Effects of influent temperature variation on floc blanket behavior and effluent water quality

Abstract

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.