Membrane Biofilm Research Articles

The interplay of sulfate and nitrate triggers abiotic reduction in a hydrogen-based membrane biofilm reactor for antimonate removal

The interplay of sulfate and nitrate triggers abiotic reduction in a hydrogen-based membrane biofilm reactor for antimonate removal

Co-metabolic biodegradation of chlorinated ethene in an oxygen- and ethane-based membrane biofilm reactor

Groundwater contamination by chlorinated ethenes is an urgent concern worldwide. One approach for detoxifying chlorinated ethenes is aerobic co-metabilims using ethane (C2H6) as the primary substrate. This study evaluated long-term continuous biodegradation of three chlorinated alkenes in a membrane biofilm reactor (MBfR) that delivered C2H6 and O2 via gas-transfer membranes. During 133 days of continuous operation, removals of dichloroethane (DCE), trichloroethene (TCE), and tetrachloroethene (PCE) were as high as 94 % and with effluent concentrations below 5 μM. In situ batch tests showed that the co-metabolic kinetics were faster with more chlorination. C2H6-oxidizing Comamonadaceae and “others,” such as Methylococcaceae, oxidized C2H6 via monooxyenation reactions. The abundant non-ethane monooxygenases, particularly propane monooxygenase, appears to have been responsible for C2H6 aerobic metabolism and co-metabolism of chlorinated ethenes. This work proves that the C2H6 + O2 MBfR is a platform for ex-situ bioremediation of chlorinated ethenes, and the generalized action of the monooxygenases may make it applicable for other chlorinated organic contaminants.

Biodegradation of nitrate and p-bromophenol using hydrogen-based membrane biofilm reactors in parallel

ABSTRACT P-bromophenol (4-BP) is a toxic halogenated phenolic organic compound. The conventional treatment processes for 4-BP elimination are costly and inefficient, with complete mineralization remaining a challenge for water treatment. To overcome these limitations, we investigated the treatment of 4-BP in a membrane biofilm reactor (MBfR) using hydrogen as an electron donor. The pathway of 4-BP degradation within the H2-MBfR was investigated through long-term operational experiments by considering the effect of nitrate and 4-BP concentrations, hydrogen partial pressure, static experiments, and microbial community diversity, which was studied using 16S rRNA. The results showed that H2-MBfR could quickly remove approximately 100% of 4-BP (up to 20 mg/L), with minimal intermediate product accumulation and 10 mg/L of nitrate continuously reduced. The microbial community structure showed that the presence of H2 created an anaerobic environment, and Thauera was the dominant functional genus involved in the degradation of 4-BP. The genes encoding related enzymes were further enhanced. This study provides an economically viable and environmentally friendly bioremediation technique for water bodies that contain 4-BP and nitrates.

Mechanistic insights into 1,2,4-trichlorobenzene removal in flue gas by aerobic denitrifying membrane biofilm reactor

1,2,4-Trichlorobenzene (1,2,4-TrClBz) as dioxin indicator in municipal solid waste incineration can increase risk of human health. Aerobic denitrifying membrane biofilm reactor (MBfR) was investigated for 1,2,4-TrClBz removal in flue gas. During the 75 days of operation, 1,2,4-TrClBz removal efficiency achieved 94%. Pseudomonas, Halomonas, Paracoccus, Thauera, Azoarcus, Proteiniphilum, Mesorhizobium, Pelagibacterium, Chelativorans were the core 1,2,4-TrClBz biodegrading-denitrifying bacteria. 1,2,4-TrClBz biodegradation genes and denitrification genes were responsible for the oxidation of 1,2,4-TrClBz and nitrate reduction. 1,2,4-TrClBz was degraded by ring-cleavage before aerobic dechlorination, 1,2,4-TrClBz bio-oxidation was coupled to denitrification formed redox between 1,2,4-TrClBz and nitrate, as shown by metagenomic sequencing and untargeted metabolomic analysis. Therefore, MBfR effectively achieved bioremoval and biodegradation of 1,2,4-TrClBz in flue gas by aerobic denitrification, which may provide a feasible and environment-friendly biotechnique for decontamination of chlorobenzene compounds in flue gas.

Response of biofilm–based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm–based systems have efficient stability to cope–up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics–laden wastewater. The biofilm models applied for estimation/prediction of biofilm–based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm–based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm–based system with biocarriers filling ratio of ∼50–70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm–based systems. Considering the significance of biofilm–based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm–based technologies with feasible regulatory strategies for treatment of mixed antibiotics–laden real wastewater.

Long-Term Continuous Test of H2-Induced Denitrification Catalyzed by Palladium Nanoparticles in a Biofilm Matrix.

Pd0 catalysis and microbially catalyzed reduction of nitrate (NO3--N) were combined as a strategy to increase the kinetics of NO3- reduction and control selectivity to N2 gas versus ammonium (NH4+). Two H2-based membrane biofilm reactors (MBfRs) were tested in continuous mode: one with a biofilm alone (H2-MBfR) and the other with biogenic Pd0 nanoparticles (Pd0NPs) deposited in the biofilm (Pd-H2-MBfR). Solid-state characterizations of Pd0NPs in Pd-H2-MBfR documented that the Pd0NPs were uniformly located along the outer surfaces of the bacteria in the biofilm. Pd-H2-MBfR had a higher rate of NO3- reduction compared to H2-MBfR, especially when the influent NO3- concentration was high (28 mg-N/L versus 14 mg-N/L). Pd-H2-MBfR enriched denitrifiers of Dechloromonas, Azospira, Pseudomonas, and Stenotrophomonas in the microbial community and also increased abundances of genes affiliated with NO3--N reductases, which reflected that the denitrifying bacteria could channel their respiratory electron flow to NO3- reduction to NO2-. N2 selectivity in Pd-H2-MBfR was regulated by the H2/NO3- flux ratio: 100% selectivity to N2 was achieved when the ratio was less than 1.3 e- equiv of H2/e- equiv N, while the selectivity toward NH4+ occurred with larger H2/NO3- flux ratios. Thus, the results with Pd-H2-MBfR revealed two advantages of it over the H2-MBfR: faster kinetics for NO3- removal and controllable selectivity toward N2 versus NH4+. By being able to regulate the H2/NO3- flux ratio, Pd-H2-MBfR has significant implications for improving the efficiency and effectiveness of the NO3- reduction processes, ultimately leading to more environmentally benign wastewater treatment.

Complete mineralization of 2,4-dichlorophenoxyacetic acid in a reduction and oxidation Synergistic Platform (ROSP)

Emissions of 2,4-dichlorophenoxyactic acid (2,4-D), one of the most widely used herbicides, pose serious risks to human and ecosystem health. Although biodegradation and abiotic chemical methods are available for 2,4-D removal, continuous treatment systems for 2,4-D removal are rare. We evaluated a Reduction and Oxidation Synergistic Platform (ROSP) that sequentially links an H2-based membrane catalyst-film reactor (H2-MCfR) and an O2-based membrane biofilm reactor (O2-MBfR). In continuous operation of the ROSP, 50 μM (or 11 ppm) of 2,4-D was completely mineralized with a total HRT of 12 h, yielding an effluent concentration < 0.2 μM 2,4-D (or < 44 ppb). In the H2-MCfR, over 80% of the influent 2,4-D was reductively hydrodechlorinated to phenoxyacetic acid (POA). The produced POA was the primary substrate supporting the co-oxidation of 2,4-D in the O2-MBfR. The biofilm community structure and genes encoding enzymes for POA and 2,4-D co-oxidation were identified through shallow metagenomic sequencing of the biofilm DNA samples. The dominant bacterial genus, Variovorax, and various mono-/dioxygenase-encoding genes related to aromatic ring hydrolysis, hydroxylation, and ring cleavage were associated with the removal of 2,4-D. In summary, reductive-dehalogenation products from the H2-MCfR become the primary substrate to enable the co-oxidation of the halogenated organic pollutants in the O2-MBfR, which does not require the addition of other organic materials. Therefore, the ROSP eliminates the need for an added organic substrate, which greatly reduces the demand for O2 and minimizes CO2 emissions.

Effects of magnetite on nitrate-dependent anaerobic oxidation of methane in an anaerobic membrane biofilm reactor: Metatranscriptomic analysis and mechanism prediction

Magnetite has been widely reported to accelerate methane production in anaerobic digestion. However, the effects of magnetite on the process of methane consumption, specifically nitrate-dependent anaerobic oxidation of methane (AOM), and its underlying mechanisms remain poorly understood. In this study, the addition of magnetite significantly improved the removal of nitrate in an anaerobic membrane biofilm reactor (AnMBfR) (25.2 ± 2.5 mg NO3−-N/L/d) compared to that in an AnMBfR without magnetite (8.7 ± 4.2 mg NO3−-N/L/d). Metatranscriptomic analysis showed that genes encoding type IV pilus assembly proteins were highly expressed in nitrate/nitrite-reducing bacteria in the biofilms of the two AnMBfRs. Specifically, the transcript abundance of these genes was observed to be higher in the presence of magnetite (gene expression levels, log2FPKM = 13.08) compared to the absence of magnetite (12.04). Biofilms with magnetite exhibited a linear increase in electron transfer resistance with increasing temperature, and the decrease in pH significantly increased their conductivity, indicating a metallic-like conductivity. Contrarily, an increase in temperature or decrease in pH did not influence the resistance or conductivity of biofilms without magnetite. Some of these cytochrome c (CYC)-like proteins were electrically active in the electrochemical Fourier transform infrared spectra and were closely associated with the outer-membrane multi-heme c-type cytochromes (OMCs). The intensities of the OMC-like bands in the surface-enhanced resonance Raman spectra with biofilms in the presence of magnetite were higher than those without magnetite. This study suggests that magnetite promotes the nitrate-dependent AOM process because of the formation of methanotrophic consortia based on direct interspecies electron transfer (DIET).

Gravity-driven membrane coupled with oxidation technology to modify the surface properties and biofilm formation: Biofouling mitigation

Biofilms caused by biological fouling play an essential role in gravity-driven membranes’ (GDMs) flux decline and rejection rate. The effects of ozone, permanganate, and ferrate (VI) in-situ pretreatment on membrane properties and biofilm formation were systematically studied. Due to the selective retention and adsorption of algal organic matter by biofilms and oxidative degradation, the rejection efficiency of dissolved organic carbon (DOC) in algae-laden water pretreated with permanganate by GDM was up to 23.63%. Pre-oxidation extraordinarily postponed flux decline and biofilm formation of GDM and reduced membrane fouling. The total membrane resistance decreased by 87.22%–90.30% within 72 h after pre-ozonation. Permanganate was more effective than ozone and ferrate (VI) in alleviating secondary membrane fouling caused by algal cells destroyed by pre-oxidation. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that the distribution of electrostatic force (EL), acid-base (AB), and Lifshitz-van der Waals forces (LW) interactions between M. aeruginosa and the released intracellular algogenic organic matter (IOM) and ceramic membrane surface was similar. The membrane and foulants are always attracted to each other by LW interaction at different separation distances. The dominant fouling mechanism of GDM combined with pre-oxidation technology shifts from complete pore blocking to cake layer filtration during operation. After pre-oxidation of algae-laden water by ozone, permanganate, and ferrate (VI), GDM can treat at least 131.8%, 37.0%, and 61.5% more feed solution before forming a complete cake layer. This study provides new insights into the biological fouling control strategies and mechanisms for GDM coupled with oxidation technology, which is expected to alleviate membrane fouling and optimize the feed liquid pretreatment procedure.

The tigecycline resistance gene tetX has an expensive fitness cost based on increased outer membrane permeability and metabolic burden in Escherichia coli

Livestock-derived tetX-positive Escherichia coli with tigecycline resistance poses a serious risk to public health. Fitness costs, antibiotic residues, and other tetracycline resistance genes (TRGs) are fundamental in determining the spread of tetX in the environment, but there is a lack of relevant studies. The results of this study showed that both tetO and tetX resulted in reduction in growth and an increased in the metabolic burden of E. coli, but the presence of doxycycline reversed this phenomenon. Moreover, the protection of E. coli growth and metabolism by tetO was superior to that of tetX in the presence of doxycycline, resulting in a much lower competitiveness of tetX-carrying E. coli than tetO-carrying E. coli. The results of RNA-seq showed that the increase in outer membrane proteins (ompC, ompF and ompT) of tetX-carrying E. coli resulted in increased membrane permeability and biofilm formation, which is an important reason for fitness costs. Overall, the increased membrane permeability and metabolic burden of E. coli is the mechanistic basis for the high fitness cost of tetX, and the spread of tetO may limit the spread of tetX. This study provides new insights into the rational use of tetracycline antibiotics to control the spread of tetX.

Development and Control of Biofilms: Novel Strategies Using Natural Antimicrobials.

Separation membranes have a wide application in the food industry, for instance, in the clarification/fractionation of milk, the concentration/separation of selected components, and wastewater treatment. They provide a large area for bacteria to attach and colonize. When a product comes into contact with a membrane, it initiates bacterial attachment/colonization and eventually forms biofilms. Several cleaning and sanitation protocols are currently utilized in the industry; however, the heavy fouling of the membrane over a prolonged duration affects the overall cleaning efficiency. In view of this, alternative approaches are being developed. Therefore, the objective of this review is to describe the novel strategies for controlling membrane biofilms such as enzyme-based cleaner, naturally produced antimicrobials of microbial origin, and preventing biofilm development using quorum interruption. Additionally, it aims to report the constitutive microflora of the membrane and the development of the predominance of resistant strains over prolonged usage. The emergence of predominance could be associated with several factors, of which, the release of antimicrobial peptides by selective strains is a prominent factor. Therefore, naturally produced antimicrobials of microbial origin could thus provide a promising approach to control biofilms. Such an intervention strategy could be implemented by developing a bio-sanitizer exhibiting antimicrobial activity against resistant biofilms.

Restoring Ampicillin Sensitivity in Multidrug-Resistant Escherichia coli Following Treatment in Combination with Coffee Pulp Extracts.

Escherichia coli, particularly multidrug-resistant (MDR) strains, is a serious cause of healthcare-associated infections. Development of novel antimicrobial agents or restoration of drug efficiency is required to treat MDR bacteria, and the use of natural products to solve this problem is promising. We investigated the antimicrobial activity of dried green coffee (DGC) beans, coffee pulp (CP), and arabica leaf (AL) crude extracts against 28 isolated MDR E. coli strains and restoration of ampicillin (AMP) efficiency with a combination test. DGC, CP, and AL extracts were effective against all 28 strains, with a minimum inhibitory concentration (MIC) of 12.5-50 mg/ml and minimum bactericidal concentration of 25-100 mg/ml. The CP-AMP combination was more effective than CP or AMP alone, with a fractional inhibitory concentration index value of 0.01. In the combination, the MIC of CP was 0.2 mg/ml (compared to 25 mg/ml of CP alone) and that of AMP was 0.1 mg/ml (compared to 50 mg/ml of AMP alone), or a 125-fold and 500-fold reduction, respectively, against 13-drug resistant MDR E. coli strains. Time-kill kinetics showed that the bactericidal effect of the CP-AMP combination occurred within 3 h through disruption of membrane permeability and biofilm eradication, as verified by scanning electron microscopy. This is the first report indicating that CP-AMP combination therapy could be employed to treat MDR E. coli by repurposing AMP.

Methanotrophic oxidation of organic micropollutants and nitrogen upcycling in a hybrid membrane biofilm reactor (hMBfR) for simultaneous O2 and CH4 supply

Pharmaceuticals and other organic micropollutants (OMPs) present in wastewater effluents are of growing concern, as they threaten environmental and human health. Conventional biological treatments lead to limited removal of OMPs. Methanotrophic bacteria can degrade a variety of OMPs. By employing a novel bubble-free hybrid membrane biofilm bioreactor (hMBfR), we grew methanotrophic bacteria at three CH4 loading rates. Biomass productivity and CH4 loading showed a linear correlation, with a maximum productivity of 372 mg-VSS·L−1·d−1, with corresponding biomass concentration of 1117.6 ± 56.4 mg-VSS·L−1. Furthermore, the biodegradation of sulfamethoxazole and 1H-benzotriazole positively correlated with CH4 oxidation rates, with highest biodegradation kinetic constants of 3.58 L·g−1·d−1 and 5.42 L·g−1·d−1, respectively. Additionally, the hMBfR recovered nutrients as microbial proteins, with an average content 39% DW. The biofilm community was dominated by Methylomonas, while the bulk was dominated by aerobic heterotrophic bacteria. The hMBfR removed OMPs, allowing for safer water reuse while valorising CH4 and nutrients.

Long-term operation and biofouling of graphene oxide membrane in practical water treatment: Insights from performance and biofilm characteristics

The widespread research of graphene oxide (GO) membranes has revealed the need to investigate their long-term performance and associated biofouling behavior in practical water treatment conditions. In this study, we have evaluated the long-term operation of GO membranes from the perspective of filtration performance and biofilm characteristics, based on two representative GO membranes (V-GO and P-GO, fabricated by vacuum and pressure filtration, respectively) with different surface properties and a natural surface water, using a gravity driven membrane system. The results showed that the GO membranes were capable of achieving sustainable water purification over 45 days of operation, associated with a complete rejection for biopolymers and desirable removal for fluorescent organic matters. Furthermore, the V-GO membrane with a rougher surface, reduced hydrophilicity and higher sheet-edge exposure than that of the P-GO membrane formed a highly heterogeneous and porous biofilm with high permeability, despite its greater biofilm thickness and extracellular polymeric substances (EPS) contents. In contrast, the P-GO membrane biofilm exhibited a thin but dense structure, and therefore an increased hydraulic resistance (∼1.5 times greater than V-GO membrane). The microbial community analysis revealed that bacteria related to biofilm formation was richer in V-GO biofilm. While bacteria associated with the degradation of organic matters and the aggregation of microorganisms accounted for a greater proportion in P-GO biofilm. These factors were responsible for forming a thick biofilm for V-GO, and a thin but high resistance biofilm for P-GO membrane. Our findings highlight the sustainable water purification performance of the GO membranes, and the P-GO membrane can alleviate biofilm formation but not necessarily reduce biofouling during the long-term filtration, while this was opposite in case of the V-GO membrane.

Predation preference for extracellular polysaccharides by paramecia and rotifers may have accelerated the decline of membrane biofilm hydraulic resistance

The hydraulic resistance of biofilm layer on membranes impacts the filtration resistance significantly. The effect of predation by two model microfauna (i.e., paramecia and rotifers) on the hydraulic resistance, structure, extracellular polymeric substance (EPS), and bacterial community of biofilms developed on supporting materials (i.e., nylon mesh) was evaluated in this study. Long-term experiments demonstrated that predation could alter biofilm compositions and accelerated the decline of hydraulic resistance by increasing biofilm heterogeneity and deformation. Importantly, predation preference of paramecia and rotifers on biofilm components were further investigated for the first time by tracking the fluorescence change in the predator bodies after exposure to the stained biofilms. Results indicated that after 12-hour’s incubation, the ratio of extracellular α-polysaccharides (α-PS) to proteins (PN) within the bodies of paramecia and rotifers increased to 2.6 and 3.9, respectively, which was 0.76 in the original biofilms. The ratios of α-PS/live cells within paramecia and rotifers increased to 1.42 and 1.64 from 0.81 in the original biofilms. The ratio of live/dead cells in the predator bodies, however, changed slightly compared to the original biofilms. These results clearly and directly evidenced that both paramecia and rotifers could feed on biofilm EPS and cells, but having a significant preference for PS over PN and cells. Since extracellular PS is recognized as a primary biofilm adhesion agent, the preference for PS could better explain why predation had accelerated the disintegration and hydraulic resistance decline of mesh biofilms.

An integrated full-scale system for the treatment of real ship domestic wastewater: Shore-test experiments

With the increasing number of ocean-sailing ships, the pollution of the oceans' water caused by the discharge of ship wastewater has become one of the serious concerns for the whole world. Most of existing ship wastewater treatment studies were carried out in bench/pilot-scale and cannot meet the latest discharge standards of International Maritime Organization (IMO) and China. To overcome those barriers and prepare for the onboard test, we evaluated the hydraulic retention time (HRT) variations (10.5-12 h) for treating low COD/TN ship wastewater by a full-scale oxic-anoxic micro-sludge membrane biofilm reactor (O-AMSMBR) system. The full-scale O-AMSMBR achieved over 82 % removal of chemical oxygen demand (COD) and 76 % removal of total nitrogen (TN) from a ship wastewater with continuous operation at a HRT of 10.5 h. Although anoxic membrane biofilm partly compensated for the deterioration of TN removal in performance of the aerobic sludge, the effluent TN concentrations still cannot meet IMO discharge standards at HRT as low as 9 h due to the inhibition of simultaneous nitrification and denitrification (SND) by low HRT and C/N. Wavelet Neural Networks (WNN) was used to explore the removal mechanism under HRT variations. Simulation results show that HRT andinfluent pollutant’s concentration are the two most sensitive factors for COD and TN removal in daily operation so special attention should be paid to the dramatic change of influent flow rate in ship sewage treatment operation. In particular, techno-economic analysis was conducted in this study to provides a baseline for developing economic options for ship wastewater treatment in practice.

Liquid-gas phase transition enables microbial electrolysis and H2-based membrane biofilm hybrid system to degrade organic pollution and achieve effective hydrogenotrophic denitrification of groundwater

Electron-donor Lacking was the limiting factor for the denitrification of oligotrophic groundwater and hydrogenotrophic denitrification provided an efficient approach without secondary pollution. In this study, a hybrid system with microbial electrolysis cell (MEC) assisted hydrogen-based membrane biofilm reactor (MBfR) was established for advanced groundwater denitrification. The liquid-gas phase transition prevented the potential pollution from organic wastes in MEC to groundwater, while the bubble-free diffusion of MBfR promoted hydrogen utilization efficiency. The negative-pressure extraction from MEC and the positive pressure for gas supply into MBfR increased the hydrogen proportion and current density of MEC, and improved the kinetic constant K of the denitrification reaction in MBfR. With actual groundwater, the MEC-MBfR hybrid system achieved a nitrate reduction of 97.8% with an effluent NO3−-N of 2.2 ± 1.0 mg L−1. The hydrogenotrophic denitrifiers of Thauera, Pannonibacter, and Azonexus, dominated the denitrification biofilm on the membrane and elastic filler in MBfR.

Anaerobic membrane bioreactor for real antibiotic pharmaceutical wastewater treatment: Positive effect of fouling layer on antibiotics and antibiotic resistance genes removals

Anaerobic membrane bioreactor (AnMBR) is a potential candidate for high-strength pharmaceutical wastewater treatment. However, its contribution to reduce the antibiotic and antibiotic resistance genes (ARGs) is still largely unclear. Herein, this study investigated the antibiotics and ARGs removal in AnMBR for real high-strength antibiotic (levofloxacin (LEV)) pharmaceutical wastewater treatment, focusing on the positive effect of membrane fouling layers (biofilms). Results indicated that membrane biofilm has a positive effect on AnMBR treatment with improved COD and LEV removal efficiency by 12% and 10%, respectively. This might be ascribed to the enhanced biodegradation ability of the organic matter by the biofilm due to the enrichment of fermentation bacteria (Anaerobium), hydrogen-producing bacteria (Clostridium_sensu_stricto_1) and hydrogenotrophic methanogenic archaea (Methanobacterium and Methanobrevibacter). Importantly, the membrane biofilm can also effectively mitigate the ARGs (qnrS, qnrA) and class 1 integrator (intI1) dissemination and the absolute abundance of ARGs in the medium fouling (MF) biofilm effluent was 0.27 orders of magnitude lower than that of low fouling (LF) biofilm effluent. This can be explained by the variation of membrane surface becoming more hydrophobic in MF than LF biofilm with increased contact angle and more negative surface zeta potential, suggesting higher adsorption and adhesion properties. The strong correlation between extracellular polymer substance (EPS) and soluble microbial product (SMP) contents and qnrA, qnrS and intI1 further indicated the important role of EPS and SMP in membrane biofilm on ARGs reduction. Furthermore, the entrapment of ARGs potential hosts bacteria of Comamonas and Enterococcus with high biofilm formation potential also attributed to the improved ARGs removal with the increase of membrane fouling degree. Our findings suggest that AnMBR is effective for antibiotic pharmaceutical wastewater treatment and membrane biofilm has a positive effect on antibiotic and ARGs removal, which promotes the AnMBR application in the pharmaceutical industry.

Flue gas arsenic trioxide removal from sludge incineration by sulfate-reducing membrane biofilm reactor

Arsenic in flue gas from sludge incineration may damage to human health and ecological environment seriously. The sulfate-reducing membrane biofilm reactor (SRBR) was investigated for arsenic trioxide(As2O3) removal in flue gas from sludge incineration. Arsenic removal efficiency attained 94.4%. Desulfovibrio, UC_Clostridiales, and Pseudodesulfovibrio were the dominant genera. Desulfovibrio was the core arsenite-oxidizing-sulfate-reducing genus. Arsenite oxidase (ArxA) and sulfate-reducing enzymes (Sat, AprAB and DsrAB) responsible for bacterial As(III)-oxidation and sulfate reduction. Desulfovibrio could synthetically regulate the expression of functional proteins that involved in As oxidation, sulfate reduction, cell wall and membrane synthesis, antioxidant, DNA repair, glycolysis and amino acid synthesis under As stress, possessed resistant and removal ability to As. The biofilm in SRBR was characterized by FTIR, XPS, XRD, EEM, and SEM-EDS. XPS and XRD spectra indicate the formation of an arsenic species (As(V)) from arsenic oxidation. Humic acid complex arsenic (HA-As) and arsenopyrite-like phase (Fe-As-S) precipitation were formed in SRBR. Microbial arsenic oxidation was coupled sulfate reduction and biostabilization of arsenic from flue gas. Arsenic in flue gas was bio-stabilized in the form of Fe-As-S and HA-As via biocomplexation of humic acids in extracellular polymeric substances (EPS), biosorption and biodeposition. These results show that the sulfate-reducing membrane biofilm reactor is achievable and open new possibilities for applying the SRBR to removal of arsenic in flue gas from sludge incineration.

Optimizing UVC-disinfection using LEDs as an energy efficient pre-treatment for biofouling control in spiral-wound membrane systems

Biofouling remains a major challenge for reverse osmosis (RO) systems. Pulsed ultraviolet (UV) pre-treatment has been proposed as a mitigation strategy for biofouling control of RO membranes. This study investigated whether increasing fluence rate during pulsed UV disinfection leads to enhanced inactivation. Further, UV irradiation from 1.5 to 61.3 mJ cm−2 was tested for optimal biofouling control. Therefore, an UVC-LED reactor was characterized by successfully adapting an actinometry method for flow-through mode. The inactivation of microorganisms was compared in flow-through biodosimetry experiments in pulsed and continuous irradiation. Finally, several settings were applied as pre-treatment in lab-scale biofouling experiments and membrane performance and biofilm removability elucidated. Whereas no enhanced inactivation was observed during biodosimetry experiments, pulsed UV disinfection resulted in an average of 20.6 % increased delay of biofilm formation. On the contrary, for pulsed UV disinfection, the biofilm hydraulic resistance seemed higher than continuous equivalents, but not significantly. Overall, savings of operational expenditures per fluence applied was highest around 4 mJ cm−2. UV pre-treated biofilms showed no enhanced removability, but delay in biofilm formation was noticeable in two of three experiments. In case the effects translate to up-scaled applications over several cleanings, UV pre-treatment for biofouling control is an interesting option.