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The aim of this study was to investigate the negative impact of a newly-formed manganese (Mn)-layer on calcite dissolution in the long-term operation of a calcite contactor. Simultaneous removal of Mn and remineralization of soft water in an up-flow calcite contactor was conducted and led to a progressive loading of Mn into the calcite matrix. The calcite contactor demonstrated high Mn removal; however, the hardness release decreased from 32 to 20 mg CaCO 3 L −1 after 600 h of operation on a high Mn concentration (5 mg L −1 ) feed. For an elevated Mn concentration (i.e. 5 mg Mn L −1 ) in the feed water, the coated layer was mainly composed of Mn which inhibits the mass transfer from the calcite core to the liquid phase. The superficial layer was identified as 5.2% Mn oxides (MnOx) by X-ray photoelectron spectroscopy (XPS). Therefore, it is postulated that Mn removal starts with an ion exchange sorption reaction between soluble Mn 2+ from aqueous phase and Ca 2+ from the CaCO 3 matrix which is followed by a slow recrystallization of MnCO 3 into MnO 2 . On the other hand, when the Mn content in the feed water was lower (i.e. 0.5 mg Mn L −1 ), a considerably lower amount of MnOx was detected on the coated media. For all the examined conditions, the formation of this coating improved Mn removal due to the autocatalytic nature of the adsorption/oxidation of dissolved manganese by MnOx. A mechanistic model based on calcite dissolution and the progressive formation of a MnO 2 layer was implemented in PHREEQC software to predict the reduction in hardness release expected in long-term operation. The model was calibrated with experimental data and resulted in realistic breakthrough curves. In order to accurately predict the pH of the effluent stream, a slow-rate recrystallization of MnCO 3 into MnO 2 was implemented (compared to the fast precipitation of MnO 2 or the absence of MnO 2 formation).

A novel pyrolusite fluidized bed (PFB) contactor, which we recently developed for dissolved manganese (Mn(II)) removal through surface adsorption and subsequent oxidation by free chlorine, was modeled in this study. The hydrodynamic behavior of the filter media and water in the fluidized bed was described by the axial dispersion model. The model incorporated the effects of axial mixing in the liquid and solid phases, mass transfer resistance in a laminar fluid boundary layer surrounding a media grain, and a second order oxidation rate expression. The experimental data from lab-scale and field pilot-scale contactors was adopted for the model development and its validation. For the former, the data was employed to estimate the oxidation rate constant, the mass transfer coefficient, and the axial solid phase dispersion coefficient for the model. The model simulations matched the experimental data with less than 20% error across a wide range of Mn(II) and free chlorine concentrations and hydraulic loading rates that might be encountered in a drinking water treatment plant. The sensitivity analysis showed that the time to breakthrough is most sensitive to the adsorption isotherm constants and the oxidation rate constant. These observations indicate that the alluded parameters mainly control the performance of the PFB contactor as well as the process stability. Finally, a sample application of the model to acquire operational inputs was illustrated by analyzing the effect of free chlorine concentration on Mn(II) removal performance and breakthrough time within a PFB contactor.

We present the first study investigating optimized regeneration strategies for anionic ion exchange (IX) resins during the removal of persistent per- and poly-fluoroalkyl substances (PFAS, including GenX) from surface and treated wastewater effluents. IX regeneration studies are of critical importance from environmental perspectives. Specifically, the knowledge is essential for water utilities who presently operate IX (for PFAS removal) in a single use-and-dispose mode. In this study, legacy PFAS such as PFOA/PFOS were tested along with other harmful short-chained PFAS (PFBA/PFBS) and other toxic perfluorinated substitutes (GenX). Studies were performed on synthetic water (spiked with Suwannee River Natural Organic Matter (SRNOM), Fulvic Acid (SRFA) and Humic Acid (SRHA)), surface water, and wastewater effluents, and the regeneration was performed in batch stirred reactors. The resin service life with and without regeneration was investigated in the presence of background organic matter. In ultra-pure waters, all PFAS (C0 ∼10 μg/L, concentrations similar to that of natural waters) were effectively removed for >100,000 Bed Volume (BV) of operation. This was reduced to ∼23,500 BV in the presence of SRNOM (C0 = 5 mg C/L), 20,500 BV in SRFA and 8500 BV in SRHA, after which the saturated resins required regeneration. More importantly, all resin breakthrough (PFAS> 70 ng/L) corresponded to > 90% resin site saturation (in meqs), an essential information for optimizing IX loading. The competitive dissolved organic matter (DOM) fractions were estimated to be approximately 5–9% of the initial DOC, as estimated by the IAST-EBC model. Finally, it was identified that IX regeneration efficiency improved with increasing brine contact time but effectiveness plateaued for brine concentrations above 10% (W/V). Nonetheless, a regeneration with 10% NaCl solution with a contact time of 2 h was found to be optimal for IX operations in synthetic and natural waters. Therefore, this study provides key knowledge essential for the scientific community and the water industry on optimizing IX operational parameters for DOM and PFAS removal and would be highly valuable for systems which presently operate IX in a use-and-dispose mode.

Microcystins are the most commonly occurring cyanotoxins, and have been extensively studied across the globe. In the present study, a strongly basic anion exchange resin was employed to investigate the removal of Microcystin-LR (MCLR), one of the most toxic microcystin variants. Factors influencing the uptake behavior included the MCLR and resin concentrations, resin dosage, and natural organic matter (NOM) characteristics, specifically, the charge density and molecular weight distribution of source water NOM. Equivalent background concentration (EBC) was employed to evaluate the competitive uptake between NOM and MCLR. The experimental data were compared with different mathematical and physical models and pore diffusion was determined as the rate-limiting step. The resin dose/solute concentration ratio played a key role in the MCLR uptake process and MCLR removal was attributed primarily to electrostatic attractions. Charge density and molecular weight distribution of the background NOM fractions played a major role in MCLR removal at lower resin dosages (200 mg/L ∼ 1 mL/L and below), where a competitive uptake was observed due to the limited exchange sites. Further, evidences of pore blockage and site reduction were also observed in the presence of humics and larger molecular weight organic fractions, where a four-fold reduction in the MCLR uptake was observed. Comparable results were obtained for laboratory studies on synthetic laboratory water and surface water under similar conditions. Given their excellent performance and low cost, anion exchange resins are expected to present promising potentials for applications involving the removal of removal of algal toxins and NOM from surface waters.

The present study investigated the impact of different loading approaches and microbial activity on the Natural Organic Matter (NOM) removal efficiency and capacity of ion exchange resins. Gaining further knowledge on the impact of loading approaches is of relevance because laboratory-scale multiple loading tests (MLTs) have been introduced as a simpler and faster alternative to column tests for predicting the performance of IEX, but only anecdotal evidence exists to support their ability to forecast contaminant removal and runtime until breakthrough of IEX systems. The overall trends observed for the removal and the time to breakthrough of organic material estimated using MLTs differed from those estimated using column tests. The results nonetheless suggest that MLTs could best be used as an effective tool to screen different ion exchange resins in terms of their ability to remove various contaminants of interest from different raw waters. The microbial activity was also observed to impact the removal and time to breakthrough. In the absence of regeneration, a microbial community rapidly established itself in ion exchange columns and contributed to the removal of organic material. Biological ion exchange (BIEX) removed more organic material and enabled operation beyond the point when the resin capacity would have otherwise been exhausted using conventional (i.e. in the absence of a microbial community) ion exchange. Furthermore, significantly greater removal of organic matter could be achieved with BIEX than biological activated carbon (BAC) (i.e. 56 ± 7% vs. 15 ± 5%, respectively) when operated at similar loading rates. The results suggest that for some raw waters, BIEX could replace BAC as the technology of choice for the removal of organic material.

Ion exchange (IX) using synthetic resins is a cost-efficient technology to cope with a wide range of contaminants in water treatment. However, implementing IX processes is constrained by the regeneration of IX resins that generates a highly concentrated brine (i.e., IX brine), the disposal of which is costly and detrimental to ecosystems. In an effort to make the application of IX resins more sustainable in water treatment, substantial research has been conducted on the optimization of IX resins operation and the management of IX brine. The present review critically evaluates the literature surrounding IX operational strategies and IX brine management which can be used to limit the negative impacts arising from IX brine. To this end, we first analyzed the physicochemical characteristics of brines from the regeneration of IX resins. Then, we critically evaluated IX operational strategies that facilitate brine management, including resin selection, contactor selection, operational modes, and regeneration strategies. Furthermore, we analyzed IX brine management strategies, including brine reuse and brine disposal (without or with treatment). Finally, a novel workflow for the IX water treatment plant design that integrates IX operational strategies and IX brine management is proposed, thereby highlighting the areas that make IX technology more sustainable for water treatment.

Combining powdered activated carbon (PAC) with magnetic iron oxides has been proposed in the past to produce adsorbents for natural organic matter (NOM) removal that can be easily separated using a magnetic field. However, the trade-off between the iron oxides' benefits and the reduced carbon content, porosity, and surface area has not yet been investigated systematically. We produced 3 magnetic powdered activated carbons (MPAC) with mass fractions of 10%, 38% and 54% maghemite nanoparticles and compared them to bare PAC and pure nanoparticles with respect to NOM adsorption kinetics and isotherms. While adsorption kinetics were not influenced by the presence of the iron oxide nanoparticles (IONP), as shown by calculated diffusion coefficients from the homogeneous surface diffusion model, nanoparticles reduced the adsorption capacity of NOM due to their lower adsorption capacity. Although the nanoparticles added mesoporosity to the composite materials they blocked intrinsic PAC mesopores at mass fractions >38% as measured by N2-adsorption isotherms. Below this mass fraction, the adsorption capacity was mainly dependent on the carbon content in MPAC and mesopore blocking was negligible. If NOM adsorption with MPAC is desired, a highly mesoporous PAC and a low IONP mass fraction should be chosen during MPAC synthesis.

Biological ion exchange (BIEX) offers removal of dissolved organic carbon (DOC) with greatly reduced regeneration frequency. In the present work, a strong base anionic exchange resin was operated without regeneration and using inlet water with either Low (12 mg L−1) or High (60 mg L−1) sulphate and DOC of 2.75 or 5.0 mg L−1. Filters operated continuously for 226 days (16,500 bed volumes) and achieved DOC removal varying from 32% to 50%. Initially, sulphate and DOC were retained by the resin with chloride being released. During this period, DOC removal occurred due to traditional mechanisms, referred to as primary ion exchange. Following this initial period, DOC removal continued even though the conventionally defined resin capacity was exhausted (based on chloride loading). During the later period, no chloride release was observed, but instead sulphate was released. Although suggested by others, the present study is the first to confirm the direct exchange in charge equivalence of anions removed (DOC and nitrate) to released (sulphate) during the secondary ion exchange mechanism. Further, increasing inlet sulphate from 12 to 60 mg L−1 resulted in a 19% decrease in DOC removal. Finally, percent DOC removal was affected only by an increase of inlet DOC but not changes to the counter ion or after DOC loading on the resin increased to 1/3 of total capacity. This work promotes BIEX as a viable alternative to biological activated carbon and a leading solution for low-maintenance DOC removal.

Combining the high adsorption capacity of powdered activated carbon (PAC) with magnetic properties of iron oxide nanoparticles (NPs) leads to a promising composite material, magnetic PAC or MPAC, which can be separated from water using magnetic separators. We propose MPAC as an alternative adsorbent in the biological hybrid membrane process and demonstrate that PAC covered with magnetic NPs is suitable as growth support for heterotrophic and nitrifying bacteria. MPAC with mass fractions of 0; 23; 38 and 54% maghemite was colonized in small bioreactors for over 90 days. Although the bacterial community composition (16s rRNA analysis) was different on MPAC compared to PAC, NPs neither inhibited dissolved organic carbon and ammonia biological removals nor contributed to significant adsorption of these compounds. The same amount of active heterotrophic biomass (48 μg C/cm(3)) developed on MPAC with a mass fraction of 54% NPs as on the non-magnetic PAC control. While X-ray diffraction confirmed that size and type of iron oxides did not change over the study period, a loss in magnetization between 10% and 34% was recorded.

Biological ion exchange (BIEX) has proved to remove natural organic matter (NOM) better than biological activated carbon (BAC). This raises the question if BIEX can be integrated into a full-scale drinking water treatment plant to remove NOM and ammonia. In this study, a pilot plant consisting of one BIEX filter, three GAC filters and one BAC filter was set up as second-stage filtration at the Sainte-Rose drinking water treatment plant (Laval, Canada). The pilot plant was operated for a period of nine months without regeneration of the ion exchange resins. The influent water showed low DOC (2.5 mg/L) and high sulfate concentrations (28.2 mg/L). Except of a short peak of DOC released at about 1 000 BV, the BIEX filter achieved a nearly constant removal of 29-36% over the whole study period. The DOC removals of GAC were similar to BIEX at8000 BV but then stabilized at 13-24% after 8 000 BV. Most DOC removal in the BIEX filter was achieved at the top 30 cm layer (81%) compared to 62-66% removal in the GAC/BAC filters in the same layer. After the rapid exhaustion of the primary ion exchange capacity (1 000 BV), sulfate displaced the fraction of NOM with lower affinity than sulfate, corresponding to the initial DOC release in the BIEX filter. The fraction of NOM with higher affinity than sulfate can still replace sulfate, which explains the good long-term performance of the BIEX filter. BIEX released ammonia with an average of 15% in warm water condition, probably related to the small diameter of the column which limited backwash effectiveness.

Groundwater (GW) is one of the most abundant water resources and around 1.5 billion people rely on GW as their main water supply. Manganese (Mn) and iron (Fe) are very common GW contaminants. Even though their presence is considered mainly as an organoleptic and operational nuisance, water with elevated Mn content may also lead to adverse health impacts. Amongst the most common treatment processes currently used to treat domestic GW supplies: catalytic filtration may lead to Mn leaching if improperly maintained; while ion exchange consumes a considerable amount of salt and produces a brine waste which pollutes the environment. Thus, it is proposed to design a simple, yet robust treatment system which can be implemented in small/remote communities or even domestic applications. To this end, the main objective of this investigation was to assess the potential application of novel outside-in sulfonated polyethersulfone thin-film composite hollow fiber nanofiltration (HFNF) membranes to remove dissolved Mn, Fe and natural organic matter (NOM) from domestic GW supplies. Of particular interest was the impact of GW matrix on performance of the HFNF membranes. Our experimental findings demonstrated that, in absence of hardness and the cumulative throughput of 1.9 L/m2, above 90 % of Mn, Fe and NOM were retained by the examined HFNF membranes (MWCO ∼ 200 Da) regardless of their initial concentrations in the feed solution (250–1000 μ g/L). In contrast, increasing the hardness level reduced the removal of Mn and Fe ions. XPS analysis revealed that the surface properties of the HFNF membranes were altered when the membranes were exposed to calcium and magnesium salts. These observations were attributed to the propensity for Ca and Mg ions to bind to the sulfonic groups present on the surface of the HFNF membranes which, subsequently, weakens rejection by charge exclusion. On the other hand, in the absence of GW hardness, charge exclusion was mainly responsible for rejection of dissolved Mn and Fe. It was also found that GW hardness had no marked impact on the NOM rejection as the later was mostly removed by size exclusion.

Anionic exchange is an effective treatment option for the removal of natural organic matter from surface waters. However, the management of the spent brine regenerant often limits the adoption of this process. The current study reports one year of operation of ion exchange resins under biological mode (BIEX, i.e. without regeneration to promote biofilm growth on the media) compared to the performance of (i) ion exchange with weekly regeneration (IEX), (ii) granular activated carbon under biological mode (BAC) and (ii) granular activated carbon under adsorption mode (GAC). Four parallel pilot filters (GAC, BAC, IEX and BIEX) were fed with a colored and turbid river water without pretreatment. Although IEX provided the best performance (80% DOC removal) throughout the study, BIEX achieved a similar performance to IEX prior to DOC breakthrough (92 days) and subsequently achieved a mean DOC removal of 62% in warm water conditions. The GAC filter was rapidly exhausted (2 weeks) while the BAC filter only provided a 5% DOC reduction. Full nitrification was observed on both the BIEX and BAC filters under warm water conditions (>15 °C). After one year of operation, BIEX was successfully regenerated with brine. According to a mass balance, 69% of DOC removal in BIEX was due to ion exchange while we assume the remainder was biodegraded. Operation of ion exchange in biological mode is a promising option to reduce spent brine production while still achieving high DOC removal.

Zooplankton has been shown to transport internalized pathogens throughout engineered drinking water systems. In this study, experimental measurements from GAC and SSF filtration tests using high influent concentrations of Cryptosporidium (1.3 × 10(6) and 3.3 × 10(4) oocysts L(-1)) and Giardia (4.8 × 10(4) cysts L(-1)) are presented and compared. A predation and transport conceptual model was developed to extrapolate these results to environmental conditions of typical (oo)cyst concentrations in surface water in order to predict concentrations of internalized (oo)cysts in filtered water. Pilot test results were used to estimate transport and survival ratios of internalized (oo)cysts following predation by rotifers in the filter beds. Preliminary indications of lower transport and survival ratios in SSF were found as compared with GAC filters. A probability of infection due to internalized (oo)cysts in filtered water was calculated under likeliest environmental conditions and under a worst-case scenario. Estimated risks under the likeliest environmental scenario were found to fall below the tolerable risk target of 10(-4) infections per person per year. A discussion is presented on the health significance of persistent pathogens that are internalized by zooplankton during granular filtration processes and released into treated water.

The purpose of this paper is to introduce a pyrolucite fluidized-bed reactor (PFBR) as a potential drinking water process to treat groundwater containing high levels of dissolved manganese (Mn(II)) (0.5-3 mg/L) and reduce its concentration to0.02 mg/L in treated water. A pilot-scale study was conducted under dynamic conditions using synthetic groundwater (SGW), to elucidate the effect of operational conditions and groundwater composition on manganese (Mn) removal achieved by the PFBR. Results demonstrated almost complete Mn removal (close to 100%) in less than 1 min under all tested operational conditions (influent Mn concentration of 0.5-3 mg/L, calcium (Ca(2+)) hardness of 0-200 mg CaCO3/L, pH of 6.2-7.8, temperature of 923 °C and high hydraulic loading rate (HLR) of 24-63 m/h (i.e., bed expansion of 0-30%)). Improved Mn removal profile was achieved at higher water temperature. Also, the results showed that adsorption of Mn(II) onto pyrolucite and subsequent slower surface oxidation of sorbed Mn(II) was the only mechanism responsible for Mn removal while direct oxidation of Mn(II) by free chlorine did not occur even at high concentrations of Mn(II) and free chlorine and elevated temperatures. Higher average mass transfer coefficient and consequently adsorption rate was achieved at elevated HLR. Increasing effluent free chlorine residuals from 1.0 to 2.0-2.6 mg Cl2/L allowed increasing the operation time needed for media regeneration from 6 days to12 days. Turbidity was maintained around 0.2 NTU during the entire test periods indicating good capture of MnOx colloids within the PFBR.

Pre-ozonation of cyanobacterial (CB) cells in raw water and inter-ozonation of settled water can cause CB cell damage. However, there is limited information about the level of lysis or changes in cell properties after ozonation, release of intracellular compounds and their contribution to the formation of disinfection by-products (DBPs). This study aims to: (1) assess the extent of the pre-ozonation effects on CB cell properties; (2) determine the CT (ozone concentration × detention time) values required for complete loss of cell viability; and (3) study the DBPs formation associated with the pre-ozonation of cyanobacterial cells in laboratorial suspensions. To these ends, both Microcystis aeruginosa and Anabaena flos-aquae suspensions were prepared at concentrations of 250,000 cells mL(-1) and 1,500,000 cells mL(-1) and were subjected to ozone dosages of 0.5, 2.0 and 4.0 mg L(-1) at pH 6 and pH 8. A quick and complete loss of viability was achieved for both CB species after exposure (CT) to ozone of

The removal of cyanobacteria cells in well water following bank filtration was investigated from a source water consisting of two artificial lakes (A and B). Phycocyanin probes used to monitor cyanobacteria in the source and in filtered well water showed an increase of fluorescence values demonstrating a progressive seasonal growth of cyanobacteria in the source water that were correlated with cyanobacterial biovolumes from taxonomic counts (r = 0.59, p

The presence of natural organic matter (NOM) poses several challenges to the commercial practice of UV/H(2)O(2) process for micropollutant removal. During the commercial application of UV/H(2)O(2) advanced oxidation treatment, NOM is broken down into smaller species potentially affecting biostability by increasing Assimilable Organic Carbon (AOC) and Biodegradable Organic Carbon (BDOC) of water. This work investigated the potential impact of UV/H(2)O(2) treatment on the molecular weight distribution of NOM and biostability of different water sources. A recently developed flow cytometric method for enumeration of bacteria was utilized to assess biological stability of the treated water at various stages through measurement of AOC. BDOC was also assessed for comparison and to better study the biostability of water. Both AOC and BDOC increased by about 3-4 times over the course of treatment, indicating the reduction of biological stability. Initial TOC and the source of NOM were found to be influencing the biostability profile of the treated water. Using high performance size exclusion chromatography, a wide range of organic molecule weights were found responsible for AOC increase; however, low molecular weight organics seemed to contribute more. Positive and meaningful correlations were observed between BDOC and AOC of different waters that underwent different treatments.

Nematodes, which occur abundantly in granular media filters of drinking water treatment plants and in distribution systems, can ingest and transport pathogenic bacteria and provide them protection against chemical disinfectants. However, protection against UV disinfection had not been investigated to date. In this study, Caenorhabditis elegans nematodes (wild-type strain N2) were allowed to feed on Escherichia coli OP50 and Bacillus subtilis spores before being exposed to 5 and 40 mJ/cm(2) UV fluences, using a collimated beam apparatus (LP, 254 nm). Sonication (15 W, 60s) was used to extract bacteria from nematode guts following UV exposure in order to assess the amount of ingested bacteria that resisted the UV treatment using a standard culture method. Bacteria located inside the gut of C. elegans were shown to benefit from a significant protection against UV. Approximately 15% of the applied UV fluence of 40 mJ/cm(2) (as typically used in WTP) was found to reach the bacteria located inside nematode guts based on the inactivation of recovered bacteria (2.7 log reduction of E. coli bacteria and 0.7 log reduction of B. subtilis spores at 40 mJ/cm(2)). To our knowledge, this study is the first demonstration of the protection effect of bacterial internalization by higher organisms against UV treatment, using the specific case of E. coli and B. subtilis spores ingested by C. elegans.

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 microm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100mg/L of Zwittergent 3-12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 microm following the dispersion protocol and 8 microm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 microm (R(2)0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.

Ballasted flocculation is widely used in the water industry for drinking water, municipal wastewater, storm water and industrial water treatment. This gravity-based physicochemical separation process involves the injection of a ballasting agent, typically microsand, to increase the floc density and size. However, the physical characteristics of the final ballasted flocs are still ill-defined. A microscopic method was specifically developed to characterize floc 1) density, 2) size and 3) shape factor. Using this information, probability density functions (PDFs) of the floc settling velocity were calculated. The impacts of the mixing intensity, polymer dosage, microsand size and contact time during the floc maturation phase were assessed. No correlation was identified between the floc diameter, form and density PDFs. The floc equivalent diameter mainly controls the settling velocity (r = 0.94), with the floc density (r = 0.26) and shape factor (r = 0.25) having lower impacts. A velocity gradient of 165 s(-1) was optimal to maintain the microsand in suspension while simultaneously maximizing the floc diameter. An anionic high molecular weight polyacrylamide formed 1.5-fold larger aggregates compared with the starch-based polymer tested, but both polymers produced flocs of similar density (relative density = 1.53 ± 0.03). Generally, the floc mean settling velocity is a good predictor of the turbidity removal. An in-depth analysis of the floc characteristics indicates a correlation between the floc size and the largest microsand grain potentially embeddable in the floc structure.

Intense accumulation of toxic cyanobacteria cells inside plants, unsuccessful removal of cells and consequent breakthrough of cells and toxins into treated water have been increasingly documented. Removal or destabilisation of cells in the pre-treatment stage using pre-ozonation could be an efficient practice as ozonation has been proven to be effective for the removal of cells and toxins. However, several unknowns including the ozone demand, the potential release of cell-bound toxins and organic matter and their impact on treatment train needs to be addressed. The general objective of this work was to study the impact of direct ozonation on different potentially toxic cyanobacteria genera from natural blooms. Water samples from five cyanobacterial bloom events in Lake Champlain (Canada) were ozonated using 2-5 mg/L O3 for a contact time of maximum 10 min. Cyanobacterial taxonomic enumeration, cyanotoxins, organic matter and post-chlorination disinfection by-product formation potential analyses were conducted on all samples. Anabaena, Aphanizomenon, Microcystis and Pseudanabaena were detected in bloom water samples. Total cell numbers varied between 197,000 and 1,282,000 cells/mL prior to ozonation. Direct ozonation lysed (reduction in total cell numbers) 41%-80% of cells and reduced released toxins to below detection limits. Microcystis was the genus the least affected by ozonation. However, DOC releases of 0.6-3.5 mg/L were observed leading to maximum 86.92 μg/L and 61.56 μg/L additional total THMs (four trihalomethanes) and HAA6 (six haloacetic acids) formation, respectively. The results of this study demonstrate that vigilant application of pre-ozonation under certain treatment conditions would help to avoid extreme toxic cells accumulation within water treatment plants.

The hybrid membrane process (HMP) coupling powdered activated carbon (PAC) and low-pressure membrane filtration is emerging as a promising new option to remove dissolved contaminants from drinking water. Yet, defining optimal HMP operating conditions has not been confirmed. In this study, ammonia removal occurring in the PAC contactor of an HMP was simulated at lab-scale. Kinetics were monitored using three PAC concentrations (1-5-10 g L(-1)), three PAC ages (0-10-60 days), two temperatures (7-22 °C), in ambient influent condition (100 μg N-NH4 L(-1)) as well as with a simulated peak pollution scenario (1000 μg N-NH4L(-1)). The following conclusions were drawn: i) Using a colonized PAC in the HMP is essential to reach complete ammonia removal, ii) an older PAC offers a higher resilience to temperature decrease as well as lower operating costs; ii) PAC concentration inside the HMP reactor is not a key operating parameter as under the conditions tested, PAC colonization was not limited by the available surface; iii) ammonia flux limited biomass growth and iv) hydraulic retention time was a critical parameter. In the case of a peak pollution, the process was most probably phosphate-limited but a mixed adsorption/nitrification still allowed reaching a 50% ammonia removal. Finally, a kinetic model based on these experiments is proposed to predict ammonia removal occurring in the PAC reactor of the HMP. The model determines the relative importance of the adsorption and biological oxidation of ammonia on colonized PAC, and demonstrates the combined role of nitrification and residual adsorption capacity of colonized PAC.

The inactivation kinetics of two strains of bacterial aerobic spores were investigated in a batch reactor for two pH levels (6.3 and 8.2) and various ozone dosages (0.5–2.5 mg/l). The kinetics of ozone decomposition was found to satisfactorily fit a first-order decay model. The CT (concentration×contact time) values were calculated using the modified Hom equation with exponential disinfectant decay. Lower pH resulted in lower CT values. The environmental spores tested were not as resistant to ozone as the reference strain of B. subtilis . Comparison of CT values for aerobic spores with published data suggests that bacterial spores could be a surrogate for evaluating the ozone inactivation of G. lamblia cysts and C. parvum (oo)cysts during drinking water disinfection. However, more information on the resistance of naturally occurring populations of bacterial spores would be needed before they are used as an indicator of ozone disinfection efficiency.

Spores from aerobic bacteria were evaluated as an indicator of the efficiency of chlorination. Several inactivation experiments were performed. The influence of temperature and water type was evaluated. Resistance of spores to chlorination was higher compared with Giardia using the values given in the surface water treatment rule. Resistance was observed to increase with temperature. Both Chick–Watson and Hom models were found to well describe the inactivation of spores by chlorine.

Despite its shortcomings, the T10 method introduced by the United States Environmental Protection Agency (USEPA) in 1989 is currently the method most frequently used in North America to calculate disinfection performance. Other methods (e.g., the Integrated Disinfection Design Framework, IDDF) have been advanced as replacements, and more recently, the USEPA suggested the Extended T10 and Extended CSTR (Continuous Stirred-Tank Reactor) methods to improve the inactivation calculations within ozone contactors. To develop a method that fully considers the hydraulic behavior of the contactor, two models (Plug Flow with Dispersion and N-CSTR) were successfully fitted with five tracer tests results derived from four Water Treatment Plants and a pilot-scale contactor. A new method based on the N-CSTR model was defined as the Partially Segregated (Pseg) method. The predictions from all the methods mentioned were compared under conditions of poor and good hydraulic performance, low and high disinfectant decay, and different levels of inactivation. These methods were also compared with experimental results from a chlorine pilot-scale contactor used for Escherichia coli inactivation. The T10 and Extended T10 methods led to large over- and under-estimations. The Segregated Flow Analysis (used in the IDDF) also considerably overestimated the inactivation under high disinfectant decay. Only the Extended CSTR and Pseg methods produced realistic and conservative predictions in all cases. Finally, a simple implementation procedure of the Pseg method was suggested for calculation of disinfection performance.

The presence of natural organic matter (NOM) poses several challenges to the commercial practice of UV/H(2)O(2) process for micropollutant removal. During the commercial application of UV/H(2)O(2) advanced oxidation treatment, NOM is broken down into smaller species potentially affecting biostability by increasing Assimilable Organic Carbon (AOC) and Biodegradable Organic Carbon (BDOC) of water. This work investigated the potential impact of UV/H(2)O(2) treatment on the molecular weight distribution of NOM and biostability of different water sources. A recently developed flow cytometric method for enumeration of bacteria was utilized to assess biological stability of the treated water at various stages through measurement of AOC. BDOC was also assessed for comparison and to better study the biostability of water. Both AOC and BDOC increased by about 3-4 times over the course of treatment, indicating the reduction of biological stability. Initial TOC and the source of NOM were found to be influencing the biostability profile of the treated water. Using high performance size exclusion chromatography, a wide range of organic molecule weights were found responsible for AOC increase; however, low molecular weight organics seemed to contribute more. Positive and meaningful correlations were observed between BDOC and AOC of different waters that underwent different treatments.

The significance of zooplankton in the transport and fate of pathogenic organisms in drinking water is poorly understood, although many hints of the role of predation in the persistence of microorganisms through water treatment processes can be found in literature. The objective of this study was to assess the impact of predation by natural zooplankton on the transport and fate of protozoan (oo)cysts in granular activated carbon (GAC) filtration process. UV-irradiated unlabelled Cryptosporidium parvum and Giardia lamblia (oo)cysts were seeded into two pilot-scale GAC filtration columns operated under full-scale conditions. In a two-week period after seeding, a reduction of free (oo)cysts retained in the filter bed was observed. Zooplankton was isolated from the filter bed and effluent water on a 30 microm net before and during the two-week period after seeding; it was enumerated and identified. Rotifers, which are potential predators of (oo)cysts, accounted for the major part of the isolated zooplankton. Analytical methods were developed to detect (oo)cysts internalized in natural zooplankton isolated from the filter bed and effluent water. Sample sonication was optimized to disrupt zooplankton organisms and release internalized microorganisms. (Oo)cysts released from zooplankton after sonication were isolated by IMS and stained (EasyStain) for microscopic counting. Both Cryptosporidium and Giardia (oo)cysts were detected in association with zooplankton in the filter bed samples as well as in the effluent of GAC filters. The results of this study suggest that predation by zooplankton can play a role in the remobilization of persistent pathogens such as Cryptosporidium and Giardia (oo)cysts retained in GAC filter beds, and consequently in the transmission of these pathogens in drinking water.

This study investigates the oxidation of pharmaceuticals, endocrine disrupting compounds and pesticides during ozonation applied in drinking water treatment. In the first step, second-order rate constants for the reactions of selected compounds with molecular ozone (k(O3)) were determined in bench-scale experiments at pH 8.10: caffeine (650+/-22M(-1)s(-1)), progesterone (601+/-9M(-1)s(-1)), medroxyprogesterone (558+/-9M(-1)s(-1)), norethindrone (2215+/-76M(-1)s(-1)) and levonorgestrel (1427+/-62M(-1)s(-1)). Compared to phenolic estrogens (estrone, 17beta-estradiol, estriol and 17alpha-ethinylestradiol), the selected progestogen endocrine disruptors reacted far slower with ozone. In the second part of the study, bench-scale experiments were conducted with surface waters spiked with 16 target compounds to assess their oxidative removal using ozone and determine if bench-scale results would accurately predict full-scale removal data. Overall, the data provided evidence that ozone is effective for removing trace organic contaminants from water with ozone doses typically applied in drinking water treatment. Ozonation removed over 80% of caffeine, pharmaceuticals and endocrine disruptors within the CT value of about 2 mg min L(-1). As expected, pesticides were found to be the most recalcitrant compounds to oxidize. Caffeine can be used as an indicator compound to gauge the efficacy of ozone treatment.

The impact of disinfection efficacy in natural waters was evaluated by performing disinfection assays using four untreated surface waters of various qualities and ultra-pure buffered waters as a baseline condition for comparison. Bacillus subtilis spores were spiked in these waters and disinfection assays were conducted at 22 °C using either free chlorine or chlorine dioxide. Assays using indigenous aerobic spores were also completed. The inactivation kinetics in natural and ultra-pure buffered waters were not statistically different (at p = 0.05 ) while using free chlorine, as long as disinfectant decay was taken into account. Filtering natural waters through a 0.45 μm did not improve the sporicidal efficacy of chlorine. For three out of the four waters tested, the efficacy of chlorine dioxide was greater in natural waters compared to that observed in ultra-pure buffered waters. Such results are consistent with previous observations using ultra-pure waters supplemented with NOM-extract from the Suwannee River. Similar to free chlorine results, the impact of filtration (0.45 μm) on the efficacy of chlorine dioxide was not statistically significant.