The temperature of the water in clarifier tanks has been shown to have a significant influence on floc blanket stability. The objective of this research was to determine the effects of variations in the influent temperature on a floc blanket using laboratory and field experiments and to assess whether the cohesivity of the blanket expressed as the sludge cohesion coefficient (SCC) can be used to interpret the effect of temperature variations. Effluent turbidity exhibited a strong positive correlation with inflow temperature during the increasing temperature phase and a strong negative correlation during the temperature recession phase. An increment of 2 °C in the influent temperature caused the effluent turbidity to increase by 1 NTU. The SCC of the blanket exhibited a significant relationship with the influent temperature. The optimum blanket cohesivity (SCC of 0.7 mm/sec) was observed at a temperature of 23.2 °C, above which the cohesivity decreased. At higher temperatures, frequent particle collisions owing to high inertial forces cause particle motion with the upward flow and increase the effluent turbidity. No correlation between SCC and blanket settling velocity was observed.
The objective of this study was to determine the applicability of the laboratory flocculation test (Jar Test) for a solid contact clarifier. Cohesivity, a parameter characterizing the sludge blanket can be established by determining the Sludge Cohesion Coefficient (SCC) by conducting a Sludge Cohesion Test (SCT). A series of laboratory tests were performed using the Jar Test and SCT. Considering the large number of variable parameters involved with natural raw water, sludge samples were prepared using synthetic raw water with varying turbidity and coagulant dose combinations. A comparison was made between the optimum coagulant dose obtained using the two tests. Highest SCC observed at the optimum coagulant dose was within the range of 0.6–3.3 m/hr. Low SCC values indicate a light and fragile sludge blanket whereas high SCC values indicate a quick settling consistent blanket. With increasing raw water turbidity, the optimum coagulant dose given by SCT is lower than that of the Jar Test. Hence, at higher raw water turbidity occurrences, it may be possible to operate the upward flow solid contact clarifiers with lower coagulant dose. A significant quadratic relationship is observed between the optimum coagulation doses with R2 = 0.9 and α < 0.05.
Water extraction at Meewathura Intake has become difficult or impossible without the assistance of submersible pumps during the dry seasons since the river water level drops below the bottom level of the lowest opening of the Intake. A new intake is also planned to be located on the left bank around 300 m downstream of Meewathura Intake to extract an additional 32,000 m3/day to expand Kandy South Water Supply Scheme. In order to ensure a total of 41,000 m 3 /day from a new intake and from the existing intake, it is envisaged that a weir across the Mahaweli is required to raise the river water level during the dry weather and to extract silt free water. The analysis also shows that weir construction is a better proposal compared to other methods available. Construction of such weir across Mahaweli Ganga would cause flood level rise in the upstream and change the river bed and river bank geometry in the area surrounding the weir, particularly downstream of weir. To investigate these effects both Mathematical (MIKE 11) and Physical model studies were conducted. Mathematical Model was used to optimize weir dimension and to predict water level rise due to weir construction. Physical Model was used to optimize weir and intake layout, to investigate river bed scouring and bank erosion pattern, and to determine erosion protection measures. The study concludes that modeling techniques could be applied very effectively for such and similar studies.
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