Removal of antibiotic-resistant genes during drinking water treatment: A review

Once contaminate the drinking water source, antibiotic resistance genes (ARGs) will propagate in drinking water systems and pose a serious risk to human health. Therefore, the drinking water treatment processes (DWTPs) are critical to manage the risks posed by ARGs. This study summarizes the prevalence of ARGs in raw water sources and treated drinking water worldwide. In addition, the removal efficiency of ARGs and related mechanisms by different DWTPs are reviewed. Abiotic and biotic factors that affect ARGs elimination are also discussed. The data on presence of ARGs in drinking water help come to the conclusion that ARGs pollution is prevalent and deserves a high priority. Generally, DWTPs indeed achieve ARGs removal, but some biological treatment processes such as biological activated carbon filtration may promote antibiotic resistance due to the enrichment of ARGs in the biofilm. The finding that disinfection and membrane filtration are superior to other DWTPs adds weight to the advice that DWTPs should adopt multiple disinfection barriers, as well as keep sufficient chlorine residuals to inhibit re-growth of ARGs during subsequent distribution. Mechanistically, DWTPs obtain direct and inderect ARGs reduction through DNA damage and interception of host bacterias of ARGs. Thus, escaping of intracellular ARGs to extracellular environment, induced by DWTPs, should be advoided. This review provides the theoretical support for developping efficient reduction technologies of ARGs. Future study should focus on ARGs controlling in terms of transmissibility or persistence through DWTPs due to their biological related nature and ubiquitous presence of biofilm in the treatment unit.     

On-going nitrification in chloraminated drinking water distribution system (DWDS) is conditioned by hydraulics and disinfection strategies

Within the drinking water distribution system (DWDS) using chloramine as disinfectant,nitrification caused by nitrifying bacteria is increasingly becoming a concern as it poses a great challenge for maintaining water quality.To investigate efficient control strategies,operational conditions including hydraulic regimes and disinfectant scenarios were controlled within a flow cell experimental facility.Two test phases were conducted to investigate the effects on the extent of nitrification of thre...     

Transformation mechanism and fate of dissolved organic nitrogen (DON) in a full-scale drinking water treatment

Dissolved organic nitrogen (DON) has attracted much attention in drinking water treatment due to its potential to produce nitrogenous disinfection by-products (N-DBPs). This work was designed to explore the transformation and fate of DON and dissolved inorganic nitrogen (DIN) in drinking water treatment. The changes of DON and formation of N-DBPs were evaluated along the water treatment route (i.e., pre-ozonation and biological-contact oxidation, delivery pipes’ transportation, coagulation-sedimentation, sand filtration, post-ozonation, biological activated carbon, ultrafiltration and disinfection) of drinking water treatment plant (DWTP). The transformation mechanism of DON was comprehensively investigated by molecular weight fractionation, three-dimensional fluorescence, LC-OCD (Liquid Chromatography-Organic Carbon Detection), total free amino acids. A detailed comparison was made between concentrations and variations of DON and DIN affected by seasons in the drinking water treatment. Regardless of seasonal variation in raw water concentration, the DON removal trends between different treatment processes remain constant in the present study. Compared to other treatment processes, pre-ozonation and coagulation-sedimentation exhibited the dominant DON removal in different seasons, i.e., 11.13%-14.45% and 14.98%-22.49%, respectively. Contrary, biological-contact oxidation and biological activated carbon negatively impacted the DON removal, in which DON increased by 1.76%-6.49% in biological activated carbon. This may be due to the release of soluble microbial products (SMPs) from bacterial metabolism, which was further validated by the rise of biopolymers in LC-OCD.     

Water-lifting and aeration system improves water quality of drinking water reservoirs: Biological mechanism and field application

Reservoirs have been served as the major source of drinking water for dozens of years. The water quality safety of large and medium reservoirs increasingly becomes the focus of public concern. Field test has proved that water-lifting and aeration system (WLAS) is a piece of effective equipment for in situ control and improvement of water quality. However, its intrinsic bioremediation mechanism, especially for nitrogen removal, still lacks in-depth investigation. Hence, the dynamic changes in water quality parameters, carbon source metabolism, species compositions and co-occurrence patterns of microbial communities were systematically studied in Jinpen Reservoir within a whole WLAS running cycle. The WLAS operation could efficiently reduce organic carbon (19.77%), nitrogen (21.55%) and phosphorus (65.60%), respectively. Biolog analysis revealed that the microbial metabolic capacities were enhanced via WLAS operation, especially in bottom water. High-throughput sequencing demonstrated that WLAS operation altered the diversity and distributions of microbial communities in the source water. The most dominant genus accountable for aerobic denitrification was identified as Dechloromonas. Furthermore, network analysis revealed that microorganisms interacted more closely through WLAS operation. Oxidation-reduction potential (ORP) and total nitrogen (TN) were regarded as the two main physicochemical parameters influencing microbial community structures, as confirmed by redundancy analysis (RDA) and Mantel test. Overall, the results will provide a scientific basis and an effective way for strengthening the in-situ bioremediation of micro-polluted source water.     

The control of red water occurrence and opportunistic pathogens risks in drinking water distribution systems: A review

Many problems in drinking water distribution systems (DWDSs) are caused by microbe, such as biofilm formation, biocorrosion and opportunistic pathogens growth. More iron release from corrosion scales may induce red water. Biofilm played great roles on the corrosion. The iron-oxidizing bacteria (IOB) promoted corrosion. However, when iron-reducing bacteria (IRB) and nitrate-reducing bacteria (NRB) became the main bacteria in biofilm, they could induce iron redox cycling in corrosion process. This process enhanced the precipitation of iron oxides and formation of more Fe₃O₄ in corrosion scales, which inhibited corrosion effectively. Therefore, the IRB and NRB in the biofilm can reduce iron release and red water occurrence. Moreover, there are many opportunistic pathogens in biofilm of DWDSs. The opportunistic pathogens growth in DWDSs related to the bacterial community changes due to the effects of micropollutants. Micropollutants increased the number of bacteria with antibiotic resistance genes (ARGs). Furthermore, extracellular polymeric substances (EPS) production was increased by the antibiotic resistant bacteria, leading to greater bacterial aggregation and adsorption, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in DWDSs. Moreover, O₃-biological activated carbon filtration-UV-Cl₂ treatment could be used to control the iron release, red water occurrence and opportunistic pathogens growth in DWDSs.     

Challenges against CO2 abatement strategies in cement industry: A review

Cement industry is an intensive source of fuel consumption and greenhouse gases (GHGs) emissions. This industry is responsible for 5% of GHGs emissions and is among the top industrial sources of carbon dioxide (CO₂) emissions. Therefore, CO₂ emissions reduction from cement production process has been always an appealing subject for researches in universities and industry. Various efforts have been carried out to mitigate the huge mass of CO₂ emissions from the cement industry. Although, majority of these strategies are technically viable, due to various barriers, the level of CO₂ mitigation in cement industry is still not satisfactory. Among numerous researches on this topic, only a few have tried to answer why CO₂ abatement strategies are not globally practiced yet. This work aims to highlight the challenges and barriers against widespread and effective implementation of CO₂ mitigation strategies in the cement industry and to propose practical solutions to overcome such barriers.     

NirS-type denitrifying bacteria in aerobic water layers of two drinking water reservoirs: Insights into the abundance, community diversity and co-existence model

The nirS-type denitrifying bacterial community is the main drivers of the nitrogen loss process in drinking water reservoir ecosystems.The temporal patterns in nirS gene abundance and nirS-type denitrifying bacterial community harbored in aerobic water layers of drinking water reservoirs have not been studied well.In this study,quantitative polymerase chain reaction (qPCR) and Illumina Miseq sequencing were employed to explore the nirS gene abundance and denitrifying bacterial community structur...     

Direct evidence of microbiological water quality changes on bacterial quantity and community caused by plumbing system

Drinking water quality deteriorates from treatment plant to customer taps, especially in the plumbing system. There is no direct evidence about what the differences are contributed by plumbing system. This study compared the water quality in the water main and at customer tap by preparing a sampling tap on the water main. The biomass was quantified by adenosine triphosphate (ATP) and the microbial community was profiled by 454 pyrosequencing. The results showed that in distribution pipes, biofilm contributed >94% of the total biomass, while loose deposits showed little contribution (< 2%) because of the low amount of loose deposits. The distribution of biological stable water had minor effects on the microbiocidal water quality regarding both quantity (ATP 1 ng/L vs. 1.7 ng/L) and community of the bacteria. Whereas the plumbing system has significant contribution to the increase of active biomass (1.7 ng/L vs. 2.9 ng/L) and the changes of bacterial community. The relative abundance of Sphingomonas spp. at tap (22%) was higher than that at water main (2%), while the relative abundance of Pseudomonas spp. in tap water (15%) was lower than that in the water from street water main (29%). Though only one location was prepared and studied, the present study showed that the protocol of making sampling tap on water main offered directly evidences about the impacts of plumbing system on tap water quality, which makes it possible to distinguish and study the processes in distribution system and plumbing system separately.     

Drivers of microbial beta-diversity in wastewater treatment plants in China

As one of the most well-documented biogeographic patterns, the distance-decay relationship provides insights into the underlying mechanisms driving biodiversity distribution. Although wastewater treatment plants (WWTPs) are well-controlled engineered ecosystems, this pattern has been seen among microbial communities in activated sludge (AS). However, little is known about the relative importance of environmental heterogeneity and dispersal limitation in shaping AS microbial community across China; especially they are related to spatial scale and organism types. Here, we assessed the distance-decay relationship based on different spatial scales and microbial phylogenetic groups by analyzing 132 activated sludge (AS) samples across China comprising 3,379,200 16S rRNA sequences. Our results indicated that the drivers of distance-decay pattern in China were scale-dependent. Microbial biogeographic patterns in WWTPs were mainly driven by dispersal limitation at both local and national scales. In contrast, conductivity, SRT, and pH played dominant roles in shaping AS microbial community compositions at the regional scale. Turnover rates and the drivers of beta-diversity also varied with microorganism populations. Moreover, a quantitative relationship between dispersal limitation ratio and AS microbial turnover rate was generated. Collectively, these results highlighted the importance of considering multiple spatial scales and micro-organism types for understanding microbial biogeography in WWTPs and provided new insights into predicting variations in AS community structure in response to environmental disturbance.     

Revealing the changes of bacterial community from water source to consumers tap: A full-scale investigation in eastern city of China

This study profiled the bacterial community variations of water from four water treatment systems,including coagulation,sedimentation,sand filtration,ozonation-biological activated carbon filtration(O₃-BAC),disinfection,and the tap water after the distribution process in eastern China.The results showed that different water treatment processes affected the bacterial community structure in different ways.The traditional treatment processes,including coagulation,sedimentation and sand f...     

Review on heterogeneous oxidation and adsorption for arsenic removal from drinking water

The long term exposure of arsenic via drinking water has resulted in wide occurrence of arsenisim globally, and the oxidation of the non-ionic arsenite (As(III)) to negatively-charged arsenate (As(V)) is of crucial importance for the promising removal of arsenic. The chemical oxidants of ozone, chlorine, chlorine dioxide, and potassium permanganate may achieve this goal; however, their application in developing countries is sometimes restricted by the complicate operation and high cost. This review paper focuses on the heterogeneous oxidation of As(III) by solid oxidants such as manganese oxide, and the adsorption of As(V) accordingly. Manganese oxide may be prepared by both chemical and biological methods to achieve good oxidation performance towards As(III). Additionally, manganese oxide may be combined with other metal oxides, e.g., iron oxide, to improve the adsorption capability towards As(V). Furthermore, manganese oxide may be coated onto porous materials of metal organic frameworks to develop novel adsorbents for arsenic removal. To achieve the application in engineering works, the adsorbents granulation may be achieved by drying and calcination, agglomeration, and the active components may also be in situ coated onto the porous materials to maintain the oxidation and adsorption activities as much as possible. The novel adsorbents with heterogeneous oxidation and adsorption capability may be carefully designed for the removal of arsenic in household purifiers, community-level decentralized small systems, and the large-scale drinking water treatment plants (DWTPs). This review provides insight into the fundamental studies on novel adsorbents, the development of innovative technologies, and the demonstration engineering works involved in the heterogeneous oxidation and adsorption, and may be practically valuable for the arsenic pollution control globally.     

Control of aliphatic halogenated DBP precursors with multiple drinking water treatment processes: Formation potential and integrated toxicity

The comprehensive control efficiency for the formation potentials(FPs) of a range of regulated and unregulated halogenated disinfection by-products(DBPs)(including carbonaceous DBPs(C-DBPs), nitrogenous DBPs(N-DBPs), and iodinated DBPs(I-DBPs)) with the multiple drinking water treatment processes, including pre-ozonation, conventional treatment(coagulation–sedimentation, pre-sand filtration), ozone-biological activated carbon(O_3-BAC) advanced treatment, and post-sand filtration, was investigated. The potential toxic risks of DBPs by combing their FPs and toxicity values were also evaluated.The results showed that the multiple drinking water treatment processes had superior performance in removing organic/inorganic precursors and reducing the formation of a range of halogenated DBPs. Therein, ozonation significantly removed bromide and iodide,and thus reduced the formation of brominated and iodinated DBPs. The removal of organic carbon and nitrogen precursors by the conventional treatment processes was substantially improved by O_3-BAC advanced treatment, and thus prevented the formation of chlorinated C-DBPs and N-DBPs. However, BAC filtration leads to the increased formation of brominated C-DBPs and N-DBPs due to the increase of bromide/DOC and bromide/DON.After the whole multiple treatment processes, the rank order for integrated toxic risk values caused by these halogenated DBPs was haloacetonitriles(HANs)》haloacetamides(HAMs) haloacetic acids(HAAs) trihalomethanes(THMs) halonitromethanes(HNMs) 》I-DBPs(I-HAMs and I-THMs). I-DBPs failed to cause high integrated toxic risk because of their very low FPs. The significant higher integrated toxic risk value caused by HANs than other halogenated DBPs cannot be ignored.     

Hotspots and trends of biological water treatment based on bibliometric review and patents analysis

In order to reveal the hotspots and trends of biological water treatment from the perspectives of scientific and technological innovation, both of the bibliometric review and patents analysis were performed in this study. The Web of Science Core Collection database and Derwent Innovation Index database recorded 30023 SCI papers and 50326 patents, respectively were analyzed via information visualization technology. The results showed that China ranked the first in both papers and patents, while the United States and Japan had advantages in papers and patents, respectively. It was concluded through literature metrology analysis that microbial population characteristics, biodegradation mechanism, toxicity analysis, nitrogen and phosphorus removal and biological treatment of micro-polluted wastewater were the research hotspots of SCI papers. Activated sludge process and anaerobic-aerobic combined process were the two mainstream technologies on the basis of patent technology classification analysis. Technology evolution path of biological water treatment was also elucidated in three stages based on the citation network analysis. Furthermore, the future directions including research on the law of interaction and regulation of biological phases and pollutants and the technology innovations towards the targeted biotransformation or selective biodegradation of pollutants and resource reuse of wastewater were prospected.     

The impact of UV treatment on microbial control and DBPs formation in full-scale drinking water systems in northern China

To manage potential microbial risks and meet increasingly strict drinking water health standards,UV treatment has attracted increasing attention for use in drinking water systems in China.However,the effects of UV treatment on microbial control and disinfection byproducts(DBPs) formation in real municipal drinking water systems are poorly understood.Here,we collected water samples from three real drinking water systems in Beijing and Tianjin to investigate the impacts of UV treatment on microbia...     

A balancing act: Optimizing free chlorine contact time to minimize iodo-DBPs, NDMA, and regulated DBPs in chloraminated drinking water

Many drinking water treatment plants in the U.S. have switched from chlorination to chloramination to lower levels of regulated trihalomethane (THM) and haloacetic acid (HAA) disinfection byproducts (DBPs) in drinking water and meet the current regulations. However, chloramination can also produce other highly toxic/carcinogenic, unregulated DBPs: iodo-acids, iodo-THMs, and N-nitrosodimethylamine (NDMA). In practice, chloramines are generated by the addition of chlorine with ammonia, and plants use varying amounts of free chlorine contact time prior to ammonia addition to effectively kill pathogens and meet DBP regulations. However, iodo-DBPs and nitrosamines are generally not considered in this balancing of free chlorine contact time. The goal of our work was to determine whether an optimal free chlorine contact time could be established in which iodo-DBPs and NDMA could be minimized, while keeping regulated THMs and HAAs below their regulatory limits. The effect of free chlorine contact time was evaluated for the formation of six iodo-trihalomethanes (iodo-THMs), six iodo-acids, and NDMA during the chloramination of drinking water. Ten different free chlorine contact times were examined for two source waters with different dissolved organic carbon (DOC) and bromide/iodide. For the low DOC water at pH 7 and 8, an optimized free chlorine contact time of up to 1 h could control regulated THMs and HAAs, as well as iodo-DBPs and NDMA. For the high DOC water, a free chlorine contact time of 5 min could control iodo-DBPs and NDMA at both pHs, but the regulated DBPs could exceed the regulations at pH 7.     

Preparation of porous adsorbent via Pickering emulsion template for water treatment: A review

Porous materials as emerging potential adsorbents have received much more attention because they are capable of capturing various pollutants with fast adsorption rate, high adsorption capacity, good selectivity and excellent reusability.In order to prepare porous materials with decent porous structure, Pickering emulsion template method has been proved to be one of the most effective technologies to create pore structure.This paper reviewed comprehensively the latest research progress on the pre...     

Embedded reservoir and constructed wetland for drinking water source protection: Effects on nutrient removal and phytoplankton succession

An embedded reservoir that provides an efficient nutrient removal system protects drinking water.However,embedded reservoirs are rarely used in eutrophic shallow lakes because of their undetermined nutrient retention efficiency and unknown effects by the phytoplankton community.In this study,we aim to investigate the nutrient retention and algae succession in an embedded reservoir and adjacent wetland from April 2017 to September 2018 in the eastern part of Lake Taihu,China.More than 40% of tota...     

Application of the health risk assessment of acetochlor in the development of water quality criteria

Acetochlor is a widely used herbicide in agricultural production. Studies have shown that acetochlor has obvious environmental hormone effects, and long-term exposure may pose a threat to human health. To quantify the hazards of acetochlor in drinking water, a health risk assessment of acetochlor was conducted in major cities of China based on the data of acetochlor residue concentrations in drinking water. The approach of the Species Sensitivity Distributions (SSD) method is used to extrapolate from animal testing data to reflect worst case human toxicity. Results show that hazard quotients related to acetochlor residues in drinking water for different age groups range from 1.94 × 10^?4 to 6.13 × 10^?4, so, there are no indication of human risk. Compared to the total estimated hazard quotient from oral intake of acetochlor, the chronic exposure imputed to acetochlor residues in drinking water in China accounts for 0.4%. This paper recommends 0.02 mg/L to be the maximum acetochlor residue concentration level in drinking water and source water criteria.     

Micropollutant removal and disinfection byproduct control by sequential peroxymonosulfate-UV treatment in water: A case study with sulfamethoxazole

UV/peroxymonosulfate (UV/PMS) advanced oxidation process has attracted significant attention for removal of micropollutants in water. However, during practical water treatment applications, the PMS treatment must be performed before the UV treatment to achieve full contact. In this study, sulfamethoxazole (SMX) was selected as the target micropollutant. Four different operational approaches, including UV alone, PMS alone, simultaneous UV/PMS and sequential PMS-UV, were compared for their differences in SMX removal and disinfection by-product (DBP) formation potentials during chlorine-driven disinfection. Among the four approaches, UV/PMS and PMS-UV achieved over 90% removal efficiencies for SMX without substantial differences. For raw water, the trichloronitromethane (TCNM) formation potential after treatment with PMS-UV was lower than that after UV/PMS treatment. The time interval over which the PMS-UV process was conducted had little effect on the final removal efficiency for SMX. However, a brief (5 min) pre-PMS treatment significantly reduced the TCNM formation potential and the genotoxicity from DBPs. The formation risk for TCNM during chlorination increased markedly with increasing PMS dosages, and the appropriate dosage under these experimental conditions was suggested to be 0.5–1.0 mmol/L. Under alkaline conditions, PMS-UV treatment can enhance SMX degradation as well as dramatically reduced the formation potentials for haloketones, haloacetonitriles and halonitromethanes. This study suggests that proper optimization of UV/PMS processes can remove SMX and reduce its DBP formation.     

A survey on heavy metal concentrations in residential neighborhoods: The influence of secondary water supply systems

Water quality deterioration often occurs in secondary water supply systems (SWSSs), and increased heavy metal concentrations can be a serious problem. In this survey, twelve residential neighborhoods were selected to investigate the influence of SWSSs on the seasonal changes in heavy metal concentrations from input water to tank and tap water. The concentrations of nine evaluated heavy metals in all groups of water samples were found to be far below the specified standard levels in China. The concentrations of Fe, Mn, and Zn increased significantly from the input water samples to the tank and tap water samples in spring and summer (p < 0.05), especially for the water samples that had been stagnant for a long time. Negative correlations were found between most of the heavy metals and residual chlorine (Fe, Cu, Zn, and As, r = -0.186 to -0.519, p < 0.05). In particular, a high negative correlation was observed between Fe and residual chlorine (r = -0.489 to -0.519, p < 0.01) in spring and summer. Fe and Mn displayed positive correlations with turbidity (r = 0.672 and 0.328, respectively; p < 0.05). In addition, Cr and As were found to be positively associated with some nutrients (NO₃⁻, TN, and SO₄²⁻; r = 0.420-0.786, p < 0.01). The material of the storage tanks had little influence on the difference in heavy metal concentrations. Overall, this survey illustrated that SWSSs may pose a chronic threat to water quality and could provide useful information for practitioners.