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Installation of aeration systems in activated sludge tanks

Description of diffuser

The Dryden Aqua high performance air diffusers are like a hybrid between a solid tubular diffuser and a flexible membrane diffuser.

The diffusers are made in lengths from 30cm to 500cm,  however the standard sized unit for use in waste water treatment is 300cm in length.  The standard 300cm diffuser is rated at 9 to 10 cubm/hr of air with a pressure drop of approximately 2psi. The diffuser is fitted with a 1/2" hose tail and non return valve at one end.   The other end of the diffuser will either have a plug,  or is fitted with another 1/2" hose tail to allow the air to enter from both ends.

The diffuser is flexible and can be bent to form a circle. The diffuser also contains its own ballast,  therefore there is no need to anchor the diffuser to the base of an aeration tank.

How to install the diffusers

Situation 1. the aeration tank is 5m in width, 4m deep and 30m long.

Run an air ring main in 90 to 125mm pipe around the perimeter of the tank. The air ring main should be fitted to the top of the tank. Fit saddle clamps onto the pipe and quick release snap couplers. Fit 4m of 1/2" hose onto the couplers and the 3m diffuser onto the end of the hose. Fit hose onto the other end of the diffuser and connect this to air ring main on the other side of the tank.  The diffuser is across the width of the tank and is held in approximate location by the hose and air ring main.  The diffuser is free to move slightly,  but it will be held in position.  Additional diffusers are fitted onto the air ring main at interval spacing of 0.5m to 5m.  The number of diffuser require will depend on the BOD loadings of the water.

The advantage of this type of installation is that it is very easy, the tank can be full of water or effluent during installation.  If any cleaning or servicing of the the diffusers are required,  they are simply pulled out of the tank using the hose.   You do not even need to turn the air blowers off during this procedure.

 

Situation 2 the tank of lagoon is  in excess of 10m wide, and up to 40m across or in diameter.

In this case the arrangement is very similar to 1 above,  the air ring main is fitted around the perimeter of the tank, hose is fitted onto the air ring main, and the diffusers onto the end of the hose.  Only one end of the diffuser is fitted to the hose.

With the above arrangement there is no aeration towards the center of the lagoon,  however what we find is that with the air diffusers in the above location, there is an upwelling of water at the sides of the lagoon.  The water then shoots out across the surface and then down at the middle.  The momentum of water motion develops, to such an extent that the entire tank of about to 4000 cubic meters can be turned over by 200 cubm/hr of air from a 11kw blower every 2 to 3 minutes.  This arrangement makes for very efficient  and effective aeration. Also because the diffusers are arranged around the side,  you can easily remove the diffusers by simply pulling on the hose. This is the arrangement that we use for large extended diffused aeration systems and it it now the most popular form of aeration of its type in the UK.