Header Spacing
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May vary, depending on your diffuser spacing.
The recommended range is 12 inches to 48 inches with different considerations for low density versus high density diffuser spacing.
Low Density Diffuser Spacing
When laying out an aeration grid many questions come up regarding header and diffuser spacing. This usually happens when the design calls for either a large quantity of diffusers (high density) or very few diffusers (low density).
Regarding few diffusers, or low density, it is important to keep in mind the Four Foot (1.2 m) Rule. The Four Foot Rule indicates that the maximum distance allowed between a wall or column and the centerline of the nearest diffuser be no more than 4 feet. Additionally, there should be no more than 4 feet between headers or between adjacent diffusers on the same header. Studies have shown that using a maximum spacing of 4 feet reduces solids deposition and improves mixing and oxygen transfer efficiency.
High Density Diffuser Spacing
Regarding larger quantities of diffusers, or high density grids, each manufacturer will have limits as to what their equipment will allow. For example, Sanitaire generally allows a minimum of 12 inches (30.5 cm) spacing between the centerlines of disc diffusers on the same header. Similarly, the closest the headers can be is 12 inches (30.5 cm) on center. To place headers more closely together, offsetting the diffuser holders on adjacent lines is possible; however this type of layout should only be used in select applications. When the header lines are 12 inches apart it leaves approximately 2 inches between the outer edges of the diffuser holders on lines that are next to each other. As a result, once the header spacing is less than about 18 inches, it becomes more practical to group the headers to allow for larger gaps called access alleys. Access alleys make it easier to install the system, perform maintenance, change membranes, and clean out the tank.
The available spacing for both the headers and diffusers are on 1 inch intervals. Experience has shown that almost any size tank and any layout are capable of being met with these limitations.
In applications where the diffusers are not the primary method of mixing, such as a sludge holding tank downstream of a digester, and oxygen transfer is only required to keep the liquid oxygenated, header and diffuser spacing greater than 48 inches is allowed.
