Iron Corrosion Scales Research Articles

Unveiling the Mechanism and Kinetics of Pollutant Attenuation by Free Radicals Triggered from Goethite in Water Distribution Systems.

Investigating the fate of persistent organic pollutants in water distribution systems (WDSs) is of great significance for preventing human health risks. The role of iron corrosion scales in the migration and transformation of organics in such systems remains unclear. Herein, we determined that hydroxyl (•OH), chlorine, and chlorine oxide radicals are generated by Fenton-like reactions due to the coexistence of oxygen vacancy-related Fe(II) on goethite (a major constituent of iron corrosion scales) and hypochlorous acid (HClO, the main reactive chlorine species of residual chlorine at pH ∼ 7.0). •OH contributed mostly to the decomposition of atrazine (ATZ, model compound) more than other radicals, producing a series of relatively low-toxicity small molecular intermediates. A simplified kinetic model consisting of mass transfer of ATZ and HClO, •OH generation, and ATZ oxidation by •OH on the goethite surface was developed to simulate iron corrosion scale-triggered residual chlorine oxidation of organic compounds in a WDS. The model was validated by comparing the fitting results to the experimental data. Moreover, the model was comprehensively applicable to cases in which various inorganic ions (Ca2+, Na+, HCO3-, and SO42-) and natural organic matter were present. With further optimization, the model may be employed to predict the migration and accumulation of persistent organic pollutants under real environmental conditions in the WDSs.

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.

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.

Hexavalent Chromium Release in Drinking Water Distribution Systems: New Insights into Zerovalent Chromium in Iron Corrosion Scales.

Upon cast iron corrosion in contact with residual disinfectants, drinking water distribution systems have become potential geogenic sources for hexavalent chromium Cr(VI) release. This study investigated mechanisms of Cr(VI) release from cast iron corrosion scales. The oxidation of the corrosion scales by residual disinfectant chlorine released Cr(VI) and exhibited a three-phase kinetics behavior: an initial 2 h fast reaction phase, a subsequent 2-to-12 h transitional phase, and a final 7-day slow reaction phase approximately 2 orders of magnitude slower than the initial phase. X-ray absorption spectroscopy analysis discovered that zerovalent Cr(0) coexisted with trivalent Cr(III) solids in the corrosion scales. Electrochemical corrosion analyses strongly suggested that Cr(0) in the corrosion scales originated from Cr(0) in the cast iron alloy. Cr(0) exhibited a much higher reactivity than Cr(III) in the formation of Cr(VI) by chlorine. The presence of bromide in drinking water significantly accelerated Cr(VI) release because of its catalytic effect. Meanwhile, chlorine consumption was mainly attributed to the oxidation of organic matter and ferrous iron. Findings from this study point to a previously unknown but important pathway of Cr(VI) formation in drinking water, that is, direct oxidation of Cr(0) by chlorine, and suggest new strategies to control Cr(VI) in drinking water by inhibiting Cr(0) reactivity.

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 (SO42−) 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 SO42− 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 SO42− 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 SO42− 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.

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.

Characteristics of pipe corrosion scales in untreated water distribution system and effect on water quality in Peshawar, Pakistan.

This study investigated the characteristics of iron corrosion scales in pipes at tube well, overhead tank, and consumers' end in older untreated water distribution system in Peshawar city, Pakistan. Effect of water quality conditions on corrosion scales and that of scales on drinking water quality in such systems was also assessed by undertaking a comparison with new piped distribution systems. The scales were analyzed for chemical composition and morphology using X-ray diffraction (XRD), inductively coupled plasma (ICP), and a scanning electron microscope (SEM), while water quality was examined for physicochemical and biological characteristics. The main crystalline phases of corrosion scales were goethite, magnetite, siderite, and quartz. From tube well to consumers' end, goethite increased from 36 up to 48%, quartz declined from 22 to 15%, while magnetite fluctuated and siderite disappeared. Elemental composition of scales showed the deposition of Zn, Al, Mn, Cr, Pb, Cu, As, and Cd with Zn (13.9g/kg) and Al (3.6g/kg) in highest proportion. The SEM analysis illustrated the presence of microbial communities indicating the formation of biofilms in the corrosion scales. The significant difference (P< 0.05) in levels of dissolved oxygen (DO), Cl-, SiO44-, electrical conductivity (EC), SO42-, NO3-, alkalinity, hardness, and trace metals between old (DS-O) and new piped systems indicated their role in corrosion scale formation/destabilization and the effect of scale dissolution on water quality. In DS-O, EC, Cu, and Mn were significantly higher (P < 0.05), whereas turbidity, EC, DO, and SiO44- significantly increased from source to consumers' end implying a higher dissolution of scales and lowered corrosion rates in DS-O to utilize SiO44- and DO for iron oxidation.

Impact of sulphate and heavy metals release on household portable water in Nigeria

The paper attempts frequent hitches regarding household portable water in Nigeria. It enlighten both end user and portable water providers about the heavy metals potential discharge that pre-accumulate in iron corrosion scales as it poses an contaminants health threat when released into household portable water. Likewise offers conjectural knowledge about formation, main uses, health effects of both heavy metals and sulphate on human for example arsenal causes immunotoxic, zinc creates abdominal pain etcetera besides common methods for removing both sulphate and heavy metals like distillation or reverse osmosis for small water and ion exchange for large water quantities because chemical reaction between sulfates and heavy metals discharge from portable water distribution system can affect the water quality by decreasing or oxidizing the heavy metals in the water therefore, awareness about the impacts of sulfate on heavy metals release from portable water distribution system is required . Also users and portable water provider must develop habit of testing portable water from consumer tap because despite water quality parameters of the finished water reached portable water healthy standards from water distribution system nonetheless the tap water which the customers exactly exploited could be infected, since the portable water undertake an extensive Hydraulic Retaining Period (HRP) of storing and transference in water distribution systems.

Iodinated trihalomethane formation during chloramination of iodate-containing waters in the presence of zero valent iron

Iodide (I−) and iodinated X-ray contrast media (ICM) are the primary iodine sources for the formation of iodinated disinfection byproducts (I-DBPs), and iodate (IO3−) is believed to be a desired sink of iodine in water. This study found that highly cytotoxic iodinated trihalomethanes (I-THMs) also can be generated from iodate-containing waters (without any other iodine sources) in the presence of zero valent iron (ZVI) during chloramination, which could be a big issue in the wide usage of iron pipes. The effect of major factors including ZVI dosage, NH2Cl and IO3− concentrations, initial pH, Br−/IO3− molar ratio, phosphate concentration, iron corrosion scales (goethite and hematite) on the formation of I-THMs were investigated. Formation of I-THMs from IO3− increased with the increase of ZVI dosage, IO3− and NH2Cl concentrations. Chloramines can also remarkably accelerate the reduction of IO3− by ZVI. Peak I-THM formation was found at pH 8. As the Br−/IO3− molar ratio increased from 0 to 20, I-THM formation considerably enhanced, especially for the bromine-incorporated species. Goethite and hematite enhanced the formation of I-THMs in the presence of ZVI. Additionally, a significant suppression on I-THM formation was observed with the addition of phosphate. Considering that a large number of water distribution networks contain unlined cast iron pipes, transformation of IO3− in the presence of ZVI during chloramination may contribute to the formation of I-THMs in such systems.

Effects of sulfate on heavy metal release from iron corrosion scales in drinking water distribution system

Trace heavy metals accumulated in iron corrosion scales within a drinking water distribution system (DWDS) could potentially be released to bulk water and consequently deteriorate the tap water quality. The objective of this study was to identify and evaluate the release of trace heavy metals in DWDS under changing source water conditions. Experimental pipe loops with different iron corrosion scales were set up to simulate the actual DWDS. The effects of sulfate levels on heavy metal release were systemically investigated. Heavy metal releases of Mn, Ni, Cu, Pb, Cr and As could be rapidly triggered by sulfate addition but the releases slowly decreased over time. Heavy metal release was more severe in pipes transporting groundwater (GW) than in pipes transporting surface water (SW). There were strong positive correlations (R2 > 0.8) between the releases of Fe and Mn, Fe and Ni, Fe and Cu, and Fe and Pb. When switching to higher sulfate water, iron corrosion scales in all pipe loops tended to be more stable (especially in pipes transporting GW), with a larger proportion of stable constituents (mainly Fe3O4) and fewer unstable compounds (β-FeOOH, γ-FeOOH, FeCO3 and amorphous iron oxides). The main functional iron reducing bacteria (IRB) communities were favorable for the formation of Fe3O4. The transformation of corrosion scales and the growth of sulfate reducing bacteria (SRB) accounted for the gradually reduced heavy metal release with time. The higher metal release in pipes transporting GW could be due to increased Fe6(OH)12CO3 content under higher sulfate concentrations.

Characteristics of iron corrosion scales and water quality variations in drinking water distribution systems of different pipe materials

Interaction between old, corroded iron pipe surfaces and bulk water is crucial to the water quality protection in drinking water distribution systems (WDS). Iron released from corrosion products will deteriorate water quality and lead to red water. This study attempted to understand the effects of pipe materials on corrosion scale characteristics and water quality variations in WDS.A more than 20-year-old hybrid pipe section assembled of unlined cast iron pipe (UCIP) and galvanized iron pipe (GIP) was selected to investigate physico-chemical characteristics of corrosion scales and their effects on water quality variations. Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Inductively Coupled Plasma (ICP) and X-ray Diffraction (XRD) were used to analyze micromorphology and chemical composition of corrosion scales. In bench testing, water quality parameters, such as pH, dissolved oxygen (DO), oxidation reduction potential (ORP), alkalinity, conductivity, turbidity, color, Fe2+, Fe3+ and Zn2+, were determined. Scale analysis and bench-scale testing results demonstrated a significant effect of pipe materials on scale characteristics and thereby water quality variations in WDS.Characteristics of corrosion scales sampled from different pipe segments show obvious differences, both in physical and chemical aspects. Corrosion scales were found highly amorphous. Thanks to the protection of zinc coatings, GIP system was identified as the best water quality stability, in spite of high zinc release potential. It is deduced that the complicated composition of corrosion scales and structural break by the weld result in the diminished water quality stability in HP system. Measurement results showed that iron is released mainly in ferric particulate form.

Characterization of the bacterial communities and iron corrosion scales in drinking groundwater distribution systems with chlorine/chloramine

The effect of chlorine and chloramine disinfection on bacterial communities and the corrosion of cast iron pipes was studied in drinking water distribution systems (DWDSs) transporting groundwater. α-FeOOH was the main corrosion product for both systems. However, loose corrosion products were formed in DWDSs with chlorine, whereas dense crystallized particles were formed in DWDSs with chloramine. Based on the functional genes and pyrosequencing assay results, both DWDSs had different compositions of corrosion-related bacteria in the bulk water and biofilms. The percentage of total denitrifying gene copy numbers in the 16S rRNA and the bacterial diversities were much higher at 220 d within the bulk water and biofilm in DWDSs disinfected with chloramine compared with those disinfected with chlorine. Most of the NO3−–N in the raw water was biologically denitrified through chlorine DWDSs in the experimental period, whereas the same phenomena occurred only when denitrifying bacteria were increased in the effluent due to the role of autotrophic microbial nitrification in chloramine DWDSs. Furthermore, nitrate-dependent Fe(II) oxidation occurred to a greater extent, leading to denser corrosion scales in DWDSs with chloramine compared with those disinfected with chlorine.

Characteristics of biofilms and iron corrosion scales with ground and surface waters in drinking water distribution systems

The composition of biofilm bacterial communities and iron corrosion scales were studied in two drinking water distribution systems transporting groundwater (DWDS-GW) and surface water (DWDS-SW). Loose corrosion products were formed containing α-FeOOH in DWDS-GW, while dense crystallized particles were formed in DWDS-SW, including α-FeOOH, Fe3O4 and CaCO3. The biofilms in the two systems had the same bacterial diversity, denitrifying functional genes and 16S rRNA gene copies, but the bacterial communities were very different. It was found that nitrate-reducing bacteria in biofilms that are associated with iron cycling played a large role in the formation of Fe3O4 and corrosion layers.

Speciation of iron and development of iron corrosion scales in drinking water distribution systems

The major objective of this work is to study the speciation of iron impacted by water quality including dissolved oxygen (DO), pH, alkalinity, sulfate, chloride, and monochloramine and the development of iron corrosion scales in drinking water distribution systems. Alkalinity, pH, and monochloramine had significant impacts on iron oxidation rate, and suspended iron particle, and DO, sulfate, and chloride had a slight effect on iron oxidation rate and suspended iron particle. Except at low pH, the oxygenation process of ferrous iron to ferric iron can be well described by oxidation kinetics model which also fits the monochloramine oxidation reaction. In the initial experiment stage with pipe corrosion scales having been destroyed and the iron being released seriously, the newly formed free and amorphous iron contents increased, instable iron compound dominated the iron corrosion scales and the mass fraction of the total iron in iron corrosion scales rose. With the iron release amount being relatively stable, the free and amorphous iron contents dropped, magnetite and goethite were the main components of iron corrosion scales, and the total iron in iron corrosion scales decreased.

Effect of sulfate on the transformation of corrosion scale composition and bacterial community in cast iron water distribution pipes

The chemical stability of iron corrosion scales and the microbial community of biofilm in drinking water distribution system (DWDS) can have great impact on the iron corrosion and corrosion product release, which may result in “red water” issues, particularly under the situation of source water switch. In this work, experimental pipe loops were set up to investigate the effect of sulfate on the dynamical transformation characteristics of iron corrosion products and bacterial community in old cast iron distribution pipes. All the test pipes were excavated from existing DWDS with different source water supply histories, and the test water sulfate concentration was in the range of 50–350 mg/L. Pyrosequencing of 16S rRNA was used for bacterial community analysis. The results showed that iron release increased markedly and even “red water” occurred for pipes with groundwater supply history when feed water sulfate elevated abruptly. However, the iron release of pipes with only surface water supply history changed slightly without noticeable color even the feed water sulfate increased multiply. The thick-layered corrosion scales (or densely distributed tubercles) on pipes with surface water supply history possessed much higher stability due to the larger proportion of stable constituents (mainly Fe3O4) in their top shell layer; instead, the rather thin and uniform non-layered corrosion scales on pipes with groundwater supply history contained relatively higher proportion of less stable iron oxides (e.g. β-FeOOH, FeCO3 and green rust). The less stable corrosion scales tended to be more stable with sulfate increase, which was evidenced by the gradually decreased iron release and the increased stable iron oxides. Bacterial community analysis indicated that when switching to high sulfate water, iron reducing bacteria (IRB) maintained dominant for pipes with stable corrosion scales, while significant increase of sulfur oxidizing bacteria (SOB), sulfate reducing bacteria (SRB) and iron oxidizing bacteria (IOB) was observed for pipes with less stable corrosion scales.

Bacterial community of biofilms developed under different water supply conditions in a distribution system

In order to understand the bacterial community characteristics of biofilms developed under different finished water supply histories in drinking water distribution systems (DWDS), biofilm samples on different type of iron corrosion scales in a real DWDS were collected and systematically investigated using 454 pyrosequencing of 16S rRNA gene. The richness and diversity estimators showed that biofilms formed in DWDS transporting finished groundwater (GW) had the lowest level of bacterial diversity. From phylum to genus level, the dominant bacterial groups found in the biofilms under finished surface water (SW) and GW conditions were distinct. Proteobacteria was the dominant group in all biofilm samples (in the range of 40%–97%), but was relatively higher in biofilms with GW. The relative abundance of Firmicutes in biofilms with SW (28%–35%) was significantly higher (p<0.01) than that in biofilms with GW (0.5%–2.88%). Statistical analysis (Spearman's rank) revealed that alkalinity and chemical oxygen demand (CODMn) positively correlated with the relative abundance of Proteobacteria and Firmicutes, respectively. The abundance of sequences affiliated to iron-reducing bacteria (mainly Bacillus) and iron-oxidizing bacteria (mainly Acidovorax) were relatively higher in biofilms with SW, which might contribute to the formation of much thicker or tubercle-formed corrosion scales under SW supply condition. Several potential opportunistic pathogens, such as Burkholderia fungorum, Mycobacterium neoaurum, Mycobacterium frederiksbergense were detected in the biofilms.

Role of the water main in lead service line replacement: A utility case study

To understand the role of water mains in lead and iron release following lead service line (LSL) replacement, samples were collected from the tap water of 28 homes in Halifax, N.S., after a minimum 6‐h stagnation. In full replacements, average lead concentrations in service lines connected to cast‐iron mains with three different maintenance conditions—pigged, pigged and lined, and not pigged or lined—were 31.5±11.0, 3.3±2.3, and 3.7±2.7 μg/L, respectively, compared with 0.58±0.2 μg/L for ductile‐iron mains. In partial replacements, average lead concentrations were 63.09±30.9, 14.60±2.9, and 6.82±3.3 μg/L, respectively, for the three cast‐iron main conditions, compared with 8.5±3.1 μg/L for ductile‐iron mains. Adsorption of lead on iron corrosion scales dissolved or dislodged from tuberculated mains could account for the higher lead release observed. In this study, full replacement LSLs connected to ductile‐iron mains had the lowest lead concentrations.

Morphological and physicochemical characteristics of iron corrosion scales formed under different water source histories in a drinking water distribution system

The corrosion scales on iron pipes could have great impact on the water quality in drinking water distribution systems (DWDS). Unstable and less protective corrosion scale is one of the main factors causing “discolored water” issues when quality of water entering into distribution system changed significantly. The morphological and physicochemical characteristics of corrosion scales formed under different source water histories in duration of about two decades were systematically investigated in this work. Thick corrosion scales or densely distributed corrosion tubercles were mostly found in pipes transporting surface water, but thin corrosion scales and hollow tubercles were mostly discovered in pipes transporting groundwater. Magnetite and goethite were main constituents of iron corrosion products, but the mass ratio of magnetite/goethite (M/G) was significantly different depending on the corrosion scale structure and water source conditions. Thick corrosion scales and hard shell of tubercles had much higher M/G ratio (>1.0), while the thin corrosion scales had no magnetite detected or with much lower M/G ratio. The M/G ratio could be used to identify the characteristics and evaluate the performances of corrosion scales formed under different water conditions. Compared with the pipes transporting ground water, the pipes transporting surface water were more seriously corroded and could be in a relatively more active corrosion status all the time, which was implicated by relatively higher siderite, green rust and total iron contents in their corrosion scales. Higher content of unstable ferric components such as γ-FeOOH, β-FeOOH and amorphous iron oxide existed in corrosion scales of pipes receiving groundwater which was less corroded. Corrosion scales on groundwater pipes with low magnetite content had higher surface area and thus possibly higher sorption capacity. The primary trace inorganic elements in corrosion products were Br and heavy metals. Corrosion products obtained from pipes transporting groundwater had higher levels of Br, Ti, Ba, Cu, Sr, V, Cr, La, Pb and As.

Contributions to drinking water lead from galvanized iron corrosion scales

Replacement of lead service lines can cause elevated lead levels immediately after construction, even after removal of the full lead source. Recent data collected by the District of Columbia Water and Sewer Authority in Washington, D.C., indicated that this can be partly attributed to lead release from iron corrosion scales on old, galvanized in‐home plumbing. This article summarizes a three‐part study investigating the phenomenon of capture and release of lead mobilized from an upstream service line by iron corrosion scales in galvanized plumbing. The study used profile sampling data from homes in the District of Columbia, corrosion scale analyses, and pipe‐loop experiments to examine whether iron corrosion scales can contribute meaningfully to drinking water lead. The study concluded that iron corrosion scales can be a persistent lead source, identified factors that can trigger release, and characterized potential long‐term effects.

Corroded scale analysis from water distribution pipes

The subject of this study was the steel pipes that are part of Belgrade's drinking water supply network. In order to investigate the mutual effects of corrosion and water quality, the corrosion scales on the pipes were analyzed. The idea was to improve control of corrosion processes and prevent impact of corrosion on water quality degradation. The instrumental methods for corrosion scales characterization used were: scanning electron microscopy (SEM), for the investigation of corrosion scales of the analyzed samples surfaces, X-ray diffraction (XRD), for the analysis of the presence of solid forms inside scales, scanning electron microscopy (SEM), for the microstructural analysis of the corroded scales, and BET adsorption isotherm for the surface area determination. Depending on the composition of water next to the pipe surface, corrosion of iron results in the formation of different compounds and solid phases. The composition and structure of the iron scales in the drinking water distribution pipes depends on the type of the metal and the composition of the aqueous phase. Their formation is probably governed by several factors that include water quality parameters such as pH, alkalinity, buffer intensity, natural organic matter (NOM) concentration, and dissolved oxygen (DO) concentration. Factors such as water flow patterns, seasonal fluctuations in temperature, and microbiological activity as well as water treatment practices such as application of corrosion inhibitors can also influence corrosion scale formation and growth. Therefore, the corrosion scales found in iron and steel pipes are expected to have unique features for each site. Compounds that are found in iron corrosion scales often include goethite, lepidocrocite, magnetite, hematite, ferrous oxide, siderite, ferrous hydroxide, ferric hydroxide, ferrihydrite, calcium carbonate and green rusts. Iron scales have characteristic features that include: corroded floor, porous core that contains both fluid and solid, relatively dense shell-like layer that covers the porous core and provides structural integrity to the scale, and surface layer that is present on top of the shell-like layer at scale-water interface and loosely attached to the shell-like layer. Iron(II) deposits are formed under reducing conditions. The presence of relatively soluble Fe(II) deposits such as siderite and ferrous hydroxide was confirmed by XRD and SEM analysis. In the presence of carbonic species, siderite (FeCO3) is prevailing ferrous deposit. Further studies are needed for obtaining greater knowledge on the mechanism of iron release from corroded pipes and the influence of water quality to iron corrosion.