Study on the inactivation effect and mechanism of EGCG disinfectant on Bacillus subtilis.

The widespread use of chlorine-based disinfectants in drinking water treatment has led to the proliferation of chlorine-resistant bacteria and the risk of disinfection byproducts (DBPs), posing a serious threat to public health. This study aims to explore the effectiveness and potential applications of epigallocatechin gallate (EGCG) against chlorine-resistant Bacillus and its spores in water, providing new insights for the control of chlorine-resistant bacteria and improving the biological stability of distribution systems. The inactivation effects of EGCG on Bacillus subtilis (B. subtilis) and its spores were investigated using transmission electron microscopy, ATP measurement, and transcriptome sequencing analysis to determine changes in surface structure, energy metabolism, and gene expression levels, thereby elucidating the inactivation mechanism. The results demonstrate the potential application of EGCG in continuously inhibiting chlorine-resistant B. subtilis in water, effectively improving the biological stability of the distribution system. However, EGCG is not suitable for treating raw water with high spore content and is more suitable as a supplementary disinfectant for processes with strong spore removal capabilities, such as ozone, ultraviolet, or ultrafiltration. EGCG exhibits a disruptive effect on the morphological structure and energy metabolism of B. subtilis and suppresses the synthesis of substances, energy metabolism, and normal operation of the antioxidant system by inhibiting the expression of multiple genes, thereby achieving the inactivation of B. subtilis.

Slow filtration operating conditions for the removal of opportunistic pathogens in a secondary effluent.

The secondary effluent of urban sewage treatment plants contains many opportunistic pathogens (OPs), which pose a potential threat to human health. In this study, the slow filtration technique is employed as the advanced treatment procedure, with the secondary effluent as the treatment object. The effectiveness of the operating conditions of the slow filtration process (filtration rate and Ca2+ concentration) in removing OPs (Pseudomonas aeruginosa, Legionella and Mycobacterium avium) and Escherichia coli from water, as well as the dynamic deposition process of pollutants on the surface of the slow filtration biofilm, was investigated. The results showed that under different filtration rates and different Ca2+ concentrations, biofilm slow filtration was more effective in removing OPs than slow filtration. The optimal filtration rate of biofilm slow filtration was 5 cm/h, and the optimal inlet Ca2+ concentration was 60 mg/L. When the filtration rate was 5 cm/h, the deposition of pollutants in the secondary effluent on the surface of biofilm slow filtration was mainly dominated by the physical adhesion of extracellular polymeric substances (EPS). When the concentration of Ca2+ was 60 mg/L, the adsorption of microorganisms was the primary method.

Current understanding on antibacterial mechanisms and research progress of tea polyphenols as a supplementary disinfectant for drinking water.

Disinfection by-products (DBPs) generated during the disinfection of drinking water have become an urgent problem. So, tea polyphenol, a natural green disinfectant, has attracted widespread attention in recent years. This review summarizes the antibacterial mechanism of tea polyphenols and the recent findings on tea polyphenols as disinfectants for drinking water. These studies show that tea polyphenol is an antibacterial agent that works through different mechanisms and can be used as a supplementary disinfectant because of its higher lasting effect and economical cost. The dosage of tea polyphenols as a disinfectant of ultrafiltration effluent is the lowest among all the tea polyphenols disinfection methods, which can ensure the microbial safety of drinking water. This application of tea polyphenols is deemed a practical solution to solving the issue of disinfecting drinking water and reducing DBPs. However, it is necessary to further explore the influence of factors such as pipeline materials on the disinfection process and efficacy to expand the application scope of tea polyphenols. The large-scale application of tea polyphenols still needs to be fine-tuned but with new developments in tea polyphenol purification technology and the long-term need for drinking water that is safe for human consumption, tea polyphenols have good prospects for further development.

Removal of antibiotic resistance genes in secondary effluent by slow filtration-NF process.

In this study, the combined process of slow filtration and low pressure nanofiltration (NF) has been used to deeply remove the antibiotic resistance genes (ARGs) in a secondary effluent, and the mechanism of ARGs removal has been subsequently explored. It is observed that the optimal filtration rate for the slow filtration without biofilm, slow filtration with the aerobic heterotrophic biofilm, slow filtration with the nitrification biofilm and slow filtration with the denitrification biofilm to remove tet A, tet W, sul I, sul II and DOC is 20 cm/h, and the slow filtration with the aerobic heterotrophic biofilm exhibits the highest removal amount. The slow filtration with biofilms removes a high extent of free ARGs. As compared with the direct NF of the secondary effluent and the slow filtration without biofilm-NF, the slow filtration with the aerobic heterotrophic biofilm-NF combined process exhibits the best ARGs removal effect. The microbial population structure and the high filtration rate in the aerobic heterotrophic biofilm promote the removal of ARGs. Strengthening the removal of 16S rDNA, intI 1 and DOC can improve the ARGs removal effect of the combined process. Overall, the slow filtration-NF combined process is a better process for removing ARGs.

Removal of antibiotic resistance genes from secondary effluent by processes combining nano-iron, ultrasound-activated persulfate, and ultrafiltration.

Antibiotic resistance genes (ARGs), as a new type of environmental pollutant that threaten human health, have been detected in the effluent of sewage treatment systems. In this study, the removal from water of ARGs, 16S rRNA, class 1 integron (intI1), and dissolved organic carbon (DOC) were investigated using processes combining nano-iron (nFe), ultrasound (US), activated persulfate (PS) and ultrafiltration (UF). The oxidation mechanism was also studied. The results showed that both nFe and US activation could improve the oxidative effect of PS, and the effect of nFe was better than that of US. Compared with PS-UF, nFe/PS-UF and US/PS-UF significantly enhanced the removal of various ARGs and DOC. nFe/PS-UF was the most effective treatment, reducing cell-associated and cell-free ARGs by 1.74-3.14-log and 1.00-2.61-log, respectively, while removing 30% of DOC. Pre-oxidation methods using PS, nFe/PS, and US/PS significantly enhanced the efficacy of UF for removing DOC with molecular weights above 50 kDa and below 10 kDa, but the removal of DOC between 10 and 50 kDa decreased. The free radicals SO4·- and ·OH were shown to participate in the process of ARGs oxidation.

Research on Operation Efficiency and Membrane Fouling of A2/O-MBR in Reclaimed Water Treatment.

Taking the public building domestic wastewater as an example, the combination of the MBR (membrane bioreactor) process and the traditional A2/O (anaerobic-anoxic-oxic) process was established and analyzed in terms of the removal effect of the pollutants, the impact of the microbial community changes on the process, the MBR membrane fouling, the cleaning methods, and the cleaning performance. The results indicated that the effluent water quality of the domestic wastewater treated with the A2/O-MBR process was stable and met the emission requirement to the natural water body. There was good microbial diversity in raw water, the anaerobic tank, the anoxic tank, the aerobic MBR tank and the disinfection tank, and the aerobic MBR tank has a wide variety of aerobic microorganisms, which elevates the removal of organics and the nitrification of ammonia nitrogen and ensures the qualification of nitrogen and phosphorus indexes of the system effluent water. For the fouled membrane, the surface of the contaminated membrane was covered by macromolecular contaminants, causing the membrane flux to drop, and after different cleaning methods to the membrane were compared, it was discovered that the combined use of cleaning agents had better effects than the single ones, and the cleaning method of sodium hydroxide followed by hydrochloric acid showed the best effect, achieving a membrane flux restoration ratio above 80% after cleaning.

Effects of the Structure of TiO2 Nanotube Arrays on Its Catalytic Activity for Microbial Fuel Cell.

To enhance the microbial fuel cell (MFC) for wastewater treatment and chemical oxygen demand degradation, TiO2 nanotubes arrays (TNA) are successfully synthesized on Ti foil substrate by the anodization process in HF and NH4F solution, respectively (hereafter, denoted as TNA-HF and TNA-NF). The differences between the two kinds of TNA are revealed based on their morphologies and spectroscopic characterizations. It should be highlighted that 3D TNA-NF with an appropriate dimension can make a positive contribution to the high photocatalytic activity. In comparison with the TNA-HF, the 3D TNA-NF sample exhibits a significant enhancement in current generation as the MFC anode. In particular, the TNA-NF performs nearly 1.23 times higher than the TNA-HF, and near twofold higher than the carbon felt. It is found that the two kinds of TiO2-based anodes have different conductivities and corrosion potentials, which are responsible for the difference in their current generation performances. Based on the experimental results, excellent stability, reliability, and low cost, TNA-NF can be considered a promising and scalable MFC bioanode material.

Highly Ordered Hierarchical Pt and PtNi Nanowire Arrays for Enhanced Electrocatalytic Activity toward Methanol Oxidation.

Highly ordered hierarchical Pt and PtNi nanowire arrays were prepared using CdS hierarchical nanowire arrays (HNWAs) as sacrificial templates and demonstrated high electrochemical active surface areas. For the resulting Pt HNWAs sample, the peak current for methanol oxidation at +0.74 V was almost 1 order of magnitude higher than that of Pt solid nanowire arrays prepared in a similar manner but without the use of CdS template, and the addition of a Ni cocatalyst effectively enhanced the tolerance against CO poisoning. The results demonstrated that highly ordered Pt and PtNi HNWAs may be exploited as promising anode catalysts in the application of direct methanol fuel cells.

The membrane fouling mechanisms of the PAC/BPAC-UF combined process used to treat the secondary effluent from municipal wastewater treatment plant.

The combined processes of powdered activated carbon/biological powdered activated carbon- ultrafiltration (PAC/BPAC-UF) were used to treat secondary effluent. In this study, the effect of PAC and BPAC on membrane flux, membrane resistance and the removal of different molecular weight organic compounds were investigated. In addition, the structure characteristics of the microorganisms of the BPAC were analyzed. The results showed that the optimum dosage of PAC and BPAC was 10 mg/L and 40 mg/L respectively. The reversible membrane fouling resistance of BPAC-UF was higher than that of PAC-UF, and the two processes had the least irreversible resistance at the best dosage. The biodegradation of BPAC increased the concentration of small molecular weight organic matter up to 10,000 Da in the membrane effluent. So the dissolved organic carbon (DOC) removal effect of BPAC-UF process worsened. Microorganisms such as Proteobacteria, Bacteroidetes, Planctomycetes and other microorganisms on the surface of the BPAC enhanced the removal of organic matter in water. The results of scanning electron microscopy (SEM) scans showed that there was net mucus membrane on the UF membrane surface before the backwashing of the BPAC-UF process which increased the proportion of reversible pollution resistance. The physical flushing effect of BPAC-UF was better than that of direct UF and PAC-UF processes.

The removal of typical pollutants in secondary effluent by the combined process of powdered activated carbon-ultrafiltration.

This paper focused on the effects of powdered activated carbon (PAC) dosage on ultrafiltration (UF) membrane flux caused by natural organic matter (NOM). Three model foulants, humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA), were adopted to represent different NOM fractions in secondary effluent treated by the combined process of PAC-UF. Moreover, the membrane fouling resistance and fouling mechanism were also analyzed. The results indicated that the best PAC dosage for the membrane flux variation was 20 mg/L for HA and SA, and 10 mg/L for BSA. SA caused the most serious membrane fouling, which was mainly reversible fouling. The membrane fouling caused by HA and BSA was mainly irreversible membrane fouling. The membrane fouling caused by organics happened mainly at the initial stage of filtration. Because the filter cake layer formed by a moderate amount of PAC could intercept organics, the membrane fouling, especially the irreversible fouling, could be reduced.