Aeration Energy Consumption
Tech Talk 52
Mechanical aerators break water into droplets to produce liquid/air contact, while underwater diffusers introduce bubbles from a depth to achieve oxygen transfer and mixing. Bubble type aeration systems are replacing many mechanical aerators because of their low maintenance, reliability, safety, flexibility and overall efficiency. They excel where small amounts of aeration, circulation and carbon dioxide degassing are needed in many locations. Bubble aerators are also better at removing gases, such as ammonia and carbon dioxide. Diffusers are made to deliver either coarse (approximately 6 mm), medium (approximately 3 mm), or fine (approximately 1 mm) air bubbles.
Coarse-bubble systems require the lowest air pressure and are very resistant to clogging, but are about a third as efficient as medium-bubble systems in transferring oxygen to the water. The medium-bubble diffuser requires only slightly higher air pressure, but its superior oxygen transfer more than compensates for the increase in maintenance. The fine-bubble diffuser’s superior oxygen transfer usually does not compensate for its higher pressure and maintenance requirements. Fine-bubble diffusers are typically chosen for pure oxygen or ozone systems where pressure requirements are less important than transfer efficiency. Overall, when aerating with air, medium-bubble diffusers are the most popular among aquaculturists.
Diffuser clogging can occur from the inside of medium and fine pore diffusers by dust and dirt particles carried by the air supply, if an air inlet filter is not used. But clogging is most often due to calcium carbonate deposits. (This source of plugging is prevalent in hard water and salt water.) Another source of plugging is bacterial slime, which also forms on the external surface of the diffuser.
Replacing medium- and fine-bubble diffusers with coarse-bubble diffusers might seem like a good way to avoid periodic cleaning, but it’s not very cost effective. Let’s work out the economics on a 10 horsepower system:
If a 10-horsepower, medium-bubble aeration system can support 40,000 pounds of fish, a coarse-bubble system would require 30 horsepower! Electricity currently costs about $70 per horsepower per month in our area. This would make the utility cost rise from $700a month to $2,100— that’s an extra $16,800 per year paid to the power company. An additional 20 horsepower in blowers would need to be purchased, as well as a larger diameter air-distribution pipe, if coarse-bubble diffusers were chosen over medium bubble diffusers.
System Design With Medium-Bubble Diffusers
Diffuser placement should allow for easy removal and time should be allotted to clean all the diffusers in one section at one time. This not only reduces the aggravation created by multiple individual cleanings, but also it suggests when to schedule the next cleaning. With our Sweetwater® glass-bonded diffusers, frequency of cleaning can range between monthly in very hard water to once per year in soft water. Aquatic Eco-Systems, Inc. introduced the low-pressure, low-maintenance, medium-bubble air diffuser to the aquaculture industry in 1978. Our glass-bonded silica, medium-pore diffuser is still the standard . We’re always looking for a better diffuser; that is, one with finer bubbles, lower pressure loss, self-weighting, non-clogging and less expensive. When we find one, we’ll let you know. If you find one better than the Sweetwater®, please let us know.
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