ABSTRACT
In recent years, organophosphorus flame retardants (OPFRs) have been widely used as substitutes for brominated flame retardants with excellent properties, and their initial toxicological effects on the water ecosystem and human health have gradually emerged. However, to date, research on the cytotoxicity and health risks of OPFRs is still limited. Therefore, this study aims to systematically explore the cytotoxic effects and toxic mechanisms of OPFRs on cells. Human liver cancer (HepG2) cells were adopted as an ideal model for toxicity evaluation due to their rapid growth and metabolism. This study proposes a sensitive electrochemical cell-based sensor constructed on a graphitized multi-walled carbon nanotube/ionic liquid/gold nanoparticle-modified electrode. The sensor was used to detect the cytotoxicity of tri(2-butylxyethyl) phosphate (TBEP), tributyl phosphate (TnBP), triphenyl phosphate (TPhP), tri(1,3-dichloro-2-propyl) phosphate (TDCIPP), tri(2-chloropropyl) phosphate (TCPP) and tri(2-chloroethyl) phosphate (TCEP) in the liquid medium, providing insight into their toxicity in water environments. The half-maximal inhibitory concentration (IC50) of TBEP, TnBP, TPhP, TDCIPP, TCPP and TCEP on HepG2 cells were 179.4, 194.9, 219.8, 339.4, 511.8 and 859.0 µM, respectively. Additionally, the cytotoxic mechanism of six OPFRs was discussed from the perspective of oxidative stress and apoptosis, and four indexes were correlated with toxicity. Furthermore, transcriptome sequencing was conducted, followed by a thorough analysis of the obtained sequencing results. This analysis demonstrated a significant enrichment of the p53 and PPAR pathways, both of which are closely associated with oxidative stress and apoptosis. This study presents a simplified and efficient technique for conducting in vitro toxicity studies on organophosphorus flame retardants in a water environment. Moreover, it establishes a scientific foundation for further investigation into the mechanisms of cytotoxicity associated with these compounds.
ABSTRACT
Membrane fouling has always been a critical constraint in the operation of the reverse osmosis (RO) process, and chemical cleaning is essential for mitigating membrane fouling and ensuring smooth operation of the membrane system. This paper presents an optimized chemical cleaning method for the efficient cleaning of RO membranes in full-scale applications. Compared to the regular cleaning method (cleaning with 0.1 % NaOH + 1 % ethylenediaminetetraacetic acid + 0.025 % sodium dodecyl benzene sulfonate followed by 0.2 % HCl), the optimized cleaning method improves the cleaning efficiency by adding sodium chloride to the alkaline cleaning solution and citric acid to the acid cleaning solution. Notably, the membrane flux recovery rate with the optimized cleaning method is 45.74 %, and it improves the cleaning efficiency by 1.65 times compared to the regular cleaning method. Additionally, the optimized cleaning method removes 30.46 % of total foulants (organic and inorganic), which is 2.11 times higher than the regular cleaning method. The removal of inorganic ions such as Fe, Ca, and Mg is significantly improved with the optimized cleaning method. For organic matter removal, the optimized cleaning method effectively removes more polysaccharides, proteins, and microbial metabolites by disrupting the complex structures of organic matter. Furthermore, it also changes the microbial community structure on the RO membrane surface by eliminating microorganisms that cannot withstand strong acids, bases, and high salt environments. However, Mycobacterium can adapt to these harsh conditions, showing a relative abundance of up to 84.13 % after cleaning. Overall, our results provide a new chemical cleaning method for RO membranes in full-scale applications. This method effectively removes membrane foulants and enhances the understanding of the removal characteristics of foulants on RO membrane surfaces by chemical cleaning.
Subject(s)
Membranes, Artificial , Osmosis , Wastewater , Water Purification , Wastewater/chemistry , Water Purification/methods , Waste Disposal, Fluid/methodsABSTRACT
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.
ABSTRACT
The release of nanoplastics (NPs) into the environment is growing due to the extensive use of plastic products. Numerous studies have confirmed the negative effects of NPs on microorganisms, which poses uncertainties concerning their impact on nanofiltration (NF) membrane biofouling. This study investigated the initial cell adhesion process, NF membrane biofouling kinetic processes and bacterial responses of Pseudomonas aeruginosa (P. aeruginosa) exposed to varied NPs concentrations (0-50 mg·L-1). Transcriptome analysis demonstrated that low concentration of NPs (0.1 mg·L-1) promoted bacterial quorum sensing, energy metabolism, exopolysaccharide biosynthesis and bacterial secretion systems. Correspondingly, the polysaccharide content increased remarkably to 2.77 times the unexposed control, which served as a protective barrier for bacteria to avoid the impact of NPs-induced stress. Suppressed homologous recombination, microbial metabolic potentials and flagellar assembly were detected in bacteria exposed to a high concentration (50 mg·L-1) of NPs, mainly due to the triggered reactive oxygen species (ROS) generation, genomic DNA damage, and decreased energy production. Overall, enhanced formation of the extracellular polymeric substances (EPS) and aggravated membrane flux decline were observed when NPs interacted with the membrane surface by cell secretions (low NPs levels) or cell lysis (high NPs levels). These findings shed light on understanding the microbial metabolism mechanism and membrane biofouling propensity with NPs stress at both the molecular and gene levels.
Subject(s)
Biofouling , Microplastics , Membranes, Artificial , Quorum Sensing , Bacteria , BiofilmsABSTRACT
Membrane biofouling is a challenge to be solved for the stable operation of the seawater reverse osmosis (SWRO) membrane. This study explored the regulation mechanism of quorum sensing (QS) inhibition on microbial community composition and population-level behaviors in seawater desalination membrane biofouling. A novel antibiofouling SWRO membrane (MA_m) by incorporating one of quorum sensing inhibitors (QSIs), methyl anthranilate (MA) was prepared. It exhibited enhanced anti-biofouling performance than the exogenous addition of QSIs, showing long-term stability and alleviating 22 % decrease in membrane flux compared with the virgin membrane. The results observed that dominant bacteria Epsilon- and Gamma-proteobacteria (Shewanella, Olleya, Colwellia, and Arcobacter), which are significantly related to (P ≤ 0.01) the metabolic products (i.e., polysaccharides, proteins and eDNA), are reduced by over 80 % on the MA_m membrane. Additionally, the introduction of MA has a more significant impact on the QS signal-sensing pathway through binding to the active site of the transmembrane sensor receptor. It effectively reduces the abundance of genes encoding QS and extracellular polymeric substance (EPS) (exopolysaccharides (i.e., galE and nagB) and amino acids (i.e., ilvE, metH, phhA, and serB)) by up to 50 % and 30 %, respectively, resulting in a reduction of EPS by more than 50 %, thereby limiting the biofilm formation on the QSI-modified membrane. This study provides novel insights into the potential of QSIs to control consortial biofilm formation in practical SWRO applications.
Subject(s)
Biofouling , Microbiota , Water Purification , Quorum Sensing , Biofilms , Extracellular Polymeric Substance Matrix , Osmosis , Seawater/microbiology , Membranes, Artificial , Water Purification/methodsABSTRACT
In this study, two membrane-aerated biofilm reactors (MABRs) were constructed: one solely utilizing biofilm and another hybrid MABR (HMABR) incorporating both suspended-sludge and biofilm to treat low C/N aquaculture wastewater under varying lumen air pressure (LAP). Both HMABR and MABR demonstrated superior nitrogen removal than conventional aeration reactors. Reducing LAP from 10 kPa to 2 kPa could enhance denitrification processes without severely compromising nitrification, resulting in an increase in total inorganic nitrogen (TIN) removal from 50.2±3.1 % to 71.6±1.0 %. The HMABR exhibited better denitrification efficacy than MABR, underscoring its potential for advanced nitrogen removal applications. A decline in LAP led to decreased extracellular polymeric substance (EPS) production, which could potentially augment reactor performance by minimizing mass transfer resistance while maintaining microbial matrix stability and function. Gene-centric metagenomics analysis revealed decreasing LAP impacted nitrogen metabolic potentials and electron flow pathways. The enrichment of napAB at higher LAP and the presence of complete ammonia oxidation (Comammox) Nitrospira at lower LAP indicated aerobic denitrification and Comammox processes in nitrogen removal. Multifunctional microbial communities developed under LAP regulation, diversifying the mechanisms for simultaneous nitrification-denitrification. Increased denitrifying gene pool (narGHI, nirK, norB) and enzymatic activity at a low LAP can amplify denitrification by promoting denitrifying genes and electron flow towards denitrifying enzymes. Sulfamethoxazole (SMX) was simultaneously removed with efficiency up to 80.2 ± 3.7 %, mainly via biodegradation, while antibiotic resistome and mobilome were propagated. Collectively, these findings could improve our understanding of nitrogen and antibiotic removal mechanisms under LAP regulation, offering valuable insights for the effective design and operation of MABR systems in aquaculture wastewater treatment.
Subject(s)
Microbiota , Wastewater , Denitrification , Nitrogen/metabolism , Extracellular Polymeric Substance Matrix/metabolism , Anti-Bacterial Agents/pharmacology , Air Pressure , Bioreactors , Nitrification , BiofilmsABSTRACT
Marine harmful algae bloom (HAB) is a growing threat to desalination plants worldwide. This work proposes ferrous iron/peroxymonosulfate (Fe2+/PMS) as a novel pretreatment technology for seawater reverse osmosis (SWRO) under HAB. Herein, Fe2+/PMS achieved a significantly higher reduction of negative charge of algae-laden seawater as compared to conventional coagulation (i.e., coagulant is Fe3+), which thereby facilitated improved flocculation to remove algal cells, turbidity and algal organics matters (AOMs), and marine Ca2+ (â¼430 mg/L) could partially contribute to the enhanced coagulation performance. A new understanding of the improved coagulation efficiency achieved with Fe2+/PMS in seawater has been proposed as compared to freshwater: seawater matrix (e.g., 504 mM Cl-) was demonstrated to significantly enhance the generation of high-valent iron (FeO2+) as the main reactive intermediate instead of the long-recognized Fe3+ and free radicals, as revealed by methyl phenyl sulfoxide (PMSO) probe, radicals scavenging analysis and electron spin resonance (ESR) spectra. This new mechanism is expected to provide valuable insights for the development of more novel oxidative seawater treatment technologies. Of note, while trade-off between particles and AOMs played an important role in membrane fouling reduction by different dosages of Fe2+/PMS, Fe2+/PMS with an optimal dosage of 0.1 mM/0.05 mM achieved an unprecedentedly higher reduction (95.26%) of modified fouling index (MFI) as compared to conventional coagulation (13.28%-42.36% with 0.1-0.2 mM of Fe3+). Optical-photothermal infrared spectromicroscopy with sub-micron spatial resolution was employed to analyze membrane foulants for the first time, and Fe2+/PMS was found to mainly cause reduced cake layer resistance, which was attributed to the collectively reduced concentration of algae cells, micro-particles with sizes from 2 to 10 µm, humic substances and biopolymers. Moreover, Fe2+/PMS resulted in lower dissolved Fe3+ (<0.027 mg/L) in ultrafiltration (UF) permeate, which would make it more reliable for SWRO operation as compared to conventional coagulation. When energy-intensive dissolved air flotation (DAF) was employed to withstand HAB, Fe2+/PMS outperformed it and was instrumental in achieving reduced MFI with 56.4% lower operational cost. In this context, Fe2+/PMS would facilitate a high-performance and low-cost pretreatment technology for seawater desalination plants under HAB.
Subject(s)
Iron , Water Purification , Harmful Algal Bloom , Water Purification/methods , Membranes, Artificial , SeawaterABSTRACT
Membrane aerated biofilm reactors (MABRs) can be used to treat domestic wastewater containing sulfamethoxazole (SMX) because of their favorable performance in the treatment of refractory pollutants. However, biologics are generally subjected to antibiotics stress, which induces the production of antibiotic resistance genes (ARGs). In this study, a simulated-sunlight assisted MABR (L-MABR) was used to promote SMX removal and reduce ARGs production. The SMX removal efficiency of the l-MABR system was 9.62 % superior to that of the MABR system (83.13 %). In contrast from MABR, in the l-MABR, only 28.75 % of SMX was removed through microbial activity because functional bacteria were inactivated through radiation by simulated sunlight. In addition, photolysis (64.61 %) dominated SMX removal, and the best performing indirect photolysis process was the excited state of effluent organic matters (3EfOMs*). Through photolysis, ultraviolet (UV) and reactive oxygen species (ROS) enriched the SMX removal route, resulting in the SMX removal pathway in the l-MABR no longer being limited by enzyme catalysis. More importantly, because of the inactivation of functional bacteria, whether in the effluent or biofilm, the copy number of ARGs in the l-MABR was 1-3 orders of magnitude lower than that in the MABR. Our study demonstrates the feasibility of utilizing simulated-sunlight to enhance the antibiotic removal efficiency while reducing ARG production, thus providing a novel idea for the removal of antibiotics from wastewater.
Subject(s)
Anti-Bacterial Agents , Wastewater , Anti-Bacterial Agents/metabolism , Sulfamethoxazole/metabolism , Sunlight , Bioreactors/microbiology , Bacteria/metabolism , Biofilms , Drug Resistance, Microbial/geneticsABSTRACT
Thermophilic anaerobic digestion (TAD) provides a promising solution for sustainable high-strength waste treatment due to its enhanced methane-rich biogas recovery. However, high organic loading rates (OLR) exceeding 3.0 kgCOD/m3/day and short hydraulic retention times (HRT) below 10 days pose challenges in waste-to-energy conversion during TAD, stemming from volatile fatty acids (VFAs) accumulation and methanogenesis failure. In this study, we implemented a stepwise strategy for acclimatizing waste activated sludge (WAS) in a thermophilic anaerobic fixed-bed biofilm reactor (TA-FBBR) to optimize methanogen populations, thereby enhancing waste-to-energy efficiencies under elevated OLRs in food waste treatment. Results showed that following stepwise acclimatization, the TA-FBBR achieved stable methane production of approximately 5.8 L/L-reactor/day at an ultrahigh OLR of â¼20 kgCOD/m3/day and â¼15 kgVS/m3/day at 6-day HRT in food waste treatment. The average methane yield reached 0.45 m3/kgCODremoval, attaining the theoretical production in TAD. Moreover, VFA concentrations were stabilized below 1000 mg/L at the ultrahigh OLR under 6-day HRT, while maintaining an acetate/propionate ratio of > 1.8 and a VFA/TAK ratio of < 0.3 serving as effective indicators of system stability and methane yield potential. The microbial community analysis revealed that the WAS acclimatization strategy fostered the microbial diversity and abundance of Methanothermobacter and Methanosarcina. Methanosarcina in the biofilm were observed to be twice as abundant as Methanothermobacter, indicating a potential preference for biofilm existence among methanogens. The findings demonstrated an effective strategy, specifically the stepwise acclimatization of WAS in a thermophilic fixed-bed biofilm reactor, to enhance the food waste treatment performance at high OLRs, contributing valuable mechanistic and technical insights for future sustainable high-strength waste management.
Subject(s)
Refuse Disposal , Sewage , Food , Anaerobiosis , Biofuels , Methane , Biofilms , BioreactorsABSTRACT
Antibiotic resistome can be carried by the bioaerosols and propagate from wastewater treatment plants (WWTPs) to the atmosphere, but questions remain regarding their mobility, bacterial hosts, source, and resistome risk. Here, fine particulate matter (PM2.5) was collected within and around a large WWTP and analyzed by the metagenomic assembly and binning. PM2.5 was discovered with increasing enrichment of total antibiotic resistance genes (ARGs), potentially mobile ARGs, and antibiotic-resistant bacteria (ARB) along the WWTP-downwind-upwind gradient. Some ARGs were found to be flanked by certain mobile genetic elements and generally mediated by plasmids in WWTP-PM2.5. Totally, 198 metagenome assembled genomes assigning to seven phyla were identified as the ARB, and a contig-based analysis indicated that 32 pathogens were revealed harboring at least two ARGs. Despite disparate aerosolization potentials of ARGs or ARB at different WWTP units, high resistome risks were found, along with the dominant contribution of wastewater for airborne ARGs (44.79-62.82%) and ARB (35.03-40.10%). Among the detected WWTP matrices, the sludge dewatering room was characterized by the highest resistome risk associated with PM2.5. This study underscores the dispersion of ARGs and ARB from WWTPs to the atmosphere and provides a reference for managing risks of antibiotic resistance.
Subject(s)
Genes, Bacterial , Wastewater , Angiotensin Receptor Antagonists , Angiotensin-Converting Enzyme Inhibitors , Bacteria/genetics , Atmosphere , Particulate Matter , Anti-Bacterial AgentsABSTRACT
Along with rapid urbanization and intensive human activities, polycyclic aromatic hydrocarbon (PAH) pollution in the Pearl River Estuary (PRE) and its effects on the microbial community have attracted extensive attention. However, the potential and mechanism of microbial degradation of PAHs across water and sediment habitats remain obscure. Herein, the estuarine microbial community structure, function, assembly process and co-occurrence patterns impacted by PAHs were comprehensively analyzed using environmental DNA-based approaches. The contamination and distribution of PAHs were jointly affected by anthropogenic and natural factors. Some of the keystone taxa were identified as PAH-degrading bacteria (i.e., genera Defluviimonas, Mycobacterium, families 67-14, Rhodobacteraceae, Microbacteriaceae and order Gaiellales in water) or biomarkers (i.e., Gaiellales in sediment) that were significantly correlated with PAH levels. The proportion of deterministic process in the high PAH-polluted water (76%) was much higher than that in the low pollution area (7%), confirming the significant effect of PAHs on the microbial community assembly. In sediment, the communities with high phylogenetic diversity demonstrated a great extent of niche differentiation, exhibited a stronger response to environmental variables and were strongly influenced by deterministic processes (40%). Overall, deterministic and stochastic processes are closely related to the distribution and mass transfer of pollutants, and substantially affect the biological aggregation and interspecies interaction within communities in the habitats.
Subject(s)
Microbiota , Polycyclic Aromatic Hydrocarbons , Water Pollutants, Chemical , Humans , Polycyclic Aromatic Hydrocarbons/analysis , Rivers/chemistry , Estuaries , Water , Phylogeny , Water Pollutants, Chemical/analysis , Geologic Sediments/chemistry , Bacteria/genetics , Bacteria/metabolism , Water Pollution , ChinaABSTRACT
Large volumes of iron-containing sludge (Fe-Sludge) would be generated with the application of iron salts in drinking water treatment plants, which must be disposed appropriately. One of the common disposal solutions for Fe-Sludge is through direct disposal into the municipal sewer system, whereby it would be mixed with domestic wastewater and treated in the wastewater treatment plant. To better understand the properties of Fe-Sludge and the effect of dosing Fe-Sludge to the real domestic wastewater (WW) on the wastewater characteristics, a serial batch tests were conducted on a local wastewater reclamation plant (WRP). It was found that the impact of dosing Fe-Sludge at a Fe/P ratio of 5 did not vary with the types of WW, i.e., filtered or non-filtered by the 5 mm screen. In addition, the soluble organic, phosphate and total soluble iron concentrations mostly decreased with the dosing of Fe-Sludge within the dosage range of 0-5 (Fe/P ratio). In contrast, the suspended solid (SS) and volatile suspended solid (VSS) concentrations increased with the dosage of Fe-Sludge within the dosage range of 0-5 (Fe/P ratio). Furthermore, the pH condition of the domestic wastewater affected the phosphate removal efficiency by Fe-Sludge and influenced the total soluble iron concentration and iron species distribution. These findings will provide fundamental support for the further study of the effect of Fe-Sludge on the biological treatment performance and membrane filtration performance of the membrane bioreactor (MBR) system.
Subject(s)
Sewage , Wastewater , Iron/chemistry , Waste Disposal, Fluid , Phosphates/chemistry , Bioreactors , Hydrogen-Ion ConcentrationABSTRACT
Hydroxylamine (NH2OH), nitrite (NO2-) and nitric oxide (NO), intermediates enzymatically formed during biological nitrogen removal processes, can engage in chemical (abiotic) transformations of antibiotics. This study determined the kinetics, mechanisms and pathways of abiotic transformations of the antibiotic sulfamethoxazole (SMX) by NH2OH, NO2- and NO in a series of batch tests under different pH and oxygen conditions. While NH2OH was not able to directly transform SMX, NO2- (with HNO2 as the actual reactant) and NO can chemically transform SMX primarily through hydroxylation, nitration, deamination, nitrosation, cleavage of S-N, N-C and C-S bonds, and coupling reactions. There were substantial overlaps in transformation product formations during abiotic transformations by HNO2- and NO. The second order rate constants of SMX with NO2- and NO were determined in the range of 1.5 × 10-1 - 4.8 × 103 M-1 s-1 and 1.0 × 102 - 3.1 × 104 M-1 s-1, respectively, under varying pH (4 - 9) and anoxic or oxic conditions. Acidic pH significantly enhanced abiotic transformation kinetics, and facilitated nitration, nitrosation, and cleavage of S-N and N-C bonds. The findings advance our understanding of the fate of antibiotics during biological nitrogen removal, and highlight the role of enzymatically formed reactive nitrogen species in the antibiotic degradation.
Subject(s)
Nitrites , Sulfamethoxazole , Hydroxylamine , Nitric Oxide , Wastewater , Nitrogen Dioxide , Hydroxylamines , Nitrogen , Anti-Bacterial Agents , Hydrogen-Ion ConcentrationABSTRACT
Rational design of cross-sectional microstructure in ceramic membranes has shown to improve membrane filtration efficacy without affecting rejection performance. In this work, we adopted 3D spray-coating technique to generate multi-layered membrane layers on macro-porous flat-sheet ceramic supports. The thickness of each layer was controlled by spray-coating cycles, and a gradient membrane layer was rationalized by successively coating three ceramic slurries containing alumina powders of gradually refined particle sizes, followed by co-sintering. Gradient membrane layers on both sides of the various sized flat-sheet ceramic supports were fabricated. Compared to the non-gradient counterpart, the gradient membranes showed both higher pure water flux (at the same TMP) and lower membrane resistance, which clearly evidenced the benefits of gradient profile in the membrane layer. Further, their performance in aerobic membrane bioreactors (AeMBR) was comparably studied for the first time. The treatment performance was not significantly affected by the types of membranes used, while the gradient membrane showed better filtration performance (i.e., a slower rise in TMP). Although the fouling mechanisms were revealed to be similar, the fouling layer in the gradient membrane was composed of a higher percentage of smaller foulants compared to that of the non-gradient counterpart. The observed differences were closely correlated to the larger internal pore structure in the gradient membrane. The present work provides a feasible 3D spray-coating technique for the fabrication of gradient flat-sheet ceramic membranes, and clarifies the benefits in AeMBR for domestic wastewater treatment.
Subject(s)
Membranes, Artificial , Water Purification , Bioreactors , Ceramics , Cross-Sectional Studies , Filtration , WastewaterABSTRACT
The demand for highly permeable and selective thin-film composite (TFC) nanofiltration membranes, which are essential for seawater and brackish water softening and resource recovery, is growing rapidly. However, improving and tuning membrane permeability and selectivity simultaneously remain highly challenging owing to the lack of thickness control in polyamide films. In this study, we fabricated a high-performance interlayered TFC membrane through classical interfacial polymerization on a MoS2-coated polyethersulfone substrate. Due to the enhanced confinement effect on the interface degassing and the improved adsorption of the amine monomer by the MoS2 interlayer, the MoS2-interlayered TFC membrane exhibited enhanced roughness and crosslinking. Compared to the control TFC membrane, MoS2-interlayered TFC membranes have a thinner polyamide layer, with thickness ranging from 60 to 85 nm, which can be tuned by altering the MoS2 interlayer thickness. A multilayer permeation model was developed to delineate and analyze the transport resistance and permeability of the MoS2 interlayer and polyamide film through the regression of experimental data. The optimized MoS2-interlayered TFC membrane (0.3-inter) had a 96.8% Na2SO4 rejection combined with an excellent permeability of 15.9 L m-2 h-1 bar-1 (LMH/bar), approximately 2.4 times that of the control membrane (6.6 LMH/bar). This research provides a feasible strategy for the rational design of tunable, high-performance NF membranes for environmental applications.
ABSTRACT
This study aimed to implement quorum quenching (QQ) to mitigate membrane fouling in membrane bioreactors (MBRs) treating phenol-rich pharmaceutical wastewater using Rhodococcus sp. BH4 and isolated QQ consortium (QQcs) from activated sludge. Neither BH4 nor QQcs impacted the removal efficiency of chemical oxygen demand (COD) (>94%), phenol (>99%), and ammonium (>99%), indicating that QQ did not have adverse impact on treatment performance. In addition, both BH4 and QQcs effectively retarded membrane fouling, which could be attributed to the reduction of soluble microbial products (SMP). Interestingly, the TMP increase was delayed 68.7% by Rhodococcus sp. BH4, while 31.3% was achieved by QQcs. This difference may be due to the relatively higher degradation for short- and medium-chain N-acyl-homoserine lactones (AHLs) by BH4 compared to the QQcs. Furthermore, the possible presence of quorum sensing (QS) bacteria within QQcs also could have contributed to the less effective fouling control than that of BH4.
Subject(s)
Biofouling , Rhodococcus , Bioreactors/microbiology , Feasibility Studies , Membranes, Artificial , Pharmaceutical Preparations , Phenol , Quorum Sensing , Wastewater/microbiologyABSTRACT
Microbial carbon fixation pathways have not yet been adequately understood for their role in membrane case layer formation processes. Carbon fixation bacteria can play critical roles in either causing or enhancing cake layer formation in some autotrophic-prone anoxic conditions, such as sulfur-cycling conditions. Understanding the microbes capable of carbon fixation can potentially guide the design of membrane biofouling mitigation strategies in scientific ways. Thus, we used meta-omics methods to query carbon fixation pathways in the cake layers of a full-scale anoxic-oxic biofilm-MBR system treating textile wastewater in this study. Based on the wastewater constituents and other properties, such as anoxic conditions, sulfide-reducing and sulfur-oxidizing bacteria could co-exist in the membrane unit. In addition, low-light radiation conditions could also happen to the membrane unit. However, we could not quantify the light intensity or total energy input accurately because the whole experimental setup was a full-scale system. Potentially complete carbon fixation pathways in the cake layer included the Calvin-Benson-Bassham cycle, Wood-Ljungdahl pathway, and the 3-hydroxypropionate bicycle. We discovered that using aeration could effectively inhibit carbon fixation, which resulted in mitigating membrane cake layer development. However, the aeration resulted in the 3-hydroxypropionate bicycle pathway, presumably used by aerobic sulfur-oxidizing prokaryotes, to become a more abundant carbon fixation pathway in the cake layer under aerobic conditions.
Subject(s)
Bioreactors , Wastewater , Bacteria , Biofilms , Carbon Cycle , Membranes, Artificial , Sulfur , TextilesABSTRACT
Membrane fouling is generally considered as a major bottleneck to the wide application of membrane bioreactor (MBR) for high saline mariculture wastewater treatment. Though numerous researches have investigated the membrane fouling of MBR combined with bio-carriers, few studies reveal the impacts of bio-carriers on the characteristics of cake layer and the mechanism of bio-carriers alleviating membrane fouling. In this study, two systems, namely carriers-enhanced MBR (R1) and conventional MBR (R2) were parallel operated, drawing a conclusion that bio-carriers effectively improved the characteristics of cake layer, thus mitigating membrane fouling. Fluorescence excitation emission matrix (EEM) analysis indicated that bio-carriers reduced the adhesion of proteins and humic acid-like materials on membrane surface. Molecular weight (Mw) distribution suggested that soluble microbial products (SMP) with small Mw (6-20 kDa) and biopolymers in extracellular polymeric substances (EPS) (50-300 kDa) was easier to accumulate on membrane surface in R2. The above results indicated that the presence of bio-carriers could effectively reduce the attachment of these organics on membrane surface, contributing to a larger porosity of cake layer and thus mitigating membrane fouling. Meanwhile, gas chromatography-mass spectrometry (GC-MS) clarified that more components were present in R2 than R1. Moreover, the majority of compounds in the SMP were present in both systems, while only 14 compounds in the EPS were the same between R1 and R2. Noticeably, certain aromatics only existed in R2, suggesting that bio-carriers effectively reduced the accumulation of recalcitrant materials, especially aromatics. These results revealed that bio-carriers shifted the precise composition of cake layers.
Subject(s)
Wastewater , Water Purification , Bioreactors , Humic Substances , Membranes, Artificial , Sewage , Wastewater/chemistryABSTRACT
This study is the first to enrich a facultative QQ consortium for AI-2-based quorum sensing (QS) disruption (FQQ2) and discover its quorum quenching (QQ) performance in an anaerobic membrane bioreactor (AnMBR) for membrane fouling retardation. Herein, FQQ2 was enriched by the enrichment culture using 4,5-dihydroxy-2,3-pentanedione (DPD) followed by anaerobic screening. FQQ2 was composed of various facultative AI-2-based QQ microorganisms including Acinetobacter, Comamonas, Stenotrophomonas, and FQQ2 was capable to degrade 96.96% of DPD in 9 h. More importantly, FQQ2 prolonged membrane filtration operation by an average of 3.72 times via reduction of DPD in the AnMBR treating domestic wastewater (p ≤ 0.05). QQ was implicated to reduce the content of proteins and carbohydrates of the extracellular polymeric substances (EPS) of suspended biomass by 24.16% and 10.39%, respectively, and concentration of proteins of the soluble microbial products (SMP) by 18.77%. Parallel factor (PARAFAC) modelling of excitation-emission matrix (EEM) demonstrated that QQ could reduce the content of fulvic acid-like and humic acid-like substances, aromatic proteins and soluble-microbial-by-product-like proteins of the EPS (p ≤ 0.05) and abate the content of soluble-microbial-by-product-like proteins in the SMP (p ≤ 0.05). The lower EPS content of suspended biomass could be rendered with the reduced relative abundance of AI-2-regulated Christensenellaceae;g-, Hyphomicrobium, Leucobacter and Microbacterium by 48.48%, 76.56%, 64.78% and 59.26%, respectively, and QQ led to the reduction of the relative abundance of Christensenellaceae;g- and Leucobacter in the cake layer by 31.07% and 51.43%, respectively. Moreover, quantity of organics as well as planktonic microorganisms in the supernatant decreased in presence of FQQ2 (p ≤ 0.05). Of note, markedly lower relative abundance of AI-2-regulated Sulfurovum in supernatant by 97.74% resulted in its lower abundance of cake layer. Intriguingly, in the presence of QQ, methane production was statistically enhanced by 62.5% (p ≤ 0.05). It was closely linked to the decrease of sulfate reduction (p ≤ 0.05), which resulted from 37.93% lower abundance of sulfate-reduction Desulfomonile in the suspended biomass (p ≤ 0.05). Collectively, this study sheds lights on the development of AI-2-based QQ for biofouling control in AnMBRs.