Raymond Desjardins

LIVE/DEAD® BacLight: application of a new rapid staining method for direct enumeration of viable and total bacteria in drinking water

A rapid epifluorescence staining method using the LIVE/DEAD Bacterial Viability Kit (BacLight) was applied to estimate both viable and total counts of bacteria in drinking water. BacLight is composed of two nucleic acid-binding stains: SYTO 9 and propidium iodide. SYTO 9 penetrates all bacterial membranes and stains the cells green, while propidium iodide only penetrates cells with damaged membranes, and the combination of the two stains produces red fluorescing cells. Optimal incubation conditions were found to be 15 to 20 min, at room temperature in the dark. Total (red + green) and viable (green) cells can hence be counted simultaneously. Factors affecting the staining procedure were tested (addition of glutaraldehyde, staining time, chlorine impact). In the absence of stress, BacLight viable counts were comparable and to 5-cyano-2,3-ditolyl tetrazolium (CTC) counts. BacLight total counts were comparable to acridine orange counts (differing by <0.1 log/ml). However, the increase in environmental stresses (chlorine, growth rate or temperature) induced a decrease in viability that was more pronounced for CTC and plate counts than for BacLight viable counts.

Laboratory study of ballasted flocculation.

Ballasted flocculation is applied successfully in the water treatment industry, but the concept has not yet been subject to extended experimental studies. The use of a microsand and a polymer together to increase the weight of the flocs and the rate at which they settle is radically changing the coagulation flocculation-settling methodology. The objective of this research is to study ballasted flocculation in the laboratory by means of a modified jar-test procedure. The first tests, conducted using a statistical approach, enabled us to identify those parameters that have a significant influence on the quality of settled water. The principal treatment parameters considered in this study were the chemical dosage, the contact times in the different basins, the pH of coagulation and the dosage of microsand. The parameters used to evaluate the quality of the settled water, and hence treatment performances, were turbidity, UV absorbance, TOC and membrane filterability. The results showed that the coagulant dosage and the coagulation pH have a preponderant effect on the variability of the quality of the settled water. By contrast, filterability as measured by the laboratory filter tests, was found to be more sensitive to coagulant and microsand dosages. It was dependent on the ratio of microsand to polymer dosage, and improved when this ratio increased.

Examining the use of aerobic spore-forming bacteria to assess the efficiency of chlorination

Abstract 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.

Including operational data in QMRA model: development and impact of model inputs

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 x 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).

Removal of Amino Acids, Biodegradable Organic Carbon and Chlorine Demand by Biological Filtration in Cold Water

This paper presents the removal profiles of total amino acids (TAAs), total dissolved amino acids (TDAAs), biodegradable organic carbon (BDOC) and chlorine demand in a biological filter operating in cold water (< 2° C). Biological filtration achieved a removal of 46% for TDAAs (0.08 ± 0.04 mg C l−1) and a removal of 24% for BDOC (0.2 ± 0.1 mg C l−1). Since the filter studied was functioning in biological mode, these results suggest that TDAAs have a higher biodegradability than that shown by the global BDOC pool. The use of the CHABROL model, which predicts BDOC removal in biological filters, permitted comparison of the TDAA removal profile with removal profiles associated with the three classes of BDOC distinguished by the model. The theoretical chlorine demand associated with TAAs, calculated with individual amino acid chlorine demands, varied from 5.6 to 6.4 mg Cl2 per mg TAA. The removal of the chlorine demand associated with TAA removal (0.5 ± 0.15 mg Cl2) accounted for 34% of the 240 hour water chlo...

Chlorine demand removal by biological treatment in cold water

Abstract A major strategy to reduce or prevent the formation of undesirable by‐products is to reduce chlorine demand before the application of chlorine. The major objective of this study was to evaluate the performance of different water treatment processes at full scale, specifically the combination of ozonation and biological activated carbon (BAG) filtration, for the removal of chlorine demand over a range of natural organic matrix and water temperature (l°‐23 °C). Both long term and short term chlorine demand were measured using a 2:1/C12:TOC ratio and pH 7,0 phosphate buffer at 20 °C in darkness. Results show that chlorine demand increases over a period of 200 hours and that long term chlorine demand can be modeled using a second order relation. Chlorine demand can be reduced by 55% for short term (4h) and by 61% long term (168h) by coagulation, floculation and sedimentation. The net effect of ozonation is variable depending on the prevalent oxidation conditions and on the organic matrix. In warm tem...

The Use of Jar-Filtration Tests to Compare Performances of Coagulants in Direct Filtration

Modified jar tests were performed in order to compare performances of coagulants treating, by direct filtration, raw water having a low turbidity and dissolved organic carbon. The object of this direct filtration is to produce water with a turbidity equal to or less than 0.10 NTU. The tests comprise a coagulation step with a laboratory flocculator, followed by a filtration step on a granular medium. Two poly aluminium silicate sulphates (PASS 100 and PASS 55), poly aluminium chloride (PACl), aluminium sulphate (alum), Ferriclear (prehydrolized ferric sulphate) and ferric chloride were studied. It was observed that all these coagulants are capable of lowering the turbidity of filtered water to 0.10 NTU or even less. Among the aluminium-based coagulants, PACl seems to be the most effective; while for iron-based coagulants, ferric chloride performs best. Although the doses are higher, alum offers a commercial advantage over the other aluminium-based coagulants because it costs less. When the turbidity objective of 0.10 NTU is reached, the amount of dissolved organic carbon removed is small. The best removal rate, which is 23%, is obtained with ferric chloride.

Bioreactors for the Rapid Determination of Biodegradable Dissolved Organic Carbon (BDOC) in Drinking Water: Feed Mode Impact

Bioreactors performing at a stable temperature of 20°C were used to achieve a rapid determination of the amount of biodegradable dissolved organic carbon (BDOC) present in ozonated water. Two feed modes, continuous feed and batch feed, were compared and evaluated. Bioreactors fed from holding tanks filled weekly with water passed through 1 and 75 µm filters were found to perform better in the short term (7 months after start-up) than those fed continuously with water filtered on 75 µm, in terms of the reduction in the amount of DOC between the intake and outflow points of the bioreactors, or BDOC (biodegradable dissolved organic carbon). It is believed that the difference in performance of batch-fed and continuously-fed bioreactors can be attributed to the more rapid bacterial colonization of batch-fed bioreactors. Moreover, it was observed that biological growth in the prefilter had an important role in the overall removal of BDOC through the continuously-fed bioreactor system.

Effect of sodium bicarbonate recarbonation on the biodegradable dissolved organic carbon measured by fixed biomass

It was observed that biodegradable dissolved organic carbon (BDOC), measured by a fixed biomass method, in samples recarbonated with sodium bicarbonate, were always lower than those obtained in similar non recarbonated samples. Biomass used for all measurement was developed and sustained with non-recarbonated water (base water). The increase of alkalinity, pH and sodium concentration resulting from recarbonation seems to affect BDOC values. Results have shown little variation of BDOC (0.1 to 0.2 mg l−1 C) when the sodium concentration is raised from 3 mg l−1 (base water; alkalinity = 25 mg l−1 as CaCO3) to 40 mg l−1 (recarbonated water; alkalinity = 100 mg l−1 as CaCO3). However, when sodium concentration was increased to 109 mg l−1 (recarbonated water; alkalinity = 250 mg l−1 as CaCO3) important underestimation of BDOC (0.4 mg l−1 C to 0.6 mg l−1 C) occurred. In order to obtain better results, it was decided to adapt the biomass to the physico-chemical characteristics of each water for 45 days, 80 days a...