The prevention of waterborne diseases requires rapid detection of pathogens in drinking water, with an ultimate goal of in-line monitoring in real time. Standard cultivation-based methods are too time-consuming and thus not suitable for this purpose. Many technologies were proposed to achieve this goal, such as ELISA, PCR, FISH, FTIR and flow cytometry. However, they still have limitations of non-specificity, complexity and high cost. Therefore, an optical system is proposed and developed towards the in-line monitoring of bacteria, which combines the advantages of FTIR and micro-flow cytometer for bacterial identification and precise quantification. The in-line use requires obtaining IR spectra of bacterial cells directly in water, which is achieved using a CaF2 liquid cell. The spectra of a series of bacterial samples are collected and analyzed using principal component analysis for their differentiation. A preliminary study on fabricating a CaF2 concentrator is conducted, in which a novel phenomenon on stress release of silicon nitride film on CaF2 substrate is discovered and studied. To determine the concentration of bacteria in drinking water, a micro-flow cytometer is built based on a micro-fabricated device that integrates on-chip beam-shaping optics and microfluidic channels. With this micro-flow cytometer and optimized data analysis for counting particles in real time, linearity with correlation coefficient of over 0.99 is achieved for the dependences of throughput on both volumetric flow rate and concentration of sample. With a one-dimensional hydrodynamic focusing, no degradation of the counting efficiency is demonstrated when the focused sample stream expands. The high accuracy of counting makes this micro-flow cytometer a promising candidate for low concentration applications. Counting of E. coli DH5α cell suspensions in phosphate buffered saline is performed using the micro-flow cytometer. Side-scattered light signals are used to count the E. coli cells. A detection efficiency of 92% is achieved when compared with the expected count from a haemocytometer. It is demonstrated that E. coli can be easily distinguished from beads of similar sizes (2-4µm) as their scattering intensities are different. / Thesis / Doctor of Philosophy (PhD)

Conventional drinking water treatment consists of a coagulation, flocculation, gravity separation, filtration and disinfection processes each working individually but also as an interdependent system. One of the main reagents used for drinking water treatment are coagulants that destabilise the suspended particles which results in the formation of flocs. For many years, the coagulant of choice was aluminum sulphate, also know as alum. Alum has slowly been replaced by new coagulants, such as polyalumium sulphates and polyaluminum chlorides, because they yield more consistent plant performance than with alum over the wide temperature range experienced by Canadian treatment plants. Recent research has determined that the alum solubility envelop varied significantly in terms of pH range with temperature, thus cold temperature performance may be improved by adjusting the coagulation pH. Dissolved air flotation (DAF) is now used at some water treatment plants to replace sedimentation because it is much more compact than gravity settling, and it is somewhat better than sedimentation for the removal of algae, organics and operation in cold temperatures. The objective of this thesis is to help operators and managers of drinking water treatment plants incorporating DAF by: a) investigating the cold water turbidity removals of DAF systems using alum, the most economical coagulant; and b) investigating the impact of DAF saturator pressure on the bubble sizes produced and floc removal. This first initiative is based on fairly recent research on the impact of pH on the cold-temperature aluminum solubility. It uses this knowledge about the impact of pH to evaluate DAF treatment of Ottawa River water in cold-water conditions using DAF batch tests. The effect of pH against final turbidity at cold temperatures was first evaluated by increasing the pH of the coagulated water, the higher pH helped attain good turbidity removals. For the coagulant dose tested, good turbidity removals were observed for both warm and cold waters at nearly the same pOH conditions. At room temperature the turbidity removals increase with both increasing flocculation G and flocculation time. While at cold temperatures, when aluminum flocs are known to be much more fragile, the turbidity removals appear to be independent of G and GT. The second initiative studied the relationship between floc size and bubble size in DAF systems by changing the DAF saturator pressure. Increasing the saturator pressure did not significantly decrease the mean bubble size. The flocs attach to bubbles that were significantly larger than the bubbles. The assessment of DAF efficiency based on the unitized effluent floc distribution proved inconclusive, it may be possible that the conditions resulting with the larger mean effluent floc size has a greater removal efficiency since it began with a smaller fraction of small flocs entering the flotation stage.

<p dir="ltr">Interactions between drinking water quality and delivery systems, pipe materials, and attitudes</p>

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