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Wastewater Treatment good mixing. Conversely, the larger the COV, the greater the overall deviation from the mean of the measured tracer concentration. Most static mixer manufacturers guarantee a COV of 0.05 or less. This is normally used as an adequate standard for uniform mixing. The mixing length required, however, may vary according to the efficiency of the mixing device. Besides COV, another useful parameter to plot is the deviation from mean tracer concentration at sections along the outfall. Tracer concentrations are shown in Figure 2. Results of the modelling exercise for improved chlorine dosing are best represented by the simulated tracer concentrations at planes downstream of the injection point as presented in Figure 3. The disinfection agent, as represented by the tracer concentrations, would be expected to be fully mixed approximately 100 metres downstream of the injection point, thus defining the location for the sampling intakes for the control of the chlorination/dechlorination system upgrade.
Figure 3. Deviation from mean tracer concentration = low COV = good mixing.
The second portion of the project assessed dechlorination upgrades. The plant’s outfall configuration certainly presented a significant challenge. Investigation revealed that, when experiencing above-average flows, the 75 m long dechlorination zone would only provide ample residence time if dechlorination agent/chlorinated effluent mixing were to be enhanced. Immediately, the plant’s senior professional recommended a static mixer concept involving flow rotation and shear. Designers proceeded with an eval-
uation of simplistic static mixer geometries that could be installed in the submerged outfall (under Lake Ontario) through an existing 1200 mm diameter diffuser. Preliminary modeling was developed, and results presented. Plant staff elaborated on their initial design, proposing an improved injection/static mixer apparatus, and offered several improvements in order to reduce the risk of trapping rags, protect the dechlorination agent injectors, and minimize head continued overleaf...
YSI ProODO Handheld Opt Optical ical Dissolved Oxygen Met Meter er Expanded DO range of 0-500% Non-consumptive luminescent method eliminates stirring Easy to read graphic, backlit display and keypad Designed to fit in standard 300 mL BOD bottles Truly field-worthy, impact resistant, IP-67 waterproof case User-replaceable cables in lengths of 1 to 100-meters USB connection and powerful desktop Data Manager software Stores 2000 data sets Multiple languages support
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