Real Drinking Water Distribution Systems Research Articles

Structural property and risk assessment of loose deposits in drinking water distribution systems

Abstract Discoloration events caused by loose deposits resuspension in drinking water distribution systems (DWDS) are the main aspects of customer complaints across the world, but the understanding of the potential risks of loose deposits is insufficient. In this study, loose deposits in real DWDS were collected from regions frequently experiencing ‘yellow water’. Cytotoxicity of healthy human liver cells was used to evaluate the toxicity risks of the particle samples. The results showed that the loose deposits would have a realistic discoloration risk (turbidity > 10 NTU) when their concentrations were higher than 10 mg/L. The water sample containing 1,000 mg/L loose deposits had a dark yellow color (100–300 PCU) and cytotoxicity (viability of human liver cells during cytotoxicity tests 59.18–80.69%), while the water sample containing 1 mg/L loose deposits did not have obvious color (<15 PCU) and cytotoxicity (>97.00%). Particle size showed a stronger correlation with relative viability (r = 0.761) than other properties (specific area, metal content, contact angle, saturation magnetization and electron transfer number). However, it is interesting to note that both turbidity and color had a low correlation with relative viability, thus the toxicity of the particles could not be properly judged using turbidity or color. This study gives an important guidance that although the loose deposits could be visualized during water discoloration, its toxicity risks could not be evaluated through aesthetic indicators.

Effects of residual disinfectants on the redox speciation of lead(ii)/(iv) minerals in drinking water distribution systems.

This study investigated the reaction kinetics on the oxidative transformation of lead(ii) minerals by free chlorine (HOCl) and free bromine (HOBr) in drinking water distribution systems. According to chemical equilibrium predictions, lead(ii) carbonate minerals, cerussite PbCO3(s) and hydrocerussite Pb3(CO3)2(OH)2(s), and lead(ii) phosphate mineral, chloropyromorphite Pb5(PO4)3Cl(s) are formed in drinking water distribution systems in the absence and presence of phosphate, respectively. X-ray absorption near edge spectroscopy (XANES) data showed that at pH 7 and a 10 mM alkalinity, the majority of cerussite and hydrocerussite was oxidized to lead(iv) mineral PbO2(s) within 120 minutes of reaction with chlorine (3 : 1 Cl2 : Pb(ii) molar ratio). In contrast, very little oxidation of chloropyromorphite occurred. Under similar conditions, oxidation of lead(ii) carbonate and phosphate minerals by HOBr exhibited a reaction kinetics that was orders of magnitude faster than by HOCl. Their end oxidation products were identified as mainly plattnerite β-PbO2(s) and trace amounts of scrutinyite α-PbO2(s) based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. A kinetic model was established based on the solid-phase experimental data. The model predicted that in real drinking water distribution systems, it takes 0.6-1.2 years to completely oxidize Pb(ii) minerals in the surface layer of corrosion scales to PbO2(s) by HOCl without phosphate, but only 0.1-0.2 years in the presence of bromide (Br-) due the catalytic effects of HOBr generation. The model also predicts that the addition of phosphate will significantly inhibit Pb(ii) mineral oxidation by HOCl, but only be modestly effective in the presence of Br-. This study provides insightful understanding on the effect of residual disinfectant on the oxidation of lead corrosion scales and strategies to prevent lead release from drinking water distribution systems.

Mechanism study on organic pollutant accumulation by iron-based particles in drinking water conditions

Discoloration events in drinking water distribution systems (DWDSs) caused by iron oxide particles have occurred worldwide, but the mechanism of organic pollutant accumulation by iron-based particles in DWDSs has not yet been fully recognized. Here, iron particle-dominated loose deposits were collected from a real DWDS through pipe flushing. Also, FeOOH-based particles, as an important component of deposits, were grown with various coexisting substances to further simulate the influence of structure on accumulation effects. Here, we found that the presence of cations, including Al3+ and Mn2+; phosphate anion; and organic pollutants, such as the disinfection byproducts (DBPs) and persistent organic pollutants (POPs) with trichloroacetic acid (TCA) and perfluorosulfonic acid (PFOA) as representatives, could influence the accumulation effects of FeOOH particles in DWDSs due to the structural transformation. The FeOOH particles grown with coexisting organic matter (FeOOH-TCA and FeOOH-PFOA) had a higher specific area and more OH groups than other samples. With abundant contact sites due to their hairy urchin-like structures and rich surface oxygen-containing functional groups, the FeOOH-based particles had higher accumulation abilities for antibiotics, with FeOOH-TCA presenting the highest ability. The formation of Fe-O-C confirmed that the OH groups in organics could bind with iron ions and guide hydrolysis to induce obvious structural transformation into a material with a higher specific area and more contact sites. Moreover, molecular dynamics (MD) simulations suggested that hydrogen bonding played an important role in this accumulation process. The results not only revealed the importance of focusing on the complex iron-based particles in DWDSs, but also showed previously unknown risks of DBPs and POPs, as such compounds may promote the accumulation effect of deposits.

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

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

Risk assessment of heavy metals in pipe scales and loose deposits formed in drinking water distribution systems

The accumulation of inorganic contaminants in drinking water distribution systems (DWDS) can greatly threaten water quality and safety. This work mainly focused on the accumulation, speciation and risk assessment of inorganic contaminants found in pipe scales and loose deposits in DWDS. Global contamination factor (GCF), risk assessment code (RAC) and consensus-based sediment quality guidelines (CBSQGs) were adopted for the potential health risk assessment of inorganic contaminants. The Tessier sequential extraction method was used to study the speciation distribution of inorganic contaminants in fourteen samples (six pipe scale samples, eight loose deposit samples) collected from real DWDS. The significant correlation between Al and Mn showed there was a co-occurrence behavior of Al and Mn in pipe scales and loose deposits. In addition to the possible interactions between Al and Mn, Ba, Cu and As were possibly accumulated during the formation of Al and Mn commixtures. Mn, Cu, Pb, Zn, Ni, Co and Ba in the samples were mainly associated with the Fe-Mn oxides fraction, which indicated Fe-Mn oxides might play an important role in the accumulation and release of these inorganic contaminants. Fe, Al, As, Cr, V and Cd mainly existed in the residual fraction, which indicated their low mobility. The GCF results demonstrated that most of the sample sites had a certain environmental risk. The RAC results showed that high risk mainly resulted from Cd both in pipe scales and loose deposits. According to the CBSQGs evaluation, heavy metals in loose deposits were more harmful, and Ba exhibited the highest risk among all heavy metals.

Evaluating the chemical stability in drinking water distribution system by corrosivity and precipitation potential

Abstract Calcium carbonate equilibrium-based indices, such as calcium carbonate precipitation potential (CCPP), have long been used as indicators of water chemical stability. The Larson ratio (LR) is a non-CaCO3 based index for measuring water corrosivity against iron pipes, but the involved mechanisms and application of LR are not completely understood. To understand the applicability of the two indices on iron corrosion product release in drinking water distribution systems (DWDS), unlined cast iron pipes were harvested from a real DWDS to establish pilot-scale experimental systems, and different chemicals were used to adjust LR and CCPP values of the pipe feed waters. Results showed that iron release increased with LR increase, but at the same LR, chloride adjustment could lead to more iron release than sulphate. When using different chemicals to adjust CCPP to the same level, the iron release could be significantly different, with NaHCO3 addition causing the lowest release. Increasing the alkalinity by Ca(OH)2 and CO2, which could be the most efficient and economic method for inhibiting iron release in DWDS, increased the CCPP and reduced the LR simultaneously. The crystalline composition characteristics of iron pipe corrosion scales also played a critical role in the iron release behavior.

Dynamics of Biofilm Regrowth in Drinking Water Distribution Systems.

ABSTRACTThe majority of biomass within water distribution systems is in the form of attached biofilm. This is known to be central to drinking water quality degradation following treatment, yet little understanding of the dynamics of these highly heterogeneous communities exists. This paper presents original information on such dynamics, with findings demonstrating patterns of material accumulation, seasonality, and influential factors. Rigorous flushing operations repeated over a 1-year period on an operational chlorinated system in the United Kingdom are presented here. Intensive monitoring and sampling were undertaken, including time-series turbidity and detailed microbial analysis using 16S rRNA Illumina MiSeq sequencing. The results show that bacterial dynamics were influenced by differences in the supplied water and by the material remaining attached to the pipe wall following flushing. Turbidity, metals, and phosphate were the main factors correlated with the distribution of bacteria in the samples. Coupled with the lack of inhibition of biofilm development due to residual chlorine, this suggests that limiting inorganic nutrients, rather than organic carbon, might be a viable component in treatment strategies to manage biofilms. The research also showed that repeat flushing exerted beneficial selective pressure, giving another reason for flushing being a viable advantageous biofilm management option. This work advances our understanding of microbiological processes in drinking water distribution systems and helps inform strategies to optimize asset performance.IMPORTANCE This research provides novel information regarding the dynamics of biofilm formation in real drinking water distribution systems made of different materials. This new knowledge on microbiological process in water supply systems can be used to optimize the performance of the distribution network and to guarantee safe and good-quality drinking water to consumers.

Effects of pH value, chloride and sulfate concentrations on galvanic corrosion between lead and copper in drinking water

Environmental context Galvanic corrosion has been recently reported as the main cause of lead contamination in drinking water in urban cities. Conditions that can deter or promote galvanic corrosion, however, are not well understood. Fundamental investigations exploring the mechanisms and processes involved in galvanic corrosion in drinking water could help to implement proper corrective measures to safeguard public health from lead contamination. Abstract This study investigates the effects of pH value, chloride and sulfate concentrations on galvanic corrosion between lead and copper in drinking water. We hypothesised that galvanic corrosion would occur immediately when a lead–copper couple is first formed and that the release of lead would be suppressed by the subsequent formation of lead corrosion products. Therefore, unlike previous long-term studies using harvested lead pipes, batch experiments employing high-purity lead and copper (99.9%) wires under stagnant and completely mixed conditions were conducted for a 7-day period to test our hypotheses. It was found that enhanced lead release was indeed observed after the lead–copper couple was formed and the lead profiles after 48h were strongly influenced by lead corrosion products formed in the system. Under stagnant conditions, reducing pH and increasing either chloride or sulfate concentrations promoted lead release, leading to the formation of lead corrosion products such as cerussite and hydrocerussite as experiments proceeded. The effect of chloride concentration on total lead concentration measured in the aqueous phase was similar to that of sulfate at the same molar concentration, showing that the chloride-to-sulfate mass ratio may not provide a good indication for total lead concentration in water. This study provides essential information on fundamental mechanisms and processes involved in galvanic corrosion in drinking water and may be used to explain related phenomena observed in real drinking-water distribution systems.

Biofilm bacterial communities in urban drinking water distribution systems transporting waters with different purification strategies.

Biofilm formation in drinking water distribution systems (DWDS) has many adverse consequences. Knowledge of microbial community structure of DWDS biofilm can aid in the design of an effective control strategy. However, biofilm bacterial community in real DWDS and the impact of drinking water purification strategy remain unclear. The present study investigated the composition and diversity of biofilm bacterial community in real DWDSs transporting waters with different purification strategies (conventional treatment and integrated treatment). High-throughput Illumina MiSeq sequencing analysis illustrated a large shift in the diversity and structure of biofilm bacterial community in real DWDS. Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Nitrospirae, and Cyanobacteria were the major components of biofilm bacterial community. Proteobacteria (mainly Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria) predominated in each DWDS biofilm, but the compositions of the dominant proteobacterial classes and genera and their proportions varied among biofilm samples. Drinking water purification strategy could shape DWDS biofilm bacterial community. Moreover, Pearson's correlation analysis indicated that Actinobacteria was positively correlated with the levels of total alkalinity and dissolved organic carbon in tap water, while Firmicutes had a significant positive correlation with nitrite nitrogen.

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.

Phylogenetic diversity of microbial communities in real drinking water distribution systems

Microbial regrowth in drinking water distribution systems (DWDS) is a major concern in the water supply industry. Detailed knowledge of the microbial community in DWDS will be of great importance for assessing the microbiological risks of drinking water. The spatial heterogeneity of microbial community structures in the bulk waters of a large real DWDS was investigated using 16S rRNA clone library analysis. The results indicate that high residual chlorine in drinking water could not control microbial regrowth in DWDS. The bacterial communities in the bulk waters were spatially heterogenic, mainly composed of Alphaproteobacteria and Betaproteobacteria (or Cyanobacteria). Microorganisms from the genera Acinetobacter, Sphingomonas and Gemella were detected, implying there is microbiological risk from drinking water. This work provides new insight into microbial ecology in DWDS.

Study on inactivation of iron bacteria isolated from real drinking water distribution systems by free chlorine and chloramine

To study the inactivation characteristic of iron bacteria isolated from real drinking water distribution systems and investigate the influence of disinfectants, pH and temperature on inactivation process. Two kinds of iron bacteria were isolated from the water phase in distribution systems and identified asAcinetobacter baumannii andMicrobacterium oxydans. Bench-scale study on inactivation of the two kinds of iron bacteria were carried out, with the impact of disinfectants, pH and temperature under different levels concerned. Free chlorine and monochloramine could achieve an inactivation rate of 99.9% on bothA. Baumannii andM. Oxydans with the CT-value of 10 mg/L·min. Free chlorine was more effective than monochloramine with 1∼2 log higher inactivation rate.Microbacterium oxydans was more resistant to disinfectant thanA. Baumannii. High pH enhanced the inactivation of A.baumannii and low temperature availed the inactivation of bothA. Baumannii andMicrobacterium. For iron bacteria in the water, inactivation ratio could not reach 99% when residual chlorine was 0.05 mg/L in drinking water distribution systems according to Standards for Drinking Water Quality.