Pond Boss Forums AERATION Systems questions Hypolimnetic aerator idea

I've been thinking about keeping trout in small ponds, and considering aeration systems to allow this in upper-midwestern ponds without seepage or spring inflow.

Andedammen posted a helpful link to hypolimnetic aeration systems (http://www.env.gov.bc.ca/wat/wq/reference/aerationapd22.pdf) designed to aerate water below the thermocline without disrupting the thermocline. System A on page 11 looked simplest to me.

After putting my brain to work, I came up with the idea of modifying system A by pumping cold water from a well into the top. This would raise the level of water in the pipe above the pond's surface level, forcing water out of the bottom of the pipe and the pipe branches below the thermocline. Because the well water would be cold and entering below thermocline, the thermocline would not be disrupted. Well water is normally very low in DO, but the diffusor (diffuser?) would fix this: the well water would be aerated for its entire path down the pipe. (system illustrated below)

The well pump could be rigged to run from a thermostat with a temperature probe located in the pond below thermocline level, so that water below thermocline was kept below 63F or so. The pump would need to be adjusted to not pump so quickly that water spilled out of the top of the pipe. The aerator could be left on regardless of well pumping, as it would just be aerating the sub-thermocline water and causing minimal mixing.

The main engineering challenge I see is in keeping this system vertical and in the proper area of the pond. Flotation devices could be attached around the top and the system kept in place using cables attached to shore, or could be anchored to bottom. The well water hose could be run along one of these cables. The well pump could be run to keep the pond deeper than the system's height.

The pipe could be insulated above the thermocline (maybe foam casing could be put around it, to double as both flotation and insulation), and painted in reflective material for the top few feet to prevent solar heating.

Trout would probably have to be fed using sinking food.

Cecil has mentioned that his trout pond operation requires about $100 of electricity per month during summer for the well, but it has to be operated 24/7. My thinking is that with less mixing of warm and cool water, the well would run less, resulting in significant savings. Actually building the system shouldn't be too expensive as long as a well was already in place. PVC pipe and off-shelf components could be used for everything.

The ideal pond for this setup would probably be small (minimize volume to be cooled), steep (minimize mixing), on a north-facing slope (minimize solar heating), and surrounded by trees (minimize wind mixing of water). A pipe overflow would almost certainly be necessary.

Can anyone see any obvious flaws with this system? I have little experience and look forward to feedback.


(not to scale)

Another possible variation of this system, for ponds with very steep walls, might be to just lay the pipe on the bottom, from below thermocline to the surface, pump cold water into the top, and drop an aeration hose down into the pipe. This would resolve the anchoring issue, but might not work well unless the pump was running constantly.

What about dropping the well water through a packed column, into a pipe and then running the pipe underground close to the bottom of the pond? That way the water is aerated and degassed before it hits the pond, and since it is colder than the water above it in the water column, it should stay on the bottom and not disrupt the thermocline.

I haven't done this in my trout pond but had thought of it. I have dropped the well water through a packed column before adding it to the trout pond, but it was added at the surface. I had enough flow to keep the entire pond no higher than the mid sixties. With the above you may be able to get away with pumping in much less.

I tried doing this a couple years ago and while it did keep temps colder it added a new set of problems due to low DO and gas build up at the bottom of the pond. I think it would have worked if I had followed Cecil's advice and run it through a packed column to add O2 and degas. A deep pond will also help if you can keep DO up in the depths.

Bender,

What specifically did you do other than not use a packed column? Which approach did you use?

Definitely an interesting idea. Hypolimnetic aeration seems to be kind of a sketchy art, most of the discussions I can find on the internet center around using it in 100+ acre lakes and reservoirs, not <2 acre ponds.

You're right, it might be simplest and most reliable to pump water up, then gravity feed through a packed column and down through a pipe below the thermocline. Aeration could be done in a separate unit, either an attempted hypolimnetic aerator as detailed above or a simple bottom diffuser/thermostat setup.

Maybe the simplest set would be:

1. Well & pump -> packed column -> pipe below thermocline; with the well pump hooked to a thermostat set to activate when the bottom of the pond is above ~65F, and

2. Aerator & bottom diffuser; with the aerator hooked to a thermostat set to activate when the surface of the pond (perhaps 6" deep) is below ~64F.

Main concern would probably be, in the dogs days of summer, the bottom waters becoming O2 depleted but still cold. Perhaps the pump or aerator could just run every night for a bit, regardless of temperature.

This might be slightly more expensive in terms of electricity, but would be much simpler and have lower fixed costs than a hypolimnetic system. Pond position and construction would probably have a significant impact on how well this worked: a steep, deep pond on a north-facing slope with trees planted to the south should be ideal.

Would there be any downside to pumping the well water directly into a 3/4 or 1 inch pipe to say maybe 1-2 ' off the bottom and then using a venturi type aeration directly into the pipe at the surface ?

This would carry super oxygenated water to the bottom along with the fresh cold water. As stated above it would only work when the fresh water is flowing so maybe pumping sessions of 8-10 hours in the evening.

I could set this up realtively easy by adding about 12' of pipe to my current system but I have nothing in the way of thermo's or tests to document the results.

My main concern would be whether the water output is sufficiently oxygenated. Maybe you could run the output from this pipe into a large bucket, then see if a small trout can survive in the bucket up to 65F? This is probably the best way to test how well it will work in the pond.

These guys seem to have done a lot of work on the subject: http://leisure.prior-it.co.uk/diy-build-pond-venturi.shtml

What temperature does water come out of the faucet at?

Your venturi idea is really interesting, I look forward to reports on how well it works. Even if it requires more electricity than a recirculating hypolimnetic aerator, the reliability and and fixed-cost savings could be well worth it. The equipment for your system could also all be contained in a small shed onshore, with the outflow pipe to the pond buried underground.

Maybe you could rig up some kind of system using the 2HP pump you mentioned, so that you pump water from the pond bottom back through the venturi if the pond bottom is below maybe 65F, and cuts off the pump and turns on the well water hose only when the pond bottom is above 65F? This would prevent you from constantly pumping well water, and might control overflow and introduction of minerals to the pond.

One of the more interesting aspects of a system that pumps water out of, then back into a pond is that it could be used to not only keep the pond cool in summer, but also to aerate and warm the water in winter. It would be neat to do some research into solar water heating systems. With a small enough pond, a solar heating system might be able to make enough of a difference in temperature to impact growth rates.

I made a diy oxygen cone with a venturi and pumped well water to the bottom of my pond. I also had my aerator set to turn on when temps were below 70. Found out the venturi does not function well when the output is at the bottom of the pond, due to the pressure of the water above the output. After a few minutes the air intake on the venturi would start spitting water. I tried to compensate for this by dumping the water out closer to the surface, although I probably should have dumped it out on the rocks above the water for the venturi (and well pump) to really work well.

Temps at 6' stayed chilly but I was losing perch from what I suspect was gas build up and low DO from the well water.

Bender,

How deep was your output originally ? and do you know how much head pressure you had behind the water from the well ?

Just thinking out loud here. It might be necessary to initially pump the well water into a small holding tank ( maybe 50-100 gallons ) and then use a small booster pump with a higher head pressure to push the water and air to the bottom.

The venturi we have setup right now is only 3' underwater but theres a clear trail of bubbles for 15-20 ' from the outlet. This water is being pushed by a 2hp pump.

I would think starting a system like this and disturbing the lower water levels would have the same effect as adding a diffuser would. Perhaps short sessions initially or following the startup procedure for aeration would eliminate the YP die off ?

Keep in mind that when we talk about things like venturi's and relying on the bubbles for aeration, this is a much different application than your standard pond aeration system. It is the difference between mixing and oxygenation. Generally we pondmeisters rely on mixing from an aeration device to deliver oxygen via transfer from exposure to the atmosphere. Oxygenation refers to the transfer of oxygen between the bubble and the water. Oxygenation is enhanced with smaller bubbles and longer contact times between bubble and water.

Txelen, assuming your well water has zero dissolved oxygen, I'm skeptical as to whether you would have enough contact time with the bubbles in your original design to provide the oxygen that your fish need. However, oxygenation could be enhanced with this design by incorporating ozone with the aeration system. Ozone transfers oxygen into water about 11 times faster than atmospheric air. Higher oxygen transfer rate = more oxygen in less time.

You could insert a venturi and corona discharge ozone system on shore near the well. The water would then be ozonated and under pressure in the pipe that leads to your column in the pond. These are ideal conditions for mass transfer of any gas and I would guess should be effective in providing your DO goals. Then simply allow the oxygen rich water to cascade into you column as originally planned. Of course this assumes that your well is pumping enough gpm to provide vacuum on your venturi.

Alternatively, you could go with your current drawing and simply incorporate an ultraviolet ozone system between your compressor and the diffuser so that the bubbles would achieve better oxygen transfer as they rose through the column.

I agree with the Wizard. My limited experience with oxygenating well water has taught me that air bubbles alone will not bring DO levels up enough for trout. I transfer fish in a 100 gallon stock tank, filled up the night before and aerated with two 18" aquarium airstones. When I get to the fish farm I have them check DO levels. The DO levels after 18 hrs of bubble aeration, are not high enough to support long term trout survival (although sufficient for short term travel).

I haven't experimented with using O2 or O3, but I like the idea of Cecil's packed column because it would be less costly than purchasing gas or O2/O3 generators. I like the mechanics of Cecil's packed Column, because we switch the ratio of water/air, so it is droplets of water passing through air. This frees up trapped gasses and exposes more of the water's surface area to air.

Water output was somewhere around 20'. The pump definitely was undersized for this and could not produce enough pressure.

I like your stock tank idea, but if you are going to pump water you might as well pump up from the bottom. You can then spray into the stock tank and gravity drain back to the bottom of the pond. You could add well water at the stock tank using sweeper nozzles (like Condello did in his pond) to oxygenate and cool the water. You also might be able to use earth tubes to ensure the air around the tank is not too warm.

well, I'm back to the drawing board for creative ideas. I added 10' of 1 inch hose on the end of my existing setup thinking the water and bubbles would simply go further down. I figured it was worth a shot to try it for 2-3 days and see what happened but even with a 2hp pump the back pressure from adding 10' of pipe was too much for the venturi to produce bubbles.

a couple more nights on the dock gazing at the water and I'll come up with a new grip it and rip it idea.