The collection of waste water in large ponds, commonly referred to as “lagoons” and to let “nature do its work”, is one of the oldest solutions for the treatment of waste water and has been used for hundred of years. The underlying principle of a lagoon systems in its simplest form (facultative unaerated lagoon) is actually quite complex: Waste water is led into a large pond with many days of hydraulic retention time, sometime up to 50 days or more. Organic solids will settle at the bottom and slowly decay under anaerobic conditions. On the water surface, oxygen is introduced by wind activity and provides the bacteria in the waste water with oxygen to digest pollutants in the water. Substantial algae growth will add to the cleaning effect. Usually several lagoons are arranged one after the other and the last lagoons will serve as polishing or settling stage. After several years, the lagoons will be full with sedimented sludge and need to be emptied.
While exceptionally simple in its design and practically non-energy consuming, this kind of treatment has however some serious disadvantages:
- Strong odors are emitted, in particular in summer when the water is warm. Sometimes H2S is released which is hazardous and leads to corrosion
- Enormous land requirement, about 50 times more than for a conventional activated sludge treatment.
- Low cleaning efficiency, no Nitrogen removal at all
- Excessive Algae bloom
- Serious breeding room for Mosquitos
Decades ago, several of this disadvantages where overcome by introducing “artificial” aeration to this kind of treatment. Commonly mechanical surface aerators where used, to mix the lagoons and to provide more oxygen. Several improvements could be achieved. In particular improved cleaning results and mitigation of Odors as well as reducing the land requirement. Aerated lagoons can be much smaller than unaerated ones. However the introduction of mechanical surface aerators brought some new problems, mainly very high or even excessive consumption of electrical energy, due to the very poor efficiency of the aerators. Also the mixing result was still poor. The creation of aerosols by the aerators created new issues regarding health and safety.
However in recent years, aerated lagoon system have experience a sort of revival, thanks to their rather simple operation and maintenance and due to the following significant improvements:
- New fine bubble aeration systems with much higher efficiency had been introduced, which basically reduces the former energy consumption to less than 50 %
- Better provision of oxygen prevents odor nuisance
- Implementation of the “complete mix design” concept, which achieves better cleaning result while consuming less footprint than unaerated lagoons
- Partial Nitrification in Summer can be achieved, due to better mixing conditions
Nowadays, so called “high performance” aerated lagoon system are used very often as alternative to activated sludge systems, if there is no particular or stringent requirement on Nitrogen removal.
The OXIWORKS® aeration system is exceptional well suited for the use in any aerated lagoons system, both as green field design as well as retrofit of existing lagoons.
- The simple design of OXIWORKS® basically allows a “plug and play” approach. The flexibility of the system allows it to be adapted to all kinds of lagoon shapes and dimensions.
- The self propelled movement of the diffusers will result in excellent mixing of the lagoon. Deadzones are avoided as much as physically possible.
- The superior oxygen transfer of the OXIWORKS® will result in much less energy consumption than surface aerators, sometimes less than 40 %.
In particular for complete mix systems, the OXIWORKS® aeration is the technology of choice.