Impacts of water quality on the corrosion of cast iron pipes for water distribution and proposed source water switch strategy

A revised digestion method to characterize manganese content in solids

Quantifying manganese (Mn) content in solids is critical for understanding its roles in aquatic ecosystems, soils, water treatment plants and distribution systems. No studies have yet used standard Mn oxides to compare the performance of the numerous digestion methods found in the literature. Nine digestion methods (including USEPA 3050B) were compared using four Mn oxides with varying oxidation states. The HCl concentrate (12.4 M) heated to at least at 40 °C provided quantitative digestion of all Mn oxides tested with ≈ 100 % recovery. HCl concentration is important only for MnO2 digestion, while temperature influences both MnO and MnO2 recovery. Complete recovery of various Al, Cu and Fe standard oxides using a 12.4 M HCl digestion at 95 °C. Digestion of environmental samples for Al, Ca, Fe, Mg and Mn content yielded higher metal content using the HCl method (except for Al). HCl 12.4 M digestion provided better performance than other digestion methods found in the scientific literature because of its high reducing capacity. •Most digestion methods found in the literature do not digest all Mn oxidation states.•Hydrochloric acid is shown to be essential to dissolve all oxidation state of Mn oxides.

Selective dissolution of zinc and lead from duplex β-phase brasses in low and high conductivity water

This study provides insights regarding the selective metal leaching of brass in various tap water conditions, which benefits water utilities to predict the potential of metal released from brass water meters. The long-term time-dependent selective metal dissolution of brass with various β phase fractions have not previously been investigated. In this study, a 201-d immersion experiment was carried out in low and high conductivity tap water (LCTW and HCTW, respectively). Three commercialized brass samples in different β phase fractions (β = 51%, β = 43%, β = 39%), named brass 51, brass 43, and brass 39, respectively, were used. The results showed that brass 51 had the most negative corrosion potential (-0.17 V) and the lowest polarization resistance (8.5 kΩ) compared to brass 43 and brass 39 (-0.04 V and 10.1-14.7 kΩ, respectively) in LCTW. This trend was verified by the 201-d immersion experiment in which brass 51 exhibited the highest zinc leaching rate (21-30 μg L-1 cm-2 d-1), followed by brass 43 and brass 39 (16-23 μg L-1 cm-2 d-1) in both waters. The leaching amounts of lead and copper were extremely low compared to zinc. In LCTW, the uniform corrosion (UC) mechanism dominated from day 1 to day 120. Afterwards, UC was replaced by the galvanic corrosion (GC) mechanism, with the selective leaching coefficient of Zn over Cu (SZn/Cu) increasing from 10 to 25 to 40-80. In HCTW, however, the SZn/Cu reached 300-1000, and the transition of UC to GC occurred earlier on day 30 due to the rapid formation of the ZnO layer on the brass surface that hindered the ion attack.

Effects of chloride on corrosion scale compositions and heavy metal release in drinking water distribution systems

Variations in water chemistry may lead to the release of harmful heavy metals in drinking water distribution systems (DWDSs). In this study, the effects of chloride on the release of heavy metals such as Fe, Mn, As, Cr, Mo, V, Sr, and Co were examined using steel and cast iron pipe loops. After chloride was added, the relative contents of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and siderite (FeCO3) in pipe scales increased, but the contents of magnetite (Fe3O4) decreased. The most prevalent compounds were α-FeOOH and γ-FeOOH. When the chloride levels were increased, the effluent concentrations of Fe, Mn, As, Cr, Mo, V, Sr, and Co significantly increased. These heavy metals were released presumably because of the destabilization and dissolution of corrosion scales induced by chloride and adsorption site competition. Strong positive correlations were also observed between Fe&Mn, Fe/Mn&As, Fe/Mn&Cr, Fe/Mn&Mo, Fe/Mn&V, Fe/Mn&Sr, and Fe/Mn&Co, indicating the co-release of Fe, Mn, and other metals. This study may be helpful for the potential strategies on avoidance of heavy metal release and improvement of water supply security.

Copper ion affects oxidant decay and combined aspartic acid transformation during chlorination in water pipes: Differentiated action on the yield of trihalomethanes and haloacetonitriles

The chlorination of extracellular polymeric substances (EPS) secreted by biofilm often induces the formation of high-toxic disinfection byproducts (DBPs) in drinking water distribution systems. The protein components in EPS are the main precursors of DBPs, which mostly exist in the form of combined amino acids. The paper aimed to study the action of a pipe corrosion product (Cu2+) on the formation of DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as a precursor. Cu2+ mainly promoted the reaction of oxidants with TAsp (i.e., TAsp-induced decay) to produce DBPs, rather than self-decay of oxidants to generate BrO3‒ and ClO3‒. Cu2+ increased THMs yield, but decreased HANs yield due to the catalytic hydrolysis. Cu2+ was more prone to promote the reaction of TAsp with HOCl than with HOBr, leading to a DBPs shift from brominated to chlorinated species. The chemical characterizations of Cu2+-TAsp complexations demonstrate that Cu2+ combined with TAsp at the N and O sites in both amine and amide groups, and the intermediate identification suggests that Cu2+ enhanced the stepwise chlorination process by promoting the substitution of chlorine and the breakage of CC bonds. The effect of Cu2+ on THMs yield changed from promoting to inhibiting with the increase of pH, while that on HANs yield was inhibiting regardless of pH variation. Additionally, the impact of Cu2+ on the formation of DBPs was also affected by Cu2+ dose, Cl2/C ratio and Br- concentration. This study helps to understand the formation of EPS-derived DBPs in water pipes, and provides reference for formulating control strategies during biofilm outbreaks.

Mechanisms of iopamidol transformation catalyzed by a copper corrosion product (c-Cu2O) during peroxymonosulfate disinfection

Peroxymonosulfate (PMS) is an alternative disinfectant for drinking water. This study aimed to investigate the transformation of iopamidol (IPM) catalyzed by a main copper corrosion product (c-Cu2O) with PMS as a disinfectant. The observed pseudo-first-order constant (kobs) for the IPM degradation in the c-Cu2O/PMS system (0.033 min-1) was 3 times that in the CuO/PMS system (0.011 min-1). The quenching tests and the electron paramagnetic resonance (EPR) experiments indicate that O2•- and 1O2 contributed to IPM degradation in the c-Cu2O/ PMS system. The complexation of metastable Cu(II) with a PMS molecule polarized the OO bond and then facilitated the electron transfer from the PMS molecule to other PMS and O2 molecules, which directly and indirectly promoted the yield of O2•- and 1O2. The iodine balance indicated that 26.0% of initial TOI was converted to IO3-, and CHI3 only accounted for 0.6% of the residual TOI. In the c-Cu2O/PMS system, IPM conversion was started with amide C-N bond breakage, deiodination reaction and hydrogen abstraction. This study helps to better understand the conversion mechanisms of iodine-containing organic micropollutants when PMS is deployed as a disinfectant in copper pipes.

Inhibition of Hexavalent Chromium Release from Drinking Water Distribution Systems: Effects of Water Chemistry-Based Corrosion Control Strategies

In drinking water distribution systems, the oxidation of zerovalent chromium, Cr(0), in iron corrosion scales by chlorine residual disinfectant is the dominant reaction to form carcinogenic hexavalent chromium, Cr(VI). This study investigates inhibitive corrosion control strategies through adjustments of chemical water parameters (i.e., pH, silicate, phosphate, calcium, and alkalinity) on Cr(VI) formation through oxidation of Cr(0)(s) by free chlorine under drinking water conditions. The results show that an increase in pH, silicate, alkalinity, and calcium suppressed Cr(VI) formation that was mainly attributed to in situ surface precipitation of new Cr(III) solids on the surface of Cr(0)(s), including Cr(OH)3(s), Cr2(SiO3)3(s), CrPO4(s), Cr2(CO3)3(s), and Cr10Ca(CO3)16(s). The Cr(III) surface precipitates were much less reactive with chlorine than Cr(0)(s) and suppressed the Cr redox reactivity. The concentration of surface Cr(III) solids was inversely correlated with the rate constant of Cr(VI) formation. Adding phosphate either promoted or inhibited the Cr(VI) formation, depending on the phosphate concentration. This study provides fundamental insight into the Cr(VI) formation mechanisms via Cr(0) oxidation by chlorine and the importance of surface precipitation of Cr(III) solids with different corrosion control strategies and suggests that increasing the pH/alkalinity and addition of phosphate or silicate can be effective control strategies to minimize Cr(VI) formation.

Recent advances in the unlined cast iron pipe scale characteristics, cleaning techniques and harmless disposal methods: An overview

Drinking water discoloration and its potential health risks (e.g., heavy metals, pathogens, carcinogenic organics) have aroused wide public concerns around the world, and the characteristics and corresponding cleaning techniques of pipe scales are one of the most important research fields closely related to people's lives and health. This Overview Article summarizes the latest research achievements about the new insights into the unlined cast iron pipe corrosion scale characteristics as well as the advanced cleaning techniques applied in drinking water distribution systems. The typical pollutants such as heavy metal ions, pathogens and disinfection by-products (DBPs) in pipe scales and the main cleaning techniques including unidirectional flushing (UDF), air scouring, ice pigging and guided ultrasonic waves (GUW) are categorized and elaborated. In the final part, the current challenges and future opportunities are also further discussed from the viewpoint of evolution process of pipe scales as well as the widespread application of advanced cleaning techniques. Moreover, the possible technical route for the innocent treatment and resource utilization of pipe scale waste is also proposed. It is anticipated that this review will attract more attention toward the in-depth study of pipe scales and their cleaning techniques to enjoy cleaner and healthier drinking water for people.

Removal of Fe and Mn from the groundwater by using zeolite with Rossellomorea sp

Groundwater is one of the alternatives to surface water that can be used for drinking water; however, it normally exists with high iron and manganese content. In this study, a column study was conducted to observe the elimination of iron (Fe) and manganese (Mn) in the groundwater under different retention times by using zeolite immobilized with iron-oxidizing bacteria (IOB). Rossellomorea sp., representing an IOB, was found from the isolation process and was further cultured in the laboratory for immobilization into the natural zeolite as replacement materials for the sand filter. When the zeolite assisted with the Rossellomorea sp. was used, the elimination of Fe and Mn were 99.34% and 88.92%, respectively, compared to the removal of Fe and Mn, which were 93.62% and 93.73%, respectively, for media without immobilization. The presence of Rossellomorea sp. enhances the Fe oxidation, resulting in high removal of Fe. The Thomas and Yoon-Nelson models were performed in both raw zeolite and zeolite with IOB. The total coliform (most probable number [MPN]) increased from 70.8 to 307.6 MPN/100 mL because of the Rossellomorea sp. present that promotes the growth of coliform bacteria. In conclusion, the immobilization of zeolite with IOB is a potential technique to extract the Fe and Mn in the groundwater. PRACTITIONER POINTS: Zeolite incorporated with Rossellomorea sp. has higher removal performance of Fe, whereas the removal of Mn reduced compared to the raw zeolite. The presence of Rossellomorea sp. enhances the oxidation of ferrous iron and improves the removal of Fe in the groundwater because the ferric iron is the priority ion to be exchanged. The removal of UV254 increase when Rossellomorea sp. present in the zeolite because the Rossellomorea sp. consume the natural organic matter as carbon source.

Stability of arsenic(Ⅲ, Ⅴ) in galvanized steel pipe scales coexisting with colloidal polystyrene microplastics under drinking water conditions

The stability of metalloid arsenic (As(Ⅲ)) and As(V) in corrosion scales of drinking water distribution systems (DWDS) is closely related to drinking water safety. The effects of colloidal microplastics entering the DWDS on the stability of As(Ⅲ) and As(V) have not been understood. This study investigated the migration and transformation behaviors of As (Ⅲ) and As(V) in the galvanized steel pipe scales employing speciation simulation and sequential extraction methods. The stability of As(Ⅲ) and As(V) in the pipe scales coexisting with colloidal polystyrene microplastics (CPMPs) under drinking water conditions was studied for the first time from the release behaviors and form distributions. Finally, the optimum water quality conditions for As(Ⅲ) and As(V) fixation were summarized. The existing forms of As(Ⅲ) and As(V) under different pH conditions, the competitive action of anions, and the hydrolysis of cations all would significantly affect the stability of As(Ⅲ) and As(V). Sequential extraction method results revealed that the content of As fractions increased in different forms after the pipe scales adsorbed As(Ⅲ) and As(V). The contents of As and iron (Fe) in the form of residual fractions increased in the presence of CPMPs. The effect of three cations on the stability of As(Ⅲ) and As(V) was Fe³⁺ > Zn²⁺ > Ca²⁺. Neutral to weak alkalescence, proper Cl^- and cation concentrations were conducive to the fixation of As in DWDS. Notably, the presence of CPMPs could increase the stability of As(Ⅲ) and As(V) in corrosion scales, thus reducing the risk of metalloid As release in DWDS.

Study on electrochemical reduction mechanisms of iron oxides in pipe scale in drinking water distribution system

Iron release from pipe scale is an important reason for water quality deterioration in drinking water distribution systems (DWDS) globally. Disruption of pipe scale, release and transformation of iron compounds are hot topics in the field of water supply. The aim of this study is to determine whether and how ferric components in pipe scale be reduced under anoxic condition. In this study, new investigation approaches were applied, which include simplifying the complex scale into electrode pairs, developing novel simulating reactors and conducting tailored electrochemical assays. A galvanic cell reactor with anode of metallic iron (Fe⁰) and various cathode made of certain iron oxide (FeO_x) was firstly developed to simulate the complex niche and components of pipe scale. Electrochemical methods were used to study the reduction characteristics of scale. The results proved that reduction of iron oxide scale did occur under anoxic condition. Electromotive forces between various electrodes match the Nernst Equation quite well. As main components in pipe scale, lepidocrocite (γ-FeOOH) was found to be the most reducible iron oxide but at low rate, while goethite (α-FeOOH) has weak reducibility but can be quickly reduced. As a result of electrochemical reactions, goethite in pipe scale was transformed into magnetite (Fe₃O₄). By these means, electrochemical reaction mechanisms of pipe scale disruption were revealed, which is helpful to restrain pipe corrosion and water deterioration in DWDS.

Characteristics of vanadium release from layered steel pipe scales to bulk, steady, and occluded water in drinking water distribution systems

The release of vanadium (V) from drinking water distribution systems (DWDS) can endanger water quality and human health. Therefore, in this study, the physicochemical characteristics of old steel pipe scales were analyzed, and dynamic pipeline devices were constructed. Subsequently, static release experiments were conducted to find an optimum scale-water ratio and investigate the release behaviors of V in lumpy pipe scales. Besides, the release behaviors of V from layered pipe scales to bulk, steady, and occluded water under the combined effect of multiple water quality conditions were studied for the first time. Computational fluid dynamics (CFD) was adopted to explain the release behaviors of V in the dynamic pipeline. Results revealed that the adsorption performance of the layered scales decreased in the order of surface layer > porous core layer > hard shell-like layer. The release behaviors of V in the lumpy pipe scales were mainly divided into rapid desorption and colloidal agglomeration stages. The Double constant and Weber-Morris models can suitably describe release stage I (R² > 0.919) and release stage II (R² > 0.948), respectively. Notably, the release of V was aggravated by low pH, high temperature, and high SO₄^2- concentration, and the release amount of V in the pipeline was more significant than the layered pipe scales. Steady water in the gaps of scales contained more V than bulk water, and the malignant occluded water encased in scales contained relatively low V concentrations. In short, the main mechanism of V release was competitive adsorption in the early stage, and pH was the main influencing factor in the later stage. The above results are of great significance for revealing the release behaviors of V and reducing its release in DWDS.

Mn(II) Oxidation by Free Chlorine Catalyzed by the Hydrolytic Products of Ferric and Aluminum Species under Drinking Water Conditions

Mn(II) oxidation by free chlorine can be applied to remove Mn(II) at water treatment plants. This reaction also results in particulate MnO_x formation and accumulation in drinking water distribution systems. This study investigated the effect of Fe(III) and Al(III) hydrolysis products (mainly precipitates) on Mn(II) oxidation by free chlorine under drinking water conditions. The results showed that Fe³⁺ added as FeCl₃ and Al(III) added as polyaluminum chloride (PACl) at tens to hundreds of micrograms per liter dramatically catalyzed Mn(II) oxidation by free chlorine. Through hydrolytic precipitation at circumneutral pH, Fe³⁺ and Al₁₃ (the dominant preformed Al species in PACl) generated Fe(OH)₃-like particles and Al₁₃ aggregates, respectively, which initiated heterogeneous Mn(II) oxidation. Kinetic modeling indicated that, once some MnO_x was formed, MnO_x and Fe(OH)₃ catalyzed the subsequent Mn(II) oxidation to an equal extent. The particles (aggregates) formed from Al₁₃ species exhibited a weaker catalytic capacity in comparison to MnO_x and Fe(OH)₃ at equivalent molar concentrations. Interestingly, unlike Al₁₃ species in PACl, Al(III) added as AlCl₃ had a negligible influence on Mn(II) oxidation, even when Al(OH)₃(am) precipitates were formed. The catalytic effects of Fe³⁺ and Al₁₃ hydrolysis products were confirmed by experiments with natural water and finished water, and the lower Mn(II) oxidation rate was mainly attributed to organic matter.

Iron release and characteristics of corrosion scales and bacterial communities in drinking water supply pipes of different materials with varied nitrate concentrations

Changes of drinking water quality can lead to iron release in drinking water distribution systems (DWDSs), which is one of the most important reasons for the deterioration of tap water quality. The objective of this study was to investigate the effects of nitrate on the iron release and characteristics of corrosion scales and bacterial communities in DWDSs using simplified pipe section reactors. With nitrate addition, the percentages of goethite (α-FeOOH), hematite (Fe₂O₃), and lepidocrocite (γ-FeOOH) in scales were decreased, whereas those of magnetite (Fe₃O₄) were increased. The growth of nitrate-reducing bacteria (NRB) was promoted significantly, with the fractions of 25.70% and 23.79% in the steel and cast iron pipes, respectively. Approximately 3.40% of iron-reducing bacteria (IRB) were reduced in both pipes. Moreover, under higher nitrate levels, iron release was inhibited obviously. The maximum decreased percentages of total iron in the steel and cast iron pipes were 44.90% (with 10.00 mg/L NO₃^--N) and 88.29% (with 30.00 mg/L NO₃^--N), respectively. This study may be helpful for improving drinking water supply safety.

Facilely tuning the intrinsic catalytic sites of the spinel oxide for peroxymonosulfate activation: From fundamental investigation to pilot-scale demonstration

Heterogeneous peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have shown a great potential for pollutant degradation, but their feasibility for large-scale water treatment application has not been demonstrated. Herein, we develop a facile coprecipitation method for the scalable production (∼10 kg) of the Cu-Fe-Mn spinel oxide (CuFeMnO). Such a catalyst has rich oxygen vacancies and symmetry-breaking sites, which endorse it with a superior PMS-catalytic capacity. We find that the working reactive species and their contributions are highly dependent on the properties of target organic pollutants. For the organics with electron-donating group (e.g., -OH), high-valent metal species are mainly responsible for the pollutant degradation, whereas for the organics with electron-withdrawing group (e.g., -COOH and -NO₂), hydroxyl radical (•OH) as the secondary oxidant also plays an important role. We demonstrate that the CuFeMnO-PMS system is able to achieve efficient and stable removal of the pollutants in the secondary effluent from a municipal wastewater plant at both bench and pilot scales. Moreover, we explore the application prospect of this PMS-based AOP process for large-scale wastewater treatment. This work describes an opportunity to scalably prepare robust spinel oxide catalysts for water purification and is beneficial to the practical applications of the heterogeneous PMS-AOPs.

Pilot investigation on biostability of drinking water distribution systems under water source switching

Water quality deterioration of drinking water distribution systems (DWDSs) caused by water source switching has been reported previously. However, systematic investigation of the biostability of DWDS under water source switching is limited. Aged pipes, including three commonly used pipe materials dug out from a practical DWDS, were used to systematically investigate the biofilm stability mechanism of DWDS under water source switching to quality-improved water. An increase in adenosine triphosphate (ATP) concentration in the bulk water during the initial stage of the switching period was observed, indicating the risk of biofilm release through aged pipe surfaces after water source switching. Sloughing of biofilms might contribute to temporary instability. From day 35, the ATP concentration in the polyethylene (PE) and plastic stainless steel composite (PS) pipes were maintained at approximately 2.40 and 2.56 ng/L, respectively. In contrast, the ATP concentration in the ductile iron (DI) pipes was higher, at approximately 3.43 ng/L from day 42. The water quality variation could cause areas of the biofilm to slough and reduce the biomass of biofilm, causing partial alteration of the microbial community. 16S rRNA gene amplicon sequencing-based functional prediction revealed that the biofilm could increase the abundance of chlorine-resistant bacteria attributed to the increase in Pseudomonas and Methylobacterium after switching to quality-improved water. Moreover, the profiles of specific pathways linked to human diseases, antibiotic resistance, and antibiotic biosynthesis revealed that the safety of the biofilm could improve after switching to quality-improved water. KEY POINTS: • The PE and PS biofilm showed improved resistance to water quality perturbation. • Greater number of Methylobacterium was found in the biofilm after water source switching. • 3.16S gene-based metagenomics prediction revealed that the safety of the biofilm under water source switching.

Impact of different source-water switching patterns on the stability of drinking water in an estuarine urban water distribution system

Source-water switching can lead to instability in drinking water distribution systems. In estuarine cities using surface water as source water where salt tide occasionally happens, the influence can be particularly complex due to changes of Larson Index (LI). The objective of this study was to investigate the effects of different switching patterns on the stability of water in an estuarine city. Fluctuated LI was found in the current distribution system. LI of the new source water was lower and more stable. Susceptible areas with a high frequency of over standard water quality were identified and pipe scales there were mainly composed of relatively stable iron oxides with dense crystal structures (Fe₃O₄ and α-FeOOH). Two old pipe sections were used to simulate different switching patterns. The microbial risk did not increase significantly when the original and new water sources were combined in different ratios (2∶8, 5∶5), when multiple water sources were used (3∶3∶4) or when salinity increased. The better water quality, lower LI of the new source water, and stability of the current distribution system together contributed to the biostability. Total iron increased after switching, then declined and stabilized for most switching patterns. Salt tide can lead to sharp iron release. The results provided insightful information for distribution systems that have cast iron pipes and that might encounter source-water switching patterns.

Review on corrosion and corrosion scale formation upon unlined cast iron pipes in drinking water distribution systems

The qualified finished water from water treatment plants (WTPs) may become discolored and deteriorated during transportation in drinking water distribution systems (DWDSs), which affected tap water quality seriously. This water stability problem often occurs due to pipe corrosion and the destabilization of corrosion scales. This paper provides a comprehensive review of pipe corrosion in DWDSs, including corrosion process, corrosion scale formation, influencing factors and monitoring technologies utilized in DWDSs. In terms of corrosion process, corrosion occurrence, development mechanisms, currently applied assays, and indices used to determine the corrosion possibility are summarized, as well as the chemical and bacterial influences. In terms of scale formation, explanations for the nature of corrosion and scale formation mechanisms are discussed and its typical multilayered structure is illustrated. Furthermore, the influences of water quality and microbial activity on scale transformation are comprehensively discussed. Corrosion-related bacteria at the genus level and their associated corrosion mechanism are also summarized. This review helps deepen the current understanding of pipe corrosion and scale formation in DWDSs, providing guidance for water supply utilities to ensure effective measures to maintain water quality stability and guarantee drinking water safety.

Novel elimination method of iron and manganese ions from drinkable groundwater in Assiut, Egypt, by using sodalite-bearing modified illite

The world's interest now is focusing on the applying of the principles of sustainable development in managing natural resources, especially in managing freshwater, which is one of the greatest challenges the whole world face. In this paper, the illite ore was tested to remove the excess of iron and manganese from groundwater which is used for drinking and household purposes in Assiut. To accomplish this goal, the study was based on two directions. The first direction focused on achieving a physicochemical analytical survey for all the groundwater produced by wells in Assiut governorate, and its averages are plotted on GIS maps, to illustrate the difference in the concentrations of iron and manganese. However, the second direction focused on the preparation and examination of the modified illite ore, and it was characterized by using XRD, SEM, FT-IR, and XRF techniques. The results showed that the sodalite-bearing modified illite (SBMI) was able to remove the excess of iron and manganese from raw groundwater with the efficiency of 99% and 97%, respectively.

Cr release after Cr(III) and Cr(VI) enrichment from different layers of cast iron corrosion scales in drinking water distribution systems: the impact of pH, temperature, sulfate, and chloride

Chromium accumulated from source water and pipeline lining materials in corrosion scales could potentially be released into bulk water in drinking water distribution systems (DWDS). This study examined the influence of pH (pH 4, pH 5.5, pH 7, pH 8.5, pH 10), temperature (5 °C, 15 °C, 25 °C), sulfate (50 mg/L, 150 mg/L, 250 mg/L), and chloride (50 mg/L, 150 mg/L, 250 mg/L) on chromium accumulation and release between iron corrosion scale phase and the surrounding water phase. For the first time, the accumulation and release behaviors of chromium were assessed and compared in two distinct layers of iron corrosion scales based on the speciation distributions of heavy metals. Results showed that in the outer and inner layers of corrosion scales, chromium exhibited an almost similar trend but significant differences in quantity, with the outer layer accumulating less and releasing more. In particular, the average difference of chromium released after Cr(VI) enrichment from the outer and inner layers was 50.53 μg/L under the same conditions. Further studies conclusively showed that in Cr(VI) accumulation process, a portion of Cr(VI) would be reduced to Cr(III) by Fe(II) in iron corrosion scales. The mechanisms of chromium retention based on different iron (oxyhydr)oxides were discussed.

Modeling iron release from cast iron pipes in an urban water distribution system caused by source water switch

Significant iron release from cast iron pipes in water distribution systems (WDSs), which usually occurs during the source water switch period, is a great concern of water utilities because of the potential occurrence of "red water" and customer complaints. This study developed a new method which combined in-situ water stagnation experiments with mathematical models and numerical simulations to predict the iron release caused by source water switch. In-situ water stagnation experiments were conducted to determine the total iron accumulation in nine cast iron pipes in-service in Beijing when switching the local water to treated Danjiangkou Reservior water. Results showed that the difference in the concentration increment of total iron in 24 hr (ΔCI_TI,24), i.e. short-term iron release, caused by source water switch was mainly dependent on the difference in the key quality parameters (pH, hardness, nitrate, Larson Ratio and dissolved oxygen (DO)) between the two source waters. The iron release rate (R_Fe) after switch, i.e. long-term iron release, was closely related to the pipe properties as well as the DO and total residual chlorine (TRC) concentrations. Mathematical models of ΔCI_TI,24 and R_Fe were developed to quantitatively reveal the relationship between iron release and the key quality parameters. The R_Fe model could successfully combine with EPANET-MSX, a numerical simulator of water quality for WDSs to extend the iron release modeling from pipe level to network level. The new method is applicable to predicting iron release during source water switch, thus facilitating water utilities to take preventive actions to avoid "red water".

The role of metal oxides on oxidant decay and disinfection byproduct formation in drinking waters: Relevance to distribution systems

Maintaining a residual disinfectant/oxidant (e.g., chlorine and chlorine dioxide), is a generally used strategy to control microbial contaminants and bacterial regrowth in distribution systems. Secondarily oxidant, such as hypobromous acid (HOBr), can be formed during chlorination of bromide-containing waters. The decay of oxidants and formation of disinfection byproducts (DBPs) due to the interaction between oxidants and selected metal oxides were studied. Selected metal oxides generally enhanced the decay of these halogen-containing oxidants via three pathways: (1) catalytic disproportionation to yield an oxidized form of halogen (i.e., halate) and reduced form (halide for chlorine and bromine or chlorite for chlorine dioxide), (2) oxygen formation, and (3) oxidation of a metal in a reduced form (e.g., cuprous oxide) to a higher oxidation state. Cupric oxide (CuO) and nickel oxide (NiO) showed significantly strong abilities for the first pathway, and oxygen formation was a side reaction. Cuprous oxide can react with oxidants via the third pathway, while goethite was not involved in these reactions. The ability of CuO on catalytic disproportionation of HOBr remained stable up to four cycles. In chlorination process, bromate formation tends to be important (exceeding 10 µg/L) when initial bromide concentration is above 400 µg/L in the presence of dissolved organic matter. Increasing initial bromide concentrations increased the formation of DBPs and calculated cytotoxicity, and the maximum was observed at pH 8.6 during chlorination process. Therefore, the possible disinfectant loss and DBP formation should be carefully considered in drinking water distribution systems.

Implications for emergency response to the severe odor incident occurred in source water: Potential odorants and control strategy

Sudden odor incidents occurring in the source water have been a severe problem for water suppliers. In order to apply emergency control measures effectively, it is necessary to identify the target compounds responsible for odor incidents rapidly. The present work identified the odorants and explored emergency disposal mechanisms for sudden and severe odors in the QT River's drinking water source (HZ city, China). Medicinal, chemical, septic, and musty odors with strong intensities were detected in the source water. The effect of conventional treatments of drinking water treatment plant (DWTP) on odors' removal was limited, which was evident by the presence of medicinal, chemical, and musty odors with moderate intensities in the effluent of DWTP. Total seventeen odorants were identified successfully in the source water of QT River and the effluent of DWTP. The measured OAVs and reconstituting the identified odorants explained 87, 87, 89, and 94% of medicinal, chemical, septic, and musty odors, respectively, in the source water of the QT River and 90, 87, and 88% of medicinal, chemical, and musty odors in the effluent. Styrene, phenol, 2-chlorophenol, 2-tert-butylphenol, and 2-methylphenol were associated with the medicinal odor, while propyl sulfide, diethyl disulfide, propyl disulfide, and indole were related to the septic odor. Geosmin and 2-methylisoborneol (2-MIB) were responsible for the musty odor, and cyclohexanone, 1,4-dichlorobenzene, and nitrobenzene were involved with the chemical odor. Based on the characteristics of identified odorants, powdered activated carbon (PAC) was applied to control the odors in the QT River. The results indicated that the medicinal, chemical, septic, and musty odors could be removed entirely after adding 15 mg/L PAC, which effectively controlled emergency odor problems. Overall, the study would offer a scientific basis and operational reference for emergency odor management and control in DWTP with similar complicated odor incidents.

Using complex network analysis for water quality assessment in large water distribution systems

Assessing and modelling the water quality in a water distribution system (WDS) are highly important to ensure a reliable supply with sufficient water quality. Owing to the high computational burden of such an analysis, frequently, simplifications are required or surrogate models are used (e.g., reducing the level of detail of the network model), neglecting significant aspects. For large (currently all-pipe) models and/or recurrent simulations (e.g., integrated studies, sensitivity analysis, deep uncertainty analysis, design, and optimization), the computational burden further increases. In this study, a novel complex network analysis-based approach for high-computational efficiency water quality assessment in a WDS is developed and comprehensively tested (R² values in comparison with state-of-the-art nodal water qualities in median of 0.95 are achieved). The proposed model is successfully utilized in a design study to identify the design solutions exceeding water quality thresholds with a correct identification rate between 96% and 100%. The computational efficiency is determined to be a factor 4.2e-06 less than that of state-of-the-art models. Therefore, the proposed model significantly improves the water quality assessment for such tasks in large WDSs.

Microbial composition and diversity of drinking water: A full scale spatial-temporal investigation of a city in northern China

The microbiological water quality of drinking water distribution systems (DWDSs) is of primary importance for public health. The detachment of biofilm attached on the pipe wall attribution to water source switch and the occurrence of potentially pathogenic chlorine-resistant bacteria (CRB) under chlorine disinfection get lots of attention. Studies examining microbial communities after the water source switch, particularly in low-salinity water, have been scant. The UV‑chlorine combined disinfection applied in one of the investigated drinking water plants provided insight into the control of CRBs. We applied high-throughput sequencing of the 16S rRNA gene to characterize the bacterial communities of the DWDS in northern China over 1 year. A network comprising four different DWDSs was sampled at 48 sites every season (temperate continental monsoon climate), and the impact of key spatial-temporal and physicochemical parameters was investigated. Overall, the entire bacterial community was not significantly different among the four DWDSs (spatial parameter) but varied with seasons (temporal parameter). The switch in water sources might increase the relative abundance of potentially opportunistic pathogens in DWDSs. UV‑chlorine combined disinfection can decrease community diversity and is likely to control the growth of potential opportunistic pathogens in DWDSs.

Iron-modified biochar and water management regime-induced changes in plant growth, enzyme activities, and phytoavailability of arsenic, cadmium and lead in a paddy soil

The aim of this study was to evaluate the effect of raw (RawBC) and iron (Fe)-modified biochar (FeBC) derived from Platanus orientalis Linn branches on the plant growth, enzyme activity, and bioavailability and uptake of As, Cd, and Pb by rice in a paddy soil with continuously flooded (CF) or alternately wet and dry (AWD) irrigation in a pot experiment. Application of RawBC (3%, w/w) significantly increased soil pH, while FeBC decreased it. The FeBC was more effective in reducing As and Pb bioavailability, particularly under the AWD water regime, while RawBC was more conducive in reducing Cd bioavailability under the CF water regime. The FeBC decreased As concentration, but increased concentrations of Cd and Pb in the straw and brown rice, as compared to the untreated soil. Soil catalase and urease activities were enhanced by RawBC, but decreased by FeBC treatment. The FeBC increased the grain yield by 60% and 32% in CF and AWD treatments, respectively. The FeBC can be recommended for immobilization of As in paddy soils, but a potential human health risk from Cd and Pb in FeBC-treated soils should be considered due to increased uptake and translocation of the metals to brown rice.

Characteristics of biostability of drinking water in aged pipes after water source switching: ATP evaluation, biofilms niches and microbial community transition

Delivering quality-changed water often contributes to the biological instability of drinking water distribution systems (DWDS). However, the potential effects of quality-changed water on the biostability within DWDS are not well understood, especially after water switching to quality-improved water. The objective of this study was to investigate the effects of quality-improved water on DWDS, focusing on the stability of biofilm. The practical aged-pipe was assembled into pipe reactors to simulate the effect of switching to quality-improve water. The adenosine triphosphate (ATP) concentration of bulk water in the pipe reactors increased from ∼1.2 ng/L to almost above 5 ng/L when fed water switching to TP 2. Biomass quantified by measuring ATP concentration confirmed that the risk of biofilm release through aged cast-iron (CI) pipe surfaces after water source switching. The changes in water characteristics due to quality-improved water source could cause bacteria release in DWDS at the initial period (at the first 7 days). However, the DWDS can establish the new stable phase after 42 days. Over time, biomass in the bulk water of the distribution system decreased significantly (The ATP concentration in the bulk maintains around 3 ng/L) after 42 days, indicating the improvement of water quality. The biofilm was dominated by bacteria related to iron-cycling process, and at the genus level, Desulfovibrio had the highest relative abundance, however, it decreased significantly (from 48% to 9.3%) after water source switching. And there was a slightly increase in the fraction of iron-oxidizing bacteria (IOB) and siderophore-producing bacteria (SPB), but a relatively higher increase in nitrate-reducing bacteria (NRB), nitrobacteria (NOB), and iron-reducing bacteria (IRB) was observed. Taken together, these results and the corrosion morphology, indicate that pipe biofilm and corrosion were chemically and microbially stable after re-stability under water source switching. In addition, the bulk water environment showed a marked decrease in selected bacteria at genus level, including pathogenic species, indicating the improvement of quality in drinking water.

Transformation of iopamidol and atrazine by peroxymonosulfate under catalysis of a composite iron corrosion product (Fe/Fe3O4): Electron transfer, active species and reaction pathways

Cast iron pipes are commonly applied in drinking water distribution systems (DWDSs); peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; organic micropollutants is still present in drinking water after waterworks' treatment. However, iron corrosion products may affect the reactions between a disinfectant and organic micropollutants. The study investigated the transformation of iopamidol (IPM) and atrazine (ATZ) by PMS under the catalysis of a composite iron corrosion product (Fe/Fe₃O₄). The pseudo-first-order rate constants (k) for the degradation of IPM and ATZ were 1.47 and 1.03 min^-1, respectively. Electron paramagnetic resonance (EPR) experiments indicated that PMS was effectively activated to yield sulfate radical (SO₄^•-) and hydroxyl radical (HO^•), mainly via the reduction by Fe component, dissolved Fe²⁺ and generated Feocta2+. SO₄^•- contributed more than HO^• to the degradation of IPM and ATZ, and the radical yield achieved 0.97 mol/mol. The k values reached maximum with Fe/Fe₃O₄ and PMS doses of 2.5 g L^-1 and 25 mg L^-1, respectively. The optimum mass fraction of Fe₃O₄ in Fe/Fe₃O₄ (MF_mag) and pH were 10% and 7.0, respectively. The k values increased with increasing temperature, while decreased in the presence of water matrix. Most of the iodine released from IPM was oxidized to IO₃^-, and NH₄⁺ was the dominant species of nitrogen released from ATZ. The identification of transformation intermediates showed that the radical chain reactions of IPM was mainly initiated from single electron transfer and radical adduct formation, while those of ATZ was primarily initiated from hydrogen atom abstraction and radical adduct formation.

Manganese release from corrosion products of cast iron pipes in drinking water distribution systems: Effect of water temperature, pH, alkalinity, SO42- concentration and disinfectants

Manganese accumulated in corrosion scales on drinking water distribution systems (DWDSs) can be released into bulk water, causing discolouration and thereby leading to customer concerns about drinking water quality. A static release experiment was conducted on iron pipe scales under three different temperatures, pH values, alkalinity values, sulfate (SO₄^2-) concentrations, and disinfectants to study the separate effect of these factors on Mn release from pipe scales under stagnant conditions. Results showed that more Mn was released from corrosion scales under the conditions of lower pH, lower alkalinity, higher temperature, and higher SO₄^2- concentrations. Three commonly used disinfectants, sodium hypochlorite (NaClO), chlorine dioxide (ClO₂), and monochloramine (NH₂Cl) were found to inhibit the release of Mn from iron corrosion scales, with the ranked order of inhibitory effect of ClO₂≈NaClO > NH₂Cl under the same CT (product of disinfectant concentration and contact time) value. The orthogonal experimental results indicated that SO₄^2- and alkalinity had extremely significant effects on the release of Mn from pipe scales, while pH and disinfectant type had a significant impact on the release of Mn from pipe scales. Thus, the SO₄^2- concentration and alkalinity of the bulk water should be determined to avoid excessive release of Mn into drinking water. However, further investigation of the effect of disinfectants on Mn release in DWDSs is necessary. This research helps establish a systematic understanding of the influential factors in Mn release from pipe scales into bulk water, as well as their significant relationships.

Chloride corrosion behavior on heating pipeline made by AISI 304 and 316 in reclaimed water

In order to transport reclaimed water safely through stainless steel (SS) heat-supply pipeline networks during their idle period, one must understand the degree to which chlorine in reclaimed water is corrosive to SS. In this study, electrochemical methods were used to evaluate the corrosion resistances of two types of SS materials, AISI 304 and AISI 316, in simulated reclaimed water at chloride concentrations of 25 to 400 mg L⁻¹, which are similar to those present in practice. The differences in corrosion resistance between the two types of SS material were investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests (Tafel curves). The passivation layers on the two types of SS exhibited obvious similarities under several experimental conditions. However, EIS, polarization resistance, effective capacitance, Tafel curve, and Scanning Electron Microscope (SEM) data showed that AISI 316 has better corrosion resistance than AISI 304. The corrosion behaviours could be described as a series of reactions between Fe, Cr, and H₂O that generate several precipitated products such as Fe₂O₃, Cr₂O₃, FeOOH, and CrOOH.

It would be economical if heating pipes were used to transport reclaimed water during its idle period. The most important thing is to study the causes and processes of the corrosion on it for practical application.

The effect of chloride, sulfate and dissolved inorganic carbon on iron release from cast iron

Iron corrosion in drinking water distribution systems causes water discoloration, water quality deterioration, hydraulic loss, and even pipe failures, which are usually influenced by pipe scale structure, water hydraulics, water chemistry, and other factors. This work evaluated the effects of chloride, sulfate, and dissolved inorganic carbon (DIC) on iron release from a 90-year-old cast iron pipe section at water pH 8.0 under stagnant conditions. Experimental results showed that the addition of 150 mg/L sulfate to water significantly increased the mean total iron concentrations to 1.13-2.68 mg/L, relative to 0.54-0.79 mg/L for the baseline water with only 10 mg C/L DIC. Similar results were observed under conditions when chloride was added, and when sulfate and chloride were added together. In contrast, the mean total iron concentrations were significantly reduced by 53-80% in waters with higher DIC of 50 mg C/L, as compared to similar waters with lower DIC of 10 mg C/L. The Larson Ratio could be a good indicator for iron release depending on the circumstances. Iron release was predicted by molecular radial diffusion modelling that accounted for water quality, scale characteristics, hydraulics, and other condition-related information. The results provided insightful information for water systems that have cast iron pipes and galvanized iron pipes and that might encounter changes in water treatment and water sources. More studies are needed to better understand the cast iron corrosion mechanisms under the examined water chemistries.

Early period corrosion and scaling characteristics of ductile iron pipe for ground water supply with sodium hypochlorite disinfection

The corrosion and scaling phenomenon have crucial impact on drinking water distribution systems (DWDS), which might lead to pipe blockage or leakage, colored water and other chemical stability issues. In this study, a simulating pipe system with continuous water flow was prepared to investigate the characteristics of corrosion and scaling on ductile iron pipe transporting ground water with sodium-hypochlorite (NaOCl) disinfection. Electrochemical assays, such as polarization curves and electrochemical impedance spectra were applied to monitor the corrosion and scaling process. Results showed the morphology and components of scale were closely related with the electrochemical analysis results. The corrosion current density decreased continuously as corrosion and scaling proceeded. The process could be divided into three stages. During Stage I (0-20 days), the corrosion current intensity of low NaOCl dosage experiments (1, 2 mg/L) were higher than those of high NaOCl dosage experiments (5, 10 mg/L). The difference could be explained by different oxidation potentials, pH and CaCO₃ deposition. During Stage II (20-80 days), higher proportions of Fe₃O₄ in scale in experiments with no or low NaOCl dosages restrained the corrosion process and presented smaller corrosion current. Subsequently, the ductile iron surface became passivated and the difference of various NaOCl dosages affecting corrosion and scaling process turned to be negligible during Stage III (80-90 days). A negative linear relationship between the proportion of stable scale component and the corrosion current density was established. Besides the direct corrosion reaction with iron substrate, NaOCl dosing was accompanied by an increase in pH and calcium carbonate precipitation potential values, which affected the early period corrosion and scaling phenomenon greatly.

Metal-release potential from iron corrosion scales under stagnant and active flow, and varying water quality conditions

The release of potentially toxic metal ions from corrosion scales formed on pipe surfaces is of great concern for water quality in drinking water distribution systems (DWDS). This study examined the effects of alkalinity, chloride, and sulfate on metal release from corrosion scales sampled from a corroded iron pipe. Jar tests and recirculation pipe systems were used to investigate the metal-release potential during stagnant and active flow conditions. The experimental data show that both the ambient water chemistry and hydraulic conditions exerted complex influences on metal release from the exposed corrosion scales. Fe, Mn, and Ni were more labile to be released during a 132-h period of stagnation, while the release of Al, Zn, and Cu was an order of magnitude higher under flow conditions compared to stagnant conditions. Increasing concentrations of chloride (from 5 mg/L to 60 mg/L) and sulfate (from 20 mg/L to 100 mg/L) resulted in the increased release of Fe, Al, and Zn, especially under active flow conditions. This effect could be effectively mitigated by increasing alkalinity from 50 mg/L to 200 mg/L as CaCO₃. While increasing alkalinity suppressed the release of Fe and stimulated the release of Al and Cu under stagnant conditions, this contradictory effect was not observed under active flow conditions.

Water quality induced corrosion of stainless steel valves during long-term service in a reverse osmosis system

The current study analyzes the contribution of 10 water quality parameters (including pH, turbidity, conductivity, total dissolved solids (TDS), hardness, total organic carbon (TOC), alkalinity, calcium ions, chlorides and sulfates) to corrosion extent of stainless steel valves taken from different locations in a reverse osmosis system of a reclaimed water plant. The valves were in service for 5 years. Raman spectroscopy and X-ray photoelectron spectroscopy analyses are conducted to quantify corrosion products on different valves under various water quality conditions. On that basis, bivariate and multivariate regression analyses between the 10 water quality parameters and the corrosion extent of valve specimens (represented by metal loss percentage (MLP) values) are carried out to check the contribution of those water quality parameters to MLP. The results indicate that the proportions of metal oxides as corrosion products vary according to the corrosion extent of the valves. Although no linear correlation is found, all 10 water quality parameters except for pH show a significant positive correlation with the MLP values of the valve specimens. Moreover, results of multivariate regression suggest that the variation of MLP can be explained by turbidity, TDS, TOC and sulfates. A positive contribution of turbidity, TDS and TOC to MLP is observed, whereas the contribution of sulfates is negative. The results from the current work help to identify the reasons for water quality-induced failure of stainless steel equipment in RO systems.

The feasibility of UF-RO integrated membrane system combined with coagulation/flocculation for hairwork dyeing effluent reclamation

This paper aims to validate the feasibility of hairwork dyeing effluent (HDE) reclamation using an ultrafiltration (UF)-reverse osmosis (RO) integrated membrane system combined with coagulation-flocculation and sedimentation acquiring the highest possible product water recovery rate along with both satisfactory separation performance and well controlled membrane fouling. Under the circumstance of only physical cleaning involved, the laboratory-scale test yielded a higher and satisfactory reuse ratio of 76% for HDE, and the corresponding RO product as reclaimed water contained only 223 mg·L^-1 of TDS, 3.87 mg·mL^-1 of DOC and 10.3 mg·mL^-1 of total hardness, which was obviously better than the quality of existing feedwater in hairwork dyeing process. After each processing unit, the distributions of fulvic (region III) and humic (region V) organics decreased continuously, while an overall rising trend in distribution of protein-like organics (regions I and II) was observed. Contact angle for the fouled UF and RO membranes significantly increased by 19.5° and decreased by 19.7°, respectively, which suggested that different polarity of organic or inorganic adsorption rather than membrane roughness was the main factors affecting wetting properties of the fouled employed membranes. Both ATR-FTIR and XPS spectra indicated that organic fouling on UF membrane surface under harsh condition (R_UF = 90%) was mild and tolerable, whereas a surprising amount of hydrophilic micromolecular organics riched in carboxyl and hydroxyl functional groups were absorbed on RO membrane surface after permeation.

Impacts of Human Activities on the Composition and Abundance of Sulfate-Reducing and Sulfur-Oxidizing Microorganisms in Polluted River Sediments

Water system degradation has a severe impact on daily life, especially in developing countries. However, microbial changes associated with this degradation, especially changes in microbes related to sulfur (S) cycling, are poorly understood. In this study, the abundance, structure, and diversity of sulfate-reducing microorganisms (SRM) and sulfur-oxidizing microorganisms (SOM) in the sediments from the Ziya River Basin, which is polluted by various human interventions (urban and agricultural activities), were investigated. Quantitative real-time PCR showed that the S cycling-related (SCR) genes (dsrB and soxB) were significantly elevated, reaching 2.60 × 10⁷ and 1.81 × 10⁸ copies per gram of dry sediment, respectively, in the region polluted by human urban activities (RU), and the ratio of dsrB to soxB abundance was significantly elevated in the region polluted by human agricultural activities (RA) compared with those in the protected wildlife reserve (RP), indicating that the mechanisms underlying water system degradation differ between RU and RA. Based on a 16S rRNA gene analysis, human interventions had substantial effects on microbial communities, particularly for microbes involved in S cycling. Some SCR genera (i.e., Desulfatiglans and Geothermobacter) were enriched in the sediments from both RA and RU, while others (i.e., Desulfofustis and Desulfonatronobacter) were only enriched in the sediments from RA. A redundancy analysis indicated that NH₄⁺-N and total organic carbon significantly influenced the abundance of SRM and SOM, and sulfate significantly influenced only the abundance of SRM. A network analysis showed high correlation between SCR microorganisms and other microbial groups for both RU and RA, including those involved in carbon and metal cycling. These findings indicated the different effects of different human interventions on the microbial community composition and water quality degradation.

The bacterial community significantly promotes cast iron corrosion in reclaimed wastewater distribution systems

BACKGROUND

Currently, the effect of the bacterial community on cast iron corrosion process does not reach consensus. Moreover, some studies have produced contrasting results, suggesting that bacteria can either accelerate or inhibit corrosion.

RESULTS

The long-term effects of the bacterial community on cast iron corrosion in reclaimed wastewater distribution systems were investigated from both spatial (yellow layer vs. black layer) and temporal (1-year dynamic process) dimensions of the iron coupon-reclaimed wastewater microcosm using high-throughput sequencing and flow cytometry approaches. Cast iron coupons in the NONdisinfection and UVdisinfection reactors suffered more severe corrosion than did those in the NaClOdisinfection reactor. The bacterial community significantly promoted cast iron corrosion, which was quantified for the first time in the practical reclaimed wastewater and found to account for at least 30.5% ± 9.7% of the total weight loss. The partition of yellow and black layers of cast iron corrosion provided more accurate information on morphology and crystal structures for corrosion scales. The black layer was dense, and the particles looked fusiform, while the yellow layer was loose, and the particles were ellipse or spherical. Goethite was the predominant crystalline phase in black layers, while corrosion products mainly existed as an amorphous phase in yellow layers. The bacterial community compositions of black layers were distinctly separated from yellow layers regardless of disinfection methods. The NONdisinfection and UVdisinfection reactors had a more similar microbial composition and variation tendency for the same layer type than did the NaClOdisinfection reactor. Biofilm development can be divided into the initial start-up stage, mid-term development stage, and terminal stable stage. In total, 12 potential functional genera were selected to establish a cycle model for Fe, N, and S metabolism. Desulfovibrio was considered to accelerate the transfer of Fe0 to Fe2+ and speed up weight loss.

CONCLUSION

The long-term effect of disinfection processes on corrosion behaviors of cast iron in reclaimed wastewater distribution systems and the hidden mechanisms were deciphered for the first time. This study established a cycle model for Fe, N, and S metabolism that involved 12 functional genera and discovered the significant contribution of Desulfovibrio in promoting corrosion.

Effects of pipe material on nitrogen transformation, microbial communities and functional genes in raw water transportation

Raw water transportation pipelines are vital in an urban water supply system for transporting raw water to drinking water treatment plants. This study investigated the effects of pipe material on nitrogen transformation, microbial communities and characteristics of related function genes in paint-lined steel pipe (PLSP) and cement-lined steel pipe (CLSP) raw water model systems. We established quantitative relationships between specific functional genes and change rates of nitrogen pollutants, which were verified by field investigation on nitrogen pollutant transformations in real raw water transportation systems. The results showed that the CLSP produced higher ammonia nitrogen (NH₄⁺-N) transformation rates and higher effluent concentrations of nitrate nitrogen (NO₃^--N) and dissolved organic nitrogen (DON) than the PLSP. Both pipes achieved high and stable nitrite nitrogen (NO₂^--N) and low total nitrogen (TN) removal efficiency. Nitrification was found to be the dominant process in both model systems, especially in the CLSP. Characteristics of microbial communities and nitrogen functional genes, which were analysed by high-throughput pyrosequencing and quantitative polymerase chain reaction (qPCR), respectively, varied between the two pipe systems. Nitrogen transformation pathways, identified by path analysis, were also different between the PLSP and CLSP due to different microbial community characteristics and synergistic effects of nitrogen functional genes. In the CLSP, (NH₄⁺-N→NO₂^--N) with part denitrification, was the primary transformation pathway of ammonia nitrogen (NH₄⁺-N), while only ammonia oxidization contributed to NH₄⁺-N transformation in the PLSP. (NO₂^--N→NO₃^--N) was the main pathway involved in NO₂^--N transformation and NO₃^--N accumulation. The TN removal showed complex relationships with nitrification, denitrification and nitrogen fixation processes. These findings provided molecular-level insights into nitrogen pollutant transformations during the transportation of raw water through different types of pipes and technical support for the selection of raw water pipe materials. In our study area, the Taihu basin, China, PLSP was better than CLSP for distributing raw water in a short transportation distance, due to the lower effluent concentrations of DON and NO₃^--N and less abundance of microorganisms.