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Ion exchange (IX) process is increasingly used as a cost-effective treatment for the removal of natural organic matter (NOM) from drinking water. However, fundamental studies under the influence of variable NOM characteristics and inorganic anions have often been overlooked. This is important given NOM characteristics (such as charge density and molecular weight) and inorganic anions concentrations are geographically and seasonally variable. We examined the performance of a strongly basic IX resin for the simultaneous removal of NOM, inorganic ions and micropollutants (Per- and polyfluoroalkyl substances (PFAS) and algal toxins), from different surface and recycled waters. The results indicated >70% removal of NOM for ∼20,000 Bed Volumes (BV) with an uptake of NOM fractions following the order of their respective charge densities. IX pore blockage and consequent site reduction was observed in the presence of higher molecular weight NOM fractions (breakthrough ∼7,000 BV). Moreover, NOM and inorganic ions breakthrough corresponded to ∼85–90% site occupancy (in meq) in the absence of pore blocking compounds. IX also provided simultaneous removal of inorganic ions (>90%) and charged micropollutants. Complete removals of Microcystin-LR and multiple long- and short-chained PFAS were achieved at environmentally relevant concentrations with dosages of 1,000 mg/L (or 4.5 mL/L) or higher.

The natural organic matter (NOM) removal efficiency and regeneration behavior of ion-exchange filters with promoted biological activity (BIEX) was compared to operation where biological activity was suppressed (i.e. abiotic conditions). The impact of BIEX pre-treatment on fouling in subsequent ultrafiltration was also investigated. Biological operation enhanced NOM removal by approximately 50% due to an additional degradation of smaller humic substances, building blocks and low molecular weight acids. Promotion of biological activity significantly increased the time to breakthrough of the filters and, therefore, is expected to lower the regeneration frequency as well as the amount of regenerate of which to dispose. Pre-treatment using BIEX filters resulted in a significant decrease in total and irreversible fouling during subsequent ultrafiltration. The decrease was attributed to the effective removal of medium and low molecular weight NOM fractions. The results indicate that BIEX filtration is a robust, affordable and easy-to-operate pre-treatment approach to minimize fouling in ultrafiltration systems and enhance the quality of the produced permeate.

Bench-scale experiments were conducted to evaluate disinfection by-product (DBP) precursor removal by coagulation with alum and ferric sulfate (FS), intermediate ozonation (IO 3 ), powdered-activated carbon (PAC), ion exchange resin (IX), and spiral-wound nanofiltration (NF). The effect of source water quality on process performance was also assessed on six source waters. Overall, NF offered the best performance in terms of dissolved organic carbon (DOC) removals along with lower DBP concentrations in every tested condition except for DOC-rich waters (13–15 mg/L). Conventional treatment coupled with recirculated PAC adsorption (Actiflo ® Carb) was the process configuration providing the most consistently low DOC (less than 2 mg/L), facilitating DBP regulation compliance. IX/alum and alum/IO 3 reduced DBP concentration to a lesser extent, but proved to be more efficient than conventional treatment with alum alone. In terms of effluent DBP concentration, FS outperformed alum at higher coagulant dosages, whereas alum offered a superior performance at lower dosages. Finally, this investigation shows the relevance of conducting treatability assays to identify the most suitable treatment alternative for DBP control.

Polyacrylamide polymers (PAM) are one of the most common water treatment chemicals used in clarification processes. Concerns have been raised with regards to the aquatic and human toxicity of acrylamide monomer. Greener polymers, produced using potato starch, were investigated at lab-scale as a potential non-toxic alternative to the use of PAM within a ballasted flocculation process (Actiflo®). Even under extreme temperature (1 °C), starch and PAM showed comparable turbidity removal performances, although higher starch dosages (four to five times) were needed to achieve such results. Compared to PAM, activated starch polymers also benefited from the use of lower mixing energy and smaller microsand. A slight biodegradable dissolved organic carbon (BDOC) release (≈0.15 mg C/L) was also measured while using starch polymer, but this did not impact trihalomethane and haloacetic acid formation. These results indicate that activated starch polymers represent a promising alternative to the use of PAM polymers in a ballasted flocculation process.

Hybrid processes coupling the use of powder activated carbon (PAC) with membrane filtration for drinking water production are emerging as promising alternatives to conventional technologies due to their enhanced control of dissolved contaminants. The quantification of biomass colonizing PAC is crucial for modeling, designing control strategies and improving the overall performance of these processes. The aim of this study was to examine the applicability of several common methods developed for colonized granular activated carbon (GAC) to PAC. Six analytical methods (based on the measurement of proteins, polysaccharides, heterotrophic plate counts, potential glucose respiration, bacterial ATP and a potential acetate uptake rate, which is proposed herein) were compared. The results showed that the rates of glucose respiration and of acetate consumption could be used interchangeably. Proteins were also an interesting alternative for on-site measurements. It was concluded that biological PAC-based processes sustained a level of heterotrophic activity similar to or greater than that observed in GAC biofilters.

Granular filtration remains a key barrier for Cryptosporidium removal in water treatment plants without UV irradiation. To assess the impact of clay particles in source water on Cryptosporidium removal efficiency by granular filtration, this study investigated the co-transport of Cryptosporidium-sized microspheres and kaolinite particles in sand columns. To investigate the influence of clay load on microsphere transport and deposition, varying influent kaolinite concentrations (0–106particles/mL) and microsphere concentrations (102–106microspheres/mL) were tested. The spatial distribution of retained microspheres was examined subsequent to experiments via filter coring. Results demonstrate that increasing the influent microsphere concentration impaired filter performance due to a blocking mechanism whereby previously retained particles repel incoming particles. In contrast, when the particulate load was dominated by kaolinite (for an equivalent particulate load), filter performance improved as a result of filter ripening whereby previously deposited particles act as additional collectors. Thus, microsphere-kaolinite interactions proved to be favorable although both particles possessed negative zeta potentials in the tested conditions. This study demonstrates that granular filter performance is vulnerable to peak events of microbial contamination. Conversely, Cryptosporidium-sized microsphere removal by granular filtration is enhanced in the presence of kaolinite in source water.

A high concentration powdered activated carbon (PAC) membrane bioreactor (MBR) was fed by clarified-ozonated surface water. As a control, a MBR without PAC was run in parallel. Water quality was also compared with a full-scale biological activated carbon (BAC) filter. Biological PAC inside the MBR caused a higher fouling rate as compared to the MBR without PAC, although it was still possible to maintain operation for about 3 months at 25 L m � 2 h � 1 before a chemical cleaning was needed. The fouling rate inside the MBR with PAC increased as the PAC age increased from 0 to 60 d. Full nitrification was achieved in the PAC-MBR down to 7 W C. Preozonation had no significant impact on dissolved organic carbon removal. Although the PAC-MBR globally provided superior removal of natural organic matter, haloacetic acid precursors and UV absorption at 254 nm (UVA254), its removal of trihalomethane (THM) precursors was inferior compared to the BAC filter. This effect was shown to be caused by the accumulation of suspended solids inside the bioreactor.

In this study, an environmental sampling campaign was conducted to detect internalized E. coli and C. jejuni bacteria in zooplankton and amoebae samples collected at various stages of three water treatment plants in Amsterdam, the Netherlands. Eight sampling locations were selected and sampling was performed twice, at a two-week interval, at each location. Chlorination was used to inactivate free (external) bacteria in the concentrated zooplankton samples and sonication was used to disrupt zooplankton organisms in order to release and recover internalized bacteria. Zooplankton enumeration was performed by microscopy. No internalized E. coli or C. jejuni bacteria were recovered from all of the samples analyzed. The occurrence of internalized E. coli or C. jejuni bacteria in drinking water was estimated to be lower than one internalized bacteria in 10 5 zooplankton organisms, as derived from the detection limit of the sampling campaign. By using the QMRA approach and the Beta-Poisson model, a risk of infection of less than 9.2E-6 and 5.9E-5 was estimated for internalized E. coli and C. jejuni in drinking water, respectively. This study remains preliminary due to the limited number of samples taken at each location.

This study investigated the use of biological powdered activated carbon (PAC) for the removal of natural organic matter (NOM) and ammonia from drinking water. The impact of solids retention time (SRT), hydraulic retention time (HRT), PAC diameter and PAC concentration on the process efficiency was evaluated. Five bioreactors were filled with a slurry using two PAC concentrations (5 or 25 g l−1), two PAC mean diameters (25 or 200 μm) and two SRTs (30 or 100–160 days). The bioreactors were operated during 161 days using post-ozonated water as influent. It was determined that the PAC concentration in the bioreactors was a key parameter for the improvement of biological removal. The higher PAC concentration (25 g l−1) was more efficient for the removal of ammonia, dissolved organic carbon (DOC) and biodegradable dissolved organic carbon (BDOC). Full nitrification was observed after 90 days in bioreactors with 25 g l− of PAC. The PAC diameter (25 vs. 200 μm) did not significantly influence BDOC, DOC and N-NH4 removals under stable conditions, although nitrification was initiated faster using a 25-μm diameter PAC. Increasing HRT from 15 to 30 minutes improved NOM and ammonia removals. Reducing SRT from 100–161 to 30 days improved DOC removals but reduced BDOC and ammonia removals. The overall performances observed during this study demonstrate the efficiency of biological PAC. Its combination with ultrafiltration in a hybrid membrane process appears promising but the feasibility from an operational standpoint still has to be demonstrated

Cyanobacteria are a growing concern in the province of Quebec due to recent highly publicised bloom episodes. The health risk associated with the consumption of drinking water coming from contaminated sources was unknown. A study was undertaken to evaluate treatment plants' capacity to treat cyanotoxins below the maximum recommended concentrations of 1.5 μg/L microcystin-LR (MC-LR) and the provisional concentration of 3.7 μg/L anatoxin-a, respectively. The results showed that close to 80% of the water treatment plants are presently able to treat the maximum historical concentration measured in Quebec (5.35 μg/L MC-LR equ.). An increase, due to climate change or other factors, would not represent a serious threat because chlorine, the most popular disinfectant, is effective in treating MC-LR under standard disinfection conditions. The highest concentration of anatoxin-a (2.3 μg/L) measured in natural water thus far in source water is below the current guideline for treated waters. However, higher concentrations of anatoxin-a would represent a significant challenge for the water industry as chlorine is not an efficient treatment option. The use of ozone, potassium permanganate or powder activated carbon would have to be considered.

A Monte Carlo model, based on the Quantitative Microbial Risk Analysis approach (QMRA), has been developed to assess the relative risks of infection associated with the presence of Cryptosporidium and Giardia in drinking water. The impact of various approaches for modelling the initial parameters of the model on the final risk assessments is evaluated. The Monte Carlo simulations that we performed showed that the occurrence of parasites in raw water was best described by a mixed distribution: log-Normal for concentrations > detection limit (DL), and a uniform distribution for concentrations < DL. The selection of process performance distributions for modelling the performance of treatment (filtration and ozonation) influences the estimated risks significantly. The mean annual risks for conventional treatment are: 1.97E−03 (removal credit adjusted by log parasite = log spores), 1.58E−05 (log parasite = 1.7 × log spores) or 9.33E−03 (regulatory credits based on the turbidity measurement in filtered water). Using full scale validated SCADA data, the simplified calculation of CT performed at the plant was shown to largely underestimate the risk relative to a more detailed CT calculation, which takes into consideration the downtime and system failure events identified at the plant (1.46E−03 vs. 3.93E−02 for the mean risk).

The measurement of spores of aerobic spore-forming bacteria (ASFB) is becoming a widely accepted method for validating the effectiveness of treatments applied in drinking water treatment plants. These bacteria have been proposed as indicators of soil intrusion in distribution systems. There are, nevertheless, some limitations to the measurement of ASFB spores by membrane filtration with respect to the rate of recovery of spores present in distributed water. This is mainly due to the low concentrations of these spores. Two factors may decrease spore recovery: the presence of a cake on the filter and the aggregation of spores. For distributed water, our data suggest limiting the volume of water filtered (V in ml) as a function of its turbidity, according to the relation: V = 500/turbidity. The addition of a surfactant, Tween 80 ® , can increase the recovery of spores very significantly (1000 X). The experimental results show that a triple manual inversion will ensure a significantly higher rate of recovery.

The goal of this study was to review and confirm experimentally chlorite effectiveness as a drinking water disinfectant. The steps in the experiment were a series of laboratory assays performed on three types of microorganisms, Bacillus subtilis spores, MS2 coliphages, as well as heterotrophic (HPC) bacteria, to verify chlorite action in water. The tests showed that chlorites have no disinfectant effect on B. subtilis spores (CT > 106 mg min/L), that they slightly decrease HPC bacterial regrowth and, finally, that a dose of 1 and 10 mg ClO2-/L can inactivate almost 2 log and 4.5 log of MS2 phages, respectively, after 9 days of contact time. It would therefore appear that chlorites are not a good primary disinfectant, but do exhibit a bacteriostatic effect.

The objective of this study was to assess the effect of natural organic matter (NOM) on disinfection efficacy using two types of disinfectants: Cl2 and ClO2. Bacillus subtilis spores were used as a surrogate for monitoring disinfection efficacy. The effect of natural organic matter was tested using two series of experimental assays. Initially, assays were conducted in ultra-pure buffered waters supplemented with various NOM extracts. Second, confirmation assays were performed on three surface waters. In both natural and synthetic waters, the presence of NOM improved disinfection efficacy where chlorine dioxide was used. This phenomenon was significant, as Ct values required for 2 log inactivation of B. subtilis spores were reduced by a factor of 2.3 to 7.1 depending on the NOM source and concentration. However, such a phenomenon was not observed while disinfecting with free chlorine. It is proposed that (i) free radicals are generated following the reaction of chlorine dioxide and NOM and (ii) those radicals can enhance chlorine dioxide disinfection efficacy.

The effectiveness of routine spot flushing in two dead-end locations of the Montreal distribution system (DS) was assessed. The two 203 mm (8 in) pipes were roughly 500 m long. Two successive annual spot flushings, 25 minutes each, were performed and the impact on water quality was assessed during the first 24 hours, 2 weeks later, and the following year. The flushing water was also analysed in order to evaluate the quantity and nature of loose deposits that were drained. High numbers of atypical coliforms were removed during the first annual flushing procedure. No atypical coliforms were recovered from the flushing water during the second annual procedure, suggesting that the first procedure was effective in eliminating these organisms. During the first 24 h after flushing, chlorine decreased rapidly at both dead-end locations while heterotrophic plate counts (HPC) counts increased during the same period. Therefore, only minor improvements in water quality (mainly turbidity and total iron) were measured during the two weeks after the flushing procedure. With respect to spot flushing dead-end locations on a routine basis, the principal benefits observed in this specific DS were related to short-term improvements in the aesthetic characteristics of the distributed water.

The assessment of water treatment facilities for their efficiency using alternate indicators is of paramount importance. Current methods for assessing efficiency are limited by the specific characteristics of the microorganisms, such as their different sensitivities to disinfectants. A pilot study was carried out to compare different treatment scenarios for the future upgrade of the Sergio Cuevas Water Treatment plant (the largest in the Caribbean) in San Juan, Puerto Rico. The treatment units under investigation included a coagulation-flocculation-sedimentation unit, dual-media filters, micro-filtration units, intermediate ozone injection and contact columns as well as a biological filtration unit. The plant was challenged at different stages of treatment with Bacillus subtilis spores and MS2 coliphages in an attempt to test them as possible alternate indicators of treatment plant performance. These organisms were chosen because of their resistance to disinfection and desiccation, their low analysis costs and ease of detection. The removal of spores and coliphages by each treatment unit tested was calculated by seeding a known concentration (5-7 log10) of spores and coliphages and following the removal or disinfection rates. The seeded indicators were detected using traditional culture techniques. Ballasted clarification was shown to be highly efficient at removing 99.1% (approximately 3 log10) of the spores and 85.1% (approximately 0.86 log10) of MS2. Ozone treatment inactivated 80.37% (approximately 1.4 log10) spores and 99.95% (approximately 3.07 log10) coliphages. The coliphage inactivation rate obtained confirmed data obtained by previous studies indicating that MS2 was less resistant to ozonation than B subtilis spores. The membrane technology had the best efficiency in terms of physical removal of spores achieving over 99.9% (> 3 log10) removal. Coliphage removal mechanisms remain to be determined and will be a future focus of the study. Preliminary results indicate that aerobic spores and coliphages may be useful as indicators to determine the efficiency of different drinking water treatment technologies.

The concentrations of suspended particles were measured in the drinking water of two distribution systems, and the nature of these particles documented. The concentrations of particulate matter were invariably found to be small (maximum 350 μg/L). They are globally in the very low range in comparison with dissolved matter concentrations, which are measured in several hundreds of mg/L. Except during special water quality events, such as turnover of the raw water resource, results show that organic matter represents the most important fraction of suspended solids (from 40 to 76%) in treated and distributed water. Examination of the nature of the particles made it possible to develop several hypotheses about the type of particles penetrating Montreal's distribution system during the turnover period (algae skeleton, clays). These particles were found to have been transported throughout the distribution systems quite easily, and this could result in the accumulation of deposits if their surface charge were ever even slightly destabilised, or if the particles were to penetrate the laminar flow areas that are fairly typical of remote locations in distribution systems.

To support a water treatment plant in meeting trihalomethanes (THM) legislation, different THM control strategies using existing treatment processes were investigated. The effectiveness of optimised coagulation and of powdered activated carbon (PAC) (0–25 mg/L) as a mean of supplementing natural organic matter (NOM) removal was assessed. Simultaneous full-scale and bench-scale trials were performed to document THM reductions. At the plant, source and treated water total organic carbon (TOC) was monitored online. At full scale, optimised acidified alum coagulation (3.2 mg/L Al) achieved the maximum NOM removal and the lowest THMFP concentration. Although PAC (11 mg/L) showed a small reduction in TOC (7%) and taste- and odour-causing compounds, results indicated no significant THM reductions. Coagulation and PAC adsorption trials showed a good agreement between bench-scale and plant results.