Sizing a Leachate Treatment system


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Sizing of an Aeration system for waste water

installation of the air diffusers basic design

The information given in this page is only for the Dryden Aqua air diffusers, which are now recognized as being one of the finest air diffusers available for any aeration application.

One 3m long diffusers code 6.2.10 will pass 10 cubm/hr of air and will dissolve into the water 1 kg to 2kg of oxygen per hour when the oxygen tension is around 2mg/l at a depth of 4 to 6m.

Transfer efficiency equates with 2kg to 5 kg of oxygen per kw of energy expended, transfer depends on the depth of the tank, water chemistry, temperature and oxygen tension. Typical one diffuser code 6.2.10 will provide sufficient oxygen for 100 PE in sewage effluent treatment

Table Relationship between Ammonium, BOD, Phosphate and alkalinity

Kg of component required	Ammonium nitrogen 1kg	COD/BOD 1 kg	Phosphate 1kg
Oxygen required =	5 Kg	2 Kg	***
Ammonium nitrogen consumed =	***	0.1 Kg	10 Kg
COD/BOD consumed =	10 Kg	***	100 Kg
Phosphate required =	0.1 Kg	0.01 Kg	***
Alkalinity required
Sodium hydroxide =	4 kg
Sodium bicarbonate =	12 kg
Calcium carbonate =	7 kg
Magnesium oxide =	2 kg

The above table is used to set the parameter values required to calculate the size of an aeration system and the number of Dryden Aqua diffusers required to treat the water.

The algae factor in shallow tank lagoon systems

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.

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

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Raw leachate

5-10,000mg/l COD
1000-14000 mg/l ammonium

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

BOD < 5mg/l
COD < 100mg/l
Ammonium < 5mg/l