VaraCorp Blog – A Guide to Choosing Your Next Lagoon Aerator
by Shea Casey
We appreciate the challenge which confronts the small plant operator who has the task of choosing the aeration system for a waste water lagoon. There is no shortage of aeration systems from which to choose, and each manufacturer claims to have the best aerator on the market. Plus, there are a myriad of other concerns which must be addressed in finding the perfect aerator for the task at hand.
We at VaraCorp have decided to put together the following short list of things to consider when choosing an aerator.
•Oxygen Transfer Efficiency: The primary value of any aerator is its ability to transfer dissolved oxygen into the water. The efficiency of this process is expressed as Pounds of (Dissolved) Oxygen per Horsepower Hour, stated as lbsO2/hphr. The magnitude of this efficiency can range from less than 1 lb/hphr to 4 lbs or more. The good news is that this number lets the plant operator directly compare two competing aerators which have motors with different horsepower sizes. The bad news is that this number is sometimes criticized as being “squishy” since it requires the use of nebulous multipliers called alpha factors, etc. Also, it is doubtful that two different laboratory analysts would come up with the SAME transfer efficiency for the SAME aerator. Regardless, government regulators and wastewater engineers make their living on this parameter. Thus, in many, but not all, cases the plant operator must consider the transfer efficiency when selecting an aeration system.
•Capital Costs: The plant operator is always under budget constraints when selecting the best aerator. While transfer efficiency is important, it takes a back seat to the budget limitations of the municipality. Not surprisingly, the purchase price of aeration systems is all over the map. Aerators suitable for aerating one to twenty acre lagoons can range in price from $4,000 each to $20,000 each. The attendant question is how many aerators will be needed. While a $4,000 price tag could be appealing, it might take 20 of these aerators (at $80,000 total) to achieve the aeration ability of only two aerators at $20,000 each (at $40,000 total.)
•Operating Costs: The electrical power consumed by the aeration system often represents the highest ongoing expense of operating a wastewater lagoon. Such expenses supposedly are wrapped up in the calculus for determining transfer efficiency. AS A PRACTICAL MATTER many operators are shocked when the first electrical bill arrives, and it is through the roof.
In addition to the above, finding the best aerator sometimes requires the plant operator to verbally talk to others in the industry to ascertain which aerator works best.