Iron stability in drinking water distribution systems in a city of China

A field study on the estimation and analysis of iron stability in drinking water distribution system was carried out in a city of China. The stability of iron ion was estimated by pC-pH figure. It was found that iron ion was unstable, with a high Fe （OH）3 precipitation tendency and obvious increase in turbidity. The outer layer of the corrosion scale was compact, while the inner core was porous. The main composition of the scale was iron, and the possible compound constitutes of the outer scale were α-FeOH, γ-FeOOH, α-Fe2O3, γ-F2O3, FeCl3, while the inner were Fe3O4, FeCl2, FeCO3. According to the characteristics of the corrosion scale, it was thought that the main reason for iron instability was iron release from corrosion scale. Many factors such as pipe materials, dissolved oxygen and chlorine residual affect iron release. Generally, higher iron release occurred with lower dissolved oxygen or chlorine residual concentration, while lower iron release occurred with higher dissolved oxygen or chlorine residual concentration. The reason was considered that the passivated out layer of scale of ferric oxide was broken down by reductive reaction in a condition of low oxidants concentration, which would result more rapid corrosion of the nine and red water phenomenon.

Effects of O3/Cl2 disinfection on corrosion and opportunistic pathogens growth in drinking water distribution systems

The effects of O3/Cl2 disinfection on corrosion and the growth of opportunistic pathogens in drinking water distribution systems were studied using annular reactors （ARs）. The corrosion process and most probable number （MPN） analysis indicated that the higher content of iron-oxidizing bacteria and iron-reducing bacteria in biofilms of the AR treated with O3/Cl2 induced higher Fe304 formation in corrosion scales. These corrosion scales became more stable than the ones that formed in the AR treated with Cl2 alone. O3/Cl2 disinfection inhibited corrosion and iron release efficiently by changing the content of corrosion-related bacteria. Moreover, ozone disinfection inactivated or damaged the opportunistic pathogens due to its strong oxidizing properties. The damaged bacteria resulting from initial ozone treatment were inactivated by the subsequent chlorine disinfection. Compared with the AR treated with Cl2 alone, the opportunistic pathogens M. auium and L. pneumophila were not detectable in effluents of the AR treated with O3/Cl2, and decreased to （4.60 ± 0.14） and （3.09 ± 0.12） loglo （gene copies/g corrosion scales） in biofilms, respectively. The amoeba counts were also lower in the AR treated with O3/Cl2. Therefore, O3/Cl2 disinfection can effectively control opportunistic pathogens in effluents and biofilms of an AR used as a model for a drinking water distribution system.

Characterization of bacterial community and iron corrosion in drinking water distribution systems with O3-biological activated carbon treatment

Bacterial community structure and iron corrosion were investigated for simulated drinking water distribution systems（DWDSs） composed of annular reactors incorporating three different treatments： ozone, biologically activated carbon and chlorination（O3-BAC-Cl2）;ozone and chlorination（O3-Cl2）; or chlorination alone（Cl2）. The lowest corrosion rate and iron release, along with more Fe3O4 formation, occurred in DWDSs with O3-BAC-Cl2 compared to those without a BAC filter. It was verified that O3-BAC influenced the bacterial community greatly to promote the relative advantage of nitrate-reducing bacteria（NRB）in DWDSs. Moreover, the advantaged NRB induced active Fe（III） reduction coupled to Fe（II） oxidation, enhancing Fe3O4 formation and inhibiting corrosion. In addition, O3-BAC pretreatment could reduce high-molecular-weight fractions of dissolved organic carbon effectively to promote iron particle aggregation and inhibit further iron release. Our findings indicated that the O3-BAC treatment, besides removing organic pollutants in water, was also a good approach for controlling cast iron corrosion and iron release in DWDSs.

The control of red water occurrence and opportunistic pathogens risks in drinking water distribution systems:A review

Many problems in drinking water distribution systems(DWDSs)are caused by microbe,such as biofilm formation,biocorrosion and opportunistic pathogens growth.More iron release from corrosion scales may induce red water.Biofilm played great roles on the corrosion.The iron-oxidizing bacteria(IOB)promoted corrosion.However,when iron-reducing bacteria(IRB)and nitrate-reducing bacteria(NRB)became the main bacteria in biofilm,they could induce iron redox cycling in corrosion process.This process enhanced the precipitation of iron oxides and formation of more Fe3 O4 in corrosion scales,which inhibited corrosion effectively.Therefore,the IRB and NRB in the biofilm can reduce iron release and red water occurrence.Moreover,there are many opportunistic pathogens in biofilm of DWDSs.The opportunistic pathogens growth in DWDSs related to the bacterial community changes due to the effects of micropollutants.Micropollutants increased the number of bacteria with antibiotic resistance genes(ARGs).Furthermore,extracellular polymeric substances(EPS)production was increased by the antibiotic resistant bacteria,leading to greater bacterial aggregation and adsorption,increasing the chlorine-resistance capability,which was responsible for the enhancement of the particle-associated opportunistic pathogens in DWDSs.Moreover,O3-biological activated carbon filtration-UV-Cl2 treatment could be used to control the iron release,red water occurrence and opportunistic pathogens growth in DWDSs.

Responses of bacterial strains isolated from drinking water environments to N-acyI-L-homoserine lactones and their analogs during biofilm formation

Often as a result ofbiofilm formation, drinking water distribution systems （DWDS） are regularly faced with the problem of microbial contamination. Quorum sensing （QS） systems play a marked role in the regulation of microbial biofilm formation; thus, inhibition of QS systems may provide a promising approach to biofilm formation control in DWDS. In the present study, 22 bacterial strains were isolated from drinking water-related environments. The following properties of the strains were investigated： bacterial biofilm formation capacity, QS signal molecule N-acyl-L-homoserine lactones （AHLs） production ability, and responses to AHLs and AHL analogs, 3-chloro-4-（dichloromethyl）-5-hydroxy-2（5H）- furanone （MX） and 2（5H）-furanone. Four AHLs were added to developed biofilms at dosages ranging from 0.1 nmol.L J to 100nmol.L1. As a result, the biofilm growth of more than 1/4 of the isolates, which included AHL producers and non-producers, were significantly promoted. Further, the biofilm biomasses were closely associated with respective AHLs concentrations. These results provided evidence to support the idea that AHLs play a definitive role in biofilm formation in many of the studied bacteria. Meanwhile, two AHLs analogs demon- strated unexpectedly minimal negative effects on biofilm formation. This suggested that, in order to find an applicable QS inhibition approach for biofilm control in DWDS, the testing and analysis of more analogs is needed.

Impact of disinfection on drinking water biofilm bacterial community

Disinfectants are commonly applied to control the growth of microorganisms in drinking water distribution systems. However, the effect of disinfection on drinking water microbial community remains poorly understood. The present study investigated the impacts of different disinfectants（chlorine and chloramine） and dosages on biofilm bacterial community in bench-scale pipe section reactors. Illumina MiS eq sequencing illustrated that disinfection strategy could affect both bacterial diversity and community structure of drinking water biofilm. Proteobacteria tended to predominate in chloraminated drinking water biofilms, while Firmicutes in chlorinated and unchlorinated biofilms. The major proteobacterial groups were influenced by both disinfectant type and dosage. In addition, chloramination had a more profound impact on bacterial community than chlorination.

Investigation of drinking water bacterial community through high-throughput sequencing

Delivery of safe and pathogen-free drinking water is crucial to public health.However,there exist challenges to the maintenance of the sterility of drinking water throughout the drinking water distribution systems（DWDS）.Microbial growth in DWDS,such as growth of opportunistic pathogenic microorganisms,can lead to severe health problems in consumers（Berry et al.,2006;Brettar and Hofle,2006;Lu et al.,2014;Zhang et al.,2015）.

Synergistic effects of sodium hypochlorite disinfection and iron-oxidizing bacteria on early corrosion in cast iron pipes

Corrosion in drinking water distribution systems(DWDSs)may lead to pipe failures and water quality deterioration;biocorrosion is the most common type.Chlorine disinfectants are widely used in DWDSs to inhibit microorganism growth,but these also promote electrochemical corrosion to a certain extent.This study explored the independent and synergistic effects of chlorine and microorganisms on pipeline corrosion.Sodium hypochlorite(NaOCl)at different concentrations(0,0.25,0.50,and 0.75 mg/L)and iron-oxidizing bacteria(IOB)were added to the reaction system,and a biofilm annular reactor(BAR)was employed to simulate operational water supply pipes and explain the composite effects.The degree of corrosion became severe with increasing NaOCl dosage.IOB accelerated the corrosion rate at an early stage,after which the reaction system gradually stabilized.When NaOCl and IOB existed together in the BAR,both synergistic and antagonistic effects occurred during the corrosion process.The AOC content increased due to the addition of NaOCl,which is conducive to bacterial regrowth.However,biofilm on cast iron coupons was greatly influenced by the disinfectant,leading to a decrease in microbial biomass over time.More research is needed to provide guidelines for pipeline corrosion control.