Aquaculture: Maintaining Oxygen Levels

The oxygen level in fish tanks and ponds needs to be maintained at levels above 5mg/l for the heath and efficient performance of the fish and filter bacteria. Aeration is usually the preferred method of replenishing the oxygen and removing the carbon dioxide from the culture environment, and two devices are commonly used to supply this aeration in tanks: air pumps and blowers. Each device represents a range of options - but which is the most appropriate equipment choice to use in a particular situation?

The oxygen level in fish tanks and ponds needs to be maintained at levels above 5mg/l for the heath and efficient performance of the fish and filter bacteria. Aeration is usually the preferred method of replenishing the oxygen and removing the carbon dioxide from the culture environment, and two devices are commonly used to supply this aeration in tanks: air pumps and blowers. Each device represents a range of options - but which is the most appropriate equipment choice to use in a particular situation? Air pumps provide low amounts of air (up to about 10/m3/hr) but can deliver it to a depth exceeding what is normally utilized in fish farming (3.5m). By contrast, blowers typically produce massive quantities of air, but are inefficient in deep water (>1.5m). Being small, air pumps are also typically less expensive than blowers. When fish farming, we very seldom use water deeper than 1.5m, and when we do it is generally combined with the use of liquid oxygen, so this evaluation falls away. Thus, the power of the air pump is seldom of relevance, so let’s focus on the other factors relevant to the comparison. Going forward all comparisons are done at a water depth of 1.0m. The graph above provides a comparison of a range of air pumps (ACQ models) and blowers (S and K models) ranging in size from 75W to 11kW. To make matters more interesting the larger blowers are 3-phase units whereas the smaller models are all single phase, but, although highly relevant in reality, we can ignore this for now for illustrative purposes. Consider the graph which displays the efficiency of each machine in 2 ways for comparison, the amount of aeration delivered at 1.0m water depth vs. the amount of power consumed, and the aeration delivered vs. the retail price of the unit. It can be seen that the blowers are significantly more efficient per unit of aeration in terms of cost, but even the larger blowers are more cost efficient than the smaller blowers. In terms of power efficiency, a more complex picture emerges where there is more variation between models than between the different equipment types. The ACQ9 air pump is as efficient as some of the blowers, whereas the two smallest blowers, S2M and S3M are the least efficient of all.

Comparison of the efficiency of a range of air pumps and blowers