In-situ biogas sparging enhances the performance of an anaerobic membrane bioreactor (AnMBR) with mesh filter in low-strength wastewater treatment.

In the recent years, anaerobic membrane bioreactor (AnMBR) technology is being considered as a very attractive alternative for wastewater treatment due to the striking advantages such as upgraded effluent quality. However, fouling control is still a problem for the application of AnMBR. This study investigated the performance of an AnMBR using mesh filter as support material to treat low-strength wastewater via in-situ biogas sparging. It was found that mesh AnMBR exhibited high and stable chemical oxygen demand (COD) removal efficiencies with values of 95 ± 5 % and an average methane yield of 0.24 L CH4/g CODremoved. Variation of transmembrane pressure (TMP) during operation indicated that mesh fouling was mitigated by in-situ biogas sparging and the fouling rate was comparable to that of aerobic membrane bioreactor with mesh filter reported in previous researches. The fouling layer formed on the mesh exhibited non-uniform structure; the porosity became larger from bottom layer to top layer. Biogas sparging could not change the composition but make thinner thickness of cake layer, which might be benefit for reducing membrane fouling rate. It was also found that ultrasonic cleaning of fouled mesh was able to remove most foulants on the surface or pores. This study demonstrated that in-situ biogas sparging enhanced the performance of AnMBRs with mesh filter in low-strength wastewater treatment. Apparently, AnMBRs with mesh filter can be used as a promising and sustainable technology for wastewater treatment.

Transcriptomic Insights into Metabolism-Dependent Biosynthesis of Bacterial Nanocellulose.

Bacterial nanocellulose (BNC) is an attractive green-synthesized biomaterial for biomedical applications and various other applications. However, effective engineering of BNC production has been limited by our poor knowledge of the related metabolic processes. In contrast to the traditional perception that genome critically determines biosynthesis behaviors, here we discover that the glucose metabolism could also drastically affect the BNC synthesis in Gluconacetobacter hansenii. The transcriptomic profiles of two model BNC-producing strains, G. hansenii ATCC 53582 and ATCC 23769, which have highly similar genomes but drastically different BNC yields, were compared. The results show that their BNC synthesis capacities were highly related to metabolic activities such as ATP synthesis, ion transport protein assembly, and carbohydrate metabolic processes, confirming an important role of metabolism-related transcriptomes in governing the BNC yield. Our findings provide insights into the microbial biosynthesis behaviors from a transcriptome perspective, potentially guiding cellular engineering for biomaterial synthesis.

Phosphorus removal in an enhanced biological phosphorus removal process: roles of extracellular polymeric substances.

Phosphorus-accumulating organisms are considered to be the key microorganisms in the enhanced biological phosphorus removal (EBPR) process. A large amount of phosphorus is found in the extracellular polymeric substances (EPS) matrix of these microorganisms. However, the roles of EPS in phosphorus removal have not been fully understood. In this study, the phosphorus in the EBPR sludge was fractionated and further analyzed using quantitative (31)P nuclear magnetic resonance spectroscopy. The amounts and forms of phosphorus in EPS as well as their changes in an anaerobic-aerobic process were also investigated. EPS could act as a reservoir for phosphorus in the anaerobic-aerobic process. About 5-9% of phosphorus in sludge was reserved in the EPS at the end of the aerobic phase and might further contribute to the phosphorus removal. The chain length of the intracellular long-chain polyphosphate (polyP) decreased in the anaerobic phase and then recovered under aerobic conditions. However, the polyP in the EPS had a much shorter chain length than the intracellular polyP in the whole cycle. The migration and transformation of various forms of phosphorus among microbial cells, EPS, and bulk liquid were also explored. On the basis of these results, a model with a consideration of the roles of EPS was proposed, which is beneficial to elucidate the mechanism of phosphorus removal in the EBPR system.

Face mask derived micro(nano)plastics and organic compounds potentially induce threat to aquatic ecosystem security revealed by toxicogenomics-based assay.

Micro(nano)plastics widely detected in aquatic environments have caused serious threat to water quality security. However, as a potential important source of micro(nano)plastics in surface water during the COVID-19 pandemic, the ecological risks of face mask waste to aquatic environments remain poorly understood. Herein, we comprehensively characterized the micro(nano)plastics and organic compounds released from four daily used face masks in aqueous environments and further evaluated their potential impacts on aquatic ecosystem safety by quantitative genotoxicity assay. Results from spectroscopy and high-resolution mass spectrum showed that plastic microfibers/particles (∼11%-83%) and leachable organic compounds (∼15%-87%) were dominantly emitted pollutants, which were significantly higher than nanoplastics (< ∼5%) based on mass of carbon. Additionally, a toxicogenomics approach using green fluorescence protein-fused whole-cell array revealed that membrane stress was the primary response upon the exposure to micro(nano)plastics, whereas the emitted organic chemicals were mainly responsible for DNA damage involving most of the DNA repair pathways (e.g., base/nucleotide excision repair, mismatch repair, double-strand break repair), implying their severe threat to membrane structure and DNA replication of microorganisms. Therefore, the persistent release of discarded face masks derived pollutants might exacerbate water quality and even adversely affect aquatic microbial functions. These findings would contribute to unraveling the potential effects of face mask waste on aquatic ecosystem security and highlight the necessity for more developed management regulations in face mask disposal.

Development of a novel bioelectrochemical membrane reactor for wastewater treatment.

A novel bioelectrochemical membrane reactor (BEMR), which takes advantage of a membrane bioreactor (MBR) and microbial fuel cells (MFC), is developed for wastewater treatment and energy recovery. In this system, stainless steel mesh with biofilm formed on it serves as both the cathode and the filtration material. Oxygen reduction reactions are effectively catalyzed by the microorganisms attached on the mesh. The effluent turbidity from the BEMR system was low during most of the operation period, and the chemical oxygen demand and NH(4)(+)-N removal efficiencies averaged 92.4% and 95.6%, respectively. With an increase in hydraulic retention time and a decrease in loading rate, the system performance was enhanced. In this BEMR process, a maximum power density of 4.35 W/m(3) and a current density of 18.32 A/m(3) were obtained at a hydraulic retention time of 150 min and external resister of 100 Ω. The Coulombic efficiency was 8.2%. Though the power density and current density of the BEMR system were not very high, compared with other high-output MFC systems, electricity recovery could be further enhanced through optimizing the operation conditions and BEMR configurations. Results clearly indicate that this innovative system holds great promise for efficient treatment of wastewater and energy recovery.

Characterization of extracellular polymeric substances produced by mixed microorganisms in activated sludge with gel-permeating chromatography, excitation-emission matrix fluorescence spectroscopy measurement and kinetic modeling.

In this work the extracellular polymeric substances (EPS) produced by mixed microbial community in activated sludge are characterized using gel-permeating chromatography (GPC), 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy measurement and mathematical modeling. Chromatograms of extracted EPS exhibit seven peaks, among which proteins have four peaks and polysaccharides have three peaks. Evolution of the chromatogram area indicates that the quantity of produced EPS increases significantly in the substrate utilization process. With the parallel factor analysis (PARAFAC) approach, two components of the polymer matrix are identified by the EEM analysis, one as EPS proteins at Ex/Em 280/340 nm and one matrix associated as fulvic-acid-like substances at 320/400 nm. The proteins and fulvic-acid-like substances in the EPS increase in the substrate utilization phase, but decrease in the endogenous phase. To have a better insight into EPS production, the kinetic modeling of EPS is performed with regard to their molecular weight distribution and chemical natures identified by GPC and EEM. In this way, the dynamics of these important microbial products are better understood.

Co-doping polymethyl methacrylate and copper tailings to improve the performances of sludge-derived particle electrode.

Three-dimensional electrochemical reactor (3DER) is a highly efficient technology for refractory wastewater treatment. Particle electrodes filled between anode and cathode are the core units of 3DER, determining the treatment efficiency of wastewater. However, particle electrodes deactivation due to catalytic sites coverage seriously impedes the continuous operation of 3DER. In this work, granular sludge carbon (GSC) particle electrodes being resistant to deactivation are fabricated by pyrolyzing the mixture of waste sludge, polymethyl methacrylate (PMMA), and copper tailings, whose performances are evaluated by degrading rhodamine B (RhB) wastewater in a continuous-flow 3DER. Results indicate that hierarchical-pore structure comprising macro-, meso-, and micropores is developed in GSC-10-CTs by doping 10 g PMMA and 5 g copper tailings into 100 g waste sludge. PMMA contributes to construct macropores, which is essential for the mass transfer of RhB into GSC particle electrodes of centimeter-size. Copper tailings promote the formation of meso- and micro-pores in GSCs, as well as improving the electrochemical properties. Consequently, GSC-10-CTs packed 3DER exhibits the highest removal efficiency and lowest energy consumption for RhB treatment. In addition, the compressive strength of GSC-10-CTs is enhanced by copper tails, that is crucial to fill into 3DER as particle electrodes. The high-efficient and cost-effective GSC-10-CTs fabricated by waste materials have the potential of substituting commercial granular activated carbon catalysts in the future, consequently promoting the application of 3DER in wastewater treatment.

Characterization of adsorption properties of extracellular polymeric substances (EPS) extracted from sludge.

Extracellular polymeric substances (EPS) of sludge play an important role in the adsorption of organic pollutants in wastewater biological treatments. Experiments were conducted to characterize the adsorption properties of EPS extracted from aerobic sludge (AE-EPS) and anaerobic sludge (AN-EPS) using a dye-probing method in this study. A model cationic dye, Toluidine blue (TB), was used as the dye probe. The adsorption of dye onto EPS to produce a dye-EPS complex would cause a change in the solution absorbance, attributed to the difference between the visible spectra of the dye and dye-EPS complex. From the change in the absorbance, the equilibrium absorption capability of EPS could be evaluated. Results indicate that Langmuir adsorption isotherm was able to adequately describe the adsorption equilibrium of TB onto both EPS at various pH values. From the Langmuir adsorption isotherm, the maximum binding capabilities were calculated to be 1.9 and 2.5 mmol/g EPS for AE-EPS at pH 7.0 and 11.0, and 1.6 and 1.9 mmol/g EPS for AN-EPS at pH 7.0 and 11.0, respectively. The first-order rate constants were calculated to be 0.033 and 0.35 min(-1) for AE-EPS at pH 7.0 and 11.0, and 0.069 and 0.18 min(-1) for AN-EPS at pH 7.0 and 11.0, respectively. The results of the present study demonstrated that the dye-probing method was appropriate for investigating the adsorption process of EPS in aqueous solution.

Characterization of extracellular polymeric substances of aerobic and anaerobic sludge using three-dimensional excitation and emission matrix fluorescence spectroscopy.

In this study three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy was applied to characterize the extracellular polymeric substances (EPS) extracted from aerobic and anaerobic sludge in wastewater treatment. Three fluorescence peaks were identified in EEM fluorescence spectra of the EPS samples. Two peaks were attributed to the protein-like fluorophores, and the third to the humic-like fluorophores. The effects of both pH and EPS concentration were significant on EEM fluorescence spectra of EPS, but the ionic strength had no substantial effect on EEM spectra of the EPS. The differences in the EPS fluorescence parameters, e.g., peak locations, intensities and ratios of various peak intensities, indicate the difference in the chemical structures of the EPS from various origins. EEM spectroscopy was proven to be an appropriate and effective method to characterize the EPS from various origins in wastewater treatment systems.

Silver nanoparticles formation by extracellular polymeric substances (EPS) from electroactive bacteria.

Microbial extracellular polymeric substances (EPS) excreted from microorganisms were a complex natural biological polymer mixture of proteins and polysaccharides, which played an important roles in the transport of metals, such as Ag(+). Electroactive bacteria, is an important class of environmental microorganisms, which can use iron or manganese mineral as terminal electron acceptors to generate energy for biosynthesis and cell maintenance. In this work, the EPS extracted of three electroactive bacteria (Shewanella oneidensis, Aeromonas hydrophila, and Pseudomonas putida) were used for reducing Ag(+) and forming silver nanoparticles (AgNPs). Results showed that all the three microbial EPS could reduce Ag(+) to AgNPs. The formed AgNPs were characterized in depth by the UV-visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The main components in the EPS from the three electroactive bacteria were analyzed. The presence of cytochrome c in these EPS was confirmed, and they were found to contribute to the reduction of Ag(+) to AgNPs. The results indicated that the EPS of electroactive bacteria could act as a reductant for AgNPs synthesis and could provide new information to understand the fate of metals and their metal nanoparticles in the natural environments.

Redox properties of extracellular polymeric substances (EPS) from electroactive bacteria.

Although the capacity for electroactive bacteria to convert environmental metallic minerals and organic pollutants is well known, the role of the redox properties of microbial extracellular polymeric substances (EPS) in this process is poorly understood. In this work, the redox properties of EPS from two widely present electroactive bacterial strains (Shewanella oneidensis and Pseudomonas putida) were explored. Electrochemical analysis demonstrates that the EPS extracted from the two strains exhibited redox properties. Spectroelectrochemical and protein electrophoresis analyses indicate that the extracted EPS from S. oneidensis and P. putida contained heme-binding proteins, which were identified as the possible redox components in the EPS. The results of heme-mediated behavior of EPS may provide an insight into the important roles of EPS in electroactive bacteria to maximize their redox capability for biogeochemical cycling, environmental bioremediation and wastewater treatment.

Roles of extracellular polymeric substances in enhanced biological phosphorus removal process.

Enhanced biological phosphorus removal (EBPR) process is known to mainly rely on the ability of phosphorus-accumulating organisms to take up, transform and store excess amount of phosphorus (P) inside the cells. However, recent studies have revealed considerable accumulation of P also in the extracellular polymeric substances (EPS) of sludge, implying a non-negligible role of EPS in P removal by EBPR sludge. However, the contribution of EPS to P uptake and the forms of accumulated extracellular P vary substantially in different studies, and the underlying mechanism of P transformation and transportation in EPS remains poorly understood. This review provides a new recognition into the P removal process in EBPR system by incorporating the role of EPS. It overviews on the characteristics of P accumulation in EPS, explores the mechanism of P transformation and transportation in EBPR sludge and EPS, summarizes the main influential factors for the P-accumulation properties of EPS, and discusses the remaining knowledge gaps and needed future efforts that may lead to better understanding and use of such an EPS role for maximizing P recovery from wastewater.

Simultaneous effective carbon and nitrogen removals and phosphorus recovery in an intermittently aerated membrane bioreactor integrated system.

Recovering nutrients, especially phosphate resource, from wastewater have attracted increasing interest recently. Herein, an intermittently aerated membrane bioreactor (MBR) with a mesh filter was developed for simultaneous chemical oxygen demand (COD), total nitrogen (TN) and phosphorous removal, followed by phosphorus recovery from the phosphorus-rich sludge. This integrated system showed enhanced performances in nitrification and denitrification and phosphorous removal without excess sludge discharged. The removal of COD, TN and total phosphorus (TP) in a modified MBR were averaged at 94.4 ± 2.5%, 94.2 ± 5.7% and 53.3 ± 29.7%, respectively. The removed TP was stored in biomass, and 68.7% of the stored phosphorous in the sludge could be recovered as concentrated phosphate solution with a concentration of phosphate above 350 mg/L. The sludge after phosphorus release could be returned back to the MBR for phosphorus uptake, and 83.8% of its capacity could be recovered.

Development of an energy-saving anaerobic hybrid membrane bioreactors for 2-chlorophenol-contained wastewater treatment.

A novel energy-saving anaerobic hybrid membrane bioreactor (AnHMBR) with mesh filter, which takes advantage of anaerobic membrane bioreactor and fixed-bed biofilm reactor, is developed for low-strength 2-chlorophenol (2-CP)-contained wastewater treatment. In this system, the anaerobic membrane bioreactor is stuffed with granular activated carbon to construct an anaerobic hybrid fixed-bed biofilm membrane bioreactor. The effluent turbidity from the AnHMBR system was low during most of the operation period, and the chemical oxygen demand and 2-CP removal efficiencies averaged 82.3% and 92.6%, respectively. Furthermore, a low membrane fouling rate was achieved during the operation. During the AnHMBR operation, the only energy consumption was for feed pump. And a low energy demand of 0.0045-0.0063kWhm(-3) was estimated under the current operation conditions. All these results demonstrated that this novel AnHMBR is a sustainable technology for treating 2-CP-contained wastewater.

Polyethylenimine modified biochar adsorbent for hexavalent chromium removal from the aqueous solution.

A chemical modified biochar with abundant amino groups for heavy metal removal was prepared using polyethylenimine (PEI) as a modification reagent, and used as an adsorbent for the removal of Cr(VI) from aqueous solution. The biochars before and after modification were characterized by Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy etc. The adsorption of Cr(VI) by the modified biochar was obeyed pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Its maximum adsorption capacity was 435.7 mg/g, which was much higher than that of pristine biochar (23.09 mg/g). Results also indicated that the removal of Cr(VI) by the PEI modified biochar depended on solution pH, and a low pH value was favorable for the Cr(VI) removal. The results herein revealed that the PEI modified biochar had a good potential as a suitable material for sorption and detoxification of Cr(VI) from aqueous solution.

In-situ utilization of generated electricity in an electrochemical membrane bioreactor to mitigate membrane fouling.

How to mitigate membrane fouling remains a critical challenge for widespread application of membrane bioreactors. Herein, an antifouling electrochemical membrane bioreactor (EMBR) was developed based on in-situ utilization of the generated electricity for fouling control. In this system, a maximum power density of 1.43 W/m(3) and a current density of 18.49 A/m(3) were obtained. The results demonstrate that the formed electric field reduced the deposition of sludge on membrane surface by enhancing the electrostatic repulsive force between them. The produced H2O2 at the cathode also contributed to the fouling mitigation by in-situ removing the membrane foulants. In addition, 93.7% chemical oxygen demand (COD) removal and 96.5% NH4(+)-N removal in average as well as a low effluent turbidity of below 2 NTU were achieved, indicating a good wastewater treatment performance of the EMBR. This work provides a proof-of-concept study of an antifouling MBR with high wastewater treatment efficiency and electricity recovery, and implies that electrochemical control might provide another promising avenue to in-situ suppress the membrane fouling in MBRs.

A novel electrochemical membrane bioreactor as a potential net energy producer for sustainable wastewater treatment.

One possible way to address both water and energy shortage issues, the two of major global challenges, is to recover energy and water resource from wastewater. Herein, a novel electrochemical membrane bioreactor (EMBR) was developed to recover energy from wastewater and meantime harvest clean water for reuse. With the help of the microorganisms in the biocatalysis and biodegradation process, net electricity could be recovered from a low-strength synthetic wastewater after estimating total energy consumption of this system. In addition, high-quality clean water was obtained for reuse. The results clearly demonstrate that, under the optimized operating conditions, it is possible to recover net energy from wastewater, while at the same time to harvest high-quality effluent for reuse with this novel wastewater treatment system.

Species of phosphorus in the extracellular polymeric substances of EBPR sludge.

In this study, the species of extracellular phosphorus and their transformation during extracellular polymeric substances (EPS) extraction were explored by using (31)P nuclear magnetic resonance spectroscopy. Results show that the extraction methods had a substantial influence on the phosphorus species in the extracted EPS. Cation exchange resin method was more appropriate for extracting EPS from the enhanced biological phosphorus removal (EBPR) sludge. Orthophosphate, pyrophosphate and polyphosphate were the main species of phosphorus found to be present in the EPS, which together accounted for about 6.6-10.5% of the total phosphorus in the EBPR sludge. The high percentage of extracellular phosphorus and their diverse species might reveal a new insight into the characteristics of the phosphorus in EPS in EBPR system.

Phenothiazine derivative-accelerated microbial extracellular electron transfer in bioelectrochemical system.

In bioelectrochemical system (BES) the extracellular electron transfer (EET) from bacteria to anode electrode is recognized as a crucial step that governs the anodic reaction efficiency. Here, we report a novel approach to substantially enhance the microbial EET by immobilization of a small active phenothiazine derivative, methylene blue, on electrode surface. A comparison of the currents generated by Shewanella oneidensis MR-1 and its mutants as well as the electrochemical analytical results reveal that the accelerated EET was attributed to enhanced interactions between the bacterial outer-membrane cytochromes and the immobilized methylene blue. A further investigation into the process using in situ Raman spectro-electrochemical method coupled with density functional theory calculations demonstrates that the electron shuttling was achieved through the change of the molecule conformation of phenothiazine in the redox process. These results offer useful information for engineering BES.

Thermodynamic analysis on the binding of heavy metals onto extracellular polymeric substances (EPS) of activated sludge.

Metal binding to microbial extracellular polymeric substances (EPS) greatly influences the distribution of heavy metals in microbial aggregates, soil and aquatic systems in nature. In this work, the thermodynamic characteristics of the binding between aqueous metals (with copper ion as an example) and EPS of activated sludge were investigated. Isothermal titration calorimetry was employed to estimate the thermodynamic parameters for the binding of Cu²âº onto EPS, while three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis was used for quantifying the complexation of Cu²âº with the EPS. The binding mechanisms were further explored by X-ray absorption fine structure (XAFS) and Fourier transform infrared (FTIR) spectroscopy analysis. The results show that the proteins and humic substances in EPS were both strong ligands for Cu²âº. The binding capacity N, binding constant K, binding enthalpy ΔH were calculated as 5.74 × 10⁻² mmol/g, 2.18 × 105 L/mol, and -11.30 kJ/mol, respectively, implying that such a binding process was exothermic and thermodynamically favorable. The binding process was found to be driven mainly by the entropy change of the reaction. A further investigation shows that Cu²âº bound with the oxygen atom in the carboxyl groups in the EPS molecules of activated sludge. This study facilitates a better understanding about the roles of EPS in protecting microbes against heavy metals.