Installation of Air diffusers

This section relates to the installation of Dryden Aqua air diffusers in ponds, lakes and reservoirs. The section does not constitute a complete method statement, nor does it include any electrical installation details

The aeration systems comprise of  three components.

1. Air blower(s)

2. Air delivery pipe/hose

3. Air diffusers

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 lagoons up  50m 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 or tank,  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.

Air blowers

The air blowers used with Dryden Aqua air diffusers could range from our small diaphragm units, through the range of rotary vane compressors and up to roots type or screw compressors.  In all cases the blowers should be located in an environment that protects them from the elements.

The blowers must be firmly secured,  normally they will be anchored onto a concrete floor or shelf.  The blowers should be located above the level of water into which the air diffusers are installed.  If the blowers are level with the water,  or below water level,  there is a danger that water could be drawn back up the air lines and into the air blower. When the air blowers are running,  the air supply line will be under pressure,  the air temperature in the supply pipe will also be warmer than the ambient air temperature.  When the air blowers are turned off,  the pressure in the air delivery pipe will reach equilibrium with the hydrostatic water pressure in the pond in a few seconds. The air in the pipe now starts to cool,  this generates a reduce pressure which in turn draws water back up the air lines.  If there is any possibility of this occurring with your aeration system,  a siphon prevention valve should be fitted to the air line.

Air lines

The air blowers are connected on to the delivery pipe or hose.  If the air flowrate is less than 40 cubm/hr,  then hose may be used.  However if the air flowrate is greater,  or if it is passing under ground,  or if you require a more robust installation,  then we recommend MDPE pipe.  The diameter of the pipe will also depend on the length of the pipe run.  As a guide use the table below;

Air flow, cubm/hr	size of pipe mdpe, assuming not longer than 200m
6	1/2"	15mm
10	3/4"	25mm
15	1"	32mm
25	1.5"	50mm
40	2"	63mm
100	3"	90mm
200	3"	90mm
300 - 500	4"	125mm

The air blowers compress the air,  and this in turn will heats up the air.   In all cases we recommend that there is a short length of metal pipe ( usually copper,  mild steel or stainless steel).  For the rotary vane compressor, approx. 3m of pipe is usually sufficient.  The metal pipe is used for heat dissipation,  since high temperatures can affect the stability of the the delivery hose or pipe.  A caution  ( hot pipe) sign may be required on the metal pipe,  in some cases a guard may be required.

The main air delivery pipe work will transport the air to the approximate location of the air diffuser, in most cases the final connection onto the air diffusers will be 1/2" pvc hose.  In order to connect the 1/2" pvc hose onto the rigid MDPE pipe, a mechanical saddle clamp is used.

Saddle clamps are available in sizes ranging from 25mm pipe up to 250mm pipe.  In order to fit the saddle clamp you position both halves of the fitting around the pipe and then insert the bolts and tighten the bolt to secure the clamp onto the pipe.  An `o` ring will seal onto the pipe. A drill is the used though the threaded fitting of the saddle,  to make a hole into the MDPE pipe.  We find a wood drill quite useful for this procedure,  make sure that you remove all of the swarf.

The saddle is fitted with a bsp female thread,  normally the thread size will be 3/4".  A hose adapter is now screwed into the saddle  fitting.

The hose adapter will have a 1/2" tail,  the 1/2" hose is push fitted onto the tail, and then secured using a stainless steel screw clip.

The other end of the the 1/2" hose s now connected onto the air diffuser.   The diffuser will be fitted with a similar 1/2" hose adapter, either in plastic, brass or stainless steel.

Air diffuser

Physical details of our air diffusers can be found by following the link (diffusers).  A summary of the the data is presented below. The adjacent photo shows the flexible nature of the product.  the diffusers own internal ballast will keep the unit on the bottom.  Simply connect the 1/2" hose onto the end of the diffusers and drop in the water.
Close up photo showing the end of the diffuser where the 1/2" hose is connected.

A summary table is presented below.

Additional Installation comments

In some cases the air diffusers will be located at considerable depth at a distance off the shore of the lake.  In these cases the MDPE pipe is normally fully assembled on shore,  the diffusers and hose could also be fitted onto the pipe at this stage.   If the pipe is being floated out on the lake,  then it is useful to have a 1/2" valve on the air hose in order to prevent the water entering the pipework.

The MDPE pipe work has almost a neutral buoyancy,  however if you require the pipe to be on the bottom,  then sufficient weight must be added to the pipe in order to compensate for its buoyancy.  In some cases steel pipe may be used to avoid the need to add extra ballast.

Servicing of the air diffusers

The air diffusers require very little attention,  however they do require occasional cleaning,  especially if the water is very hard. In most cases we recommend that the diffusers are inspected and possibly  cleaned once every 6 months.   It is useful to have a spare set of diffusers that can be rotated every 6 months.   The used diffusers are the cleaned and stored ready to used for the following 6 months.  The diffusers will give many years of service.

Cleaning of the diffusers is very simple, just clean with a brush and a  low to medium pressure hose. If the water is hard then carbonate deposits may have formed on the diffusers.  To remove carbonates simply soak the diffuser in a dilute acid for 5 minutes.  We recommend a 10 to 20% solution of phosphoric acid.  If you maintan the diffusers the will give many years of service. W have some installations that are nearly 20 years old

Removing the diffusers from the water

If the diffusers are connected to a submerged manifold,  then it is best to connect the diffusers onto the manifold using the PVC hose of sufficient length to reach the surface of the lake. The 1/2" supply hose is simply hooked with a gedge anchor in order to lift the diffuser. If a long length of 1/2" hose is used to connect to the diffuser,  then this hose may require additional ballast to stop it lifting the diffuser.  Alternatively additional ballast can be fitted onto the diffuser.

Fitting of air diffusers to ring main

Dryden Aqua Air diffusers

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