Technical Bulletin 162: High Efficiency Diffusers versus Surface Aerators
EDI has engineered systems that are well suited for almost any aeration mixing application. With multiple diffuser platforms available, it gives design engineers or users choices for coarse bubble, fine bubble of different types, and several different configurations for the diffuser systems. With this flexibility and multiple configurations of diffuser systems available it has become obvious that the process efficiency gains and the energy efficiency of diffusers are causing diffused air technology to supplant and replace surface aeration components.
Many people want a comparison of the surface aerators versus diffusers. There is a wide spectrum of diffuser choices and a wide difference of performance of the splash type surface aerators versus induced draft aerators. With all of the variations, it is clear that EDI Advanced Technology Diffuser Systems offer huge process and economic advantages over surface aeration systems. The process benefits and control capabilities of diffused aeration are particularly attractive. The ability to save energy of 30% to 70% over surface aerators depending on the type of surface aerator used is a big benefit of fine bubble diffusers. Coarse bubble diffusers by comparison with surface aeration are still attractive from process standpoint, but the energy consumption of a coarse bubble diffuser system is virtually identical to the splashing type surface aerators while saving about 35% energy versus the induced draft aerators!
Key elements in the comparison of diffusers versus surface aerators are to get the performance on a common basis. Items that are important to evaluate are as follows:
It should also be noted that on the electrical controls, when there is a 50% to 100% standby of blowers provided there should be an accounting for a similar electrical switch for capability on the surface aerators.
In general, mechanical aerators have been considered as the lowest first cost of most systems. In reality when total system cost are considered on a similar design criteria and similar design basis, diffusers and surface aerators can be very similar in capital cost.
Once the capital cost issue has been addressed, the operating savings from diffused aeration systems will typically pay for complete abandonment of new surface aeration systems and converting to fine bubble diffusers with less than 3 year pay back. When comparing surface aerators with diffusers for new construction, comparing them on an equal scope of supply basis will show that the diffusers are very close to the same first cost and if the first year’s operation cost are incorporated, the installed cost of diffusers are less! Beyond that point, savings of energy is huge and is contributing to the owner or to the operating entity.
For convenience, a quick checklist of operating and performance characteristics of high efficiency diffusers versus surface aerators is below for reference and use.
Major Energy Savings
|Maximum Process Flexibility
|Suitable for cold weather operation
|Freezing in may require removal
|Generates foam and/or nuisance aerosols
|Reduced maintenance with no moving parts in aeration basin
|Major maintenance of mechanical items in aeration basins
|Can be installed in earthen basins with no floor protection required
|Floor protection or erosion control required
|No protection required of basin liners
|Liners vulnerable to aerator vortex
|System life 10 – 20 years
|10 years approximately
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