turning air pump off for 30min every 2hrs? what do u guys think?

turn pump off for 30 min every 2hrs?

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Darknes01

Darknes01

Well-Known Member
So i have my air pump turning off for 30 min every 2hrs to give it some rest.
I was wondering what you guys think about this? also i was thinking maybe when it turns off it would give the roots some time to rest.
do u guys think this is a good idea or a bad idea?
should it be on all the time? or say off less frequent or more frequent?
i have everything automated so its easy to set whatever parameter i want.
 
Darknes01

Darknes01

Well-Known Member
im thinking like this, in nature, roots dont move around while in soil. so my air stones are creating some good bubbles and moving the roots around constantly. Thought process was, hey lets let them rest a little.
 
Keesje

Keesje

Well-Known Member
Plants are not humans.
Although we talk about 'sleep', 'work', 'rest' etc. plants' hormones mainly react on circumstances.

So, for rest you don't need it.
There is another thing: Some scientist say that moving the roots the whole time, is not good for roots.
I have no clue; I just repeat what I did read.
That's why bubbles might not be the best thing.
For getting DO in your water there are several other ways to get DO in your res.
Cheaper ones. Simpeler ones. Just as effective.
Only thing is to get the DO in your roots.
With this, bubbles might help because they 'loosen up' the rootball perhaps a bit more.
 
Keesje

Keesje

Well-Known Member
Agree on that.
With DWC I would never turn off the pump.
Why take the risk? Although it will take some time before all DO is consumed.
 
Darknes01

Darknes01

Well-Known Member
Keesje said:
Plants are not humans.
Although we talk about 'sleep', 'work', 'rest' etc. plants' hormones mainly react on circumstances.

So, for rest you don't need it.
There is another thing: Some scientist say that moving the roots the whole time, is not good for roots.
I have no clue; I just repeat what I did read.
That's why bubbles might not be the best thing.
For getting DO in your water there are several other ways to get DO in your res.
Cheaper ones. Simpeler ones. Just as effective.
Only thing is to get the DO in your roots.
With this, bubbles might help because they 'loosen up' the rootball perhaps a bit more.
Click to expand...
im interested to know what other ways is there to add DO to the res. if you could please link me something or explain more that would be awesome and thank u in advance.
 
Keesje

Keesje

Well-Known Member
Waterfalls, flooming, venturi, for example
You can find them all on this beautiful forum.

The bubbles created by an airstone will not bring DO in the water because of the bubbles full of air.
They do it because they agitate the surface of the water.
 
OldMedUser

OldMedUser

Well-Known Member
Keesje said:
Waterfalls, flooming, venturi, for example
You can find them all on this beautiful forum.

The bubbles created by an airstone will not bring DO in the water because of the bubbles full of air.
They do it because they agitate the surface of the water.
Click to expand...
Wrong. Bubbles dissolve into the water as they rise. The finer the bubbles the less air needed to saturate the water with O2 as they present much more surface are per volume. I used a 50 ft. weeper hose that made for the garden as a long airstone in my dugout. Weighted at each end and the middle it made a large m shape under the water. You could see the fizzing on the surface where the tops of the loops were close but nothing in the middle. Rowed out in the boat in the sunshine and could see the bubbles rising from the depths but never reaching the surface. Where did they go if they weren't dissolving into the water?

Micro-pore airstones are many times more efficient than the typical aquarium stone because they have such tiny bubbles.

O2 will get in where the water is agitated too but that's not the main source.
 
Keesje

Keesje

Well-Known Member
I think you are not right here.

If you can't see the bubbles anymore, it doesn't mean that all the oxygen is dissolved.
It only means that you did not see them. They just became smaller then visible bubbles.

Think about this: water of a temperature around 20 - 25 degrees can hold about 8 to 9 mg of O2 per liter. (let's not talk about supersaturation)
If you push a liter of air in your res, it contains about 20% O2.
1 liter of air weighs about 1300 mg.
20% of that (the O2) is about 260 mg of O2.
So 1 liter of air would theoretically be enough for a reservoir of about 30 liters, if it were the bubbles that would cause maximum DO.
You say that tiny bubbles totally dissolve. That would mean that if you would push 1 liters of air in tiny bubbles in this 30 liter reservoir, the maximum DO would be reached.
Then after pushing in this 1 liter of air, this dissolving could not be possible anymore. Because there is simply no more room for extra DO.
Is that the moment you should start seeing bubbles again?
I think you have to agree with me that this is not the case. The bubbles will still be invisible the nearer they get to the surface.

Besides that, under normal circumstances there will always be maximum DO in water.
Air pressure of 1 bar will make sure that at around 25 degrees 1 liter water will contain around 8 mg of DO.
The agitation of the water just makes sure that this process is fastened.
It doesn't matter how you agitate the water.
Maximum DO is very easy to reach.

Get yourself a DO meter and do some measurements with different systems.
At a certain moment you'll think your meter is broken, because even with the slightest movement the meter will show maximum DO.

Growers only face a few problems:
- Is the res big enough for your roots? > if the roots 'eat' faster then air pressure can get fresh oxygen in your res, it might lead to problems.
- Is the temperature right? >Warm water can hold less DO, so too warm water can cause problems. But we are talking around 30 Celsius and up.
- Will the DO reach the roots? > if a rootball is too dense, there might occur a problem where there is still-standing water inside the rootball.

Bubbles might help getting more moving of the roots and thus preventing water to stand still in the rootball.
That could be a benefit of bubbles. Although some scientist say that the movement of the roots is not good (I don't know)

I think people want to believe that bubbles work better, because that is what they can see with their eyes.
 
OldMedUser

OldMedUser

Well-Known Member
Quite a long diatribe to argue a wrong point of view with nothing but your opinion to support it.

Here's a short paper from one of many studies I found in seconds.

scialert.net

Effect of Bubble Size on Aeration Process - SciAlert Responsive Version

Fulltext - Effect of Bubble Size on Aeration Process
scialert.net

INTRODUCTION

Bubble columns are used as multiphase reactors in process industries and are widely used in waste water treatment plants. The construction of these devices is simple and they are easy to operate and hence are used in many process industries. In a bubble column the gaseous phase is dispersed into a stationary liquid phase. A critical parameter in the design and control of a reactor is the bubble size distribution (Zhang et al., 2012). It plays an important role in performance of gas liquid contact.

Aeration is a major process in water treatment in which certain constituents are removed or modified by bringing water and air into close contact by introducing air bubbles and allowing them to rise through water. Compressed air is dispersed in the form of bubbles after it is introduced below the surface of water in this process. Camp (1963) has noted that gas transfer is accomplished mainly through bubbles and the size of the bubble determines the transfer rate. Cumby (1987) mentioned that some mixing effect takes place due to the turbulence imparted by the bubbles as they rise. As the bubbles rise transfer of oxygen also takes place through their surface. The author has also mentioned that smaller the gas bubble, the larger interfacial area per unit volume and so bubbles of smaller size (e.g., less than 5 mm diameter) are desirable. These can be produced by sparging air through small holes, less than 3 mm diameter. When a nozzle that is submerged in water is operated, oxygen transfer to water occurs over two main interfaces. As the bubbles ascend through the water column, oxygen is transferred through the bubble water interface. This also occurs across the gas-liquid interface at the water surface. DeMoyer et al. (2003) through their experiments conclude that the total oxygen transfer takes place both through the surface and the bubble-water interface. However, oxygen transfer at bubble water interface contributes most of the oxygen. They obtained the results numerically and verified them experimentally. Fayolle et al. (2007) through their numerical studies have shown that when the bubble size decreases by 10%, the oxygen transfer coefficient is found to increase by 15%. Conversely, when the bubble diameter increases by 10% the oxygen transfer coefficient decreases by 11%. The above results confirm the necessity to measure the air bubble dimensions. The authors have concluded that adequate tools are required for the estimation and modelling of the bubble size at the diffuser level.

Can we lay it to rest now?

:peace:
 
A

Aqua Man

Well-Known Member
OldMedUser said:
Quite a long diatribe to argue a wrong point of view with nothing but your opinion to support it.

Here's a short paper from one of many studies I found in seconds.

scialert.net

Effect of Bubble Size on Aeration Process - SciAlert Responsive Version

Fulltext - Effect of Bubble Size on Aeration Process
scialert.net

INTRODUCTION

Bubble columns are used as multiphase reactors in process industries and are widely used in waste water treatment plants. The construction of these devices is simple and they are easy to operate and hence are used in many process industries. In a bubble column the gaseous phase is dispersed into a stationary liquid phase. A critical parameter in the design and control of a reactor is the bubble size distribution (Zhang et al., 2012). It plays an important role in performance of gas liquid contact.

Aeration is a major process in water treatment in which certain constituents are removed or modified by bringing water and air into close contact by introducing air bubbles and allowing them to rise through water. Compressed air is dispersed in the form of bubbles after it is introduced below the surface of water in this process. Camp (1963) has noted that gas transfer is accomplished mainly through bubbles and the size of the bubble determines the transfer rate. Cumby (1987) mentioned that some mixing effect takes place due to the turbulence imparted by the bubbles as they rise. As the bubbles rise transfer of oxygen also takes place through their surface. The author has also mentioned that smaller the gas bubble, the larger interfacial area per unit volume and so bubbles of smaller size (e.g., less than 5 mm diameter) are desirable. These can be produced by sparging air through small holes, less than 3 mm diameter. When a nozzle that is submerged in water is operated, oxygen transfer to water occurs over two main interfaces. As the bubbles ascend through the water column, oxygen is transferred through the bubble water interface. This also occurs across the gas-liquid interface at the water surface. DeMoyer et al. (2003) through their experiments conclude that the total oxygen transfer takes place both through the surface and the bubble-water interface. However, oxygen transfer at bubble water interface contributes most of the oxygen. They obtained the results numerically and verified them experimentally. Fayolle et al. (2007) through their numerical studies have shown that when the bubble size decreases by 10%, the oxygen transfer coefficient is found to increase by 15%. Conversely, when the bubble diameter increases by 10% the oxygen transfer coefficient decreases by 11%. The above results confirm the necessity to measure the air bubble dimensions. The authors have concluded that adequate tools are required for the estimation and modelling of the bubble size at the diffuser level.

Can we lay it to rest now?

:peace:
Click to expand...
Here is the problem. It goes beyond air bubbles. I can dig up plenty of evidence of needed but hoping you take my word for it. First what is a bubble. It's a pocket of air in water. This bubble is made up up different gasses with different rates of solubility. Some like CO2 dissolves easily where as o2 does not. So a bubble is simply not a bubble but needs to be looked at as individual gases. There is simply not enough dwell time for adequate gas exchange to happen in this time. It's well know that the surface area of a body of water is what will determine the gas exchange capacity of that water.l because this is where there is constant dwell time between gasses and water. The other aspect is the mixing of the water column. By mixing you bring water with lower concentrations of o2 to the surface. Now the further gasses go below equalibrium the faster the will exchange that specific gas to try and reach equalibrium. This is why surface agitation is important just like in nature the splashing and rolling of water increase the effective surface area.

In order to increase gas exchange but the bubble themselves you would need to increase pressure and dlwell time and in the depths we use this is just not adequate enough to make any significant impact.

Now with that said bubble size does play a role in this as it contributes to surface movement differently and the general consensus on this is smaller is better but only to a point. Basically whatever gives you the most agitation of the entire surface will be the most effective.

Trust me I have injected CO2 into water for years and that gas is far far far more easily dissolved than oxygen. This is where these people get this from because with CO2 being far more easily dissolved what you are suggesting with smaller bubbles giving a larger surface area of exposure and increased dwell time makes a difference. But that is not the case when it come to the much harder to dissolve oxygen.

Also micro bubbles will trick a DO meter into thinking it's dissolved o2 when in fact it is suspended because of buoyancy not actually dissolved.

I have not read this study but I can say it has to be flawed. I'm extremely busy the next few days but if ya like I can gather some info to support this over this week some time as I get time
 
Keesje

Keesje

Well-Known Member
I always like to read different point of views, and always happy with scientific papers.

I did read the paper mentioned by @OldMedUser and what is not clear to me how they concluded how the bubbles had a bigger impact on the DO then the agitation of the water surface. Also they did not explain why it was. Or I did not understand it well enough :)
Bubbles do bring O2 in the water, without a doubt, but not very efficient in our hobby.

I did read a lot of papers about bubbles in water, and in 99% of the cases these are about purification of water.
The main reason for getting oxygen in the water is that micro organisms need the O2 to do their work.
To get oxygen in the water they do use bubbles, but they use them mainly in 'deep shaft' systems.
The reason for this 'deep' is that if the basin is not deep enough, there is not enough contact time between the O2 in the bubbles and the water.
Smaller bubbles even take a bit longer to reach the surface, so probably they will get more DO in the water.
In large basins they almost never use bubbles, just for the simple fact that other systems are doing a better job (rotators for example)
A bubble would leave the water too fast.
And even if the bubble would do the same job in a large but shallow basin, they still would choose the rotators because it takes less kWh per mg O2 per liter.
What bubbles do manage, is to get fresh water to the surface all the time. That is where the most oxygen transfer takes place.
The bubbles make sure that the surface is refreshed all the time. Water that lacks DO is brought to the surface, transfer takes place and the water goes down again.
A larger surface is also a good way to get plenty of DO in your water.
 
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