Abstract
Due to the various parameters that influence air solubility and microbubble production in dissolved air flotation (DAF), a multitude of values that cover a large range for these parameters are suggested for field systems. An unpacked saturator and an air quantification unit were designed to specify the effects of power, pressure, temperature, hydraulic retention time, and air flow on the DAF performance. It was determined that a pressure of 621 kPa, hydraulic retention time of 18.2 min, and air flow of 8.5 L/h would be the best controlled parameters for maximum efficiency in this unit. A temperature of 7 °C showed the greatest microbubble production, but temperature control would not be expected in actual application. The maximum microbubble flow from the designed system produced 30 mL of air (±1.5) per L of water under these conditions with immediate startup. The maximum theoretical dissolved air volume of 107 mL (±6) was achieved at a retention time of 2 h and a pressure of 621 kPa. To isolate and have better control over the various DAF operational parameters, the DAF unit was operated without the unsaturated flow stream. This mode of operation led to the formation of large bubbles at peak bubble production rates. In a real-world application, the large bubble formation will be avoided by mixing with raw unsaturated stream and by altering the location of dissolved air output flow.
Highlights
The design of a specific dissolved air flotation (DAF) system depends upon the factors such as the volume of wastewater to be treated, the degree and nature of contamination, the extent of treatment required, and any subsequent treatment that is required for the recovered product concentration [1]
The best fit curve (R2 = 0.975) followed Henry’s Law, which states that the amount of gas that can be dissolved in a given volume of liquid at a constant temperature is directly proportional to the partial pressure of the gas (P), which is given by: P = KcM
The microbubble volume was measured at pressures of 345, 414, 483, 552, and 621 kPa; (■)The power consumed by the pump at each pressure was correlated to volume of bubbles produced
Summary
The design of a specific dissolved air flotation (DAF) system depends upon the factors such as the volume of wastewater to be treated, the degree and nature of contamination, the extent of treatment required, and any subsequent treatment that is required for the recovered product concentration [1]. These factors, in turn, indicate the appropriate dissolution pressure, flow rate, retention time, recycle ratio, coagulant and flocculent pretreatment, flotation tank design, and baffle setup for the desired treatment.
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