Membrane fouling caused by biological foams in a submerged membrane bioreactor: Mechanism insights

Quorum quenching strategy for biofouling control in membrane photobioreactor

This study aims to reduce membrane fouling in membrane photobioreactor (MPBR) through the quorum quenching (QQ) strategy. For this purpose, the QQ beads (immobilized Rhodococcus sp. BH4) were added to the MPBR, and antifouling ability was evaluated in consideration of the changes in transmembrane pressure (TMP), extracellular polymeric substance (EPS), microbial community, and cake layer morphology on the membrane surface. The results showed that the TMP of control MPBR (MPBR-C) reached 818 mbar and 912 mbar on the operation hours of 35 and 170, while the TMP of experimental MPBR (MPBR-QQ) was only 448 mbar and 676 mbar, respectively. The QQ strategy effectively reduced the EPS content in MPBR. The microscopic observations indicated that the QQ diminished the cake layer formation and pore-blocking on the membrane surface. Comparisons of 16S and 18S gene communities revealed minor differences between bacterial and eukaryotic species in MPBRs at phylum and class levels.

Role of microparticles in membrane fouling from acidogenesis to methanogenesis phases in an anaerobic baffled reactor

Microparticles (0.45-10 μm) have been recognized as key foulants in anaerobic membrane bioreactors (AnMBRs). However, their characteristics and fouling behaviors are often understood in single-stage and completely mixed reactors, failing to elucidate the occurrence of microparticles in the multi-stage anaerobic bioprocess. Here, a lab-scale anaerobic baffled reactor with four compartments (C1-C4) was employed to explore the composition and fouling potential of microparticles in different compartments. Photometric analysis showed that the microparticles had an increasing percentage in the total organics of the top supernatant but a decreasing concentration from C1 to C4. Long-term filtration and dead-end filtration tests revealed that the top supernatant in C1 had much higher fouling potential than those in C2-C4. The supernatant microparticles significantly accumulated in the cake layers for each compartment (68-95% of the total organics), particularly the fraction of 1-5 μm, and the fouling rate was positively correlated with the biomass accumulation rate. Based on reactor performance and 16S rRNA gene sequences, a significant bio-phase separation occurred between C1 (acidogenesis) and C2-C4 (methanogenesis). And hydrolytic and fermentative bacteria in the family Veillonellaceae, Streptococcaceae, and Enterobacteriaceae were dominant in the supernatant microparticles, particularly in C1, which had a positive correlation with the fouling rate and biomass accumulation rate. These above results all revealed that the microparticles in the acidogenesis phase had higher fouling potential. In summary, our results suggest that the tactic of pre-hydrolysis and acidification with feedstocks and constructing AnMBRs by coupling with multi-phase anaerobic bioprocesses and membrane units could be beneficial to fouling control.

Characterizing membrane fouling formation during ultrafiltration of high-salinity organic wastewater

High-salinity organic wastewater usually consists of diverse highly concentrated ions such as Na⁺, Ca²⁺ and Al³⁺ etc., which may significantly influence the fouling propensity when membrane technique is employed for contaminants removal. The current work investigated the effects of high salinity especially high-concentration Na⁺, Ca²⁺ and Al³⁺ on UF fouling characteristics, where 2 M Na⁺ and 0.5-1.0 M Ca²⁺ or Al³⁺ were applied according to the general composition of high-salinity wastewater. The results demonstrated that the presence of high-concentration Na⁺ alone benefited the ultrafiltration of bovine serum albumin (BSA) solution, but posed adverse effects on the ultrafiltration of humic acid (HA) solution. Further addition of Ca²⁺ or Al³⁺ on the basis of Na⁺ was found to aggravate the development of BSA fouling. Such differentiated behaviors were further elucidated by the comprehensive fouling characterizations in terms of foulant properties, specific resistances, filtration modelling and fouling layer observations. Correlation analysis suggested that irreversible fouling had strong relationship with Al³⁺ addition, while reversible fouling seemed to be primarily influenced by foulant size. Meanwhile, membrane rejection in the presence of various salts remarkably decreased, which was negatively correlated with zeta potential. Consequently, this study should shed light on the membrane fouling formation for treating high-salinity organic wastewater using membrane techniques.

The responses of activated sludge to membrane cleaning reagent H2O2 and protection of extracellular polymeric substances

Hydrogen peroxide (H₂O₂) is evaluated as a potential replacement for chlorine to control biofouling in membrane bioreactors (MBRs). However, H₂O₂ might diffuse into the mixed liquor and damage microorganisms during membrane cleaning. This study comprehensively analyzed the impacts of H₂O₂ on microbes. Key enzymes involved in phenol biodegradation were inhibited with H₂O₂ concentration increased, and thus phenol degradation efficiency was decreased. Increase of lactic dehydrogenase (LDH) and intracellular reactive oxygen species (ROS) indicated more severe cell rupture with H₂O₂ concentration increased. At the same H₂O₂ concentration, Extracellular polymeric substances (EPS) extraction further led to inhibiting the activity of key enzymes, decreasing phenol degradation efficiency, and enhancing LDH release and ROS production, demonstrating that the existence of EPS moderated the adverse impacts on microbes. Spectroscopic characterization revealed the increase of H₂O₂ decreased tryptophan protein-like substances, protein-associated bonds and polysaccharide-associated bonds. Hydroxyl and amide groups in EPS were attacked, which might lead to the consumption of H₂O₂, indicated EPS protect the microorganism through sacrificial reaction with H₂O₂.

Evaluation of membrane cake fouling mechanism to estimate design parameters of a submerged AnMBR treating high strength industrial wastewater

A mathematical model, which was previously developed for submerged aerobic membrane bioreactors, was successfully applied to elucidate the membrane cake-layer fouling mechanisms due to bound extracellular polymeric substances (eEPS) in a submerged anaerobic membrane bioreactor (SAnMBR). This biofouling dynamic model explains the mechanisms such as attachment, consolidation and detachment of eEPS produced in the bioreactor on the membrane surface. The 4th order Runge-Kutta method was used to solve the model equations, and the parameters were estimated from simulated and experimental results. The key design parameters representing the behaviour of cake fouling dynamics were systematically investigated. Organic loading rate (OLR) was considered a controlling factor governing the mixed liquor suspended solids (MLSS), eEPS production, filtration resistance (R_t), and transmembrane pressure (TMP) variations in a SAnMBR. eEPS showed a proportional relation with OLR at subsequent MLSS variations. The consolidation of EPS increased the specific eEPS resistance (α_s), influencing the cake resistance (R_c). The propensities of eEPS showed a positive correlation with R_t and TMP. The outcomes of the study also estimated a set of valuable design parameters which would be vital for applying in AnMBRs treating industrial wastewater.

Biological mechanism of alleviating membrane biofouling by porous spherical carriers in a submerged membrane bioreactor

In this study, porous spherical carriers were fixed around the hollow fiber membrane module to mitigate membrane biofouling. Two MBRs (R1 without carriers, R2 with carriers) were operated for 31 days under identical operating conditions to investigate the effects of the carriers on the reactor performances, the production of extracellular polymeric substances (EPS), the level of N-acyl-homoserine lactones (AHLs), and the microbial communities. The results showed that the presence of carriers in MBR was conducive to nitrogen removal and decreased the total membrane filtration resistance by about 1.7 times. Slower transmembrane pressure (TMP) rise-up, thinner bio-cakes, lower EPS production, and fewer tryptophan and aromatic proteins substances on the membrane surface were observed in R2. The polysaccharides secretion of EPS in bio-cakes was mainly regulated by C4-HSL and 3OC6-HSL in the presence of carriers. The microbial community analysis revealed that carriers addition reduced the relative abundance of EPS and AHL producing bacteria in the membrane bio-cakes and enriched the accumulation of functional bacteria conducive to nutrient removal in the mixed liquor. This study provided an in-depth understanding for the application of porous spherical carriers to alleviate membrane biofouling.

Comparative analysis of membrane fouling mechanisms induced by colloidal polymer: Effects of sodium and calcium ions

Polymer (anionic polyacrylamide, APAM) flooding produced wastewater has a relatively high degree of mineralization and abundant ionic species. A comprehensive and systematic investigation of the influence of ion identity on APAM-induced membrane fouling is extremely necessary but has not been conducted to date. A comparative investigation was performed herein to reveal the underlying mechanisms of the influence of Na⁺ and Ca²⁺ (1000 mg/L) on APAM-induced membrane fouling in the adsorption and microfiltration (MF) processes. Na⁺ and Ca²⁺ exhibited contrasting influences on the filtration efficiency, cleaning efficiency, and fouling resistance. Compared to Na⁺, Ca²⁺ promoted reversible fouling and the formation of a loose cake layer; moreover, a higher removal rate and flux recovery were achieved. Additionally, simulations based on adsorption kinetic and membrane fouling models, and a series of microscopic analyses were performed to validate the contradictory influences. During the APAM-based MF process, the membrane fouling was effectively mitigated at the applied ionic strength because of the stronger hydration repulsive force generated by hydrated Ca²⁺ compared to that by Na⁺. This study provides vital guidance for membrane fouling control in the microfiltration of polymer flooding produced wastewater.

FeNi2P three-dimensional oriented nanosheet array bifunctional catalysts with better full water splitting performance than the full noble metal catalysts

The 3D (three-dimensional) oriented nanosheet array FeNi₂P electrocatalyst grown on carbon cloth (FeNi₂P/CC) is explored in this work. This unique 3D oriented nanosheet array structure can expose more catalytic active sites, promote the penetration of electrolyte solution on the catalyst surface, and facilitate the transfer of ions, thus speeding up the kinetic process of Hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER). At the current densities of 10 mA/cm² in 1 M KOH solution, the HER overpotential (71 mV) of the FeNi₂P/CC self-supporting electrode is very close to that of noble metal HER catalyst of 20% Pt/C (54 mV), and its OER overpotential (210 mV) is 34% lower than that of the precious metal OER catalyst of RuO₂ (318 mV), demonstrating the excellent electrocatalytic performance of the FeNi₂P/CC catalyst. Moreover, the cell voltage for full water splitting (at 10 mA/cm² current densities) of the FeNi₂P/CC bifunctional electrode cell is 1.52 V, which is 3.8% lower than that of the full noble-metal electrode reference cell (RuO₂ || Pt/C, 1.58 V), suggesting that this FeNi₂P/CC bifunctional catalyst is likely to replace precious metals to reduce the costs in full water splitting application. According to density functional theory (DFT) calculation results, the introduction of iron atom can change the electronic structure of the Ni₂P, so it can reduce the adsorption energy of hydrogen and oxygen, and facilitate the adsorption and desorption of hydrogen and oxygen on the surface of the catalyst, improving its performance of HER and OER.

Comparison between novel vibrating ceramic MBR and conventional air-sparging MBR for domestic wastewater treatment: Performance, fouling control and energy consumption

Two crucial themes emerge from the growing application of MBRs treating domestic wastewater so far: fouling control and energy demand. The significance of in-situ shear-enhanced methods for fouling control in MBRs has been widely acknowledged with air sparging over decades. However, it is still a challenge to develop energy-efficient ways to replace energy-intensive air sparging for effective fouling control during long-term real domestic wastewater treatment. A novel vibrating flat-sheet ceramic MBR (VMBR) was established for investigating the effects of different shear rates on treatment performance, fouling control and specific energy demand compared with air-sparging MBR (ASMBR). Three levels of shear rates with vibration speed of 120, 80, and 40 RPM in the VMBR, versus specific aeration rate of 1.5, 1.0 and 0.5 LPM in the ASMBR were examined as high-, middle- and low-shear phases. Results showed that the VMBR removed over 78.35% TOC, 89.89% COD and 99.9% NH₄-N over three phases, and retarded initial increases in transmembrane pressure to control membrane fouling effectively with average fouling rate around 2.31 kPa/d, 3.59 kPa/d and 10.15 kPa/d, almost 70% lower than the ASMBR in Phase 1, 2 and 3, respectively. Particle size distribution of mixed liquor revealed that colloids and biopolymer clusters were significantly reduced in the VMBR showing less propensity for foulant formation. DOM characteristics further indicated that lower production of polysaccharides and protein (by approximately half in Phases 1 and 2) of SMP and EPS in the VMBR generated lower biopolymer content, promoting better fouling mitigation and enhanced dewaterability compared to the ASMBR. Moreover, the VMBR showed superior energy efficiency for fouling control and could save 51.7% to 78.5% energy of the ASMBR under similar-shear condition. The combination of excellent treatment performance, fouling control and energy efficiency from the VMBR makes this an attractive strategy for future improvement of MBR designs in full-scale application with the potential to replace conventional ASMBR.

Fabrication of chitosan-aminopropylsilane graphene oxide nanocomposite hydrogel embedded PES membrane for improved filtration performance and lead separation

In the present study chitosan-aminopropylsilane graphene oxide (CS-APSGO) nanocomposite hydrogel was synthesized and utilized as a hydrophilic additive in different dosages (0.5, 1, 2 and 5 wt%) in fabrication of porous polyethersulfone (PES) membranes via the phase inversion induced process by immersion precipitation method for heavy metal ion and dye removal. The modified membranes were characterized using ATR-FTIR, AFM, SEM, water contact angle, overall porosity and mean pore radius evaluations and zeta potential measurement. The addition of CS-APSGO nanocomposite hydrogel to PES doping solutions enhanced membranes hydrophilicity and consequently pure water flux permeability. Filtration performance of the CS-APSGO embedded membranes showed promising antifouling properties during BSA filtration test (FRR> 90%) and 1 wt% membranes showed the highest pure water flux of 123.8 L/m² h with BSA rejection more than 98% and removal capability more than 82% for lead (II) ion, 90.5% and 98.5% for C.I. Reactive Blue 50 and C.I. Reactive Green 19, respectively. Therefore, the CS-APSGO nanocomposite hydrogel blending in order to modification of PES-based membranes have a noticeable potential in improving filtration performance of blended membranes.

Long-Term Continuous Extraction of Medium-Chain Carboxylates by Pertraction With Submerged Hollow-Fiber Membranes

Medium-chain carboxylic acids (MCCAs), which can be generated from organic waste and agro-industrial side streams through microbial chain elongation, are valuable chemicals with numerous industrial applications. Membrane-based liquid-liquid extraction (pertraction) as a downstream separation process to extract MCCAs has been applied successfully. Here, a novel pertraction system with submerged hollow-fiber membranes in the fermentation bioreactor was applied to increase the MCCA extraction rate and reduce the footprint. The highest average surface-corrected MCCA extraction rate of 655.2 ± 86.4 mmol C m⁻² d⁻¹ was obtained, which was higher than any other previous reports, albeit the relatively small surface area removed only 11.6% of the introduced carbon via pertraction. This submerged extraction system was able to continuously extract MCCAs with a high extraction rate for more than 8 months. The average extraction rate of MCCA by internal membrane was 3.0- to 4.7-fold higher than the external pertraction (traditional pertraction) in the same bioreactor. A broth upflow velocity of 7.6 m h⁻¹ was more efficient to extract MCCAs when compared to periodic biogas recirculation operation as a means to prevent membrane fouling. An even higher broth upflow velocity of 40.5 m h⁻¹ resulted in a significant increase in methane production, losing more than 30% of carbon conversion to methane due to a loss of H₂, and a subsequent drop in the H₂ partial pressure. This resulted in the shift from a microbial community with chain elongators as the key functional group to methanogens, because the drop in H₂ partial pressure led to thermodynamic conditions that oxidizes ethanol and carboxylic acids to acetate and H₂ with methanogens as the syntrophic partner. Thus, operators of chain elongating systems should monitor the H₂ partial pressure when changes in operating conditions are made.

Effects of High Salinity on Alginate Fouling during Ultrafiltration of High-Salinity Organic Synthetic Wastewater

Ultrafiltration is widely employed in treating high-salinity organic wastewater for the purpose of retaining particulates, microbes and macromolecules etc. In general, high-salinity wastewater contains diverse types of saline ions at fairly high concentration, which may significantly change foulant properties and subsequent fouling propensity during ultrafiltration. This study filled a knowledge gap by investigating polysaccharide fouling formation affected by various high saline environments, where 2 mol/L Na⁺ and 0.5–1.0 mol/L Ca²⁺/Al³⁺ were employed and the synergistic influences of Na⁺-Ca²⁺ and Na⁺-Al³⁺ were further unveiled. The results demonstrated that the synergistic influence of Na⁺-Ca²⁺ strikingly enlarged the alginate size due to the bridging effects of Ca²⁺ via binding with carboxyl groups in alginate chains. As compared with pure alginate, the involvement of Na⁺ aggravated alginate fouling formation, while the subsequent addition of Ca²⁺ or Al³⁺ on the basis of Na⁺ mitigated fouling development. The coexistence of Na⁺-Ca²⁺ led to alginate fouling formed mostly in a loose and reversible pattern, accompanied by significant cracks appearing on the cake layer. In contrast, the fouling layer formed by alginate-Na⁺-Al³⁺ seemed to be much denser, leading to severer irreversible fouling formation. Notably, the membrane rejection under various high salinity conditions was seriously weakened. Consequently, the current study offered in-depth insights into the development of polysaccharide-associated fouling during ultrafiltration of high-salinity organic wastewater.

A high-response formaldehyde sensor based on fibrous Ag-ZnO/In2O3 with multi-level heterojunctions

Timely detection of formaldehyde is pivotal because formaldehyde is slowly released from the indoor decorative materials, jeopardizing our healthy. Herein, a high-response formaldehyde gas sensor based on Ag-ZnO/In₂O₃ nanofibers was successfully fabricated. Compared with all the control samples, the hybrid exhibits superior sensitivity (0.65 ppm^-1), excellent selectivity (≥ 12.5) and durable stability (the deviation value ≤ 3%). Particularly, an ultra-high response value of about 186 towards 100 ppm of formaldehyde at 260 °C was achieved, heading the list of outstanding candidates. Additionally, the limit of detection is as low as 9 ppb. The enhanced gas sensing properties can be mainly attributed to multi-level heterojunctions (n-n heterojunction and Ohmic junction) and the "spill-over" effect of Ag, ultimately increasing the adsorption of gas molecules on the surface of sensing material. This work verifies that proper design of multi-level heterojunctions significantly upgrade the sensing performance.

New methods based on back propagation (BP) and radial basis function (RBF) artificial neural networks (ANNs) for predicting the occurrence of haloketones in tap water

Haloketones (HKs) is one class of disinfection by-products (DBPs) which is genetically toxic and mutagenic. Monitoring HKs in drinking water is important for drinking water safety, yet it is a time-consuming and laborious job. Developing predictive models of HKs to estimate their occurrence in drinking water is a good alternative, but to date no study was available for HKs modeling. This study was to explore the feasibility of linear, log linear regression models, back propagation (BP) as well as radial basis function (RBF) artificial neural networks (ANNs) for predicting HKs occurrence (including dichloropropanone, trichloropropanone and total HKs) in real water supply systems. Results showed that the overall prediction ability of RBF and BP ANNs was better than linear/log linear models. Though the BP ANN showed excellent prediction performance in internal validation (N₂₅ = 98-100%, R² = 0.99-1.00), it could not well predict HKs occurrence in external validation (N₂₅ = 62-69%, R² = 0.202-0.848). Prediction ability of RBF ANN in external validation (N₂₅ = 85%, R² = 0.692-0.909) was quite good, which was comparable to that in internal validation (N₂₅ = 74-88%, R² = 0.799-0.870). These results demonstrated RBF ANN could well recognized the complex nonlinear relationship between HKs occurrence and the related water quality, and paved a new way for HKs prediction and monitoring in practice.

Immobilization properties and adsorption mechanism of nickel(II) in soil by biochar combined with humic acid-wood vinegar

Biochar (BC) combined with humic acid (HA) and wood vinegar (WV) was designed and prepared as an inexpensive, effective, and environmentally friendly immobilization material (BHW) for metal-polluted soil. The influences of the wood vinegar and humic acid on the immobilization properties and adsorption mechanism of this new material were also investigated. The remediation performance was evaluated using a laboratory-made, nickel-contaminated soil with a Ni²⁺ concentration of 200 mg per kg surface soil (top 20 cm from agricultural land). The results indicated that the immobilization ratio sequence of nickel (II) in the soil was BC< BH< BHW. The maximum adsorption capacity increased in the same order: BC< BH< BHW. All three adsorption isotherms were better fitted by the Freundlich model, which were consistent with the surface heterogeneity of the remediation materials. The cause of this surface heterogeneous migration may be due to the increase in oxygen-containing groups in the BC introduced by the HA and WV. The WV can increase the number of the oxygen-containing groups in the BC combined with HA, which enhanced the adsorption and immobilization of Ni²⁺ ions. The results suggested that BHW is recommended for the remediation of metal-contaminated soils, because of its high efficacy, economic feasibility, environmental and food safety.

Charge transfer channels of silver @ cuprous oxide heterostructure core-shell nanoparticles strengthen high photocatalytic antibacterial activity

Marine biological fouling has always been a hot research topic. In this study, silver @ cuprous oxide (Ag@Cu₂O) core-shell nanoparticles were synthesized via in-situ synthesis method and developed an outstanding antibacterial activity. The bacteriostasis efficiency of Ag@Cu₂O reached to 99% and 98% against Staphylococcus aureus and Pseudomonas aeruginosa, respectively. The minimum inhibitory concentration of Ag@Cu₂O decreased from 113.6 μg/mL to 56.8 μg/mL compared with Cu₂O. Ag@Cu₂O had better antibacterial activity than Cu₂O with lower content of Cu₂O and was more environment friendly. The heterostructure formed at the interface between Ag and Cu₂O promoted the separation and diffusion of photogenerated electron-hole pairs through the charge transfer channel and promoted the generation of reactive oxygen species. The outstanding antibacterial activity of Ag@Cu₂O was strongly depended on the generation of the reactive oxygen species. Density functional theory and finite element method calculations demonstrated that the structure of core-shell improved photocatalytic efficiency. Additionally, synergetic effect of released Ag⁺ and Cu²⁺ also enhanced the bacteriostasis rate and the long-term antifouling performance in 60 days. Hence, the synthesized core-shell Ag@Cu₂O can be applied as novel antifoulants in the marine field.

Thermal decomposition of ammonium perchlorate-based molecular perovskite from TG-DSC-FTIR-MS and ab initio molecular dynamics

(H₂dabco)[NH₄(ClO₄)₃] (DAP, dabco = 1,4-diazabicyclo[2.2.2]octane) is a recently synthesized ammonium perchlorate-based molecular perovskite energetic material. The high-symmetry perovskite configuration assembles the oxidant ClO₄⁻ and fuel H₂dabco²⁺ into a compact cubic crystal, realizing a high energy-releasing efficiency. In this study, the thermal decomposition of DAP has been investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) coupled with Fourier transform infrared (FTIR) spectroscopy and mass spectroscopy (MS). The TG-DSC profiles show that DAP has an intense one-stage heat release process with a weight loss of 94.7%. The evolved gas products are identified as H₂O, CO₂, CO, HCl, HCN, NH₃, HNCO by FTIR spectrum, in which the infrared characteristic peak at 2283 and 2250 cm⁻¹ is clarified not from N₂O and assigned to HNCO. The principal products are H₂O and CO₂ together with significant amounts of HCl, HCN, NH₃ in MS, while few nitrogen oxides and O₂ are detected. The experimental results show that organic components have been the prominent media for the degradation of ClO₄⁻. To refine the mechanism observed in experiment, ab initio molecular dynamics simulations are carried out to reveal the atomistic reaction mechanisms. The decomposition of DAP starts with proton transfer from NH₄⁺ and H₂dabco²⁺ to ClO₄⁻. The deprotonated carbon skeleton is preferable to NH₃ in capturing O atoms, realizing a faster consumption of O atoms. Amounts of H atoms enter the environment being active free radicals, realizing an efficient autocatalytic chain propagation of degradation of ClO₄⁻. The atomistic thermal decomposition reaction mechanism of DAP uncovers the role of organic components in promoting the degradation of ClO₄⁻, which will help improve the synthesis strategy of molecular perovskite energetic materials with improved performance.

Organic components realize a more efficient autocatalytic chain propagation for degradation of ClO₄⁻ in the thermal decomposition process of DAP.

Development of the yeast and lactic acid bacteria co-culture agent for atmospheric ammonia removing: Genomic features and on-site applications

Odorous gas (e.g. atmospheric ammonia) in low ventilation public places, such as public toilets and waste transfer stations, causes severe health problems. Many technologies are developed to purify the atmospheric ammonia, among which the microbial agents are supposed to be a green and economical approach. In this study, we developed a yeast, Pichia sp. J1, and a lactic acid bacterium (LAB), Lactobacillus paracasei B1, co-culture agent for atmospheric ammonia removing. The on-site application results indicated the yeast and LAB mixed fermented agent had a maximum ammonia removing efficiency of 98.78%, which is significantly higher than the pure cultures (78.93% for B1 and 75.00% for J1), indicating the co-culture agent is an excellent biological product for ammonia removal. The excellent performance of the agent is closely related to the synergy behaviors between the yeast and LAB. In the co-culture agents, some of the LAB cells adhered closely to the yeast, and the growth and lactic acid producing ability of LAB were significantly promoted by yeast. Genomic analysis indicated the complementary of nutrients, i.e. carbon and nitrogen resources, signal transduction, and adhesion proteins (regulates adhesion behavior) played roles in regulating the synergy effects. Our study offers a novel biological solution of odorous gas purification.

A novel single-stage ceramic membrane moving bed biofilm reactor coupled with reverse osmosis for reclamation of municipal wastewater to NEWater-like product water

In this study, a single-stage ceramic membrane moving bed biofilm reactor (CMMBBR) was developed for simultaneous COD and nitrogen removal, while its effluent was further reclaimed to ultra-clean water by a coupled reverse osmosis (RO) unit. Results showed that approximately 97% of COD and 93% of total nitrogen (TN) removal were obtained in CMMBBR, with the effluent COD and TN concentrations being 8.15 mg/L and 2.31 mg/L, respectively. The excellent performance of CMMBBR was achieved at a constant permeate flux of 30 L/m²/h (LMH), with the average dTMP/dt of 0.05 bar/d due to the low suspended sludge concentration (i.e. 75 mg VSS/L) and the effective membrane scouring by fluidized biocarriers. The excellent permeate quality of CMMBBR could lead to a very low RO fouling rate of 0.029 bar/d, with the product water quality meeting typical NEWater standards in major ions concerned. In addition, the energy and cost analyses further indicated that the proposed CMMBBR-RO process could reduce 43.8% of energy consumption and 23.5% of operating cost compared to the current NEWater production process. It is expected that the integrated CMMBBR-RO process could provide a promising alternative for municipal wastewater reclamation to high-grade product water towards minimized sludge production and energy-efficient operation.

Effect of sodium alginate molecular structure on electrospun membrane cell adhesion

Alginate-based electrospun nanofibers prepared via electrospinning technique represent a class of materials with promising applications in the biomedical and pharmaceutical industries. However, to date, the effect of alginate molecular mass and block composition on the biological response of such systems remains to some extent unclear. As such, in the present work, three alginates (i.e., M.pyr, L.hyp, A.nod) with different molecular features are employed to prepare nanofibers whose ability to promote cell adhesion is explored by using both skin and bone cell lines. Initially, a preliminary investigation of the raw materials is carried out via rheological and zeta-potential measurements to determine the different grade of polyelectrolyte behaviour of the alginate samples. Specifically, both the molecular mass and block composition are found to be important factors affecting the alginate response, with long chains and a predominance of guluronic moieties leading to a marked polyelectrolyte nature (i.e., lower dependence of the solution viscosity upon the polymer concentration). Subsequently, physically crosslinked alginate nanofibrous mats are first morphologically characterized via both scanning electron and atomic force microscopy, which show a homogenous and defect-free structure, and their biological response is then evaluated. Noticeably, fibroblast and keratinocyte cell lines do not show significant differences in terms of cell adhesion on the three mats (i.e., 30-40% and 10-20% with respect to the seeded cells, respectively), with the formers presenting a greater affinity toward the alginate-based nanofibers. Conversely, both the investigated osteoblast cells are characterized by a distinct behaviour depending on the alginate type. Specifically, polysaccharide samples with an evident polyelectrolyte nature are found to better promote cell viability (i.e., cell adhesion in the range 15-36% with respect to seeded cells) compared to the ones displaying a nearly neutral behaviour (i.e., cell adhesion in the range 5-25% with respect to seeded cells). Therefore, the obtained results, despite being preliminary, suggest that the alginate type (i.e., molecular structure properties) may play a topical role in conditioning the efficiency of healing patches for bone reparation, but it has a negligible effect in the case of skin regeneration.

Biochemical characteristics and membrane fouling behaviors of soluble microbial products during the lifecycle of Escherichia coli

The complexity of production process and chemical compositions of soluble microbial products (SMPs) largely limits the understanding of membrane fouling in membrane bioreactors (MBRs). Herein, we used a model single-strain Escherichia coli to better understand the chemical natures of SMPs and their roles in membrane fouling. The effects of carbon source and growth phase on the chemical compositions of SMPs were identified at both the compound and molecular levels by using advanced techniques including excitation emission matrix and parallel factor analysis (EEM-PARAFAC), size exclusion chromatography coupled with organic carbon detection (LC-OCD), and untargeted ultra-performance liquid chromatography - Q-Exactive - mass spectrometry (UPLC-Q-Exactive-MS). Subsequently, the roles of SMPs in the propensity of membrane fouling during ultrafiltration (UF) were studied. The results showed that the chemical compositions and fouling potentials of SMPs were carbon source- and growth phase-dependent. In the exponential phase, SMPs mainly consisted of utilization-associated products (UAPs) and remaining substrates. As the microorganism progressed into the stationary and senescent phases, UAPs and biomass-associated products (BAPs) were the main components, respectively. The SMP contents generated in glucose medium were higher than those generated in acetate medium, and higher abundances of humic fluorescent components were observed in glucose-fed SMPs. Van Krevelen diagrams of the UPLC-MS results revealed that acetate-fed SMPs contained more carboxylic-rich alicyclic molecules, peptides-like, aromatic, and carbohydrates-like components than glucose-fed SMPs in the stationary and senescent phases. These components played a significant role in irreversible membrane fouling, as evidenced in UF experiments. Standard blocking and cake filtration were the main fouling mechanisms for the filtration of SMPs collected in the exponential and stationary/senescent phases, respectively. Our findings highlight linkages between SMP compositions and membrane fouling at both the compound and molecular levels and suggest that both the carbon source and growth phase strongly determine the production potential, chemical nature, and fouling behavior of SMPs.

Flexible-templated imprinting for fluorine-free, omniphobic plastics with re-entrant structures

HYPOTHESIS

Compared to vertical micro-pillars, re-entrant micro-structures exhibited superior omniphobicity for suspending liquids to Cassie-Baxter state. However, the existing re-entrant structures rely on complex multi-step deposition and etching procedures. The conventional, rigid-templated imprinting would instead damage the re-entrant structures. This leads to the question: is it possible to preserve the re-entrant curvatures by a flexible-templated imprinting?

EXPERIMENTS

We facilely imprinted the re-entrant structures on a plastic substrate using a flexible nylon-mesh template. The effect of imprinting time (15-35 min), temperature (110-120 °C) and pressure (15-50 Bar) was investigated. To further improve the liquid-repellency and abrasion resistance, the silica nanoparticles (30-650 nm) along with epoxy resin binder (10 mg/mL) were pre-coated.

FINDINGS

A one-step imprinting is sufficient to fabricate the re-entrant structures by utilizing flexible nylon-mesh template, without damaging the imprinted structures after the demolding process. The pre-coated silica nanoparticles and epoxy resin (1) improved liquid repellency by introducing hierarchical surface structures (e.g. contact angle hysteresis of olive oil reduced > 10°), and (2) acted as a protective layer against mechanical abrasion (omniphobicity maintained after 25 cycles, ~1.6 kPa sand paper abrasion). Additionally, the fluorine-free post-treatment was sufficient for the omniphobicity on the obtained plastic structures.

Reduction of excess sludge production by membrane bioreactor coupled with anoxic side-stream reactors

While cleaning wastewater, biological wastewater treatment processes such as membrane bioreactors (MBR) produce a significant amount of sludge that requires costly management. In the oxic-settling-anoxic (OSA) process, sludge is retained for a temporary period in side-stream reactors with low oxygen and substrate, and then it is recirculated to the main reactor. In this way, excess sludge production is reduced. We studied the influence of the rate of sludge exchange between MBR and side-stream anoxic reactors on sludge yield reduction within MBR. Two MBRs, namely, MBR_OSA and MBR_control, each coupled with separate external anoxic side-stream reactors, were run in parallel for 350 days. Unlike MBR_control, MBR_OSA had sludge exchange with the external reactors connected to it. During the investigation over a sludge interchange rate (SIR) range of 0-22%, an SIR of 11% achieved the highest sludge reduction (58%). Greater volatile solids destruction i.e., bacterial cell lysis and extracellular polymeric substance (EPS) destruction occurred at the SIR of 11%, which helped to achieve the highest sludge reduction. The enhanced volatile solids destruction was evident by the release of nutrients in the external anoxic reactors. It was confirmed that the sludge yield reduction was achieved without compromising the wastewater treatment quality, sludge settleability and hydraulic performance of the membrane in MBR.

Flocculation of emulsified oily wastewater by using functional grafting modified chitosan: The effect of cationic and hydrophobic structure

In this work, modified chitosan flocculants (MCS) was synthesized by using chitosan (CS), acrylamide, cationic monomers and hydrophobic monomers via low-pressure UV-initiated copolymerization. The flocculation performance of MCS was evaluated in emulsified oily wastewater treatment. The effect of cationic and hydrophobic structure on oil removal was studied, and the interactions between these functional groups and the components in oil were also analyzed. Results suggested that MCS flocculants exhibited excellent oil removal efficiency in a wide pH range (2.0‒10). The flocculation efficiency of 91 % was achieved at the dosages of 0.6 mL/L (6 mg/L). During pH of 2.0-10, the optimal cationic and hydrophobic monomer was DMC and VT, respectively. Silane groups were favorable for oil removal than the other hydrophobic structures. The cationic groups expanded the optimal pH range of MCS in flocculation, whereas hydrophobic groups considerably reduced the dosage of MCS. The experimental results showed that alkane, cyclic aromatic hydrocarbon compounds in oil can be easily removed by using MC4, whereas cycloalkanes compounds was effectively removed by MC6 and MC7 because of preferable demulsification capacity, and the hydrophobic interaction, interfacial adsorption and electrostatic attraction played the dominant in flocculation. Thus, the synthesized MCS is favorable for emulsified oily wastewater treatment.

The impact of gamma-irradiation from radioactive liquid wastewater on polymeric structures of nanofiltration (NF) membranes

In this study, the impacts of gamma-irradiation from the low- and intermediate-level liquid radioactive wastewaters (LILW) to polyamide (PA) structures of nanofiltration (NF) membranes were investigated. As the gamma-irradiation increased to 300 kGy in the aqueous solution at 5 bar, both the salt rejection and the water permeability of NF membranes were decreased from 95.6 ± 0.1%-74.6 ± 0.5%, and from 33.7 ± 0.3 LMH to 21.4 ± 0.5 LMH, respectively. The surface free energy and Young's modulus of the membrane indicated the decrease in hydrophilicity and the increase in fragility of PA structure after gamma-irradiation. X-ray photoelectron spectroscopy and the streaming potential analysis exhibited that the gamma-irradiation resulted the increase in the cross-linked portion of the amide bonding from 28% to 45% due to the gamma-induced new bonding between unbound carboxylic groups and amine groups. Nuclear magnetic resonance analysis confirmed that the poly(p-phenylene) in polyamide structure were changed to poly(cyclohexane) and poly(cyclohexene) by hydrogen radical disproportionation generated from the gamma-irradiated water, and it is responsible to the increase of the cross-linked PA structures. The decrease in salt rejection and water permeability is attributed to the aging of PA structures by gamma-irradiation, thus, should be carefully monitored during the treatment of LILW using NF membrane processes.

Synergistic fouling behaviors and mechanisms of calcium ions and polyaluminum chloride associated with alginate solution in coagulation-ultrafiltration (UF) process

Effects of calcium ions and polyaluminum chloride (PACl) on membrane fouling in coagulation-ultrafiltration (UF) process were investigated in this study. Filtration tests demonstrated three interesting filtration behaviors: 1) high specific filtration resistance (SFR) of alginate solution with low CaCl₂ or PACl addition (e. g. 3.51×10¹⁵ m·kg ^-1 under the condition of 1.5 mM CaCl₂ addition); 2) unimodal pattern of alginate SFR with PACl or CaCl₂ addition alone; 3) synergistic effects between CaCl₂ and PACl on alginate SFR. It was found that, the foulant morphological changes driven by the thermodynamic mechanisms based on Flory-Huggins lattice theory take the critical roles in these filtration behaviors. Density functional theory (DFT) calculations showed that initial coordination of Ca²⁺ and Al³⁺ ions with alginates tended to form tetrahedron geometry and geometry of coordinating three terminal carboxyl groups, respectively, which facilitated to elongate the alginate chains (without clustering the flocs) and form more stable gel, increasing SFR. Improving Ca²⁺ and Al³⁺ dosages triggered transition to other geometries for clustering polymeric network and flocculation, reducing SFR. Due to the higher binding affinity of Ca²⁺ over Al³⁺, Ca²⁺ and Al³⁺ sequentially take roles of enlarging polymeric network and clustering the coordination compounds, and then facilitate to form large size flocs and reduce SFR, causing the synergistic effects between CaCl₂ and PACl additions. The proposed thermodynamic mechanisms satisfactorily explained these interesting fouling behaviors, allowing to further optimize coagulation-UF process.

Green preparation of polyvinylidene fluoride loose nanofiltration hollow fiber membranes with multilayer structure for treating textile wastewater

In this work, polyvinylidene fluoride (PVDF) loose nanofiltration (NF) hollow fiber membranes with multilayer structure were prepared successfully based on a solvent-free process. Graphene oxide (GO) was used to cover the interface pores of the pristine PVDF membranes via vacuum filtration, and polypyrrole (PPy) was polymerized on the surface to further decorate the membrane structure. Interestingly, the modified membranes exhibited a multilayer structure due to synergistic effect of GO and PPy. The structure and property of PVDF loose NF membranes were investigated in detail. After modifying by GO and PPy, the hydrophilicity improved obviously. Moreover, the molecular weight cut off (MWCO) was about 3580 Da, and the smallest pore size of skin layer decreased to 2.5-4 nm. Furthermore, the PVDF loose NF hollow fiber membranes presented a high dye rejection (˃98.5%) for negative dyes, whereas a low salt rejection for NaCl (about 4%), showing a great potential for separating dye/salt accurately. Specifically, there were not any solvent used in all the preparation processes. The work offered a novel strategy for green preparation of loose NF membranes.

Flame-retardant ethylene vinyl acetate composite materials by combining additions of aluminum hydroxide and melamine cyanurate: Preparation and characteristic evaluations

There is a great interest to develop efficient fire-resistant materials. While ethylene vinyl acetate (EVA) is a widely used material, it suffers from the problem of relatively high inflammability which seriously hinders its usage as the product material with a high flame-retardant requirement. In this study, a strategy to combine aluminum hydroxide (ATH) and melamine cyanurate (MCA) with EVA was proposed to prepare the EVA composite materials with high flame resistance. It was found that slight addition of MCA could increase the lubricity of EVA and raise the compatibility between EVA and ATH. Thermogravimetric analysis (TGA) indicated that the thermal stability of EVA was improved via adding MCA, which was evidenced by the delayed thermal decomposition temperature. Moreover, the combustion results indicated that the EVA composite with 60 parts per hundred (phr) ATH and 40 phr MCA addition (EVA-60-40) displayed the optimal isolated layer favoring the fire resistance. In addition, the highest limiting oxygen index (LOI) value (27.5%) and V-0 rating of the EVA-60-40 as compared with other components indicated its incombustible nature. These results suggested the synergetic effect of ATH and MCA additions, the high efficiency of the proposed strategy and the wide application prospect of the produced EVA-ATH-MCA composite materials.