indoor versus outdoor transmission of SARS-COV-2: environmental factors in virus spread and underestimated sources of risk.

The first case of Coronavirus Disease 2019 (COVID-19), which is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), in Europe was officially confirmed in February 2020. On 11 March 2020, after thousands of deaths from this disease had been reported worldwide, the WHO changed their classification of COVID-19 from a public health emergency of international concern to a pandemic. The SARS-CoV-2 virus has been shown to be much more resistant to environmental degradation than other coated viruses. Several studies have shown that environmental conditions can influence its viability and infectivity. This review summarizes current knowledge on the transmission pathways of the novel coronavirus, and directs attention towards potentially underestimated factors that affect its propagation, notably indoor spread and outdoor risk sources. The contributions of significant indoor factors such as ventilation systems to the spread of this virus need to be carefully ascertained. Outdoor risk sources such as aerosolized particles emitted during wastewater treatment and particulate matter (PM), both of which may act as virus carriers, should be examined as well. This study shows the influence of certain underestimated factors on the environmental behavior and survival of the SARS-CoV-2 virus. These aspects of coronavirus propagation need to be accounted for when devising actions to limit not only the current pandemic but also future outbreaks.

Optimizing RuOx-TiO2 composite anodes for enhanced durability in electrochemical water treatments.

Metal oxide anode electrocatalysts are important for an effective removal of contaminants and the enhancement of electrode durability in the electrochemical oxidation process. Herein, we report the enhanced lifetime of RuOx-TiO2 composite anodes that was achieved by optimizing the fabrication conditions (e.g., the Ru mole fraction, total metal content, and calcination time). The electrode durability was assessed through accelerated service lifetime tests conducted under harsh environmental conditions, by using 3.4% NaCl and 1.0 A/cm2. The electrochemical characteristics of the anodes prepared with metal oxides having different compositions were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray analyses. We noticed that, the larger the Ru mole fraction, the more durable were the electrodes. The RuOx-TiO2 electrodes were found to be highly stable when the Ru mole fraction was >0.7. The 0.8RuOx-0.2TiO2 electrode was selected as the one with the most appropriate composition, considering both its stability and contaminant treatability. The electrodes that underwent a 7-h calcination (between 1 and 10 h) showed the longest lifetime under the tested conditions, because of the formation of a stable Ru oxide structure (i.e., RuO3) and a lower resistance to charge transfer. The electrode deactivation mechanism that occurred due to the dissolution of active catalysts over time was evidenced by an impedance analysis of the electrode itself and surface elemental mapping.

Efficient Cu removal from CuEDTA complex-containing wastewater using electrochemically controlled sacrificial iron anode.

In this study, an electro-replacement/precipitation/deposition/direct reduction (ERPDD) process with scrap iron packed in a Ti mesh cage as a sacrificial anode was investigated for the treatment of wastewater containing CuEDTA complexes. The ERPDD mechanisms were responsible for the removal of Cu from CuEDTA complexes and were verified by a series of experiments using either iron or carbon plates as anodes for the Cu-containing solutions with and without EDTA. A complete Cu removal was achieved with electrical current density applied (1.18-2.36 mA/cm2), whereas only 60% of the Cu was removed without electricity. Dissolved oxygen (DO) was found to have a significant impact on Cu removal. Aeration reduced Cu removal (i.e., only 60% of the Cu was removed), whereas complete Cu removal was achieved with negligible DO concentration under mechanical mixing and N2 purging conditions. Compared to chemical replacement/precipitation (CRP) process, the ERPDD was able to save approximately 60-75% of the total operational costs during the treatment of CuEDTA-containing wastewater, due to the electrochemically controlled dosing of inexpensive sacrificial scrap iron and additional removal mechanisms not found in the CRP process.

Preparation of a mesoporous silica quorum quenching medium for wastewater treatment using a membrane bioreactor.

Various quorum quenching (QQ) media have been developed to mitigate membrane biofouling in a membrane bioreactor (MBR). However, most are expensive, unstable and easily trapped in hollow fibre membranes. Here, a sol-gel method was used to develop a mesoporous silica medium entrapping a QQ bacterial strain (Rhodococcus sp. BH4). The new silica QQ medium was able to remove quorum sensing signalling molecules via both adsorption (owing to their mesoporous hydrophobic structure) and decomposition with an enzyme (lactonase), preventing MBR biofouling without affecting the water quality. It also demonstrated a relatively long life span due to its non-biodegradability and its relatively small particle size (<1.0 mm), which makes it less likely to clog in a hollow fibre membrane module.

Isolation and characterization of novel indigenous facultative quorum quenching bacterial strains for ambidextrous biofouling control.

Quorum quenching (QQ), the disruption of microbial communication, has proven to be effective as an innovative anti-biofouling strategy for membrane bioreactors (MBRs). However, QQ bacteria for anaerobic environments have not been extensively analyzed in previous research. This study thus investigated facultative QQ bacterial strains that exhibit potential for use in aerobic and anaerobic MBRs. Two novel QQ strains from the genus Pseudomonas (KS2 and KS10) were isolated from anaerobic digester sludge using signal molecules as the sole carbon source. The two QQ strains exhibited significant signal molecule degradation depending on the oxygen levels and demonstrated endogenous QQ activity, with KS2 producing lactonase and KS10 producing acylase. The QQ strains significantly reduced the formation of the biofilm generated by both Pseudomonas aeruginosa (PAO1) and real sludge. Facultative QQ strains have the potential to offer a more flexible option for effective biofouling control in both aerobic and anaerobic MBRs.

Quorum sensing: an emerging link between temperature and membrane biofouling in membrane bioreactors.

Lab-scale membrane bioreactors (MBRs) were investigated at 12, 18, and 25 °C to identify the correlation between quorum sensing (QS) and biofouling at different temperatures. The lower the reactor temperature, the more severe the membrane biofouling measured in terms of the transmembrane pressure (TMP) during filtration. More extracellular polymeric substances (EPSs) that cause biofouling were produced at 18 °C than at 25 °C, particularly polysaccharides, closely associated with QS via the production of N-acyl homoserine lactone (AHL). However, at 12 °C, AHL production decreased, but the release of EPSs due to deflocculation increased the soluble EPS concentration. To confirm the temperature effect related to QS, bacteria producing AHL were isolated from MBR sludge and identified as Aeromonas sp., Leclercia sp., and Enterobacter sp. through a 16S rDNA sequencing analysis. Batch assays at 18 and 25 °C showed that there was a positive correlation between QS through AHL and biofilm formation in that temperature range.

Cryolite (Na3AlF6) crystallization for fluoride recovery using an electrolytic process equipped with a sacrificial aluminum anode.

An electro-crystallization process equipped with a sacrificial aluminum anode was operated under an optimum condition to promote the formation of crystalline cryolite for the recovery of fluoride from synthetic F-containing wastewater. The effects of pH, Al/F molar ratio, initial F concentration, and electrolytes were investigated experimentally, and the results were compared with data obtained from chemical equilibrium modeling. Cryolite was successfully produced under optimum pH values of 5 to 6 and Al/F molar ratios of less than 1/6. The F removal increased with increasing Al/F molar ratio until reaching the molar ratio of 1/6 and decreased thereafter due to the formation of AlFn3-n species. The adsorption of AlFn3-n by Al(OH)3 precipitates contributed part of F removal. The removal efficiency reached 100% when the initial fluoride concentration was high while it was around 90% with the low initial fluoride concentration. XRD and SEM/EDX analysis showed that the obtained solids matched well to the commercial cryolite. Finally, the operating costs of chemical-crystallization (the process with Al ions added chemically) and electro-crystallization were compared, and the cost of the former was less than the latter. Energy consumption was the main contributor to the operating cost of the electro-crystallization process.