Pierre Lafrance

Suspended bacterial biomass and activity in full-scale drinking water distribution systems: Impact of water treatment

Bacterial regrowth in drinking water distribution systems is a source of concern since it could result in non-compliance with water quality regulations, taste and odor problems, and may be associated with an increased risk of gastrointestinal illnesses. Bacterial regrowth is dependent on several factors, including the amount of substrate available for growth, such as biodegradable dissolved organic carbon (BDOC), oxidant residuals and the presence of corrosion. To investigate the impact of nutrients levels and oxidant residual maintenance, a full-scale investigation of two distribution systems was completed. This study presents data obtained from two distribution systems (DS) fed by different treatment trains: one DS has low BDOC concentrations and no free oxidant residual (St. Rose plant, Quebec, Canada), and the other has a high BDOC concentration and moderate concentrations of free oxidant residual (Pont Viau plant, Quebec, Canada). Monitoring included heterotrophic plate counts (HPC), total direct count by epifluorescence after acridine orange staining (AODC), direct viable counts (DVC-CTC method) and the measurement of bacterial production by 3H-thymidine incorporation. Results show that bacterial biomass (AODC and DVC) and bacterial production are lower in the DS fed by the treatment plant with a low BDOC concentration in the plant effluent. This difference is observed in warm water but not in cold water. The results suggest that HPCs are not a good indicator of bacterial regrowth in DSs. Finally, statistical analysis demonstrated that the treatment type and cumulative surface to volume ratio are the significant factors affecting regrowth in the distribution systems studied in warm waters.

Effect of natural dissolved organic matter found in groundwater on soil adsorption and transport of pentachlorophenol.

Kinetic, equilibrium, and transport experiments were performed to quantify pentachlorophenol (PCP) adsorption and mobility in water-saturated soil columns. The effect of natural dissolved organic matter (NDOM, <0.1 mg/L or 15 mg/L) found in groundwater was investigated. While the pH was found to greatly affect the adsorption of PCP, the adsorption rate was not affected by NDOM at either pH 5.4 or pH 6.3. For a low concentration range (PCP <0,4 nmol/mL), the effect of NDOM on PCP adsorption isotherms was negligeable at pH 5.2, 5.4, and 6.1. The breakthrough curves (BTCs) obtained from displacement studies were fitted to the analytical solution of a one-dimensional transport model that assumes a linear isotherm

Experimental design methodology applied to electrochemical oxidation of the herbicide atrazine using Ti/IrO2 and Ti/SnO2 circular anode electrodes

The degradation of the herbicide atrazine in aqueous medium (initial concentration of 100 μg l(-1)) has been studied by electrooxidation process using Ti/IrO(2) and Ti/SnO(2) circular anode electrodes. The performance of the electrolytic cell resulted from its capability of reacting on the pollutants by using indirect effect of electrical current where active chlorine is electrochemically generated. A factorial experimental design was firstly used for determining the influent parameters on the herbicide atrazine degradation. The current intensity and treatment time were the main influent parameters on the degradation rate. Using a 2(4) factorial matrix, the best performance for atrazine degradation (removal of 95%) was obtained by selecting Ti/IrO(2) anode operated at a current intensity of 2.0 A during 40 min of treatment time in the presence of 1.0 g Na Cl l(-1). Then, the optimal experimental parameters for atrazine degradation have been investigated by using a Central Composite methodology. Under the optimal conditions determined by this method, electrooxidation can economically be applied to oxidise atrazine (73% of degradation for a total cost of 0.057 US

A probabilistic approach for the groundwater vulnerability to contamination by pesticides: the VULPEST model.

m(-3)) while using Ti/IrO(2) anode operated at a current intensity of 1.4A during 22 min of treatment time in the presence of 1.0 g NaCl l(-1).

A sensitivity analysis of adsorption and degradation parameters in the modeling of pesticide transport in soils

Abstract The quantitative evaluation of the groundwater vulnerability to contamination by pesticides is the most effective way to prevent the cases of non-point source contamination and to protect the groundwater quality. An effective prevention scheme must be based on the evaluation of the quantity of pesticide which could reach the water table under specific conditions. The simulation of the transport and the fate of pesticides in the unsaturated zone can provide such prediction. The choice of a adequate methodology able to realize this evaluation is significant for the reliability of the prediction results. Such a methodology using a Monte Carlo approach for the modeling is described in this paper. This approach takes into account the variability of the parameters that control the transport and the fate of pesticides in the unsaturated zone. The results, interpreted on a statistical basis, allow the evaluation of the risks of water table contamination which can be compared to pre-define water quality criteria. The VULPEST model developed in this study is an example of management tool permitting the quantitative evaluation of the groundwater vulnerability in terms of risks of contamination.

Impact of grass and grass with poplar buffer strips on atrazine and metolachlor losses in surface runoff and subsurface infiltration from agricultural plots.

Abstract The increasing use of deterministic models in predicting the movement of pesticides in soils, has focused attention on the evaluation of major parameters which represent attenuation factors of organics in the subsurface. These parameters are the degradation rate constant and the adsorption constant for the pesticide. In view of the large in situ variability of these parameters and of the difficulty in obtaining accurate field data, there is a high degree of uncertainty associated with the results obtained from deterministic models. A sensitivity analysis is performed here to quantify the impact of such variation in each of these input parameters on the output results of an unsaturated zone transport model (PRZM). Results show that variations in these parameters about their respective mean values greatly affect the predicted concentration distributions, obtained after three years, of the pesticide aldicarb in all the soil profile. A 15–22% variation in the degradation constant, or a 24% variation in the adsorption constant, lead to a 100% uncertainty in the various simulation results defined as the cumulative quantity of aldicarb or the dissolved aldicarb concentration leached below the root zone (or the unsaturated zone) of the soil. Such a deterministic model presents a high degree of sensitivity to these input parameters. Accurate field data are then needed to obtain reliable model results in predicting pesticide movement inthe unsaturated zone.

Determination of atrazine, its degradation products and metolachlor in runoff water and sediments using solid-phase extraction

In many areas of intensive corn production, atrazine and metolachlor are among the most commonly found herbicides in surface and ground water. This 2-yr study compared the impact of grass and grass+tree buffer strips on the exported masses of atrazine, metolachlor, and a degradation product of atrazine, desethylatrazine (DEA). The experimental system consisted of four replicate plots in a three-way completely randomized design (no buffer zone, grass buffer zone, and grass+tree buffer strips). The field plots were 5 m wide and 30 m long and grown in corn. The grass and grass+tree buffer strips were 5 m and had the same grass vegetation except for eight young hybrid poplars. Over the 2-yr study, surface runoff and subsurface infiltration water (under the buffer strip) were collected after the initial three rainfall events after herbicide application. Dissolved atrazine, metolachlor, and DEA were analyzed by gas chromatography/mass spectrometry. The presence of buffer strips decreased the exported masses of atrazine and metolachlor in surface runoff. A three-way ANOVA with treatment (type of buffer strip), water (surface runoff or subsurface infiltration), and time between herbicide application and rainfall event as factors showed a significant reduction (40-60% in 2004 and 75-95% in 2005) in the total (surface runoff+infiltrated water) exported masses of atrazine and metolachlor in the presence of buffer strips. Rainfall events after herbicide application were different between the 2 yr and greatly affected the flow distribution (e.g., subsurface infiltration) and the leached herbicide concentrations. No significant difference in the capacity to reduce herbicide exports was observed between grass and grass+tree buffer strip treatments; the poorly developed young poplar biomass at the time of the study may partly explain this observation.

Fluoride sorption and desorption indices in Quebec soils

In order to determine the fate of the herbicides atrazine (as well as some of its degradation products) and metolachlor in water and sediments, a method was developed to extract and analyse these compounds. The two matrices were separated completely by centrifugation followed by filtration using nylon filters (0.45 mum). Sediments were extracted with a mixture of methanol-0.1N hydrochloric acid (50:50, v/v) using a wrist-action shaker. Filtered water and extracts of sediments were adjusted to pH 4, then concentrated and purified onto two solid-phase extraction cartridges using in tandem C(18) bonded phase column atop sulfonic acid bonded column (SCX). Atrazine, deethylatrazine, deisopropylatrazine and metolachlor retained by the C(18) column were eluted with ethyl acetate. Chlorodiaminotriazine and hydroxyatrazine retained by the SCX column were eluted with a 50:50 (v/v) acetonitrile-0.1M Na(2) HPO(4) aqueous solution (pH 8.5). The extracts were quantified by high performance liquid chromatography with diode array detector (HPLC-DAD) and by gas chromatography with nitrogen-phosphorus detector (GC-NPD). Overall percent recoveries were about 75% and detection limits were between 0.05 and 0.15 microg/l., and 0.5 and 1.5 microg/kg for water and sediments, respectively.

Potential Efficiency of Riparian Vegetated Buffer Strips in Intercepting Soluble Compounds in the Presence of Subsurface Preferential Flows.

Abstract Sorption and desorption of fluoride (F) were measured on 24 samples from the A, B, and C horizons from the most representative soil series of the aluminium smeltering areas of the province of Quebec, Canada. The sorption was estimated by 48 h contact with 0.005M NaClO4 solutions of increasing F concentration and described with the van Bemmelen‐Freundlich equation. Desorption (Qdes) was measured with two 48 h contact periods in the same electrolyte. The affinity parameter (K) was most closely correlated with ammonium oxalate extractable aluminum (Al) (AlOX, r = 0. 78*) and iron (Fe) (FeOX, r = 0.59**), and organic carbon (C) (OC, r = 0.59**) contents and to the soil pH (r = 0.56**), whereas the peak sharpness of the distribution of affinity terms parameter (n) was most closely related to AlOX (r = 0.63**). The K parameter was best predicted by a combination of AlOX, FeOX, and OC. A combination of exchangeable magnesium (Mg) and potassium (K) and FeOX predicted 75% of the variation in Qdes suggesti...

Impact of recent manure applications on natural estrogen concentrations in streams near agricultural fields

Buffer strips have been widely recognized as to promote infiltration, deposition and sorption of contaminants for protecting surface water against agricultural contamination. However, such strips do not intercept all contaminants, particularly soluble ones. Although preferential flow (PF) has been suggested as one factor among several decreasing the efficiency of buffer strips, the mechanisms involved are not well understood. This project examines buffer strip efficiency at intercepting solutes when subsurface PF occurs. Two soluble sorbed tracers, FD&C Blue #1 and rhodamine WT, were applied on an agricultural sandy loam soil to evaluate the ability of a naturally vegetated buffer strip to intercept soluble contaminants. Rhodamine was applied about 15 m from the creek, while the Blue was applied 15 m to 165 m from the creek. Tracer concentration was measured over a two-year period in both the creek and the buffer strip through soil and water samples. Although the tracers traveled via different pathways, they both quickly moved toward the creek, passing beneath the buffer strip through the soil matrix. Our results demonstrate that the risk of water contamination by soluble contaminants is high in such systems, even when a well-vegetated buffer strip is used. The design of buffer strips should be modified to account for underground bypass, either by using plants that have deep, fine roots that do not favour PF or by adding a filter extending deep underground that can be regularly changed.