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Oxygen Verses Aeration

One of our members emailed me referencing a video where I talked about oxyfertigation and stated the oxygen uses less energy than aeration in the rafts.  I was specifically talking about liquid oxygen in comparison the 80kw-h it would take to aerate the 3600m2 raft.  However, it is a great question and one we will discuss in this article. In our scenario we were talking about a 110 liter per minute air pump using 125 watts of power verses an oxygen generator producing 4 liters per minute of oxygen and consuming 250 watts of power.  Straight away we see the oxygen generator is using twice the power so it is easy to think it is not as efficient as the air pump.  Let’s take a closer look. Air Pump First we need to determine our oxygen transfer rate (OTR) for the system we are working with.  I dont have that information handy so I will set up the system as running a minimum of 5mg/L dissolved oxygen, which is great for fish and system health.  We will also be running our system temperature at 25 degrees Celsius.  The temperature and dissolved oxygen (DO) are important for calculating your Field Oxygen Transfer Rate (FOTR) as we did with the design calculator here. I have entered our values into one of my Air Pump Oxygen Transfer Calculators (will make this available shortly).  See the results below: We have used an average OTR of 1.3kg/kw-h.  This is a known transfer rate for medium pore air stones at 1.2 meters which can be between 1 and 1.6 kg/kw-h.    The resulting oxygen transfer of the selected air pump is 0.059 kg of oxygen per hour.  Under the same conditions if we double the size of the air pump to match the oxygen generator power use of 250 watts, we double the oxygen transfer of 0.118 kg of oxygen per hour. Oxygen Generator The oxygen generator in this scenario as mentioned is a 250 watt unit producing 4 liters per minute of 99% pure oxygen.  Simple math on this one provided you can achieve a 99% transfer rate with the injected oxygen using the right gear.   Putting pure oxygen into air stones wont do. The generator is producing 238 liters of oxygen per hour.  At our operating temperature of 25 degrees Celsius there is 1.309 kg of oxygen per cubic meter (1000 liters) or 0.001309 kg oxygen per liter.  Allowing for 99% efficiency transferring the oxygen from the generator we have a production of 0.307 kg of oxygen per hour  (235 liters per hour x 0.001309 kg oxygen per liter). Summary Air pump of 250 watts will produce 0.118 kg of oxygen per hour Oxygen generator of 250 watts will produce 0.307 kg of oxygen per hour In this scenario our oxygen generator produces 2.6 times more oxygen for the same energy use This was a great question which we will cover in more detail in future articles.  I encourage everyone to drop me an email if you have a question and I will give it priority. Regards Paul…

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