How to achieve air resistance control in hollow fiber membrane process: Membrane vibration or inner surface modification?

As a factor affecting the efficiency of hollow fiber membrane filtration, air resistance is gradually being discovered. To obtain a better air resistance control strategy, in the study, two representative strategies have been proposed, namely, membrane vibration and inner surface modification, which was achieved by aeration combined with looseness-induced membrane vibration and dopamine (PDA) hydrophilic modification of the inner surface, respectively. The performance of two strategies was based on Fiber Bragg Grating (FBG) sensing technology and ultrasonic phased array (UPA) technology to achieve real-time monitoring. Mathematical model result shows that in hollow fiber membrane modules, the initial appearance of air resistance causes a rapid reduction in filtration efficiency, while this effect diminishes as the air resistance increases. Besides, experimental results show that aeration combined with fiber looseness helps to inhibit air aggregation and accelerate air escape, while inner surface modification enhances the hydrophilicity of inner surface, weakens the air adhesion and increases the drag force of fluid on air bubbles. In the corresponding optimized state, both strategies perform well in optimizing the air resistance control, and the improvement in flux enhancement ability for the two strategies is 26.92 and 34.10%, respectively.

Enhancing the selective synthesis of butyrate in microbial electrosynthesis system by gas diffusion membrane composite biocathode.

The reduction of carbon dioxide (CO2) to high value-added multi-carbon compounds at the cathode is an emerging application of microbial electrosynthesis system (MES). In this study, a composite cathode consisting of hollow fiber membrane (HFM) and the carbon felt is designed to enhance the CO2 mass transfer of the cathode. The result shows that the main products are acetate and butyrate without other substances. The electrochemical performance of the electrode is significantly improved after biofilm becomes matures. The composite cathode significantly reduces the "threshold" for the synthesis of butyrate. Moreover, CO2 is dissolved and protons are consumed by synthesizing volatile fatty acids (VFAs) to maintain a stable pH inside the composite electrode. The synthesis mechanism of butyrate is that CO2 is converted sequentially into acetate and butyrate. The microenvironment of the composite electrode enriches Firmicute. This composite electrode provides a novel strategy for regulating the microenvironment.

Electrochemical impedance spectroscopy (EIS) reveals the role of microbial fuel cell-ceramic membrane bioreactor (MFC-CMBR): Electricity utilization and membrane fouling.

Ceramic membrane has become a major concern due to creasing cost and competitive efficiency. Microbial fuel cell-ceramic membrane bioreactor (MFC-CMBR) is considered alternative technology for larger-scale industrial application because of its advantages of convenient detecting and control of membrane fouling. However, MFC-CMBR are highly susceptible to membrane fouling and harsh operating requirements in these wastewaters of different compositions. This research critically discusses that electrochemical response in different types of MFC-CMBRs and control of electricity utilization on ceramic membrane fouling. The experimental results indicated that the application of sludge acclimated in coupling system with higher external resistance could ensure that lower costs (electricity utilization and membrane cleaning) provided enough membrane fouling control. The improved performance of MFC-CMBR-1 could be attributed to its enhanced nitrification/denitrification activity and capacity of electrons migration between electrode and sludge mixture. The coupling system alleviated membrane fouling and impedance increasing by improving the characteristics of sludge (increased particle size, decreased adsorption adhesion free energy), EPS (decreased hydrophobicity, molecular weight distribution regulation). And filtration tests showed that roughness and contact angle for the MFC-CMBR tend for better development compared to CMBR, dependent on the changes in the chemical surface groups as a result of electric distribution ratio. In addition, correlation analysis and filtration experiments showed that the extracellular polymer substances (EPS) enhanced the charge transfer resistance (Rct), and the protein substance in EPS was the main fouling substance when external resistance was close to the internal resistance of MFC. In summary, the low internal resistance of ceramic membrane lead to obvious better fouling control and electricity utilization than organic membrane, and the paper provides insight into the MFC-CMBR systems for a wide range of detecting membrane fouling and applications of membrane fouling mitigation.

Enhanced Antibiotic Tolerance of an In Vitro Multispecies Uropathogen Biofilm Model, Useful for Studies of Catheter-Associated Urinary Tract Infections.

Catheter-associated urinary tract infections (CAUTI) are a common clinical concern as they can lead to severe, persistent infections or bacteremia in long-term catheterized patients. This type of CAUTI is difficult to eradicate, as they are caused by multispecies biofilms that may have reduced susceptibility to antibiotics. Many new strategies to tackle CAUTI have been proposed in the past decade, including antibiotic combination treatments, surface modification and probiotic usage. However, those strategies were mainly assessed on mono- or dual-species biofilms that hardly represent the long-term CAUTI cases where, normally, 2-4 or even more species can be involved. We developed a four-species in vitro biofilm model on catheters involving clinical strains of Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca and Proteus mirabilis isolated from indwelling catheters. Interspecies interactions and responses to antibiotics were quantitatively assessed. Collaborative as well as competitive interactions were found among members in our model biofilm and those interactions affected the individual species' abundances upon exposure to antibiotics as mono-, dual- or multispecies biofilms. Our study shows complex interactions between species during the assessment of CAUTI control strategies for biofilms and highlights the necessity of evaluating treatment and control regimes in a multispecies setting.

Transition of fouling characteristics after development of membrane wetting in membrane-aerated biofilm reactors (MABRs).

The practical applications of water treatment techniques based on hydrophobic aeration membrane are limited due to membrane pores blocking. Various studies have revealed that both biofilm and microbial secretion can exacerbate membrane fouling. Recently, we constructed a membrane-aerated biofilm reactor (MABR) system for treating micro-polluted surface water in order to identify the primary cause for oxygen transfer rate (OTR) decline. It was found that microbial secretion had a more prominent negative effect than that caused by biofilm, as manifested by the fact the effect of microbial secretion (66.49%) was greater than the resistance of biofilm (38.83%). Fouling decreased the total pore volume of all membrane. The peak location of adsorption capacity was more likely to occur at smaller pore sizes with longer running time. Notably, continuous fluorescence distribution between the separating layer and pores like finger in MABR system exhibited an increasing trend with the operation time, indicating a gradual increase of microbial viability. Core protein structure was revealed by different bond peaks (0-90 d). Specifically, for different organic components of EPS, the hydrophilic HIS was the main content, while the mass transfer resistance caused by the gel increased, which reduced the contact angle and increased the bubble point pressure. Therefore, effects of EPS content and composition should be considered during the application of water treatment techniques based on MABR.

Shifts in microbial community structure and diversity in a novel waterfall biofilm reactor combined with MBBR under light and dark conditions.

In this study, a novel, low-cost, easy-maintenance and effective waterfall aeration biofilm reactor (WFBR) was designed to treat wastewater with MBBR. The chemical oxygen demand (COD), nitrogen removal efficiency, and the microbial community structure in this novel system were evaluated for 70 days under light and dark conditions. The COD and ammonium nitrogen (NH3-N) removal efficiency remained at approximately 90% and 100% respectively after 25 days, even if the influent substrate concentration and illumination condition changes. High-throughput sequencing was used to investigate the composition and function of the microbial community in different fillers in the treatment system. Dark padding, illuminate carrier and fabric play the good performance in nitrogen nitrification, denitrification and fixation respectively. The major classes present were Betaproteobacteria (30.2% on average), Cytophagia (19.8%), Gammaproteobacteria (11.7%), Alphaproteobacteria (11.2%), Sphingobacteriia (5.1%), Flavobacteriia (2.6%), Deltaproteobacteria (2.4%), Verrucomicrobiae (0.7%), Chloroplast (0.6%) and Clostridia (0.5%). These results could provide important guidance for the improvement of MBBR or other tradition wastewater treatment process, and could also enrich our theoretical understanding of microbial ecology.