A bubble diffuser is a device which uses masses of bubbles to aerate sewerage waste water to aid in the production of beneficial bacterial enzymes. These enzymes help to break down waste solids in water which make them easier to filter or clarify. Bubble diffusers typically consist of tubes, plates, or discs perforated with a large number of regularly spaced holes. Air is pumped through the diffuser heads, thereby generating the bubbles which facilitate the process. Bubble size plays an important role in the efficiency of a bubble diffuser.
Solids suspended in sewerage wastewater need to broken down and allowed to settle into secondary stage clarifiers or membrane filters. This allows for the efficient removal of solids and the highest quality of secondary effluent or discharge water. One of the best ways of doing this is to allow bacterial enzymes to naturally decompose the material. The healthy propagation of these enzymes rely on a food source and a plentiful source of oxygen. The suspended solids supply the food source while aeration of the water ensures an adequate supply of oxygen.
Aeration of wastewater represents a significant percentage of the power usage of any treatment plant. This is particularly true of plants which utilize aeration methods such as mechanical agitators. The bubble diffuser offers a low maintenance and cost effective option for infusing wastewater with oxygen. These mechanisms typically only have the diffuser heads submerged in the wastewater; air pumps situated above water makes for simple system maintenance. The lack of submerged moving parts also makes for lower running and maintenance costs.
A bubble diffuser consists of a submerged diffuser head located on the floor of the separation tank. The diffuser heads may be of a tubular, flat plate, disc or dome design. The head is perforated with a regularly spaced pattern of holes through which compressed air is pumped from the surface. The resultant mass of bubbles rise slowly through the wastewater and infuse it with oxygen. This oxygenation then creates a suitable environment for bacterial enzyme production.
Bubble size is an important variable in the efficiency values of a bubble diffuser system. In the past, fairly coarse diffuser holes were used; it was believed that a larger bubble size ensured quicker rise rates and better “pumpage” or distribution of oxygen. Current trends have tended to use smaller holes because research has shown that a finer bubble mass is more efficient at oxygenation in most applications. The average diffuser hole size in most wastewater plants is approximately 0.08 inch or 2 mm with sizes as small as 0.04 inch or 0.9 mm used in some cases.