Nontuberculous Mycobacteria in Two Drinking Water Distribution Systems and the Role of Residual Disinfection.

Nontuberculous mycobacteria (NTM) are frequently found in chloraminated drinking water distribution systems (DWDSs) due to their chloramine tolerance. NTM were investigated in the water-main biofilms and drinking water of a chloraminated DWDS in the United States (initial chloramine residual = 3.8 ± 0.1 mg L-1) and a DWDS in Norway with minimal residual disinfectant (0.08 ± 0.01 mg L-1). Total mycobacteria and Mycobacterium avium complex (MAC) were quantified by qPCR targeting, respectively, atpE genes and the internal transcribed spacer region. Mycobacteria concentrations in drinking water did not differ between the two systems (P = 0.09; up to 6 × 104 copies L-1) but were higher in the biofilms from the chloraminated DWDS (P = 5 × 10-9; up to 5 × 106 copies cm-2). MAC were not detected in either system. Sequencing of mycobacterial hsp65 genes indicated that the chloraminated DWDS lacked diversity and consisted almost exclusively of M. gordonae. In contrast, there were various novel mycobacteria in the no-residual DWDS. Finally, Mycobacterium- and Methylobacterium-like 16S rRNA genes were often detected simultaneously, though without correlation as previously observed. We conclude that, though residual chloramine may increase mycobacterial biomass in a DWDS, it may also decrease mycobacterial diversity.

Comparison of the microbiomes of two drinking water distribution systems-with and without residual chloramine disinfection.

BACKGROUND: Residual disinfection is often used to suppress biological growth in drinking water distribution systems (DWDSs), but not without undesirable side effects. In this study, water-main biofilms, drinking water, and bacteria under corrosion tubercles were analyzed from a chloraminated DWDS (USA) and a no-residual DWDS (Norway). Using quantitative real-time PCR, we quantified bacterial 16S rRNA genes and ammonia monooxygenase genes (amoA) of Nitrosomonas oligotropha and ammonia-oxidizing archaea-organisms that may contribute to chloramine loss. PCR-amplified 16S rRNA genes were sequenced to assess community taxa and diversity. RESULTS: The chloraminated DWDS had lower biofilm biomass (P=1×10-6) but higher N. oligotropha-like amoA genes (P=2×10-7) than the no-residual DWDS (medians =4.7×104 and 1.1×103amoA copies cm-2, chloraminated and no residual, respectively); archaeal amoA genes were only detected in the no-residual DWDS (median =2.8×104 copies cm-2). Unlike the no-residual DWDS, biofilms in the chloraminated DWDS had lower within-sample diversity than the corresponding drinking water (P<1×10-4). Chloramine was also associated with biofilms dominated by the genera, Mycobacterium and Nitrosomonas (≤91.7% and ≤39.6% of sequences, respectively). Under-tubercle communities from both systems contained corrosion-associated taxa, especially Desulfovibrio spp. (≤98.4% of sequences). CONCLUSIONS: Although residual chloramine appeared to decrease biofilm biomass and alpha diversity as intended, it selected for environmental mycobacteria and Nitrosomonas oligotropha-taxa that may pose water quality challenges. Drinking water contained common freshwater plankton and did not resemble corresponding biofilm communities in either DWDS; monitoring of tap water alone may therefore miss significant constituents of the DWDS microbiome. Corrosion-associated Desulfovibrio spp. were observed under tubercles in both systems but were particularly dominant in the chloraminated DWDS, possibly due to the addition of sulfate from the coagulant alum.

Occurrence of Legionella spp. in Water-Main Biofilms from Two Drinking Water Distribution Systems.

The maintenance of a chlorine or chloramine residual to suppress waterborne pathogens in drinking water distribution systems is common practice in the United States but less common in Europe. In this study, we investigated the occurrence of Bacteria and Legionella spp. in water-main biofilms and tap water from a chloraminated distribution system in the United States and a system in Norway with no residual using real-time quantitative polymerase chain reaction (qPCR). Despite generally higher temperatures and assimilable organic carbon levels in the chloraminated system, total Bacteria and Legionella spp. were significantly lower in water-main biofilms and tap water of that system ( p < 0.05). Legionella spp. were not detected in the biofilms of the chloraminated system (0 of 35 samples) but were frequently detected in biofilms from the no-residual system (10 of 23 samples; maximum concentration = 7.8 × 104 gene copies cm-2). This investigation suggests water-main biofilms may serve as a source of Legionella for tap water and premise plumbing systems, and residual chloramine may aid in reducing their abundance.

Inactivation of marine heterotrophic bacteria in ballast water by an Electrochemical Advanced Oxidation Process.

Seawater treatment is increasingly required due to industrial activities that use substantial volumes of seawater in their processes. The shipping industry and the associated management of a ship's ballast water are currently considered a global challenge for the seas. Related to that, the suitability of an Electrochemical Advanced Oxidation Process (EAOP) with Boron Doped Diamond (BDD) electrodes has been assessed on a laboratory scale for the disinfection of seawater. This technology can produce both reactive oxygen species and chlorine species (especially in seawater) that are responsible for inactivation. The EAOP was applied in a continuous-flow regime with real seawater. Natural marine heterotrophic bacteria (MHB) were used as an indicator of disinfection efficiency. A biphasic inactivation kinetic model was fitted on experimental points, achieving 4-Log reductions at 0.019 Ah L-1. By assessing regrowth after treatment, results suggest that higher bacterial damages result from the EAOP when it is compared to chlorination. Furthermore, several issues lacking fundamental understanding were investigated such as recolonization capacity or bacterial community dynamics. It was concluded that, despite disinfection processes being effective, there is not only a possibility for regrowth after treatment but also a change on bacterial population diversity produced by the treatment. Finally, energy consumption was estimated and indicated that 0.264 kWh·m-3 are needed for 4.8-Log reductions of MHB; otherwise, with 0.035 kWh·m-3, less disinfection efficiency can be obtained (2.2-Log red). However, with a residual oxidant in the solution, total inactivation can be achieved in three days.

Reversible and irreversible low-pressure membrane foulants in drinking water treatment: Identification by principal component analysis of fluorescence EEM and mitigation by biofiltration pretreatment.

With the increased use of membranes in drinking water treatment, fouling--particularly the hydraulically irreversible type--remains the main operating issue that hinders performance and increases operational costs. The main challenge in assessing fouling potential of feed water is to accurately detect and quantify feed water constituents responsible for membrane fouling. Utilizing fluorescence excitation-emission matrices (EEM), protein-like substances, humic and fulvic acids, and particulate/colloidal matter can be detected with high sensitivity in surface waters. The application of principal component analysis to fluorescence EEMs allowed estimation of the impact of surface water constituents on reversible and irreversible membrane fouling. This technique was applied to experimental data from a two year bench-scale study that included thirteen experiments investigating the fouling potential of Grand River water (Ontario, Canada) and the effect of biofiltration pre-treatment on the level of foulants during ultrafiltration (UF). Results showed that, although the content of protein-like substances in this membrane feed water (=biofiltered natural water) was much lower than commonly found in wastewater applications, the content of protein-like substances was still highly correlated with irreversible fouling of the UF membrane. In addition, there is evidence that protein-like substances and particulate/colloidal matter formed a combined fouling layer, which contributed to both reversible and irreversible fouling. It is suggested that fouling transitions from a reversible to an irreversible regime depending on feed composition and operating time. Direct biofiltration without prior coagulant addition reduced the protein-like content of the membrane feed water which in turn reduced the irreversible fouling potential for UF membranes. Biofilters also decreased reversible fouling, and for both types of fouling higher biofilter contact times were beneficial.

Identifying fouling events in a membrane-based drinking water treatment process using principal component analysis of fluorescence excitation-emission matrices.

The identification of key foulants and the provision of early warning of high fouling events for drinking water treatment membrane processes is crucial for the development of effective countermeasures to membrane fouling, such as pretreatment. Principal foulants include organic, colloidal and particulate matter present in the membrane feed water. In this research, principal component analysis (PCA) of fluorescence excitation-emission matrices (EEMs) was identified as a viable tool for monitoring the performance of pre-treatment stages (in this case biological filtration), as well as ultrafiltration (UF) and nanofiltration (NF) membrane systems. In addition, fluorescence EEM-based principal component (PC) score plots, generated using the fluorescence EEMs obtained after just 1hour of UF or NF operation, could be related to high fouling events likely caused by elevated levels of particulate/colloid-like material in the biofilter effluents. The fluorescence EEM-based PCA approach presented here is sensitive enough to be used at low organic carbon levels and has potential as an early detection method to identify high fouling events, allowing appropriate operational countermeasures to be taken.

Assessing the performance of biological filtration as pretreatment to low pressure membranes for drinking water.

Although the use of ultrafiltration membranes in drinking water treatment is increasing, fouling remains a major challenge. The objective of this study was to evaluate rapid biological filtration (without coagulant addition) as a pretreatmentto reduce fouling. Surface water was first passed through a pilot scale roughing filter followed by two parallel anthracite/sand biofilters having different contact times, before being fed to the ultrafiltration membrane. As a chemical-free pretreatment, this novel application of biofiltration removes biopolymers (polysaccharides and proteins) that are the most important component of organic matter for fouling, as well as removing particulate matter. Biopolymer removal was influenced by contact time and temperature. The biofilter with the longer contact time led to greater reductions in both hydraulically reversible and irreversible fouling. The extent of hydraulically reversible fouling was related to the membrane influent biopolymer concentration, but the level of hydraulically irreversible fouling was not, indicating that the composition of the biopolymer fraction may have been important. Biofiltration as a simple and robust pretreatment may be particularly suited for small drinking water systems.