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.

Effect of mixing iron-containing sludge to domestic wastewater on wastewater characteristics under different conditions: types of domestic wastewater, varying pH and mixing ratios.

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.

Enhancing the Permselectivity of Thin-Film Composite Membranes Interlayered with MoS2 Nanosheets via Precise Thickness Control.

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.

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.

Diversity evolution of functional bacteria and resistance genes (CzcA) in aerobic activated sludge under Cd(II) stress.

An activated sludge sequencing batch reactor (SBR) was used to treat divalent cadmium (Cd(II)) wastewater for 60 d to investigate the overall treatment performance, evolution of the bacterial community, and abundance of the Cd(II) resistance gene CzcA and shifts in its potential host bacteria. During stable operation with a Cd(II) concentration of 20 mg/L, the average removal efficiencies of Cd(II) and chemical oxygen demand (COD) were more than 85% and that of total phosphorus was greater than 70%, while the total nitrogen (TN) was only about 45%. The protein (PN) content in the extracellular polymeric substances (EPS) increased significantly after Cd(II) addition, while polysaccharides displayed a decreasing trend (p < 0.05), indicating that EPS prefer to release PN to adsorb Cd(II) and protect bacteria from damage. Three-dimensional fluorescence spectral analysis showed that fulvic acid-like substances were the most abundant chemical components of EPS. The addition of Cd(II) adversely affected most denitrifying bacteria (p < 0.05), which is consistent with the low TN removal. In addition, quantitative polymerase chain reaction analysis revealed that CzcA gene abundance decreased as the Cd(II) concentration increased, possibly because expression of the CzcA gene was inhibited by Cd(II) stress. The majority of CzcA gene sequences were carried by Pseudomonas, making it the dominant genus among Cd(II)-resistant bacteria.

Applicability of upflow anaerobic sludge blanket and dynamic membrane-coupled process for the treatment of municipal wastewater.

This study investigated the applicability of dynamic membrane filter (DMF) technology in an upflow anaerobic sludge blanket (UASB) and DMF-coupled process for the treatment of municipal wastewater. The overall treatment performance and effects of hydraulic retention time (HRT), operating flux, and mesh pore size on the UASB + DMF were assessed. The UASB + DMF-coupled process demonstrated removal efficiencies of over 64 and 86% for TCOD and TSS, respectively. The effects of filtration flux and support mesh pore size were investigated and it was found that while there was little impact on the treatment performance, a 67% increase in operating flux resulted in a 25% increase in fouling rate. Similarly, with smaller mesh pore size (Mesh 500 with pore size of 28 µm) the fouling rate increased by fourfold as compared to Mesh 300 (pore size of 46 µm). In consideration of the operation duration and contaminant removal, the DMF with Mesh 300 support layer and operating at 100 L/m2-h was the most efficient configuration for treating the effluent of the UASB operated with a HRT of 6 h. Microbial analyses of the foulant layer revealed changes in relative abundance as compared to the bulk sludge, particularly with the hydrogenotrophic methanogens completely outcompeting the acetoclastic methanogens. Overall, the coupled process improved the system robustness and reduced variability of the treated effluent.

Development and Long-Term Stability of a Novel Microbial Fuel Cell BOD Sensor with MnO2 Catalyst.

A novel microbial fuel cell (MFC)-based biosensor was designed for continuous monitoring of biochemical oxygen demand (BOD) in real wastewater. To lower the material cost, manganese dioxide (MnO2) was tested as an innovative cathode catalyst for oxygen reduction in a single chamber air-cathode MFC, and two different crystalline structures obtained during synthesis of MnO2 (namely ß- and γ-MnO2) were compared. The BOD sensor was studied in a comprehensive way, using both sodium acetate solution and real domestic wastewater (DWW). The optimal performance of the sensor was obtained with a ß-MnO2 catalyst, with R² values of 0.99 and 0.98 using sodium acetate solution and DWW, respectively. The BOD values predicted by the ß-MnO2 biosensor for DWW were in agreement with the BOD5 values, determined according to standard methods, with slight variations in the range from 3% to 12%. Finally, the long-term stability of the BOD biosensor was evaluated over 1.5 years. To the best of our knowledge, this is the first report of an MFC BOD sensor using an MnO2 catalyst at the cathode; the feasibility of using a low-cost catalyst in an MFC for online measurement of BOD in real wastewater broadens the scope of applications for such devices.

Antibiofouling Polyvinylidene Fluoride Membrane Modified by Quaternary Ammonium Compound: Direct Contact-Killing versus Induced Indirect Contact-Killing.

Widespread applications of membrane technology call for the development of antibiofouling membranes. For the traditional contact-killing strategy, the antibacterial action is restricted to the surface: the membrane loses its antibiofouling efficacy once its surface is completely covered with a fouling layer. However, in this study, polyvinylidene fluoride (PVDF) microfiltration membranes blended with quaternary ammonium compound (QAC) exhibited a surprisingly lasting antimicrobial activity in the vicinity of the membrane surface. The results indicated that QAC was capable of driving surface segregation with a high structural stability, and the QAC modified membrane shows clear antibacterial effects against both Gram-positive and Gram-negative bacteria. Covering the modified membrane surface by an abiotic alginate layer resulted in a loss of antibacterial efficiency by 86.2%. In contrast, the antibacterial efficiency was maintained after developing a biofilm of Staphylococcus aureus of 30 µm in thickness. The current study may suggest that bacteria affected by contact-killing might interact with other bacteria in the vicinity, resulting in retarded biofilm growth. The antibiofouling effect and associated mechanism of the QAC modified membrane were further validated in a membrane bioreactor during long-term operation.

Investigation of intertidal wetland sediment as a novel inoculation source for anaerobic saline wastewater treatment.

Biological treatment of saline wastewater is considered unfavorable due to salinity inhibition on microbial activity. In this study, intertidal wetland sediment (IWS) collected from a high saline environment was investigated as a novel inoculation source for anaerobic treatment of saline pharmaceutical wastewater. Two parallel lab-scale anaerobic sequencing batch reactors (AnSBR) were set up to compare the organic removal potential of IWS with conventional anaerobic digested sludge (ADS). Under steady-state condition, IWS reactor (R(i)) showed organic reduction performance significantly superior to that of ADS reactor (R(a)), achieving COD removal efficiency of 71.4 ± 3.7 and 32.3 ± 6.1%, respectively. In addition, as revealed by fluorescent in situ hybridization (FISH) analysis, a higher relative abundance of methanogenic populations was detected in R(i). A further 16S rRNA gene pyrosequencing test was conducted to understand both the bacterial and archaeal community populations in the two AnSBRs. A predominance of halophilic/tolerant microorganisms (class Clostridia of bacteria, genera Methanosarcina, and Methanohalophilus of archaea) in R(i) enhanced its organic removal efficiency. Moreover, several microbial groups related with degradation of hardly biodegradable compounds (PAHs, n-alkenes, aliphatic hydrocarbons, and alkanes, etc.) were detected in the IWS. All these findings indicated that IWS is a promising inoculation source for anaerobic treatment of saline wastewater.

Treatment of domestic wastewater with an anaerobic ceramic membrane bioreactor (AnCMBR).

In this study, a ceramic membrane with a pore size of 80 nm was incorporated into an anaerobic membrane bioreactor for excellent stability and integrity. Chemical oxygen demand (COD) removal efficiencies by biodegradation reached 78.6 ± 6.0% with mixed liquor suspended solids (MLSS) of 12.8 ± 1.2 g/L. Even though the total methane generated was 0.3 ± 0.03 L/g CODutilized, around 67.4% of it dissolved in permeate and was lost beyond collection. As a result, dissolved methane was 2.7 times of the theoretical saturating concentration calculated from Henry's law. When transmembrane pressure (TMP) of the ceramic membrane reached 30 kPa after 25.3 d, 95.2% of the total resistance was attributed to the cake layer, which made it the major contributor to membrane fouling. Compared to the mixed liquor, cake layer was rich in colloids and soluble products that could bind the solids to form a dense cake layer. The Methanosarcinaceae family preferred to attach to the ceramic membranes.

Impacts of different draw solutions on a novel anaerobic forward osmosis membrane bioreactor (AnFOMBR).

Two anaerobic forward osmosis (FO) membrane bioreactors (AnFOMBRs), Rchloride and Rsulfate, were operated for 100 days using NaCl and Na2SO4 as the draw solution, respectively. The operating conditions were identical for both systems, with a solids retention time of 30 d, hydraulic retention time of 8 h and using cellulose triacetate FO membrane. High rejection performance of FO membranes resulted in salinity accumulation in the bioreactors. Rchloride and Rsulfate reached a stable conductivity of about 35 and 11 mS/cm, respectively, at the end of the experimental run. Hypersalinity of Rchloride undesirably impacted biological growth; mixed liquor volatile suspended solids in Rchloride was much lower at 376 mg/L, whereas that of Rsulfate was 1,170 mg/L. Organic removals were excellent due to reduced organic loadings at low fluxes and thus, Rsulfate and Rchloride achieved secondary total organic carbon (TOC) removal efficiencies of at least 75%. Both AnFOMBRs started with an initial flux of 5 LMH. Flux for Rchloride stabilized at 0.25 LMH, while Rsulfate at 0.96 LMH. The high salinities of both reactors negatively impacted methanogenic growth. Application of the fluorescence in-situ hybridization (FISH) technique confirmed the ousting of methanogens by sulfate reducing bacteria from the anaerobic consortium. Sparsely located methanogens were detected in Rchloride but none were detected in Rsulfate.

Biodiesel production by microalgae cultivated using permeate from membrane bioreactors in continuous system.

Microalgae in three submerged ceramic membrane photobioreactors (SCMPBRs) with different hydraulic retention times (HRTs) were fed with permeate of a submerged ceramic membrane bioreactor for a period of 3 months to investigate the lipid content and also the biodiesel quality produced at different HRTs. The lipid content, lipid productivity and fatty acid compositions for all three SCMPBRs were not significantly different at the 95% confidence level. These results suggested that insignificant change in the amount of fatty acids was observed at different HRTs that supplied varying concentration of nitrate in the medium. Among the fatty acids, palmitic acid, palmitoleic acid, oleic acid and linoleic acid were the main components, whereas stearic acid was a minor fatty acid. Since there was insignificant effect of HRT on lipid content, lipid productivity and fatty acid compositions, the optimum HRT for SCMPBRs can then be designed based on optimum nutrient removal performance and low membrane fouling propensity.

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

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

New insights into the concentration-dependent regulation of membrane biofouling formation via continuous nanoplastics stimulation.

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.

Functionalization of seawater reverse osmosis membrane with quorum sensing inhibitor to regulate microbial community and mitigate membrane biofouling.

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.

Alleviation of RO membrane fouling in wastewater reclamation plants using an enhanced acid-base chemical cleaning method.

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.

Abiotic transformations of sulfamethoxazole by hydroxylamine, nitrite and nitric oxide during wastewater treatment: Kinetics, mechanisms and pH effects.

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.

Simulated-sunlight enhances membrane aerated biofilm reactor performance in sulfamethoxazole removal and antibiotic resistance genes reduction.

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.

Novel use of ferrous iron/peroxymonosulfate for high-performance seawater desalination pretreatment under harmful algal blooms.

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+ (∼430 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.