Graham A. Gagnon

Comparison of advanced oxidation processes for the removal of natural organic matter

This study examined the impact of UV, ozone (O(3)), advanced oxidation processes (AOPs) including O(3)/UV, H(2)O(2)/UV H(2)O(2)/O(3) in the change of molecular weight distribution (MWD) and disinfection by-product formation potential (DBPFP). Bench-scale experiments were conducted with surface river water and changes in the UV absorbance at 254 nm (UV(254)), total organic carbon (TOC), trihalomethane and haloacetic acid formation potential (THMFP, HAAFP) and MWD of the raw and oxidized water were analyzed to evaluate treatment performance. Combination of O(3) and UV with H(2)O(2) was found to result in more TOC and UV(254) reduction than the individual processes. The O(3)/UV process was found to be the most effective AOP for NOM reduction, with TOC and UV(254) reduced by 31 and 88%, respectively. Application of O(3)/UV and H(2)O(2)/UV treatments to the source waters organics with 190-1500 Da molecular weight resulted in the near complete alteration of the molecular weight of NOM from >900 Da to <300 Da H(2)O(2)/UV was found to be the most effective treatment for the reduction of THM and HAA formation under uniform formation conditions. These results could hold particular significance for drinking water utilities with low alkalinity source waters that are investigating AOPs, as there are limited published studies that have evaluated the treatment efficacy of five different oxidation processes in parallel.

An efficient biofilm removal method for bacterial cells exposed to drinking water

Abstract Reliable quantification of microbial growth in a drinking water environment has typically been difficult, primarily due to the development of thin, patchy biofilms. Therefore, initial sampling and resuspension procedures become critical to the subsequent biomass determination. Biofilm cells attached to polycarbonate coupons of an annular reactor (AR) have typically been removed by aseptically scraping the coupon surface with a sterile utility knife. The advantage of this method is its simplicity, however, scraping often compromises sterility and is highly subject to individual variation. The purpose of this research was to develop a method that could remove and resuspend biofilm cells efficiently, consistently and with a good recovery rate. This paper presents a comparison of removal and resuspension methods. Three methods used to remove cells from the polycarbonate coupons include: scraping with a utility knife, swabbing and stomaching. In addition, four methods were selected for cell resuspension and involved the use of a tissue blender, vortex, stomacher and a sonicator. Of the removal methods examined, stomaching consistently yielded the highest number of culturable and total bacterial cells, ranging from two to four times more cells than scraping procedures. For one experimental set, the number of colonies enumerated by heterotrophic plate count (HPC) from the stomacher ranged from 1.0–1.7×10 6 CFU/cm 2 , whereas numbers obtained using the scraping method were 4.6–4.9×10 5 CFU/cm 2 . It was found that the number of HPCs recovered with stomaching was significantly greater at the 5% level than that obtained using the scraping method. Similarly, for cell resuspension, stomaching provided the highest enumeration. Once removal was achieved, sonication also provided good resuspension. An analysis of variance showed that, compared to the resuspension step, the removal step is more significant at the 5% level to the recovery of biofilm cells. The stomacher has the unique advantage of combining cellular removal and resuspension into a single step. This method was, therefore, selected as an ideal method for recovery of biofilm cells. Subsequent optimization measures using the stomacher showed that sterile deionized water was a suitable diluent for recovering cells from a drinking water environment. At normal speed (i.e., 230 rpm±5%), the optimal stomacher run length for maximum cell removal was 2 min.

Sequential UV- and chlorine-based disinfection to mitigate Escherichia coli in drinking water biofilms

This study was designed to examine the potential downstream benefits of sequential disinfection to control the persistence of Escherichia coli under conditions relevant to drinking water distribution systems. Eight annular reactors (four polycarbonate and four cast iron) were setup in parallel to address various factors that could influence biofilm growth in distribution systems. Eight reactors were treated with chlorine, chlorine dioxide and monochloramine alone or in combination with UV to examine the effects on Escherichia coli growth and persistence in both the effluent and biofilm. In general, UV-treated systems in combination with chlorine or chlorine dioxide and monochloramine achieved greater log reductions in both effluent and biofilm than systems treated with chlorine-based disinfectants alone. However, during UV-low chlorine disinfection, E. coli was found to persist at low levels, suggesting that the UV treatment had instigated an adaptive mutation. During UV-chlorine-dioxide treatment, the E. coli that was initially below the detection limit reappeared during a low level of disinfection (0.2 mg/L) in the cast iron systems. Chloramine was shown to be effective in disinfecting suspended E. coli in the effluent but was unable to reduce biofilm counts to below the detection limit. Issues such as repair mechanism of E. coli and nitrification could help explain some of these aberrations. Improved understanding of the ability of chlorine-based disinfectant in combination with UV to provide sufficient disinfection will ultimately effect in improved management and safety of drinking water.

Understanding removal of phosphate or arsenate onto water treatment residual solids.

Chemical and physical characterization methods were used to analyze ferric, alum, and lime water treatment residual solids (WTRSs) in order to describe why phosphate or arsenate adsorption occurred on the WTRSs, and why ferric WTRSs were the stronger adsorbent for both phosphate and arsenate. In total, five WTRSs, two ferric, two alum, and one lime, were analyzed. Elemental analysis of the WTRSs showed lime residuals contained the greatest molar amount of the primary element (7.04 mol Ca/kg solid), followed by the ferric residuals (4.86-4.96 mol Fe/kg solid) whereas alum residuals contained the least amount of primary element as compared to the ferric or alum residual solids (3.62-4.67 mol Al/kg solid). Mercury porosimetry identified more small pores (<0.006 μm) in a ferric WTRSs when compared to an alum WTRSs, indicating that a more detailed pore structure allowing for intraparticle phosphate or arsenate diffusion might be present in the ferric solid. Similarly, SEM images at 1000 times magnification showed a porous surface in both ferric WTRSs, whereas the alum WTRSs showed a smooth surface at the same magnification. Several general equations to describe phosphate or arsenate adsorption on WTRSs were provided.

Ozone Application in Recirculating Aquaculture System: An Overview

In recirculating aquaculture systems (RAS), particulates (including feces, uneaten feed, bacteria, and algae) can cause several problems, in that they may harbor pathogens, can physically irritate the fish, and upon decomposition, release ammonia and consume oxygen. Mechanical filters, foam fractionators, and other engineered devices are used to remove particles quickly from aquaculture systems, in order to improve fish health and decrease the load on biofilters and oxygenators. Ozone is used in RAS as a disinfectant, to remove organic carbon, and also to remove turbidity, algae, color, odor and taste. Ozone can effectively inactivate a range of bacterial, viral, fungal and protozoan fish pathogens. But the effectiveness of ozone treatment depends on ozone concentration, length of ozone exposure (contact time), pathogen loads and levels of organic matter. In spite of ozone is a very effective oxidizing agent, higher ozone concentrations are a risk to cultured fish stocks causing gross tissue damage and stock mortalities, and also are a risk to bacterial films on the biofilter.

Removal of Easily Biodegradable Organic Compounds by Drinking Water Biofilms: Analysis of Kinetics and Mass Transfer

This paper evaluates the rate of utilization of easily biodegradable organic compounds by drinking water biofilms. Tap water, which had been filtered through biologically active granular activated carbon, was used as an innoculum for biofilm growth in annular reactors (ARs). Synthetic cocktails of easily biodegradable material in the concentration range of 50-2,000 mgC/m3 were used as substrate for biofilm growth. Influent and effluent aggregate concentrations of biodegradable organic matter (BOM) were calculated by adding the measurable BOM components on a mass carbon basis. The aggregate BOM values were used for calculating the observed Damköhler number and Theile modulus (based on a reaction rate per unit surface area), which were used to determine whether external or internal mass transfer limited BOM removal. For all of the experimental trials, it was shown that neither external nor internal mass transfer limited BOM removal. Because the biofilms in this research are thin and the fact that mass transfer is not limiting, it was assumed that the bulk BOM concentration was approximately equal to the average BOM concentration in the biofilm. A linear model was obtained for the aggregate BOM flux and the product of the effluent BOM concentration and the biofilm density. The slope or the areal biodegradation rate (ka) for the aggregate BOM was 0.033 m/h, as determined through a linear regression.

Adsorption of arsenic from a Nova Scotia groundwater onto water treatment residual solids.

Water treatment residual solids were examined in batch adsorption and column adsorption experiments using a groundwater from Halifax Regional Municipality that had an average arsenic concentration of 43 μg/L (±4.2 μg/L) and a pH of 8.1. The residual solids studied in this paper were from five water treatment plants, four surface water treatment plants that utilized either alum, ferric, or lime in their treatment systems, and one iron removal plant. In batch adsorption experiments, iron-based residual solids and lime-based residual solids pre-formed similarly to GFH, a commercially-available adsorbent, while alum-based residual solids performed poorly. Langmuir isotherm modeling showed that ferric residuals had the highest adsorptive capacity for arsenic (Q(max) = 2230 mg/kg and 42,910 mg/kg), followed by GFH (Q(max) = 640 mg/kg), lime (Q(max) = 160 mg/kg) and alum (Q(max) = <1 mg/kg and 3 mg/kg). Similarly, the maximum arsenic removal was >93% for the ferric and lime residuals and GFH, while the maximum arsenic removal was <49% for the alum residuals under the same conditions. In a column adsorption experiment, ferric residual solids achieved arsenic removal of >26,000 bed volumes before breakthrough past 10 μg As/L, whereas the effluent arsenic concentration from the GFH column was under the method detection limit at 28,000 bed volumes. Overall, ferric and lime water treatment residuals were promising adsorbents for arsenic adsorption from the groundwater, and alum water treatment residuals did not achieve high levels of arsenic adsorption.

Bench-scale evaluation of drinking water treatment parameters on iron particles and water quality.

Discoloration of water resulting from suspended iron particles is one of the main customer complaints received by water suppliers. However, understanding of the mechanisms of discoloration as well as role of materials involved in the process is limited. In this study, an array of bench scale experiments were conducted to evaluate the impact of the most common variables (pH, PO4, Cl2 and DOM) on the properties of iron particles and suspensions derived from the oxygenation of Fe(II) ions in NaHCO3 buffered synthetic water systems. The most important factors as well as their rank influencing iron suspension color and turbidity formation were identified for a range of water quality parameters. This was accomplished using a 2(4) full factorial design approach at a 95% confidence level. The statistical analysis revealed that phosphate was found to be the most significant factor to alter color (contribution: 37.9%) and turbidity (contribution: 45.5%) in an iron-water system. A comprehensive study revealed that phosphate and chlorine produced iron suspension with reduced color and turbidity, made ζ-potential more negative, reduced the average particle size, and increased iron suspension stability. In the presence of DOM, color was observed to increase but a reverse trend was observed to decrease the turbidity and to alter particle size distribution. HPSEC results suggest that higher molecular weight fractions of DOM tend to adsorb onto the surfaces of iron particles at early stages, resulting in alteration of the surface charge of iron particles. This in turn limits particles aggregation and makes iron colloids highly stable. In the presence of a phosphate based corrosion inhibitor, this study demonstrated that color and turbidity resulting from suspended iron were lower at a pH value of 6.5 (compared to pH of 8.5). The same trend was observed in presence of DOM. This study also suggested that iron colloid suspension color and turbidity in chlorinated drinking water systems could be lower than non-chlorinated systems.

Unintended consequences of regulating drinking water in rural Canadian communities: Examples from Atlantic Canada

Studies that explore social capital and political will [corrected] in the context of safe drinking water provision in [corrected] Canada are limited. This paper presents findings from a study that examines the capacity of rural Canadian communities to attain regulatory compliance for drinking water. Interviews were conducted with water operators and managers in ten rural communities across Atlantic Canada to identify the burden of compliance arising from the implementation of, and adherence to, drinking water regulations. This research identifies the operator as being particularly burdened by regulatory compliance, often resulting in negative consequences including job stress and a strained relationship with the community they serve. Findings indicate that while regulations are vital to ensuring safe drinking water, not all communities have the resources in place to rise to the challenge of compliance. As a result, some communities are being negatively impacted by these regulations, rather than benefit from their intended positive effect.

Quantifying the spatial and temporal variation of ground-level ozone in the rural Annapolis Valley, Nova Scotia, Canada using nitrite-impregnated passive samplers.

Abstract The spatiotemporal variability of ground-level ozone (GLO) in the rural Annapolis Valley, Nova Scotia was investigated between August 29, 2006, and September 28, 2007, using Ogawa nitrite-impregnated passive diffusion samplers (PS). A total of 353 PS measurements were made at 17 ambient and 1 indoor locations over 18 sampling periods ranging from 2 to 4 weeks. The calculated PS detection limit was 0.8 ±0.02 parts per billion by volume (ppbv), for a 14-day sampling period. Duplicate samplers were routinely deployed at three sites and these showed excellent agreement (R 2 values of 0.88 [n =11], 0.95 [n =17], and 0.96 [n =17]), giving an overall PS imprecision value of 5.4%. Comparisons between PS and automated continuous ozone analyzers at three sites also demonstrated excellent agreement with R 2 values of 0.82, 0.95, and 0.95, and gradients not significantly different from unity. The minimum, maximum, and mean (±1σ) ambient annual GLO concentrations observed were 7.7, 72.1, and 34.3 ± 10.1 ppbv, respectively. The three highest sampling sites had significantly greater (P =0.032) GLO concentrations than three Valley floor sites, and there was a strong correlation between concentration and elevation (R 2 =0.82). Multivariate models were used to parameterize the observed GLO concentrations in terms of prevailing meteorology at an elevated site found at Kejimkujik National Park and also at a site on the Valley floor. Validation of the multivariate models using 30 months of historical meteorological data at these sites yielded R 2 values of 0.70 (elevated site) and 0.61 (Valley floor). The mean indoor ozone concentration was 5.4 ± 3.3 ppbv and related to ambient GLO concentration by the equation: indoor =0.34 ×ambient & 5.07. This study has demonstrated the suitability of PS for long-term studies of GLO over a wide geographic area and the effect of topographical and meteorological influences on GLO in this region.