Ok, first, let's run some numbers: The pressure induced by air is density * (airspeed)^2. So a 10km/hour breeze would produce a pressure of about 10 Pa, or 10N / m^2. In other words, roughly a kg force for every square metre of drag area. So your air scoops might have an area of 2m^2 (generous) and a total torque of 2kgf 1.5m (30Nm). Let's say the maximum speed of the scoops is the airspeed (generous), then we have a power of 30N m * (10km/hour) / 1.5m pi or 17W.
Now the internal energy of a gas is pressure * volume, so if you want 10kPa air (1m water) then 17W will produce air at a rate of 1.7litres/s. Sounds plausible.
I think Ron is right, rather than trying to drive a refrigeration compressor you really want something optimised for large volumes of low pressure air. The most obvious system would be a diaphragm pump. Perhaps a car tyre inner rubber with a cam driving it in and out with two valves. We might be able to make one valve simply from the tank water - when the bellow compresses, the water is driven through the water directly. As the pressure is low, a simple flap type valve would probably suffice for the intake.
The next thing to consider is whether we can go directly from wind to oxygenated air. One idea would be to have a scoop direct air across the surface of the water to encourage waves to form, aerating the water.
Could we build an ET style pump using a tree as the source of oscillation?
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