Installation of air diffusers in a lagoon or tank
Dryden Aqua air diffusers are ideal suited for installation in tanks or lagoons or virtually any size or configuration. The air blowers should be positive displacement roots type blowers with an air delivery pressure of up to 1bar. If the water depth is greater than 5m you may require more than 1 bar discharge pressure from the blower.
Determine the size of the aeration system, as a guide 1kg of COD per hour requires the application of 1 x air diffusers (code 70008) delivering 10 m3/hr of air. Example, if the water flow is 50m3/hr with a COD of 500mg/l the total COD is 25kg per hour. In order to provide sufficient aeration for water treatment, use 25 air diffusers, 250 m3/hr of air. The air diffusers should be equally spaced around the perimeter of the tank or lagoon.
The lagoon may be concrete, plastic lined or even just clay lined, however it should be over 3m in depth. If the lagoon is less than 3m, then increase number of air diffusers by 50%. It is also best to try and locate all of the diffusers that are on the same air ring main at approximately the same depth.
- 1 bar discharge pressure
- fitted with an acoustic environmental enclosure
- no load valve
- pressure relife valve
- temperature transmitter alarmed for over temperature
- filter restriction indicator and switch for connection to alarm system
- pressure transmitter connected to alarm system
Locate the blower on a concrete pad, and fit at least 6m of metal discharge pipe. You may make all the
pipework metal, this is useful in tropical or hot climates. If located in a temperate zone then plastic mdpe pipe may be used after the metal pipe. The pipe should go around the perimeter of the tank or lagoon. The diameter of the air ring main is a function of the air flow and perimeter of the lagoon. As a guide,
100 to 150m3/hr of air 90mm diam pipe
150 to 500m3/hr of air 90 - 125mm
500 to 1000m3/hr of air 125 - 150mm
Drill several 3mm holes into the underside of the pipe at the lowest locations on the air ring main. Condensate will build up in the pipes, the holes will automatically vent the water.
The air ring main goes around the perimeter of the tank, 1/2" flexible hose is connected onto the air ring main, and an air diffuser is connected onto the end of the hose. The length of hose should be sufficient to reach within 0.5m of the base of the lagoon. The diffuser is now thrown into the lagoon.
You may use low cost pvc food grade reinforced pvc hose, but we recommend that you use urethane hose. We also have available very heavy duty negatively bouyant hose.
How to fit a diffusers to the pipe
1. Fit the saddle clamp around the pipe with the 3/4* bsp threaded fitting pointingtoward the tank or lagoon.
2. Through the 3/4" bsp threaded fitting drill a 1/2" hole into the pipe
3. Screw into the 3/4" female saddle clamp, a 3/4" male x 1/2" hose tail
4. Cut the flexible 1/2" hose to length, push fit onto the hose tail and secure with a screw clip
5. Fit the diffuser on to the end of the hose and drop the diffuser into the tank.
Repeat this process for all the air diffusers.
Installation is very simple and even for a large installation such as the photo, it can all be completed in a few days.
Volume of water in Lagoons / Tanks
The systems should be as large as possible, the greater the volume of water in the lagoons, the longer the aeration time and the longer bacterium have to increase in species diversity to treat your waste water.
Treatment may be as short as 12 hours, however for most applications such as industrial wastewater or landfill leachate, the minimum aeration time should be 15 days, many of our installations are at 45 days. Extended diffused aeration activated sludge is a very easy and relaxed way to treat water to a very high standard. The bacteria should also enter endogenous respiration, so there may never be a requirement to desludge the tanks.
There should be at least 3 x aeration tanks and a fourth discharge decantation tank that has a capacity for at least 1 days discharge. The whole process may operate as a continuous flow through or sequencing batch reactor.
Nutrients and pH
The bacteria will likely be short of phosphate and in some waste water ammonium may need to be added.
pH control is also important, the aerated water will have a tendency to become acidic, so the requirement to add sodium hydroxide may be necessary.
Fit the following pumps.
1 x peristaltic pump to deliver phosphoric acid. for every 100 kg of BOD you need 1 kg of phosphate. The phosphate may be in the water, in which case you are not required to add additional phosphate. Analyse the water, determine the mass of phosphate and then calculate how much you need to add.
2. x peristaltic pump for ammonium. You will not normally add ammonium to the water. If the ratio exceed 10kg of ammonium per 100kg of BOD, then do not add ammonium as ammomium chloride. Please contact Dryden Aqua before you start adding ammonium to the waste water.
3. pH control, it may be required to dose sodium hydroxide into the water. You may require 1 and 5 kg of sodium hydroxide for every 1 kg of ammonium in the waste water to be treated. Again it is best to wait until the system is running and dose caustic slowly into the system to prevent the pH going below pH 7.0 Optimum pH is between pH7.0 and 7.4.
The dissolved oxygen must be maintained above 2mg/l at all times.
Cleaning And Maintenance of the diffusers
Any surface in contact with biologically active water, will develop a biofilm. If the water has a high calcium and carbonate concentration, then there may be scale formation.
Most of the scale formation will take place during the first 12 months. During this period the diffusers will be working hard to reduce the concentration of organics in the water and any sludge in the system. It also takes around 6 moths for the bacterial cell biomass to develop,
I recommend that the diffusers are cleaned once a week. This frequency is not always required, but during the early stages it is a good discipline. In order to clean a diffuser, wear a pair of heavy duty water-proof gloves. Pull the diffuser out of the water, and using your gloves, pull the diffuser through your closed hand. The diffuser may also require a brush. Give the diffuser a shake and then throw back into the lagoon, and move onto the next diffuser. 100 diffusers can be cleaned in 2 hours.
If scale forms on the diffuser this will happen very slowly, because it is difficult for scale to form of our flexible air diffusers. However if the water is very hard then scale is a possibility. In order to remove the scale, make up a solution of phosphoric acid, diluted with 5 parts water. Soak the diffuser in the the solution for 10 minutes or until it stops fizzing wash with freshwater and connect back onto the air ring main.
If the diffusers are cleaned and looked after well, they are expected to give up to 10 years of useful life.