|
|
|
Web sites] | Home | AFM | Ozone | Reverse Osmosis | Swimming Pools | |
||
|
Sizing of an Aeration system for waste water |
||||||||||||||||||||||||||||||||
|
The information given in this page is only for the Dryden
Aqua air diffusers, which is now recognized as being one of the finest air
diffusers available for any aeration application. The data is based on
empirical information gathered and summarized over many years of installing and
running systems in all types of water and waste water.
Assumptions are made in the calculations, however the data provides a convenient and quick way of sizing a system, which in most cases gives a very close approximation to the actual aeration requirements. Table Relationship between Ammonium, BOD, Phosphate and alkalinity
|
||||||||||||||||||||||||||||||||
| Example 1 | ||||||||||||||||||||||||||||||||
|
What is the aeration requirement for an activated sludge water treatment system tank can cope with 100 cubic meters of effluent per day, at 2000mg/l of COD and 1200 mg/l of ammonium nitrogen ?. The calculations assume complete removal of the parameters. COD oxygen demand
Ammonium oxidation, oxygen demand
Number of diffusers required to gibe 1000 Kg of oxygen per day
Answer
|
The above calculation provides an over estimate of the number of diffusers required, there are water chemistry, tank dimensions and temperature variations to take into consideration. In general the calculation will give an over-estimate of the amount of aeration required in tank based system, and the correct level of aeration for lagoon system. The aeration systems need to provide quite a high degree of water turbulence and mixing, the mixing characteristics for lagoons is quite poor, so proportionally more aeration is required to compensate.
- compensation factor for lagoon based system = 1
- compensation factor for tank based system = 0.7
| Example 2 |
Total oxygen demand = 7kg + 4 kg = 11kg
|
The algae factor
When a leachate treatment system matures, there will not only be a healthy population of bacteria, but the algae levels will also be quite high. In order for their to be an input from algae the treatment system should be open to direct sunlight. The algae will metabolize the ammonium and in the process they will also produce oxygen. In system that have a high ammonium, it is best to use two or more lagoons or open tanks. Once the algae become established they will reduce the ammonium levels very quickly and in the process produce oxygen. In the 2nd example given above, the total capacity of the system was only 217 cubic meters of leachate per hour. However once algae become established the system would be able to cope with a leachate flow as high as 500 cubic meters per day.
Algae will grow heterotrophically in the absence of sunlight, while they are still beneficial in system, the algae will consume oxygen and they are more difficult to cultivate.
|
Algae level in a 4 x lagoon system |
||||
|
|
||||
Raw leachate
|
lagoon 1 50% reduction in COD and ammonium, water becomes quite clear, little to no algae present |
lagoon 2 Algae bloom develops and water turns green. |
lagoon 3 Daphnia and zooplankton bloom crops the algae and reduces the green colour |
lagoon 4 Stable algae level and biological system. Newts, frogs, and some fish now living in treatment system
|
