Efficient electrochemical oxidation of antibiotic wastewater using a graphene-loaded PbO2 membrane anode: Mechanisms and applications.

This paper aims to develop a flow-through electrochemical system with a series of graphene nanoparticles loaded PbO2 reactive electrochemical membrane electrodes (GNPs-PbO2 REMs) on porous Ti substrates with pore sizes of 100, 150, 300 and 600 µm, and apply them to treat antibiotic wastewater. Among them, the GNPs-PbO2 with Ti substrate of 150 µm (Ti-150/GNPs-PbO2) had superior electrochemical degradation performance over the REMs with other pore sizes due to its smaller crystal size, larger electrochemical active specific area, lower charge-transfer impedance and larger oxygen evolution potential. Under the relatively optimized conditions of initial pH of 5, current density of 15 mA cm-2, and membrane flux of 4.20 m3 (m2·h)-1, the Ti-150/GNPs-PbO2 REM realized 99.34% of benzylpenicillin sodium (PNG) removal with an EE/O of 6.52 kWh m-3. Its excellent performance could be explained as the increased mass transfer. Then three plausible PNG degradation pathways in the flow-through electrochemical system were proposed, and great stability and safety of Ti-150/GNPs-PbO2 REM were demonstrated. Moreover, a single-pass Ti-150/GNPs-PbO2 REM system with five-modules in series was designed, which could consistently treat real antibiotic wastewater in compliance with disposal requirements of China. Thus, this study evidenced that the flow-through electrochemical system with the Ti-150/GNPs-PbO2 REM is an efficient alternative for treating antibiotic wastewater.

Research progress of inland river water quality monitoring technology based on unmanned aerial vehicle hyperspectral imaging technology.

In recent years, increasing demand for inland river water quality precision management has heightened the necessity for real-time, rapid, and continuous monitoring of water conditions. By analyzing the optical properties of water bodies remotely, unmanned aerial vehicle (UAV) hyperspectral imaging technology can assess water quality without direct contact, presenting a novel method for monitoring river conditions. However, there are currently some challenges to this technology that limit the promotion application of this technology, such as underdeveloped sensor calibration, atmospheric correction algorithms, and limitations in modeling non-water color parameters. This article evaluates the advantages and disadvantages of traditional sensor calibration methods and considers factors like sensor aging and adverse weather conditions that impact calibration accuracy. It suggests that future improvements should target hardware enhancements, refining models, and mitigating external interferences to ensure precise spectral data acquisition. Furthermore, the article summarizes the limitations of various traditional atmospheric correction methods, such as complex computational requirements and the need for multiple atmospheric parameters. It discusses the evolving trends in this technology and proposes streamlining atmospheric correction processes by simplifying input parameters and establishing adaptable correction algorithms. Simplifying these processes could significantly enhance the accuracy and feasibility of atmospheric correction. To address issues with the transferability of water quality inversion models regarding non-water color parameters and varying hydrological conditions, the article recommends exploring the physical relationships between spectral irradiance, solar zenith angle, and interactions with water constituents. By understanding these relationships, more accurate and transferable inversion models can be developed, improving the overall effectiveness of water quality assessment. By leveraging the sensitivity and versatility of hyperspectral sensors and integrating interdisciplinary approaches, a comprehensive database for water quality assessment can be established. This database enables rapid, real-time monitoring of non-water color parameters which offers valuable insights for the precision management of inland river water quality.

Characteristics of dissolved organic matter (DOM) in Chinese farmland soils under different climate zone types: A molecular perspective.

Interactions between dissolved organic matter (DOM) and surrounding environments are highly complex. Understanding DOM at the molecular level can contribute to the management of soil pollution and safeguarding agricultural fields. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has enabled a molecular-level understanding of DOM. Accordingly, in this study, we investigated soil samples from 27 different regions of mainland China with various soil types and climatic characteristics. Based on the geographical features of the four typical climatic zones in mainland China (temperate monsoon, temperate continental, subtropical monsoon, and Qinghai-Tibet Plateau climates), we employed high-resolution mass spectrometry to determine the molecular diversity of DOM under different climatic conditions. The results indicated that lignin and tannin-like substances were the most active categories of DOM in the soils. Collectively, the composition and unsaturation of DOM molecules are influenced by sunlight, precipitation, temperature, and human activity. All climatic regions contained a substantial number of characteristic molecules, with CHO and CHON constituting over 80%, and DOM containing nitrogen and sulfur was relatively more abundant in the monsoon regions. The complex composition of DOM incorporates various active functional groups, such as -NO2 and -ONO2. Furthermore, soil DOM in the monsoon regions showed higher unsaturation and facilitated various (bio) biochemical reactions in the soil.

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 filtration, reduced the total bacterial count, while they had little effect on the bacterial community structure in the treated water (before disinfection). Compared to the traditional treatment process, O3-BAC reduced the relative abundance of Sphingomonas in the finished water. In addition, ozonation may play a role in reducing the relative abundance of Mycobacterium. NaClO and ClO2 had different effects on the bacterial community in the finished water. The relative abundance of some bacteria (e.g. Flavobacterium, Phreatobacter and Porphyrobacter) increased in the finished water after ClO2 disinfection. The relative abundance of Mycobacterium and Legionella, which have been widely reported as waterborne opportunistic pathogens, increased after NaClO disinfection. In addition, some microorganisms proliferated and grew in the distribution system, which could lead to turbidity increases in the tap water. Compared to those in the finished water, the relative abundance of Sphingomonas, Hyphomicrobium, Phreatobacter, Rheinheimera, Pseudomonas and Acinetobacter increased in the tap water disinfected with NaClO, while the relative abundance of Mycobacterium increased in the tap water disinfected with ClO2. Overall, this study provided the detailed variation in the bacterial community in the drinking water system.

Distribution characteristics and transformation mechanism of per- and polyfluoroalkyl substances in drinking water sources: A review.

Per- and polyfluoroalkyl substances (PFASs) have raised significant concerns within the realm of drinking water due to their widespread presence in various water sources. This prevalence poses potential risks to human health, ecosystems, and the safety of drinking water. However, there is currently a lack of comprehensive reviews that systematically categorize the distribution characteristics and transformation mechanisms of PFASs in drinking water sources. This review aims to address this gap by concentrating on the specific sources of PFASs contamination in Chinese drinking water supplies. It seeks to elucidate the migration and transformation processes of PFASs within each source, summarize the distribution patterns of PFASs in surface and subsurface drinking water sources, and analyze how PFASs molecular structure, solubility, and sediment physicochemical parameters influence their presence in both the water phase and sediment. Furthermore, this review assesses two natural pathways for PFASs degradation, namely photolysis and biodegradation. It places particular emphasis on understanding the degradation mechanisms and the factors that affect the breakdown of PFASs by microorganisms. The ultimate goal is to provide valuable insights for the prevention and control of PFAS contamination and the assurance of drinking water quality.

Co-occurrence of phthalate esters and perfluoroalkyl substances affected bacterial community and pathogenic bacteria growth in rural drinking water distribution systems.

The adverse health effects of phthalate esters (PAEs) and perfluoroalkyl substances (PFAS) in drinking water have attracted considerable attention. Our study investigated the effects of PAEs and PFAS on the bacterial community and the growth of potential human pathogenic bacteria in rural drinking water distribution systems. Our results showed that the total concentration of PAEs and PFAS ranged from 1.02 × 102 to 1.65 × 104 ng/L, from 4.40 to 1.84 × 102 ng/L in rural drinking water of China, respectively. PAEs concentration gradually increased and PFAS slowly decreased along the pipeline distribution, compared to concentrations in the effluents of rural drinking water treatment plants. The co-occurrence of higher concentrations of PAEs and PFAS changed the structure and function of the bacterial communities found within these environments. The bacterial community enhanced their ability to respond to fluctuating environmental conditions through up-regulation of functional genes related to extracellular signaling and interaction, as well as genes related to replication and repair. Under these conditions, co-occurrence of PAEs and PFAS promoted the growth of potential human pathogenic bacteria (HPB), therefore increasing the risk of the development of associated diseases among exposed persons. The main HPB observed in this study included Burkholderia mallei, Mycobacterium tuberculosis, Klebsiella pneumoniae, Acinetobacter calcoaceticus, Escherichia coli, and Pseudomonas aeruginosa. Contaminants including particles, microorganisms, PAEs and PFAS were found to be released from corrosion scales and deposits of pipes and taps, resulting in the increase of the cytotoxicity and microbial risk of rural tap water. These results are important to efforts to improve the safety of rural drinking water.

Electroactive microorganism-assisted remediation of groundwater contamination: Advances and challenges.

Groundwater contamination has become increasingly prominent, therefore, the development of efficient remediation technology is crucial for improving groundwater quality. Bioremediation is cost-effective and environmentally friendly, while coexisting pollutant stress can affect microbial processes, and the heterogeneous character of groundwater medium can induce bioavailability limitations and electron donor/acceptor imbalances. Electroactive microorganisms (EAMs) are advantageous in contaminated groundwater because of their unique bidirectional electron transfer mechanism, which allows them to use solid electrodes as electron donors/acceptors. However, the relatively low-conductivity groundwater environment is unfavorable for electron transfer, which becomes a bottleneck problem that limits the remediation efficiency of EAMs. Therefore, this study reviews the recent advances and challenges of EAMs applied in the groundwater environment with complex coexisting ions, heterogeneity, and low conductivity and proposes corresponding future directions.

Performance of in-service granular activated carbon for perfluoroalkyl substances removal under changing water quality conditions.

Granular activated carbon (GAC) adsorption is one of the best available technologies for removing perfluoroalkyl substances (PFASs) from drinking water. However, GAC processes in full-scale drinking water treatment plants frequently encounter unstable, even negative removal efficiency on PFASs due to the lack of understanding between the GAC characteristics and the PFASs polluted water quality conditions. In this study, the scenarios of raw water pre-chlorination and emergency contamination by multiple PFASs were simulated to evaluate the PFASs control performance by in-service GAC with different properties and ages. The results showed that the adsorption of a relatively longer-chain PFAS by the in-service GAC can be achieved by replacing the pre-adsorbed natural organic matter (NOM). The increased lower molecular weight NOM after pre-chlorination could compete with PFASs for adsorption sites and exacerbate the pore blockage, thus significantly weakening the PFASs removal ability of in-service GAC. When multiple PFASs entered the water by emergency contamination, the PFASs with stronger hydrophobicity could replace the PFASs with less hydrophobicity that had previously been adsorbed on GAC. GAC with a higher proportion of micropores had a lower risk of PFASs leakage facing the water quality changes.

Detoxification mechanisms of electroactive microorganisms under toxicity stress: A review.

Remediation of environmental toxic pollutants has attracted extensive attention in recent years. Microbial bioremediation has been an important technology for removing toxic pollutants. However, microbial activity is also susceptible to toxicity stress in the process of intracellular detoxification, which significantly reduces microbial activity. Electroactive microorganisms (EAMs) can detoxify toxic pollutants extracellularly to a certain extent, which is related to their unique extracellular electron transfer (EET) function. In this review, the extracellular and intracellular aspects of the EAMs' detoxification mechanisms are explored separately. Additionally, various strategies for enhancing the effect of extracellular detoxification are discussed. Finally, future research directions are proposed based on the bottlenecks encountered in the current studies. This review can contribute to the development of toxic pollutants remediation technologies based on EAMs, and provide theoretical and technical support for future practical engineering applications.

Iron particle formation under chlorine disinfection considering effects of deoxidizers in drinking water.

Iron oxidation inevitably occurs in drinking water distribution systems (DWDSs) and can cause water quality problems such as increased turbidity and discoloration of tap water. Considering that chlorine disinfection is also widely used in DWDSs, the role of disinfectant and disinfection byproducts (DBPs) in iron oxidation should not be neglected. Interestingly, here the well-known deoxidizer ascorbic acid (VC), which is also a food additive, could induce the formation of Fe3O4 besides FeOOH resulting in the color change from yellow to black in the presence of trichloroacetic acid (TCA, one of the most typical DBPs) and NaClO (disinfectant). The oxygen-containing functional groups in TCA and VC may bind Fe(II) to guide the crystal growth. Though the particles generated in the presence of TCA and NaClO together with VC had higher content Fe3O4 which would be more difficult to suspend, once disturbance happened, these particles could increase the turbidity and color of water into higher value than the particles formed without VC and those generated in the absence of TCA and NaClO. Therefore, the deoxidizer VC may control "yellow water" without disinfectant, but may deteriorate the water quality under disinfection conditions.

Trihalomethanes formation enhanced by manganese chlorination and deposition in plastic drinking water pipes.

Residual manganese(II) in finished water undergoes further oxidation and deposition in drinking water distribution systems (DWDS), and Mn deposits can function as sites for accumulating organic and inorganic pollutants. This study aims to explore how Mn transformation and deposition affect the formation of disinfection byproducts (DBPs) in chlorinated DWDS, and trihalomethanes (THMs) was selected as a representative DBP. In a 100 µg/L Mn system, regulated THMs (chlorinated/bromated-THMs) increased by over 20% higher than Mn-free system after 150-day operation; when 50 µg/L iodide (I-) entered pipe systems after 150 days, iodinated THMs (I-THMs) in 100 µg/L Mn system increased by over 30% compared with Mn-free system. These promotions were attributed primarily to the accumulation of biomolecules and organic substances by tight and hard chlorinated Mn deposits. The residence of inactivated cells and the bridging role of surface Mn(III) in Mn deposits increased the quantity of THM precursors in DWDS. Furthermore, the rapid catalytic oxidation of Mn(II) by preformed Mn oxides (MnOx) inhibited the conversion of free iodine (HOI/OI-) to iodate, resulting in the generation of more I-THMs. This study provides new insights into the DBP risks caused by Mn in DWDS.

Field studies of aluminum release and deposition in drinking water distribution systems.

Aluminum (Al) release and deposition in drinking water distribution systems (DWDS) are highly detrimental to tap water quality. In this study, five drinking water treatment plant supply areas in two cities of China were examined to understand the transportation stability of Al in the DWDS. The two cities were selected based on the wide disparity reported in pH and turbidity in the finished and tap water qualities, with higher fluctuation of pH (average 8.0) and turbidity (average 0.78 NTU) reported in the northern and southern cities, respectively. Results showed that hydraulic conditions such as hydraulic shock or increased flow velocity had a more significant effect on the release and deposition of particulate Al, which could be reflected by turbidity when it was greater than 0.3 NTU, since turbidity and particulate Al were significantly positively correlated. Particulate Al concentration varied by more than 140 µg/L when turbidity fluctuated within 0.45-1.67 NTU. However, when turbidity was below 0.3 NTU, the particulate Al transported stably at low concentration. pH fluctuations contributed to the change of soluble Al concentration. Even above 50 µg/L soluble Al in the finished water could transport stably in the DWDS when pH fluctuated slightly in 6.6-7.0. However, when the pH fluctuated in 7.8-8.4, the soluble Al concentration varied by more than 100 µg/L. This study provides reference indicators of turbidity and pH for identifying the risk of Al in the DWDS.

Enhanced perfluorooctanoic acid (PFOA) accumulation by combination with in-situ formed Mn oxides under drinking water conditions.

Particulate manganese oxide (MnOx) deposition in drinking water distribution systems (DWDS) gives rise to the risk of water discoloration at the consumers' tap; however, its role in the fate and transport of trace organic pollutants in DWDS is not clear. Perfluorooctanoic acid (PFOA), a persistent organic pollutant frequently detected in natural water, was selected to investigate the potential effect of MnOx on its transportation behavior under DWDS conditions through laboratory batch experiments. The results show that PFOA can be greatly combined with MnOx formed in-situ through a Mn(II) oxidation process by free chlorine. However, the accumulation of PFOA by preformed MnOx was negligible. It was found that 1 mg/L Mn captured over 50% of PFOA with an initial concentration of 50 ng/L during oxidation. The water compositions of actual water could contribute to the effect of PFOA accumulation to a certain extent. Characterization of the solid products revealed that PFOA is homogenously embedded into MnOx. The combination of PFOA with MnOx occurs through a bridging effect of Mn(II) between the surface hydroxyls of MnOx and the -COOH group of PFOA. The resulting MnOx-PFOA particles were more inclined to agglomerate, enabling possibly easy deposition onto the pipe wall than ordinary MnOx particles. This study provides insights into the co-occurrence of metal deposits with PFOA and the potential risks posed by PFOA accumulation to consumers through the water distribution process.

Control of disinfection byproducts in drinking water treatment plants: Insight into activated carbon filter.

The removal efficiencies of disinfection byproducts formation potentials (DBPFPs) and generated DBPs under pre-chlorination condition (pre-generated DBPs) during different drinking water treatment trains in eight full-scale drinking water treatment plants (WTPs) were investigated through field and laboratory studies. Haloacetic acids (HAAs) and haloacetonitriles (HANs) were identified to be two representative DBPs based on cytotoxicity and genotoxicity assessments. The performances of advanced treatment train for HAAs and HANs were better than that of conventional treatment train. However, the efficacy of ozone - biological activated carbon (O3-BAC) was affected by its service time and position in the water treatment process. In addition, the consumption of free chlorine by activated carbon in old granular activated carbon (GAC) filter was higher than that in new one under pre-chlorination condition, resulting in the increase of HAAs and HANs in the GAC filter effluent. This demonstrated that the organic matter adsorbed on older activated carbon generated more HAAs and HANs during pre-chlorination, which inhibited the adsorption of pre-generated DBPs. The ability of GAC/O3-BAC to remove HAAs and HANs was consistent with that of protein-like and low molecular weight organic substances, which could predict the performance of GAC and O3-BAC in treating DBPs.

Effect of trichloroacetic acid on iron oxidation: Implications on the control of DBPs and deposits in drinking water.

In drinking water distribution system (DWDS), disinfection byproducts (DBPs) have a large possibility of participating in iron oxidation by dissolved oxygen (DO), which may induce particle structure transformations and increase unknown risks. In this work, the influence of trichloroacetic acid (TCAA, one of the most typical DBPs) on iron oxidation processes was studied, and the potential effects of the resulting α-FeOOH particles were evaluated through two aspects: (i) influence on the bacterial community and (ii) toxicity to human cells. TCAA promoted iron oxidation process through an Fe-O-C linkage, which led to a sharper surface of the particles (TCAA-mediated Fe oxide particles, TFOP) than that without TCAA (Fe oxide particles, FOP). Interestingly, the influence of particles on the richness of bacterial community of drinking water was different under anaerobic and aerobic conditions: under anaerobic conditions, the richness of bacterial community increased with the addition of particles, while under aerobic conditions, the richness of bacterial community decreased. The higher affinity of TFOP for electron-accepting DO than FOP indicated the role of DO on TFOP under aerobic conditions. TFOP exhibited the strongest cytotoxicity among FOP and the actual deposits. DFT calculations confirmed that TCAA in iron particles promoted the adsorption and dissociation of H2O2 to generate more •OH with an obvious decrease in the energy barrier from 1.51 to 0.80 eV. This study indicates the high potential of adverse effects of DBPs on loose deposits in DWDS and gives implications for the control of DBPs and deposits in drinking water.

Field study on the transportation characteristics of PFASs from water source to tap water.

Perfluoroalkyl substances (PFASs) can occur in water sources, pass through drinking water treatment plants (DWTPs), drinking water distribution systems (DWDSs), to the consumer taps. This investigation was carried out to present the transportation behaviors of 17 PFASs, involving seven DWTPs with different water sources, raw water transportation modes, treatment processes, and DWDS structures in eastern and northern China. The results showed that the long-distance raw water transportation pipelines removed a certain extent of PFASs from raw water, probably due to the accumulation of loose deposits. The long-distance, open-channel South-to-North water diversion increased PFAS contamination risk. In the DWTPs, granular activated carbon (GAC) adsorption and ultraviolet radiation removed less than 25% of PFASs, but ozonation-biological activated carbon (O3-BAC) was superior to GAC alone in removing PFASs. Loose deposits couldsignificantly influence PFAS accumulation and release within branch-structured DWDSs. In loop-structured DWDSs, finished water with different PFAS characteristics could mix along the pipeline, with the corresponding DWTP as the center, ultimately forming a relatively uniform distribution in the entire DWDS.

Structural transformation and potential toxicity of iron-based deposits in drinking water distribution systems.

Discoloration events in drinking water distribution systems (DWDSs) are usually considered an aesthetic issue rather than a health concern, and the potential toxicity of the iron-based particles resuspended from deposits in DWDSs has not been a focus. More importantly, it has not been recognized that the iron-based particles may have structural transformation under the complex condition in DWDSs which would further increase their adverse effects. In the present study, iron particle-dominated loose deposits, which were collected from a real DWDSs through pipe flushing, were firstly found to possess obvious toxicity to human liver cells. To further evaluate the potential harms of the deposits, FeOOH crystals (which is one of the most representative components in the deposits of DWDSs) were grown with different types of coexisting matters which may emerge in DWDSs. Results showed that the FeOOH had obvious structure transformation with coexisting matters which further influenced their toxicity: the samples with sharp surfaces had higher toxicity than those with smooth surfaces. Interestingly, although the FeOOH particles formed with perfluorooctanoic acid (FeOOH-PFOA) did not have the sharpest surface or smallest particle size among all the samples, they demonstrated the highest toxicity with strong generation of reactive oxygen species. Experimental and theoretical studies verified that PFOA induced the electron migration around Fe in FeOOH-PFOA particles. The FeOOH-PFOA not only was able to capture electrons directly from DNA, but also generated ROS from O2 using DNA as an electron donor which might greatly enhance the oxidative damage to cells. This study would broaden the understanding of the potential harms of deposits in DWDSs.

Occurrence and transport behaviors of perfluoroalkyl acids in drinking water distribution systems.

Although human exposure to perfluoroalkyl acids (PFAAs) through tap water is an ongoing concern, knowledge of the PFAAs occurrence in the tap water and the associated transport behaviors of PFAAs in drinking water distribution systems (DWDSs) are scarce. This investigation profiled the occurrence of 17 kinds of PFAAs in tap water of some Chinese cities, and the transport behaviors of PFAAs in DWDS were observed in eastern China. Tap water samples both along trunk pipelines and at the distal ends were collected to display the PFAAs occurrence scenarios. Loose deposit solids were also obtained to reveal their possible accumulation effect on PFAAs. The results showed that perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA) widely existed in tap water samples, and were the predominant PFAAs in eastern China areas. The mean concentration of the 17 PFAAs was 77.49 ng/L (ranging from 9.29 ng/L to 266.68 ng/L). Short-chain PFAAs (mainly PFBA) concentrations were relatively stable from water treatment plant to consumer taps, while long-chain PFAAs (mainly PFOA) exhibited a significant decrease in concentration, which could be attributed to their accumulation by the loose deposits in the DWDSs. It was calculated that PFOA has a higher partition coefficient than PFBA; this means that the former has a stronger potential to be adsorbed by loose deposits. In addition, the accumulation ability of loose deposits might be associated with the composition of Al, Fe and Si in the loose deposits. The positive correlation between the short-chain PFAAs and dissolved organic carbon (DOC) indicated the possible interactions between PFAA and natural organic matter could favor short-chain PFAAs to retain in bulk water. When water quality conditions change or hydraulic disturbance occur, loose deposits may enter tap water bringing accumulated PFAAs with it, which may result in potential health risks.

Field studies of manganese deposition and release in drinking water distribution systems: Insight into deposit control.

Drinking water discoloration is one of the most common customer complaints. The accumulation of residual manganese (Mn) in drinking water distribution systems (DWDS) accounts for part of the discolored water that reaches household taps. Field studies were conducted at seven full-scale DWDS to investigate the deposition and release behaviors of Mn in different forms and at different concentrations in finished water. The results show that particulate Mn tended to accumulate in DWDS even at concentrations as low as 10 µg/L. The oxidation of soluble Mn(II) ions in DWDS was highly affected by water chemistries as well as water age; 10 µg/L of soluble Mn could still transform into particulate Mn under suitable conditions. When total Mn concentration in finished water was below 5 µg/L, erosion of Mn deposits occurred in DWDS with a Mn deposit inventory. Soluble Mn release was observed when chlorine or chlorine dioxide concentration was lower than 0.1 mg/L, and the release was speculated to be a result of microbial reductive dissolution of Mn oxides. Ensuring the total Mn concentration is below 10 µg/L and decreasing the particulate Mn concentration to 5 µg/L in finished water are both recommended to minimize Mn accumulation risk in DWDS. Enhanced oxidation and filtration for Mn removal during water treatment processes are proposed.

The occurrence and transformation behaviors of disinfection byproducts in drinking water distribution systems in rural areas of eastern China.

The occurrence and transformation behaviors of disinfection byproducts (DBPs) were investigated in the finished water and tap water of 14 water treatment plants in rural areas of eastern China. Mammalian cell toxicity data from previous studies were used to evaluate the cytotoxicity of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), trichloronitromethane (TCNM) and the genotoxicity of HAAs, HANs and TCNM. Correlation analysis was conducted to identify the factors that might influence the variability of DBPs. The measured median values were 29.76 µg/L for THMs, 20.47 µg/L for HAAs, 3.98 µg/L for HANs, 0.76 µg/L for haloketones (HKs) and 0.03 µg/L for TCNM. The spatial variability analysis showed that the total concentrations of HAAs and HANs decreased during long hydraulic residence time (HRT) in seven drinking water distribution systems, which could result in reduced mammalian cell cytotoxicity and genotoxicity at consumers' taps. The concentrations of trihalogenated-DBPs were more stable than those of dihalogenated-DBPs and monohalogenated-DBPs during long HRT. Bromine acted as a more efficient substituting agent than chlorine for THMs and dihaloacetonitriles (DHANs) in actual drinking water. The dominant chlorinated-THMs and chlorinated-DHANs would transfer to brominated -THMs and brominated-DHANs when the concentration of bromide ion exceeds 450.67 and 610.25 µg/L, respectively. Correlation analysis indicated that particulate and soluble manganese (Mn) might play critical roles in promoting the production of DBPs in bulk water. Hydraulic disturbance could also result in secondary release of DBPs from loose deposits accumulated on distribution pipe walls.