Membrane Biofilm Research Articles

High-Rate Sulfate Removal Coupled to Elemental Sulfur Production in Mining Process Waters Based on Membrane-Biofilm Technology.

It is anticipated that copper mining output will significantly increase over the next 20 years because of the more intensive use of copper in electricity-related technologies such as for transport and clean power generation, leading to a significant increase in the impacts on water resources if stricter regulations and as a result cleaner mining and processing technologies are not implemented. A key concern of discarded copper production process water is sulfate. In this study we aim to transform sulfate into sulfur in real mining process water. For that, we operate a sequential 2-step membrane biofilm reactor (MBfR) system. We coupled a hydrogenotrophic MBfR (H2-MBfR) for sulfate reduction to an oxidizing MBfR (O2-MBfR) for oxidation of sulfide to elemental sulfur. A key process improvement of the H2-MBfR was online pH control, which led to stable high-rate sulfate removal not limited by biomass accumulation and with H2 supply that was on demand. The H2-MBfR easily adapted to increasing sulfate loads, but the O2-MBfR was difficult to adjust to the varying H2-MBfR outputs, requiring better coupling control. The H2-MBfR achieved high average volumetric sulfate reduction performances of 1.7–3.74 g S/m3-d at 92–97% efficiencies, comparable to current high-rate technologies, but without requiring gas recycling and recompression and by minimizing the H2 off-gassing risk. On the other hand, the O2-MBfR reached average volumetric sulfur production rates of 0.7–2.66 g S/m3-d at efficiencies of 48–78%. The O2-MBfR needs further optimization by automatizing the gas feed, evaluating the controlled removal of excess biomass and S0 particles accumulating in the biofilm, and achieving better coupling control between both reactors. Finally, an economic/sustainability evaluation shows that MBfR technology can benefit from the green production of H2 and O2 at operating costs which compare favorably with membrane filtration, without generating residual streams, and with the recovery of valuable elemental sulfur.

Antibacterial mechanism of linalool emulsion against Pseudomonas aeruginosa and its application to cold fresh beef.

Pseudomonas aeruginosa (P. aeruginosa) is the dominant spoilage bacterium in cold fresh beef. The current strategy is undertaken to overcome the low water solubility of linalool by encapsulating linalool into emulsions. The results of field emission scanning electron microscopy and particle size distribution revealed that the appearance of the bacterial cells was severely disrupted after exposure to linalool emulsion (LE) with an minimum inhibitory concentration (MIC) of 1.5mL/L. Probes combined with fluorescence spectroscopy were performed to detect cell membrane permeability, while intracellular components (protein and ion leakage) and crystal violet staining were further measured to characterize cell membrane integrity and biofilm formation ability. The results confirmed that LE could destroy the structure of the cell membrane, thereby leading to the leakage of intracellular material and effective removal of biofilms. Molecular docking confirmed that LE can interact with the flagellar cap protein (FliD) and DNA of P. aeruginosa, inhibiting biofilm formation and causing genetic damage. Furthermore, the results of respiratory metabolism and reactive oxygen species (ROS) accumulation revealed that LE could significantly inhibit the metabolic activity of P. aeruginosa and induce oxidative stress. In particular, the inhibition rate of LE on P. aeruginosa was 23.03% and inhibited mainly the tricarboxylic acid cycle (TCA). Finally, LE was applied to preserve cold fresh beef, and the results showed that LE could effectively inhibit the activity of P. aeruginosa and delay the quality change of cold fresh beef during the storage period. These results are of great significance to developing natural preservatives and extending the shelf life of cold fresh beef.

Zero liquid discharge treatment of brackish water by membrane distillation system: Influencing mechanism of antiscalants on scaling mitigation and biofilm formation

• The anti-scaling performance of PBTCA, DTPMPA, and HPMA in MD system was studied. • Regulation mechanism of antiscalant on the MD fouling layer formation was presented. • Usage of DTPMPA in MD existed the risk of phosphate crystals and membrane wetting. • HPMA was suitable for the long-term operation of zero-liquid discharge MD system. Membrane distillation (MD) is increasingly regarded as a promising technique for brine management and zero liquid discharge (ZLD) disposal of seawater and brackish water owing to its excellent effluent quality and higher salt tolerance. However, membrane fouling issues of MD, especially scaling, have been confirmed as a crucial challenge impeding its large-scale utilization. Presently, the scaling issue of conventional membrane-based desalination techniques including reverse osmosis (RO) and ultrafiltration (UF), has been effectively controlled via the usage of antiscalants. Hence, this work applied three representative antiscalants of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), diethylene triamine penta methylene phosphonic acid (DTPMPA), and polymaleic acid (HPMA) in MD devices to restrain the scaling of polytetrafluoroethylene (PTFE) membrane during the ZLD treatment of synthetic brackish water. Furthermore, influences of antiscalant presence on variations of feed water qualities and the corresponding biofilm formation were also comprehensively studied via the high throughput sequencing method of 16S rDNA and 16S rRNA as well as a confocal laser scanning microscopy (CLSM). Compared to DTPMPA (77.4%-97.8%) and HPMA (42.1%-97.8%), a higher anti-scaling efficiency was obtained for PBTCA (90.6%-98.1%) in MD system, while the membrane biofilm formed in PBTCA group exhibited a remarkable appearance of live cells (14.046 μm 3 /μm 2 ). The secondary fouling of phosphate scale and pore wetting might be induced by the utilization of DTPMPA in MD plants, sharply increasing the effluent conductivity to 176.4 μS/cm (12 d). Comparatively, HPMA could be largely combined with salt ions to form loose slags with good fluidity, promoting the reuse of MD membranes and the subsequent disposal of MD brine.

Controlling the hydraulic resistance of membrane biofilms by engineering biofilm physical structure

The application of membrane technology for water treatment and reuse is hampered by the development of a microbial biofilm. Biofilm growth in micro-and ultrafiltration (MF/UF) membrane modules, on both the membrane surface and feed spacer, can form a secondary membrane and exert resistance to permeation and crossflow, increasing energy demand and decreasing permeate quantity and quality. In recent years, exhaustive efforts were made to understand the chemical, structural and hydraulic characteristics of membrane biofilms. In this review, we critically assess which specific structural features of membrane biofilms exert resistance to forced water passage in MF/UF membranes systems applied to water and wastewater treatment, and how biofilm physical structure can be engineered by process operation to impose less hydraulic resistance (“below-the-pain threshold”). Counter-intuitively, biofilms with greater thickness do not always cause a higher hydraulic resistance than thinner biofilms. Dense biofilms, however, had consistently higher hydraulic resistances compared to less dense biofilms. The mechanism by which density exerts hydraulic resistance is reported in the literature to be dependant on the biofilms’ internal packing structure and EPS chemical composition (e.g., porosity, polymer concentration). Current reports of internal porosity in membrane biofilms are not supported by adequate experimental evidence or by a reliable methodology, limiting a unified understanding of biofilm internal structure. Identifying the dependency of hydraulic resistance on biofilm density invites efforts to control the hydraulic resistance of membrane biofilms by engineering internal biofilm structure. Regulation of biofilm internal structure is possible by alteration of key determinants such as feed water nutrient composition/concentration, hydraulic shear stress and resistance and can engineer biofilm structural development to decrease density and therein hydraulic resistance. Future efforts should seek to determine the extent to which the concept of “biofilm engineering” can be extended to other biofilm parameters such as mechanical stability and the implication for biofilm control/removal in engineered water systems (e.g., pipelines and/or, cooling towers) susceptible to biofouling.

Targeted pressure-based development of membrane biofilms improves anaerobic membrane bioreactor effluent quality

Membrane biofilms were predeveloped at different transmembrane pressure and flux combinations in an AnMBR to promote better effluent quality and enhanced emerging contaminant removal.

Inhibition of citral nanoemulsion to growth, spoilage ability and AI-2/luxS quorum sensing system of Shewanella putrefaciens CN-32: a study on bacteriostasis from in vitro culture and gene expression analysis

Abstract Objectives The bacteriostatic effects of a citral nanoemulsion against Shewanella putrefaciens CN-32 (SHP CN-32) were investigated using in vitro culture and gene expression analysis, for building a potential application in spoilage microorganism control and aquatic products quality maintenance. Materials and Methods SHP CN-32 was treated by prepared citral nanoemulsion when the minimal inhibitory concentration (MIC) was verified. The growth curve, membrane integrity, scanning electron microscope (SEM) observation, biofilm formation and quorum sensing (QS) signaling molecule AI-2 content were evaluated in different MIC treatment groups (0 to 1.00 MIC). The gene expression status of SHP CN-32 in 0 and 0.50 MIC groups were compared using transcriptome sequencing and quantitative polymerase chain reaction (PCR). Results The in vitro culture revealed that the citral nanoemulsion could inhibit the growth of SHP CN-32 with MIC of approximately 200 μg/mL. Images of membrane integrity, SEM and biofilm formation suggested significant biological structure damage in bacteria after treatment. Meanwhile, the QS signaling molecule AI-2 content showed a decline with increasing treatment concentration. Transcriptome sequencing and quantitative PCR revealed that the majority genes related diversified functional metabolic pathways of SHP CN-32 were downregulated at varying degree. Conclusion A significant bacteriostasis of citral nanoemulsion against SHP CN-32 was verified via the results of growth inhibition, structural destruction, signal molecular decrease and gene expression downregulation of strains. These synergies significantly affect the characteristic expression of SHP CN-32, revealing the application potential as bacteriostat, QS inhibitor and preservative in aquatic products.

Gravity-Driven Membrane As Seawater Desalination Pretreatment: Understanding the Role of Membrane Biofilm on Water Production and Aoc Removal

Gravity-Driven Membrane As Seawater Desalination Pretreatment: Understanding the Role of Membrane Biofilm on Water Production and Aoc Removal

Alkalinity Induced Microbial Niches Succession and Antibiotic Resistance Genes Distribution in an Oxygen-Based Membrane Biofilm Reactor Treating Greywater

Alkalinity Induced Microbial Niches Succession and Antibiotic Resistance Genes Distribution in an Oxygen-Based Membrane Biofilm Reactor Treating Greywater

Membrane surface roughness promotes rapid initial cell adhesion and long term microalgal biofilm stability

In biofilm membrane photobioreactors development, conscientious works revolving around the effect of external environment factors on microalgal biofilm growth were assessed but more comparative research about the role of carrier surfaces properties such as surface roughness is necessary. Thus, commercial polyethersulfone (PES) membranes with two different molecular-weight-cut-offs (1 kDa and 30 kDa) were selected as the main representatives of surface roughness in a 20 days long-term biofilm cultivation experiment under dynamic flow condition for the biofilm evolvement of three benthic diatoms (Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta). Results depicted that rougher 30 kDa PES enable higher cell attachment degree for C. fusiformis (25.85 ± 2.75 × 109 cells m−2), followed by A. coffeaeformis (11.86 ± 2.76 × 109 cells m−2) and N. incerta (10.10 ± 0.65 × 109 cells m−2). Bounded extracellular polymeric substances (bEPS) gathered were relatively higher than soluble EPS (sEPS) while bEPS accumulated at least 10% higher on smooth 1 kDa PES than rough 30 kDa PES for the purpose of enhancing the biofilm disruption resistivity under liquid flow. Moreover, cell adhesion mechanism was proposed via computational fluid dynamics in parallel with EPS analysis. Copious amount of asperities and stagnant zones present on rough 30 kDa surfaces accelerated biofilm development and the consistency of the results have a great valence for interpretation of microalgal biofilm lifestyle on porous surfaces.

Anaerobic Dynamic Membrane Bioreactor Development to Facilitate Organic Waste Conversion to Medium-Chain Carboxylic Acids and Their Downstream Recovery

Platform chemicals such as medium-chain carboxylic acids (MCCAs) can be produced from organic waste streams via chain elongation in anaerobic mixed-culture bioreactors. A product recovery system is needed to collect MCCAs from the bioreactor effluent. Membrane-based liquid–liquid extraction, the most commonly used product recovery approach, requires suspended solids removal from the bioreactor effluent to avoid membrane fouling. An anaerobic dynamic membrane bioreactor (AnDMBR) was developed to evaluate MCCA production from brewery and prefermented food waste and to produce a permeate with low suspended solids to facilitate downstream product recovery. The AnDMBR employed an inexpensive stainless-steel mesh as the support material for the development of a biofilm or dynamic membrane, which was responsible for solids–liquid separation. The AnDMBR produced a permeate quality with an average total suspended solids (TSS) concentration of 0.12 g L–1, while the average bioreactor TSS concentration was two orders of magnitude higher (21.6 g L–1). A maximum solids removal efficiency of ≥99% was achieved and good permeate quality was sustained for over 200 days without fouling control or cleaning the support material. In addition to solids–liquid separation, the dynamic membrane was responsible for a substantial fraction of the biological activity of the AnDMBR. The relative activity of Clostridiales, as determined by 16S rRNA sequencing, correlated with MCCA production and was higher in the dynamic membrane (20.0 ± 4.9%) than in the suspended biomass (5.2 ± 2.7%) in the bioreactor. This observation was consistent with MCCA production data as the permeate MCCA concentrations were significantly (p = 8.2 × 10–5) higher than that in the bioreactor, suggesting that the dynamic membrane biofilm contributed to chain elongation.

Integrated self-forming dynamic membrane (SFDM) and membrane-aerated biofilm reactor (MABR) system enhanced single-stage autotrophic nitrogen removal

The membrane aerated biofilm reactor (MABR) is a novel bioreactor technology, facilitating single-stage autotrophic nitrogen removal. Two laboratory-scale MABRs equipped with non-woven fabrics were operated simultaneously without and with a self-forming dynamic membrane (SFDM) filtration module. After 87 days of operation (system start-up), the reactor incorporated with SFDM filtration showed better performance in terms of total nitrogen removal (>80%) and effluent suspended solid (less than1 mg/L) than the MABR in the up flow anaerobic sludge blanket (UASB) configuration (i.e., without SFDM). The incorporation of SFDM has the ability to retain more slow growing biomass (anammox) inside the reactor. Microbial characterization by 16S rRNA-based amplicon sequencing shows that the abundance and composition of microbial communities in two MABR systems were different, i.e., the genusRhodanobacterwas abundant in UASB-MABR, while Calorithrixwas dominant in SFDM-MABR. PCA-based statistical analysis demonstrated a positive association between reactor performance, membrane characteristics and microbial communities.

Seasonal shift of water quality in China Yangtze River and its impacts on membrane fouling development during the drinking water supply by membrane distillation system

Membrane distillation (MD) technique is increasingly regarded as a promising process for drinking water supply and wastewater treatment owing to its great water purification and usage of renewable energy. Like other membrane separation processes, the membrane fouling issue is widely considered as the main obstacle for real applications of large-scale MD systems. Feedwater characteristics, as the predominant factors for membrane fouling layer formation, mostly determined the membrane fouling trend of MD. Thus the impacts of seasonal shifts of initial feedwater quality on the MD membrane fouling were detailedly researched in this study, and the biofilm development mechanism was especially explored. The bacterial community structure of membrane biofilms was clearly clarified in MD runs of Yangtze River waters that collected in four seasons. The results revealed that the winter run posed a quite sharp flux drop, while a relatively milder flux decline behaviour was seen for other groups despite of the higher bacteria concentration of initial feedwaters. The poorer water quality in winter induced the establishment of a rather thick biofilm on the MD membrane, in which the biofilm-forming bacteria (Gammaproteobacteria and Alphaproteobacteria) and organic matters (EPS) were remarkably observed. Comparatively, a relatively thin biofilm containing abundant live cells and fewer organics finally formed in summer and autumn runs, causing a mitigated flux decline trend. Hence, it can be inferred that the membrane flux decline of MD was likely to be more sensitive to the organic attachment on the membrane in comparison with the bacteria adhesion. Finally, a three-phase pretreatment method was suggested for MD fouling control, including heating course, sterilization course, and filtration course.

Insights into the removal of gaseous oxytetracycline by combined ozone and membrane biofilm reactor

Gaseous emerging organic compounds (GEOCs) may harm human health and ecological environment. High temperature composting of livestock manure may produce oxytetracycline (OTC) waste gas. Here, we investigated treatment OTC in waste gas by combined ozone and membrane biofilm reactor (MBfR) with desulphurizing bacteria. The performance, the microbial community, gene function and the mechanism for OTC removal in the ozone-MBfR were evaluated. The ozone-MBfR system could achieve more degradation of OTC completely than MBfR. Desulfovibrio, Lentimicrobium, Aminivibrio, Thioalkalispira, Erysipelothrix, Mangroviflexus, Azoarcus, Thauera, Geobacter, Paracoccus, and Dethiosulfatibacter were the dominant genera. Pseudomonas, Escherichia, Bacteroides, Salmonella, Paracoccus, Stappia were contribution to OTC degradation. With the addition of ozone, the community diversity increased; some genera, such as Tenericutes- uncultured, and Desulfovibrio, increased in abundance, whereas others, such as Thauera, and Petrimonas, decreased. Ozone destroyed the enol structure in OTC molecular structure and produces biodegradable products, ozone oxidation was combined with biodegradation, to achieve thoroughly degrade OTC in waste gas. The novel hybrid ozone-MBfR is a cost-effective and robust alternative to GEOCs treatment.

Copper stimulation on methane-supported perchlorate reduction in a membrane biofilm reactor

The present study demonstrated that the perchlorate reduction rate in a methane-based membrane biofilm reactor was significantly enhanced from 14.4 to 25.6 mg-Cl/L/d by increasing copper concentration in the feeding medium from 1 to 10 μM, indicating a stimulatory effect of copper on the methane-supported perchlorate reduction process. Batch tests further confirmed that the increased copper concentration enhanced both methane oxidation and perchlorate reduction rates, which was supported by an increasing trend of functional genes (pmoA for methanotrophs and pcrA for specific perchlorate reducers) abundances through quantitative polymerase chain reaction (qPCR). Both 16S rRNA gene sequencing and functional genes (pmoA and pcrA) sequencing jointly revealed that the biofilm supplied with a higher copper concentration exhibited a more diverse microbial community. The methane-supported perchlorate reduction was accomplished through a synergistic association of methanotrophs (Methylocystis, Methylomonas, and Methylocystaceae) and perchlorate reducers (Dechloromonas, Azospira, Magnetospirillum, and Denitratisoma). Acetate may function as the key syntrophic linkage between methanotrophs and perchlorate reducers. It was proposed that the increased copper concentration improved the activity of particulate methane monooxygenase (pMMO) for methane oxidation or promoted the biosynthesis of intracellular carbon storage compounds polyhydroxybutyrate (PHB) in methanotrophs for generating more acetate available for perchlorate reduction.

Simultaneous Partial Nitrification and Denitrification Maintained in Membrane Bioreactor for Nitrogen Removal and Hydrogen Autotrophic Denitrification for Further Treatment.

Low C/N wastewater results from a wide range of factors that significantly harm the environment. They include insufficient carbon sources, low denitrification efficiency, and -N concentrations in low C/N wastewater that are too high to be treated. In this research, the membrane biofilm reactor and hydrogen-based membrane biofilm reactor (MBR-MBfR) were optimized and regulated under different operating parameters: the simulated domestic sewage with low C/N was domesticated and the domestic sewage was then denitrified. The results of the MBR-MBfR experiments indicated that a C/N ratio of two was suitable for -N, -N, -N, and chemical oxygen demand (COD) removal in partial nitrification-denitrification (PN-D) and hydrogen autotrophic denitrification for further treatment. The steady state for domestic wastewater was reached when the MBR-MBfR in the experimental conditions of HRT = 15 h, SRT = 20 d, 0.04 Mpa for H2 pressure in MBfR, 0.4–0.8 mg/L DO in MBR, MLSS = 2500 mg/L(MBR) and 2800 mg/L(MBfR), and effluent concentrations of -N, -N, and -N were 4.3 ± 0.5, 1.95 ± 0.04, and 2.05 ± 0.15 mg/L, respectively. High-throughput sequencing results revealed the following: (1) The genus Nitrosomonas as the ammonia oxidizing bacteria (AOB) and Denitratisoma as potential denitrifiers were simultaneously enriched in the MBR; (2) at the genus level, Meiothermus, Lentimicrobium, Thauera, Hydrogenophaga, and Desulfotomaculum played a dominant role in leading to -N and -N removal in the MBfR.

Assessment and optimization of the oxygen based membrane biofilm reactor as a novel technology for source-diverted greywater treatment

The oxygen based membrane biofilm (O2-MBfR) has been proved to be a novel technology in treating greywater (GW) and response surface methodology (RSM) was used to model the removal of chemical oxygen demand (COD) and total nitrogen (TN) with operation parameters COD/TN ratio, system pH and lumen air pressure (LAP). Results indicated that the all target single factors affect GW treatment efficiency, and the regression model with central composite design (CCD) showed good agreement with the experimental results with high R2 and R2 adj values (all >0.97) for all the target responses. Statistical evaluation revealed that system pH was the most significant parameter affecting COD and TN removal, followed by COD/TN ratio and LAP. The interaction between COD/TN ratio and system pH also played an important role on the GW treatment. The optimized maximum removal of COD (96.48%) and TN (133 g N/m2-day) were achieved with the COD/TN ratio 17.76 g COD/g TN, system pH 7.10 and LAP 1.00 psi. Thus, RSM combined with CCD could be used for predicting the organics and nitrogen removal during GW treatment in the O2-MBfR.

Cross flow frequency determines the physical structure and cohesion of membrane biofilms developed during gravity-driven membrane ultrafiltration of river water: Implication for hydraulic resistance

We evaluated how intermittent shear influences the physical structure, material properties and hydraulic resistance of membrane biofilms developed during gravity-driven ultrafiltration of river water, with the ultimate goal of increasing the filtration performances. Our results indicate intermittent shear helps slowing-down the flux decline but does not help to increase the level of stabilisation of the permeate flux. After several weeks, the biofilms exposed to different shear regimes were indeed characterised by similar hydraulic resistance. But the characteristic time to achieve a stable flux increased from 7 d to 25d when increasing the shear frequency. Also, most of the hydraulic resistance (up to 95%) was governed by the base layer that remained attached after erosion tests. With increasing exposure to shear conditions, the biofilms became more cohesive and more elastic, thus resisting better to cross flow conditions. Overall, our results demonstrate that engineering membrane biofilms with a desired permeability is not feasible using intermittent shear due to significant adaptability of the biofilms to their hydraulic environment.

Combating Drug-Resistant Bacteria Using Photothermally Active Nanomaterials: A Perspective Review.

Injudicious use of antibiotics has been the main driver of severe bacterial non-susceptibility to commonly available antibiotics (known as drug resistance or antimicrobial resistance), a global threat to human health and healthcare. There is an increase in the incidence and levels of resistance to antibacterial drugs not only in nosocomial settings but also in community ones. The drying pipeline of new and effective antibiotics has further worsened the situation and is leading to a potentially “post-antibiotic era.” This requires novel and effective therapies and therapeutic agents for combating drug-resistant pathogenic microbes. Nanomaterials are emerging as potent antimicrobial agents with both bactericidal and potentiating effects reported against drug-resistant microbes. Among them, the photothermally active nanomaterials (PANs) are gaining attention for their broad-spectrum antibacterial potencies driven mainly by the photothermal effect, which is characterized by the conversion of absorbed photon energy into heat energy by the PANs. The current review capitalizes on the importance of using PANs as an effective approach for overcoming bacterial resistance to drugs. Various PANs leveraging broad-spectrum therapeutic antibacterial (both bactericidal and synergistic) potentials against drug-resistant pathogens have been discussed. The review also provides deeper mechanistic insights into the mechanisms of the action of PANs against a variety of drug-resistant pathogens with a critical evaluation of efflux pumps, cell membrane permeability, biofilm, and quorum sensing inhibition. We also discuss the use of PANs as drug carriers. This review also discusses possible cytotoxicities related to the therapeutic use of PANs and effective strategies to overcome this. Recent developments, success stories, challenges, and prospects are also presented.

Quinones contained in wastewater as redox mediators for the synergistic removal of azo dye in microbial fuel cells

The present paper aimed to investigate the roles of quinones contained in wastewater and the enhanced effects on microbial fuel cells (MFCs) under different redox conditions. The feasibility of using wastewater rich in quinones to act as co-substrate and redox mediators (RMs) library to strengthen the synergistic removal of azo dye in MFCs was evaluated. The results demonstrated that quinones achieved enhanced effects on electricity generation and COD removal of MFC better at higher current intensity. The addition of pure quinone decreased electron transfer resistance (Rct) of MFCs from 4.76 Ω to 2.13 Ω under 1000 Ω resistance and 1.16 Ω–0.75 Ω under 50 Ω resistance. Meanwhile, higher coulombic efficiency was achieved. Compared with sodium acetate, using quinone-rich traditional Chinese medicine (TCM) wastewater as the co-substrate enhanced the synergistic removal of reactive red 2 (RR2) in MFCs from 79.58% to 92.45% during 24 h. RR2 was also degraded more thoroughly due to the accelerated electron transfer process mediated by RMs. Microbial community analysis demonstrated that the presence of quinone in TCM wastewater can enrich different exoelectrogens under varied redox conditions and thus influenced the enhanced effects on MFC. Metagenomic functional prediction results further indicated that the abundance of functional genes involved in carbohydrate metabolism, membrane transport metabolism, biofilm formation, and stress tolerance increased significantly in presence of RMs. Redundancy analyses revealed that RMs addition was the more important factor driving the variation of the microorganism community. This study revealed the potential effect of quinones as redox mediators on the bioelectrochemical system for pollutants removal.

Model-based analyses of chromate, selenate and sulfate reduction in a methane-based membrane biofilm reactor

Selenate (SeO42−) and sulfate (SO42−) are frequently present together with chromate (CrO42−) in certain industrial wastewaters. SeO42− and CrO42− are required to be reduced while SO42− reduction should be minimized to avoid the production of toxic sulfide. In this study, a modified biofilm model was employed to investigate the interactions between CrO42−, SeO42− and SO42− bioreduction in a methane (CH4)-based membrane biofilm reactor (MBfR). The model was calibrated using steady-state experimental data of two reported CH4-based MBfRs reducing these oxyanions. The modeling results suggested that the majority of methanotrophs (>80%) were located in the outer layer of the biofilm, while the oxyanions-reducing bacteria preferred to grow close to the membrane. The introduction of SeO42− or SO42− enriched selenate/sulfate-reducing bacteria (SeRB/SRB) but decreased the abundance of chromate-reducing bacteria (CRB). A biofilm thickness of >300 μm, an HRT of higher than 4 h and an influent dissolved oxygen concentration of 0.3 mg /L were favorable for simultaneous high-level CrO42− and SeO42− removal. A two-stage MBfR system with optimized operational conditions showed promise in retaining high-purity (>98%) selenium nanoparticles when treating both CrO42− and SeO42− impacted wastewaters. Moreover, the model indicated that efficient CrO42− removal (>90%) along with minor SO42− reduction (<10%) could be realized via maintaining appropriate biofilm thickness (200-250 μm) and influent dissolved oxygen (0.7–0.8 mg /L) in a single MBfR. These findings offer insights for the design and operation of CH4-based technology for remediating CrO42− contaminated industrial wastewaters.