Effects of blending of desalinated and conventionally treated surface water on iron corrosion and its release from corroding surfaces and pre-existing scales

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.

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.

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.

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 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.

Corrosion behavior and mechanism of ductile iron with different degrees of deterioration of cement mortar lining in reclaimed water pipelines

The influence of the degradation degree of cement mortar lining on the corrosion of the ductile iron pipe in reclaimed water.

Effects of varying temperatures and alkalinities on the corrosion and heavy metal release from low-lead galvanized steel

The presence of galvanized pipe in drinking water distribution systems is known to be associated with heavy metal release, especially after the aging of zinc coating. This study examined release of lead and other heavy metals (e.g., cadmium, chromium) from galvanized steel coupons with a low-lead zinc coating. Metal release data were obtained in 12-week long jar tests which were conducted at varying temperatures and alkalinities. The morphology of the exposed surfaces was dominated by spherical and acicular formations. Exposures at 36 °C were associated with increased corrosion rates, accelerated depletion of zinc coating and faster development of corrosion scales, compared with 4 and 20 °C. The protective action of zinc coating was enhanced at increasing alkalinities. Metal release data showed a significant enrichment of Pb and Cd levels in the particulates released from the low-Pb galvanized steel.

Identifying effects of pipe material, hydraulic condition, and water composition on elemental accumulation in pipe corrosion scales

Identification of the accumulation mechanism of major elements on pipe surface is essential to investigate the development of corrosion scales and co-occurrence of trace inorganic contaminants. In this study, corrosion scale samples were collected from old, corroded iron pipes made of different materials and exposed to different water qualities and operation conditions. Elemental composition of these scales was determined by energy dispersive X-ray spectroscopy (EDS). Cumulative occurrence analysis, Q-style hierarchical cluster analysis (CA), and principal component analysis (PCA) were conducted to ascertain major elements typical for corrosion scales and to estimate the dominant influencing factor to each elemental constituent. The major elements in the examined scales are Fe, C, Zn, Si, Ca, Al, and S in the descending prevalence. Their occurrences are influenced by an interactive effect. Pipe material imposes a significant effect on the accumulation of Fe, Zn, and Ca in corrosion scales; water composition can account for the presence of Si, Al, and S in this study; hydraulic condition is identified as the primary factor influencing the occurrence of C and Ca. Q-style CA and PCA are verified practicable for data interpretation and identification of dominant factors influencing scale characteristics.

Response of microorganisms in biofilm to sulfadiazine and ciprofloxacin in drinking water distribution systems

Effects of sulfadiazine and ciprofloxacin on microorganisms in biofilm of drinking water distribution systems (DWDSs) were studied. The results verified that the increases of 16S rRNA for total bacteria and bacterial genus Hyphomicrobium were related to the promotion of antibiotic resistance genes (ARGs) and class 1 integrons (int1) in DWDSs with sulfadiazine and ciprofloxacin. Moreover, the bacteria showed higher enzymatic activities in DWDSs with sulfadiazine and ciprofloxacin, which resulted in more production of extracellular polymeric substances (EPS). The higher contents of EPS proteins and secondary structure β-sheet promoted bacterial aggregation and adsorption onto surface of pipelines to form biofilm. EPS can serve as a barrier for the microorganisms in biofilm. Therefore, the biofilm bacterial communities shifted and the 16S rRNA for total bacteria increased in DWDSs with antibiotics, which also drove the ARGs promotion. Furthermore, the two antibiotics exhibited stronger combined effects than that caused by sulfadiazine and ciprofloxacin alone.

Mannich Base as Corrosion Inhibitors for N80 Steel in a CO₂ Saturated Solution Containing 3 wt % NaCl

In this paper, a corrosion inhibitor containing nitrogen atoms and a conjugated π bond was synthesised, and its final product synthesised by the optimal conditions of the orthogonal test results is named multi-mannich base (MBT). The corrosion inhibition effect on the N80 steel sheet of the corrosion inhibitor was evaluated in a CO₂ saturated solution containing 3 wt % NaCl; the corrosion rate was 0.0446 mm/a and the corrosion inhibition rate was 90.4%. Through electrochemical and adsorption theory study, MBT is a mixed corrosion inhibitor that mainly shows cathode suppression capacity. The adsorption of MBT on the surface of the steel sheet follows the Langmuir adsorption isotherm; it can be spontaneously adsorbed on the surface of the N80 steel sheet, which has a good corrosion inhibition effect. The surface of the N80 steel sheet was microscopically characterised by atomic force microscope (AFM). It can be seen from the results that the N80 steel sheet with MBT added is significantly different from the blank control group; the surface of the steel sheet is relatively smooth, indicating that MBT forms an effective protective film on the surface of N80 steel, which inhibits the steel sheet.

Physico-chemical Characteristics of Corrosion Scales from Different Pipes in Drinking Water Distribution Systems

Corrosion scales formed on iron pipe surfaces are an important factor defining water quality in drinking water distribution systems, since they would release contaminants and cause water discoloration at transient hydrodynamic regimes. Consequently, characterization of corrosion scales is indispensable to water quality protection. In this study, corrosion products were carefully collected from three old, corroded iron pipes made of different materials and exposed to different water qualities and operation conditions. Physico-chemical characteristics of these scales were determined using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Inductively Coupled Plasma (ICP), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Testing results show that scale characteristics, including micromorphology, porosity and composition, vary significantly due to different pipe materials, water qualities and hydraulic conditions. Zinc coatings in galvanized pipes contribute to metal corrosion prevention, while attention should be paid to zinc release. High corrosive surface water facilitates the formation of developed corrosion tubercles, in which the compact shell-like layer conduces to maintain the structural stability of corrosion scales under disturbance. Structural breaks and low-velocity zones in water distribution systems might be in high potential of contaminant release, since the inhomogeneous materials and unusual hydraulic conditions would result in unstable scale characteristics.

Sulfadiazine/ciprofloxacin promote opportunistic pathogens occurrence in bulk water of drinking water distribution systems

Effects of sulfadiazine and ciprofloxacin on the occurrence of free-living and particle-associated opportunistic pathogens in bulk water of simulated drinking water distribution systems (DWDSs) were investigated. It was found that sulfadiazine and ciprofloxacin greatly promoted the occurrence of opportunistic pathogens including Pseudomonas aeruginosa, Legionella pneumophila, Mycobacterium avium and its broader genus Mycobacterium spp., as well as the amoebae Acanthamoeba spp. and Hartmanella vermiformis, in bulk water of DWDSs. Moreover, sulfadiazine and ciprofloxacin exhibited much stronger combined effects on the increase of these opportunistic pathogens. Based on the analysis of the antibiotic resistance genes (ARGs) and extracellular polymeric substances (EPS), it was verified that EPS production was increased by the antibiotic resistant bacteria arising from the effects of sulfadiazine/ciprofloxacin. The combined effects of sulfadiazine and ciprofloxacin induced the greatest increase of EPS production in DWDSs. Furthermore, the increased EPS with higher contents of proteins and secondary structure β-sheet led to greater bacterial aggregation and adsorption. Meanwhile, large numbers of suspended particles were formed, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in bulk water of DWDSs with sulfadiazine/ciprofloxacin. Therefore, sulfadiazine and ciprofloxacin promoted the occurrence of particle-associated opportunistic pathogens in bulk water of DWDSs due to the role of EPS produced by the bacteria with ARGs.

Effects of Sulfate, Chloride, and Bicarbonate on Iron Stability in a PVC-U Drinking Pipe

In order to describe iron stability in plastic pipes and to ensure the drinking water security, the influence factors and rules for iron adsorption and release were studied, dependent on the Unplasticized poly (vinyl chloride) (PVC-U) drinking pipes employed in this research. In this paper, sulfate, chloride, and bicarbonate, as well as synthesized models, were chosen to investigate the iron stability on the inner wall of PVC-U drinking pipes. The existence of the three kinds of anions could significantly affect the process of iron adsorption, and a positive association was found between the level of anion concentration and the adsorption rate. However, the scaling formed on the inner surface of the pipes would be released into the water under certain conditions. The Larson Index (LI), used for a synthetic consideration of anion effects on iron stability, was selected to investigate the iron release under multi-factor conditions. Moreover, a well fitted linear model was established to gain a better understanding of iron release under multi-factor conditions. The simulation results demonstrated that the linear model was better fitted than the LI model for the prediction of iron release.

Assessment of tap water quality and corrosion scales from the selected distribution systems in northern Pakistan

Corrosion deposits formed within drinking water distribution systems deteriorate drinking water quality and resultantly cause public health consequences. In the present study, an attempt was made to investigate the concurrent conditions of corrosion scales and the drinking water quality in selected water supply schemes (WSS) in districts Chitral, Peshawar, and Abbottabad, northern Pakistan. Characterization analyses of the corrosion by-products revealed the presence of α-FeOOH, γ-FeOOH, Fe₃O₄, and SiO₂ as major constituents with different proportions. The constituents of all the representative XRD peaks of Peshawar WSS were found insignificant as compared to other WSS, and the reason could be the variation of source water quality. Well-crystallized particles in SEM images indicated the formation of dense oxide layer on corrosion by-products. A wider asymmetric vibration peak of SiO₂ appeared only in Chitral and Abbottabad WSS, which demonstrated higher siltation in the water source. One-way ANOVA analysis showed significant variations in pH, turbidity, TDS, K, Mg, PO₄, Cl, and SO₄ values, which revealed that these parameters differently contributed to the source water quality. Findings from this study suggested the implementation of proper corrosion prevention measures and the establishment of international collaboration for best corrosion practices, expertise, and developing standards.

Changes of the corrosion potential of iron in stagnation and flow conditions and their relationship with metal release

This study examined the behavior of corrosion potential (Ecorr) of iron exposed to drinking water during episodes of stagnation and flow. These measurements showed that during stagnation episodes, Ecorr values decrease prominently and consistently. This decrease is initially rapid but it becomes slower as the stagnation time increases. During flow episodes, the Ecorr values increase and reach a quasi-steady state. Experiments with varying concentrations of dissolved oxygen showed that the decrease of Ecorr values characteristic for stagnation is likely to be associated with the consumption of dissolved oxygen by the exposed metal. The corrosion potential of iron and its changes during stagnation were sensitive to the concentrations of sulfate and chloride ions. Measurements of iron release showed that both the absolute values of Ecorr measured prior to or after stagnation episodes were well correlated with the logarithms of concentrations of total iron. The slope of this dependence showed that the observed correlations between Ecorr values and Fe concentrations corresponded to the coupling between the oxidant consumption and changes of Fe redox status. These results demonstrate that in situ Ecorr measurements can be a sensitive method with which to ascertain effects of hydrodynamic conditions and short-term variations of water chemistry on metal release and corrosion in drinking water. This approach is valuable practically because Ecorr measurements are precise, can be carried out in situ with any desired time resolution, do not affect the state of exposed surface in any extent and can be carried out with readily available equipment.

Influence of water salinity on corrosion risk-the case of the southern Baltic Sea coast

Water corrosivity in Gdansk Bay, Poland, the southern part of the Baltic Sea, was investigated. The analysed region is heavily industrialized, and the coastline is very diverse. Twenty-seven test points along the coastline were selected. Water parameters such as salinity, total dissolved solids content, resistivity, conductivity, oxygenation, pH and corrosion rate were determined. The results of the investigation are presented. Water samples were collected, and structural steel specimens were exposed in the water for 2 months. The corrosion rate for each test point was determined and plotted on a map. The spatial distribution of water parameters was calculated using the 'inverse distance to a power' method and presented on the maps. Salinity did not exceed 0.7 %, and average corrosion rate equalled 0.0585 mm/year.

Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems

Changes in disinfectant type could trigger a cascade of reactions releasing pipe-anchored metals/metalloids into finished water. However, the effect of pre-formed disinfection by-products on the release of sorbed contaminants (arsenic-As in particular) from drinking water distribution system pipe scales remains unexplored. A bench-scale study using a factorial experimental design was performed to evaluate the independent and interaction effects of trihalomethanes (TTHM) and haloacetic acids (HAA) on arsenic (As) release from either scales-only or scale-biofilm conglomerates (SBC) both anchored on asbestos/cement pipe coupons. A model biofilm (Pseudomonas aeruginosa) was allowed to grow on select pipe coupons prior experimentation. Either TTHM or HAA individual dosing did not promote As release from either scales only or SBC, detecting <6 μg AsL(-1) in finished water. In the case of scales-only coupons, the combination of the highest spike level of TTHM and HAA significantly (p<0.001) increased dissolved and total As concentrations to levels up to 16 and 95 μg L(-1), respectively. Similar treatments in the presence of biofilm (SBC) resulted in significant (p<0.001) increase in dissolved and total recoverable As up to 20 and 47 μg L(-1), respectively, exceeding the regulatory As limit. Whether or not, our laboratory-based results truly represent mechanisms operating in disinfected finished water in pipe networks remains to be investigated in the field.

Effects of chloride, sulfate and natural organic matter (NOM) on the accumulation and release of trace-level inorganic contaminants from corroding iron

This study examined effects of varying levels of anions (chloride and sulfate) and natural organic matter (NOM) on iron release from and accumulation of inorganic contaminants in corrosion scales formed on iron coupons exposed to drinking water. Changes of concentrations of sulfate and chloride were observed to affect iron release and, in lesser extent, the retention of representative inorganic contaminants (vanadium, chromium, nickel, copper, zinc, arsenic, cadmium, lead and uranium); but, effects of NOM were more pronounced. DOC concentration of 1 mg/L caused iron release to increase, with average soluble and total iron concentrations being four and two times, respectively, higher than those in the absence of NOM. In the presence of NOM, the retention of inorganic contaminants by corrosion scales was reduced. This was especially prominent for lead, vanadium, chromium and copper whose retention by the scales decreased from >80% in the absence of NOM to <30% in its presence. Some of the contaminants, notably copper, chromium, zinc and nickel retained on the surface of iron coupons in the presence of DOC largely retained their mobility and were released readily when ambient water chemistry changed. Vanadium, arsenic, cadmium, lead and uranium retained by the scales were largely unsusceptible to changes of NOM and chloride levels. Modeling indicated that the observed effects were associated with the formation of metal-NOM complexes and effects of NOM on the sorption of the inorganic contaminants on solid phases that are typical for iron corrosion in drinking water.