Checking the Adequacy of Your Dissolved Aeration Flotation System

Selecting a new system or maximizing the benefit of an existing DAF system can be daunting. Luckily, the process doesn’t require expensive trial and error, but has a defined mathematical scientific system to aid you. There are several equations that help you to know whether a new system is in order, the old system is adequate or the right system to select if you’re about to purchase. One test to use to check for the DAF system adequacy is the test to find the hydraulic loading rate.

The hydraulic loading rate, also known as the surface overflow rate, measures the volume that covers the surface area per day. An example might be the number of gallons of water over the square footage of the surface area that flows each day. In order to find the rate, you need to know the design flow rate of the DAF system. You simply divide the DAF designed flow rate by the square footage of the surface area---length times width--of the container. You add that to any recirculation from the unit. A 25 percent recirculation factor for a unit with a DAF of 120 gallons per minute would be 30, resulting in 150 gpm.

Knowing the hydraulic loading weight is important. If the DAF is for wastewater treatment, you want an adequate rate so you don’t have clogging. However, it’s equaling important to know the rise or settling rate of the solids. It takes some time for these solids to either surface or sink in the effluent, so the DAF can remove the solid. In order to see if your unit is efficient, you need to compare the rise or settling rate of a field sample in a small one or two liter container and create a simulation of the DAF using an air sparger you can control. The sampling will give you information on the required rise rate. You simply need to compare that to the actual DAF rise or settling rate. As long as the machine produces 125 percent of the required rise rate, it’s adequate.