Synergistic Nanowire-Enhanced Electroporation and Electrochlorination for Highly Efficient Water Disinfection.

Conventional water disinfection methods such as chlorination typically involve the generation of harmful disinfection byproducts and intensive chemical consumption. Emerging electroporation disinfection techniques using nanowire-enhanced local electric fields inactivate microbes by damaging their outer structures without byproduct formation or chemical dosing. However, this physical-based method suffers from a limited inactivation efficiency under high water flux due to an insufficient contact time. Herein, we integrate electrochlorination with nanowire-enhanced electroporation to achieve a synergistic flow-through process for efficient water disinfection targeting bacteria and viruses. Electroporation at the cathode induces sub-lethal damages on the microbial outer structures. Subsequently, electrogenerated active chlorine at the anode aggravates these electroporation-induced injuries to the level of lethal damage. This sequential flow-through disinfection system achieves complete disinfection (>6.0-log) under a very high water flux of 2.4 × 104 L/(m2 h) with an applied voltage of 2.0 V. This disinfection efficiency is 8 times faster than that of electroporation alone. Further, the specific energy consumption for the disinfection by this novel process is extremely low (8 × 10-4 kW h/m3). Our results demonstrate a promising method for rapid and energy-efficient water disinfection by coupling electroporation with electrochlorination to meet vital needs for pathogen elimination.

Development of Aspirin-Inducible Biosensors in Escherichia coli and SimCells.

A simple aspirin-inducible system has been developed and characterized in Escherichia coli by employing the Psal promoter and SalR regulation system originally from Acinetobacter baylyi ADP1. Mutagenesis at the DNA binding domain (DBD) and chemical recognition domain (CRD) of the SalR protein in A. baylyi ADP1 suggests that the effector-free form, SalRr, can compete with the effector-bound form, SalRa, binding the Psal promoter and repressing gene transcription. The induction of the Psal promoter was compared in two different gene circuit designs: a simple regulation system (SRS) and positive autoregulation (PAR). Both regulatory circuits were induced in a dose-dependent manner in the presence of 0.05 to 10 µM aspirin. Overexpression of SalR in the SRS circuit reduced both baseline leakiness and the strength of the Psal promoter. The PAR circuit forms a positive feedback loop that fine-tunes the level of SalR. A mathematical simulation based on the SalRr/SalRa competitive binding model not only fit the observed experimental results in SRS and PAR circuits but also predicted the performance of a new gene circuit design for which weak expression of SalR in the SRS circuit should significantly improve induction strength. The experimental result is in good agreement with this prediction, validating the SalRr/SalRa competitive binding model. The aspirin-inducible systems were also functional in probiotic strain E. coli Nissle 1917 and SimCells produced from E. coli MC1000 ΔminD These well-characterized and modularized aspirin-inducible gene circuits would be useful biobricks for synthetic biology.IMPORTANCE An aspirin-inducible SalR/Psal regulation system, originally from Acinetobacter baylyi ADP1, has been designed for E. coli strains. SalR is a typical LysR-type transcriptional regulator (LTTR) family protein and activates the Psal promoter in the presence of aspirin or salicylate in the range of 0.05 to 10 µM. The experimental results and mathematical simulations support the competitive binding model of the SalR/Psal regulation system in which SalRr competes with SalRa to bind the Psal promoter and affect gene transcription. The competitive binding model successfully predicted that weak SalR expression would significantly improve the inducible strength of the SalR/Psal regulation system, which is confirmed by the experimental results. This provides an important mechanism model to fine-tune transcriptional regulation of the LTTR family, which is the largest family of transcriptional regulators in the prokaryotic kingdom. In addition, the SalR/Psal regulation system was also functional in probiotic strain E. coli Nissle 1917 and minicell-derived SimCells, which would be a useful biobrick for environmental and medical applications.

Carbon Fiber-Based Flow-Through Electrode System (FES) for Water Disinfection via Direct Oxidation Mechanism with a Sequential Reduction-Oxidation Process.

Flow-through configuration for electrochemical disinfection is considered as a promising approach to minimize the formation of toxic byproducts and energy consumption via the enhanced convective mass transport as compared with conventional flow-by one. Under this hydrodynamic condition, it is essential to ascertain the effect of sequential electro-redox processes with the cathode/anode then anode/cathode arrangements on disinfection performance. Here, carbon fiber felt (CFF) was utilized to construct two flow-through electrode systems (FESs) with sequential reduction-oxidation (cathode-anode) or oxidation-reduction (anode-cathode) processes to systematically compare their disinfection performance toward a model Escherichia coli ( E. coli) pathogen. In-situ sampling and live/dead backlight staining experiments revealed that E. coli inactivation mainly occurred on anode via an adsorption-inactivation-desorption process. In reduction-oxidation system, after the cathode-pretreatment, bulk solution pH increased significantly, leading to the negative charge of E. coli cells. Hence, E. coli cells were adsorbed and inactivated easily on the subsequent anode, finally resulting in its much better disinfection performance and energy efficiency than the oxidation-reduction system. Application of 3.0 V resulted in ∼6.5 log E. coli removal at 1500 L m-2 h-1 (50 mL min-1), suggesting that portable devices can be designed from CFF-based FES with potential application for point-of-use water disinfection.

Domestic wastewater treatment and biofuel production by using microalga Scenedesmus sp. ZTY1.

Cultivation of microalgae for biomass production is a promising way to dispose of wastewater and recover nutrients simultaneously. The properties of nutrient removal and biomass production in domestic wastewater of a newly isolated microalga Scenedesmus sp. ZTY1 were investigated in this study. Scenedesmus sp. ZTY1, which was isolated from a wastewater treatment plant in Beijing, grew well in both the primary and secondary effluents of a wastewater treatment plant during the 21-day cultivation, with a maximal algal density of 3.6 × 10(6) and 1.9 × 10(6) cells · mL(-1), respectively. The total phosphorus concentrations in both effluents could be efficiently removed by over 97% after the cultivation. A high removal rate (over 90%) of total nitrogen (TN) was also observed. After cultivation in primary effluent for 21 days, the lipid content of Scenedesmus sp. ZTY1 in dry weight had reached about 32.2%. The lipid and triacylglycerol (TAG) production of Scenedesmus sp. ZTY1 was increased significantly with the extension of cultivation time. The TAG production of Scenedesmus sp. ZTY1 increased from 32 mg L(-1) at 21 d to 148 mg L(-1) at 45 d in primary effluent. All the experiments were carried out in non-sterilized domestic wastewater and Scenedesmus sp. ZTY1 showed good adaptability to the domestic wastewater environment.

Effects of water quality on bacterial inactivation by ferrate(VI).

Ferrate (Fe(VI)) is an emerging green oxidant which has great potential and prospect in water disinfection. However, the effects of water quality on Fe(VI) disinfection remain unclear. This study systematically investigated the effects of pH, organic matters and inorganic ions on Fe(VI) inactivation of Escherichia coli (E. coli). Results showed that pH was the dominant influencing factor and the inactivation efficiency as well as inactivation rate constant was negatively correlated with pH (6.8-8.4). HFeO4- was found to be the critical Fe(VI) species contributing to the inactivation. As for organic matters (0-5 mg C/L), protein and humic acid significantly accelerated the decay of Fe(VI) and had negative effects on the inactivation efficiency, while polysaccharide slightly inhibited the inactivation due to the low reactivity with Fe(VI). As for inorganic ions, bicarbonate (0-2 mM) could stabilize Fe(VI) and decreased the inactivation rate constant, while ammonium (0-1 mM) had little effect on the inactivation of E. coli. In addition, the comprehensive effects of water quality on Fe(VI) disinfection in actual reclaimed water were also evaluated. The inactivation of E. coli in secondary effluent and denitrifying effluent was found to be inhibited compared to that in phosphate buffer. Overall, this study is believed to provide valuable information on Fe(VI) disinfection for water and wastewater treatment practices.

Do all algae grow faster in environments replenished by reclaimed water? Examples of two effluents produced in Beijing.

Reclaimed water with nitrogen, phosphorus, and other contaminants may trigger algal blooms during its ecological utilization in replenishing rivers or lakes. However, the effect of reclaimed water on algal growth rates is not well understood. In this study, the growth potentials of algae in terms of Cyanophyta, Chlorophyta, and Bacillariophyta, as well as mixed algae in both regular culture medium and reclaimed water produced from treatment plants in Beijing with similar N and P concentrations, were compared to evaluate whether reclaimed water could facilitate algal growth. In addition, reclaimed water was also sterilized to verify the impact of bacteria's presence on algal growth. The results indicated that most algae grew faster in reclaimed water, among which the growth rate of Microcystis aeruginosa even increased by 5.5 fold. The growth of mixed algae in reclaimed water was not enhanced due to the strong adaptive ability of the community structure. Residual bacteria in the reclaimed water were found to be important contributors to algal growth. This work provided theoretical support for the safe and efficient utilization of reclaimed water.

Critical fractions in reclaimed water responsible for membrane fouling: Isolation, fouling characteristics, quantitative and qualitative variations in practical application.

Considering the different fouling characteristics between model foulants and organic components in real reclaimed water, it is of great importance to identify the critical foulants responsible for membrane fouling. This study identified and isolated the fraction with molecular weight (MW) > 100 kDa as the critical foulant in secondary effluent by MW cut-off membrane of 100 kDa with high efficiency. This fraction accounted for 92.2% membrane fouling of raw water, including 28.7%, 29.7% and 33.8% fouling contribution by subfractions with MW between 100-300, 300-500 and > 500 kDa. Specifically, the critical fraction with MW > 100 kDa were mainly distributed in two parts: < 0.22 µm and > 0.45 µm, corresponding to 41.9% and 56.9% fouling contribution of this fraction. Furthermore, both total organic carbon (TOC) and fouling potential of fraction with MW > 100 kDa were monitored, presenting about threefold increase from September to January in next year. Membrane fouling contribution of this critical fraction in raw secondary effluent were mainly distributed in 85∼95% throughout the 5 months, demonstrating its predominant fouling propensity. Moreover, the TOC concentration of fraction with MW > 100 kDa presented distinct positive correlation with the fouling potential of raw secondary effluent (R2 = 0.947), which was promising to be a surrogate for predicting membrane fouling in practical application.

Synergistic ferrate(VI) and chlorine for reclaimed water disinfection: Microbial control and chlorine decay mitigation.

Chlorination is the most widely used disinfection technology due to its simplicity and continuous disinfection ability. However, the drawbacks of disinfection by-products and chlorine-resistant bacteria have gained increasing attention. Nowadays, ferrate (Fe(VI)) is a multifunctional and environmentally friendly agent which has great potential in wastewater reclamation and reuse. This study investigated synergistic Fe(VI) and chlorine technology for reclaimed water disinfection in terms of microbial control and chlorine decay mitigation. Specifically, synergistic disinfection significantly improved the inactivation efficiency on total coliform, Escherichia coli and heterotrophic bacteria compared to sole chlorination. Synergistic disinfection also exhibited superior performance on controlling the relative abundance of chlorine-resistant bacteria and pathogenic bacteria. In addition, the decay rate of residual chlorine was relatively lower after Fe(VI) pretreatment, which was beneficial for microbial control during the reclaimed water distribution process. Technical and economic analyses revealed that synergistic Fe(VI) and chlorine disinfection was suitable and feasible. Results of this study are believed to provide useful information and alternative options on the optimization of reclaimed water disinfection.

Flow-through electrode system (FES): An effective approach for biofouling control of reverse osmosis membranes for municipal wastewater reclamation.

Emerging electrochemical disinfection techniques provide a promising pathway to the biofouling control of reverse osmosis (RO) process. However, the comparative effectiveness and mechanism of it under flow-through conditions with low voltage remains unclear. This study investigated the effect of a flow-through electrode system (FES) with both direct current (DC) and alternating pulse current (AC) on RO biofouling control compared with chlorine disinfection. At the initial stage of biofouling development, the normalized flux of AC-FES (67% on Day 5) was saliently higher than the control group (56% on Day 5). Subsequently, the normalized fluxes of each group tended similarity in their differences until the 20th day. After mild chemical cleaning, the RO membrane in the AC-FES group reached the highest chemical cleaning efficiency of 58%, implying its foulant was more readily removable and the biofouling was more reversible. The biofouling layer in the DC-FES group was also found to be easily cleanable. Morphological analysis suggested that the thickness and compactness of the fouling layers were the major reasons for the fouling behavior difference. The abundance of 4 fouling-related abundant genera (>1%), which were Pseudomonas, Thiobacillus, Sphingopyxis, and Mycobacterium exhibited a salient correlation with the biofouling degree. The operating cost of FES was also lower than that of chlorine disinfection. In summary, AC-FES is a promising alternative to chlorine disinfection in RO biofouling control, as it caused less and easy-cleaning biofouling layer mainly due to two advantages: a) reducing the regrowth potential after disinfection of the bacteria, leading to alleviated initial fouling, (b) reshaping the microbial community to those with weaker biofilm formation capacity.

[Analysis of Regional Differences in Cadmium Ecological Risk in Surface Waters of the Yangtze River Basin].

This study primarily focused on the regional disparities in both water quality criteria and ecological risks attributed to cadmium presence within the surface waters of the Yangtze River Basin. In the initial phase, the long-term water quality criteria for cadmium were recalibrated in accordance with the guidelines outlined in China's "Water Quality Criteria for Freshwater Aquatic Organisms-Cadmium," accounting for the prevalent hardness distribution within the Yangtze River Basin's surface water. Subsequently, a more refined revision was undertaken considering the specific characteristics of the species residing within the Yangtze River Basin. This undertaking led to a comprehensive interpretation of the regional variations in both the distribution of long-term water quality criteria values and the risk quotient distribution of cadmium throughout the Yangtze River Basin. The incorporation of hardness and species-specific attributes resulted in a revised range of long-term water quality criteria for cadmium across different urban locales within the Yangtze River Basin. Notably, the recalibrated values ranged from 0.08 µg·L-1 as the lowest threshold to 0.75 µg·L-1 as the upper limit, signifying a tenfold differentiation. Correspondingly, the urban average annual risk quotient associated with cadmium exposure demonstrated a variation from 0.035 to 1.12, marking a significant 32-fold discrepancy between the lowest and highest values. It is essential to highlight that regions of paramount importance, such as the confluence area connecting the upper and middle stretches of the Yangtze River Basin and the intricate Dongting Lake system, exhibited noteworthy ecological risks attributed to cadmium presence. Consequently, further in-depth investigations into these critical regions are imperative for a comprehensive understanding of the associated risks.

Critical minority fractions causing membrane fouling in reclaimed water: Fouling characteristics, mechanisms and control strategies.

In regard to membrane-based technologies of wastewater reclamation, the reported key foulants were faced with dilemma that they could not be effectively separated and extracted from reclaimed water for thorough investigation. In this study, the crucial foulants were proposed as "critical minority fraction (FCM)", representing the fraction with molecular weight (MW) > 100 kDa which could be easily separated by physical filtration using MW cut-off membrane of 100 kDa with fairly high recovery ratio. FCM with low dissolved organic carbon (DOC) concentration (∼1 mg/L) accounted for less than 20% of the total DOC in reclaimed water, while contributed to more than 90% of the membrane fouling, and thus FCM could be considered as a "perfect criminal" causing membrane fouling. Furthermore, pivotal fouling mechanism was attributed to the significant attractive force between FCM and membranes, which led to severe fouling development due to the aggregation of FCM on membrane surface. Fluorescent chromophores of FCM were concentrated in regions of proteins and soluble microbial products, with proteins and polysaccharides accounted for 45.2% and 25.1% of the total DOC, specifically. FCM was further fractionated into six fractions, among which hydrophobic acids and hydrophobic neutrals were the dominant components in terms of DOC content (∼80%) as well as fouling contribution. Regarding to these pronounced properties of FCM, targeted fouling control strategies including ozonation and coagulation were applied and proved to achieve remarkable fouling control effect. High-performance size-exclusion chromatography results suggested that ozonation achieved distinct transformation of FCM into low MW fractions, while coagulation removed FCM directly, thus leading to effective fouling alleviation. Therefore, the investigation of the critical foulants was expected to help glean valuable insight into the fouling mechanism and develop targeted fouling control technologies in practical applications.

Modeling and optimization of synergistic ozone-ultraviolet-chlorine process for reclaimed water disinfection: From laboratory tests to software simulation.

The ozone-ultraviolet (UV)-chlorine process is a highly effective method of disinfection in water reuse system, but currently still lacks precise quantification and accurate control. It is difficult to determine the dosage of each disinfectant because of the complex interactions that occur between disinfection units and the complicated mathematical calculation required. In this study, we proposed a dosage optimization model for ozone-UV-chlorine synergistic disinfection process. The model was able to identify the cost-effective doses of the disinfectants under the constraints of microbial inactivation, decolorization, and residual chlorine retention requirements. Specifically, the simulation of microbial inactivation rates during synergistic disinfection process was accomplished through quantification of the synergistic effects between disinfection units and the introduction of enhancement coefficients. In order to solve this optimization model rapidly and automatically, a MATLAB-based software program with graphical user interface was developed. This software consisted of calibration unit, prediction unit, assessment unit, and optimization unit, and was able to simulate synergistic ozone-UV-chlorine process and identify the optimal dose of ozone, UV, and chlorine. Validation experiments revealed good agreements between the experimental data and the results calculated by the developed software. The developed software is believed to help the water reclamation plants improve disinfection efficiency and reduce the operational costs of synergistic disinfection processes.

High-efficiency and low-carbon inactivation of UV resistant bacteria in reclaimed water by flow-through electrode system (FES).

With the increasingly serious shortage of water resources globally, it has been paid more attention on how to secure the biosafety of reclaimed water and other non-traditional water sources. However, the 3 most applied disinfection technics, which are chlorine, ultraviolet (UV), and ozone disinfection, all have their disadvantages of selecting undesired bacteria and low energy utilization efficiency. Electrode disinfection is a promising solution, but the current electrode disinfection process still needs to be optimized in terms of the use conditions of the configuration reactivation. In this paper, we built a flow electrode system (FES). To evaluate the disinfection techniques more precisely, we isolated ultraviolet-resistant bacteria (URB) bacteria from the water of the full-scale water plant and tested the disinfection performance of FES and UV. The inactivation rate, reactivation potential, and energy consumption were analyzed. FES could inactivate 99.99 % of the URB and cause irreversible damage to the residual bacteria. FES could make all bacteria strains apoptosis in the subsequent 24 h of storage after alternating pulse current (APC) treatment, 3 V, within 27.7 s. Besides, the energy consumption of FES is about 2 orders lower than that of UV disinfection under the same inactivation rate. In summary, APC-FES is an efficient and low-carbon alternative for future water disinfection, which could achieve the ideal disinfection effect of a high inactivation rate, no reactivation, and low energy consumption.

Inactivation of chlorine-resistant bacteria (CRB) via various disinfection methods: Resistance mechanism and relation with carbon source metabolism.

With the widespread use of chlorine disinfection, chlorine-resistant bacteria (CRB) in water treatment systems have gained public attention. Bacterial chlorine resistance has been found positively correlated with extracellular polymeric substance (EPS) secretion. In this study, we selected the most suitable CRB controlling method against eight bacterial strains with different chlorine resistance among chloramine, ozone, and ultraviolet (UV) disinfection, analyzed the resistance mechanisms, clarified the contribution of EPS to disinfection resistance, and explored the role of carbon source metabolism capacity. Among all the disinfectants, UV disinfection showed the highest disinfection capacity by achieving the highest average and median log inactivation rates for the tested strains. For Bacillus cereus CR19, the strain with the highest chlorine resistance, 40 mJ/cm2 UV showed a 1.90 log inactivation, which was much higher than that of 2 mg-Cl2/L chlorine (0.67 log), 2 mg-Cl2/L chloramine (1.68 log), and 2 mg/L ozone (0.19 log). Meanwhile, the UV resistance of the bacteria did not correlate with EPS secretion. These characteristics render UV irradiation the best CRB controlling disinfection method. Chloramine was found to have a generally high inactivation efficiency for bacteria with high chlorine-resistance, but a low inactivation efficiency for low chlorine-resistant ones. Although EPS consumed up to 56.7% of chloramine which an intact bacterial cell consumed, EPS secretion could not explain chloramine resistance. Thus, chloramine is an acceptable CRB control method. Similar to chlorine, ozone generally selected high EPS-secreting bacteria, with EPS consuming up to 100% ozone. Therefore, ozone is not an appropriate method for controlling CRB with high EPS secretion. EPS played an important role in all types of disinfection resistance, and can be considered the main mechanism for bacterial chlorine and ozone disinfection resistance. However, as EPS was not the main resistance mechanism in UV and chloramine disinfection, CRB with high EPS secretion were inactivated more effectively. Furthermore, carbon source metabolism was found related to the multiple resistance of bacteria. Those with low carbon source metabolism capacity tended to have higher multiple resistance, especially to chlorine, ozone, and UV light. Distinctively, among the tested gram-negative bacteria, in contrast to other disinfectants, chloramine resistance was negatively correlated with EPS secretion and positively correlated with carbon source metabolism capacity, suggesting a special disinfection mechanism.

Comparison of the reverse osmosis membrane fouling behaviors of different types of water samples by modeling the flux change over time.

Fouling of RO membranes has long been a complex but inevitable problem in wastewater reclamation. In this study, a modified intermediate blocking model with two parameters was applied to describe the flux change of RO membranes treating various water samples, including municipal secondary effluent, treated industrial wastewater, surface water, and groundwater. The model was validated by 55 sets of data reported by 13 articles, and the results were promising, with 90% of the determination coefficient (R2) exceeding 0.90. Relatively large flux and high operational pressure were found likely to aggravate membrane fouling. Treated industrial wastewater had the highest fouling potential (fouling constant k: 0.061-2.433) compared to municipal wastewater secondary effluent, surface water, and groundwater, even with similar dissolved organic carbon concentration. With industrial wastewater excluded, water samples exhibited lower fouling potential than organic matter solutions, with the majority (25%∼75%) of k distributing in 0.03-0.12, much lower compared to the major k range of the latter (0.05-0.28). This suggested a deviation in fouling behaviors between model organic matters and real water samples. Xanthan gum and guar gum were proposed to be model polysaccharides based on their model parameters, which were relatively close to real water samples.

Ultrafiltration significantly increased the scaling potential of municipal secondary effluent on reverse osmosis membranes.

Ultrafiltration (UF) was often used as pretreatment in front of reverse osmosis (RO) unit because of its high rejection efficiency of microbes and particles. However, in some cases UF pretreatment might show adverse effects on the RO membrane flux. In this study, the effects of UF pretreatment on secondary effluent water quality and its RO membrane fouling characteristics were explored. There was almost no change of water quality after UF with different molecular weight cut-off (MWCO) membranes (100, 30 and 10 kDa), including total dissolved solid (TDS), alkalinity, conductivity, ion concentrations, etc., while pH increased a little and dissolved organic carbon (DOC) declined by about 1 mg/L. On the contrary, the RO membrane flux of UF permeates presented clear decline in comparison to the secondary effluent. The membrane fouling velocity and steady-state flux of secondary effluent was 0.052 and 0.656, while fouling velocity increased (0.077, 0.071, 0.067) and steady-state flux decreased significantly (0.397, 0.416, 0.448) after 100, 30, 10 kDa UF membrane pretreatment. Scanning electron microscope (SEM) images showed many crystals on the fouled membrane surfaces, which turned out to be CaCO3 by Energy dispersive spectrometer (EDS) analysis and precipitation calculation. After the addition of UF retentates to UF permeates, scaling was prevented and crystals on the RO membrane almost disappeared, which implied the anti-scaling effect of the UF retentates with low concentration. According to anti-scaling performance experiments, the anti-scaling performance of 100 k, 30 k, 10 k retentates was 2.7%, 4.0% and 7.3%, respectively. Excitation emission matrix (EEM) and fourier transform infra-red (FTIR) results showed that these retentates retained by different MWCO membranes were similar and composed of protein-like substances and soluble microbial products. The effect of key minority components in RO system deserved further exploration.

Increased risks of antibiotic resistant genes (ARGs) induced by chlorine disinfection in the reverse osmosis system for potable reuse of reclaimed water.

The reverse osmosis (RO) process has been applied extensively in wastewater reclamation for industrial and potable reuse. To prevent biofouling, chlorine disinfection was usually used in pretreatment. However, this study found that chlorine disinfection could significantly increase risks of antibiotic resistant genes (ARGs) in the RO system. With the increase of chlorine concentration from 0 to 5 mg/L, the accumulative relative abundance of 14 common ARGs in the membrane foulants increased by 49.6%. Among these ARGs, tolC, acrA and acrB (resistance to multiple drugs) showed the highest increament after chlorine disinfection. Especially, the relative abundance of tolC in the group with 5 mg/L chlorine increased by 113.3% compared with the control group. These ARGs tended to be enriched in a few bacterial genus, including Candidatus, Thiomonas, Silanimonas, Xanthomonas and Pseudomonas. These results indicated that the foulants on RO membranes might become a potential sink of ARGs. Considering the possibility of membrane breach, the ARGs may contaminate the permeate and bring great biological risks.

The noteworthy chloride ions in reclaimed water: Harmful effects, concentration levels and control strategies.

Chloride ions (Cl-), which are omnipresent in reclaimed water, can cause various problems in water reuse systems, especially during water transmission and at end use sites. Although reverse osmosis (RO) is considered as an effective technology to reduce chloride, its high investment and complex maintenance requirements hinder its application in many water reclamation plants (WRPs). Recently, several technologies bringing new options to better deal with chloride have gained increased attention. This review provides detailed information on the harmful effects, concentration levels, and sources of chloride in reclaimed water and summarizes and discusses various chloride removal technologies, including non-selective methods (e.g., membrane filtration, adsorption and ion exchange, oxidation, and electrochemical methods) and selective methods (e.g. precipitation and specially designed electrochemical methods). Among these, Friedel's salt precipitation and capacitive deionization showed attractive development potential. This review also proposes a holistic framework for chloride control from aspects of "Fit-for-Purpose" planning, technical system development, and whole process optimization, which could facilitate the planning and operation of long-term sustainable water reuse practices.

Photolysis of free chlorine and production of reactive radicals in the UV/chlorine system using polychromatic spectrum LEDs as UV sources.

Recently, ultraviolet light-emitting diodes (UV-LEDs) and chlorine combined system has been employed as an emerging advanced oxidation process. However, UV-LEDs were commonly considered as monochromatic UV sources. In this study, the obvious quantum yields of chlorine photolysis under 265 nm and 280 nm LEDs irradiations were investigated with treating LEDs as polychromatic UV sources. Particularly, Φobs-poly of HOCl and OCl⁻ for 265 nm LED were found to be 1.50 and 0.70 mol E-1, respectively, whereas Φobs-poly of HOCl and OCl⁻ for 280 nm LED were 1.28 and 0.64 mol E-1, respectively. It was identified that Φobs-poly were 5.66-14.63 % lower than Φobs-mono. This suggests that obvious quantum yield using peak emission wavelength would overestimate the true quantum yield. The production of radical species in LED UV/chlorine systems were determined by the degradation of BA, and illustrated by a mathematical model. Different trends were observed for 265 nm and 280 nm LED UV/chlorine systems as pH increased from 5.0 to 10.0. As pH increased, the formation of OH continuously decreased in both 265 nm and 280 nm LED systems. The formation of Cl increased at neutral pH and more Cl and OH were formed due to the higher molar absorbance coefficient at 280 nm. The chlorine dose-dependent effects on radical productions at pH of 5.0, 7.5 and 10.0 were also assessed. At pH of 5.0, OH was the main radical product and had linear correlation with chlorine dose. At pH of 7.5, the productions of OH and Cl showed similar profiles that increased rapidly at low chlorine dosage and then slowed down.

Comparison of disinfection-residual-bacteria (DRB) after seven different kinds of disinfection: Biofilm formation, membrane fouling and mechanisms.

Membrane fouling is the Achilles' heel of the reverse osmosis (RO) system for high-quality reclaimed water production. Previous studies have found that after the significant selection effect of traditional disinfection, the remaining disinfection-residual bacteria (DRB) may possess more severe biofouling potentials. To provide more constructive advice for the prevention of biofouling, we compared the RO membrane fouling characteristics of DRB after using five commonly used disinfection methods (NaClO, NH2Cl, ClO2, UV, and O3) and two novel disinfection methods (K2FeO4 and the flow-through electrode system (FES)). Compared with the control group (undisinfected, 21.1 % flux drop), the UV-DRB biofilm aggravated biofouling of the RO membrane (23.4 % flux drop), while the FES, K2FeO4, and NH2Cl treatments showed less severe biofouling, with final flux drops of 6.9 %, 8.1 %, and 8.1 %, respectively. Adenosine triphosphate (ATP) was found to be a capable indicator for predicting the biofouling potential of DRB. Systematic analysis showed that the thickness and density of the DRB biofilms were most closely related to the different fouling degree of RO membranes. Moreover, the relative abundance of bacteria with higher extracellular polymeric substance (EPS) secretion levels, such as Pseudomonas and Sphingomonas, was found closely related with the biofouling degree of RO membranes.