Cement mortar lining (CML) is commonly used for iron pipe internal corrosion inhibition in drinking water distribution system (DWDS), however, the corrosion of CML itself is still a problem, particularly under soft water conditions. In this study, both long-term experimental study and theoretical studies were conducted to evaluate the effects of graphene oxide (GO) and three-dimensional reduced graphene oxide (3D-rGO) as additives on the stability of CML and the corresponding water quality. Results showed that during a 182-day leaching experiment, the 3D-rGO modified cement had a higher ability to inhibit the cement constituent leaching than GO modified and original cements. Structural characterization indicated that the addition of 3D-rGO could slightly promote the degree of calcium hydroxide crystallization in CML. Molecular dynamics simulation demonstrated that the 3D-rGO nanosheets strengthened the tensile strain of the cement and restricted the movement of calcium ions by forming strong bonds with the calcium-silicate-hydrate gel network. In addition, compared with GO modified cement and original cement, the 3D-rGO modified cement could somewhat reduce the disinfection by-products formation and the microbial richness in drinking water. Thus, the reinforcement of cement by 3D-rGO could enhance the safety and durability of CML iron pipes in DWDS.

Metal contaminants in corrosion products of drinking water distribution systems (DWDS) can be released into potable water under specific conditions, thereby polluting drinking water and posing a health risk. Under stagnation conditions, the release characteristics, occurring forms, and environmental risks of ten metals were determined in loose and tubercle scale solids of an unlined cast iron pipe with a long service history, before and after immersion. Most Al, As, Cr, Fe, and V in corrosion scales existed in the residual fraction, with the released concentration and pollution risk being low. Since more than 59% of Ca in pipe scales existed in the exchangeable fraction, Ca release was high. Although the Pb and Cd content of corrosion solids was low, a high proportion of Pb and Cd was present in non-residual fractions with high mobility. Sudden severe Pb or Cd pollution events in DWDS could result in high pollution and environmental risk levels. The total content and released amount of Mn and Zn in corrosion scales were both high. Therefore, while special attention should be paid to Mn and Zn, Pb and Cd also present a high risk in pipe scales, despite their low concentrations. During stagnation immersion, metal release from powdered pipe scales occurred via the processes of mass release, re-adsorption into scales, and slow release until equilibrium was reached. The levels of metal re-adsorption into scales were much higher than the concentrations dissolved into bulk water. However, the amount of metal re-adsorption into tubercle scale blocks was less. Importantly, these findings highlight that during DWDS operation, the sudden release of metal pollutants caused by pipe scale breakage should be avoided.

Microbial corrosion and heavy metal accumulation in metal water supply pipelines aggravate scale formation and may result in pipeline leakage or bursting events. To better understand the corrosion and corrosion products in the damaged pipes, deposits excavated from three damaged pipes after 22-26 year service periods were analyzed. Using a combination of advanced micro-mineral techniques and 16S rRNA high-throughput sequencing, the micromorphology, chemical composition, and bacterial community were investigated systematically. Unlined pipe wall scales ruptured while lined pipes leaked due to joint scales. Dendrogram correlation results demonstrated that V/As, Al/Pb, and Cr/Mn clusters exhibited co-adsorption and co-precipitation characteristics. FTIR and XRD analysis detected the presence of γ-FeOOH, α-FeOOH in loose scales, and Fe3O4 in rigid scales. Scales were colonized by various corrosion bacteria, with sulfate reducing bacteria and ammonia producing bacteria being dominant in the scales of anticorrosive and non-corrosive pipe, respectively. Tl, Ca, Al, and Pb exhibited an extremely positive correlation with Rhodocyclaceae, Ferritrophicum, Thermodesulfovibrionia, and Clostridiaceae. Al and V presented a potential Hazard Quotient risk to consumers, while Cd was potentially bioavailable in all inner scales. Overall, this study provides valuable information for the effective management and avoidance of corrosion-induced pipeline damage and heavy metal release.

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

With the expansion of cities, the deterioration of drinking water quality undergoing complex and long-distance distribution is gaining increasing attention. However, spatial variations between free-living bacteria (FLB) and particle-associated bacteria (PAB) in chlorinated drinking water distribution systems (DWDSs) have not been fully explored, especially in complex water supply areas with multiple interconnected DWDSs. To fill this gap, this study utilized 16S rRNA approaches to characterize the spatial patterns of FLB and PAB in DWDSs with intersection regions. Based on distance-decay analysis, transportation distance is a potential driver of bacterial variation for both FLB (Pearson\'s r = -0.476, p < 0.01) and PAB. (Pearson\'s r = -0.352, p < 0.01). Moreover, the influence of transportation distance was further confirmed by a 1.20-99.45% decline in microbial contribution to the source of FLB and PAB communities in pipe water along the transportation pipelines. Meanwhile, significant difference (PERMANOVA, R2 = 0.14, p < 0.01) was found between FLB and PAB in DWDSs. Average proportions of Pseudomonas spp. were 59.84% and 45.59% for the PAB and intersection regions based on the 16S rRNA results, respectively, suggesting that PAB are potential reservoirs for high-risk bacteria, and a greater microbial risk may exist in intersection regions. In summary, transportation distance and pipeline intersection exerted significant impacts on the FLB and PAB in DWDSs. Therefore, precautionary strategies for controlling microbial risks that consider different microbial components and intersection regions in long-distance and multi-plant DWDSs should be implemented.