Flow Through DSB

[bioload]

Thanks for the link....and a great visual representation of a DSB.

Looking at the diagram above, could one conclude that the "layers" may fluctuate in depth periodically based on the rise in ORP observed.....or am I just reading too much into what I observed.

Maybe some channelling in the DSB allowing some water from the surface to make its way directly to the drip outlet (a result if not having a "fine" substrate).

Wish I had a continuous monitor that could network with my PC to trend.

 

[Allmost]

Just a note : OPR is not representation of amount of O2. it is oxidation reduction potential.

http://reefkeeping.com/issues/2003-12/rhf/feature/index.php

now maybe the water is not going through all the sand and just about.

 

[TheFishMan65]

I really don't know this stuff - not sure anyone does. I it would be nice if we could define a minimum depth where hypoxic goes anoxic. That (I think) would be the depth that we don't want a sand bed any deeper. Of course it probably depends on too many variables to define.

I do not think they would fluctuate much or if they did not very fast. The bacteria would have to repopulate as the fluctuation occurs. OK, they do that pretty quick but I would guess hours rather than in seconds when a wave might produce more pressure on a section of the bed and push oxygen a little deeper.

I think I read that someone had 3 inch worms in there DSP so I think it is possible to get some deep channeling.

Too late know (wish i though of this earlier), but maybe you should have used smaller tubing for your test flow. At 1 drop a second or so. How long does it take to change the water in the testing area. I don't know if this will have any affect, but I guess we will see.

DISCLAIMER: I really don't know much about this, but am throwing out ideas.

 

[bioload]

Did a few couple test and things don't seem to be going as I thought........or again maybe just to early to make any conclusions.

ORP: 326mV (Back to original range)
pH: 7.18
Drip Rate: 0.73 drops/sec

Nitrate No Change

Test DO as well and there doesn't appear to be a difference???

 

[TheFishMan65]

Is it possible the water hasn't really changed in the output tube? There is an awful lot of volume to replace at 1 drop a second. Nitrates don't surprise me yet. However I would have thought it was oxygen free by know. Fill a 1/4 measuring cup and time it. Then guesstimate how long it will take to replace the water in your pipe.

 

[ruprecht]

Test DO as well and there doesn't appear to be a difference???

By dripping anoxic water into your vial you are introducing oxygen into the sample. I am not surprised by your result.

 

[bioload]

Hi ruprecht,

Is there a way I could obtain a sample that would prevent this. I currently place the drip tube at the bottom of the vial to avoid.

 

[bioload]

Is it possible the water hasn't really changed in the output tube? There is an awful lot of volume to replace at 1 drop a second. Nitrates don't surprise me yet. However I would have thought it was oxygen free by know. Fill a 1/4 measuring cup and time it. Then guesstimate how long it will take to replace the water in your pipe.

Got me thinking and did a couple calculations. Let me know is this sounds right?

1 drop = 0.05 milliliter = 1.32086E-05 gallon [US, liquid] / sec

1.32086E-05 gallon [US, liquid] / sec = 1.141223 g/day

Since I'm running a little less than 1 drop/sec so lets say 1 gal/day

Didn't calculate the volume of the output plumbing but I would guess that the flow would be enough to empty the plumbing several times per day.

May possibly be that flow is only part of what makes a sand bed anaerobic, and a few other key elements are missing.......wish I had more 5 gallon tanks and meters to work with (hint to sponsors).

Lokking at some factors that affect the amount of oxygen dissolved in water:

1. Temperature: As water becomes warmer, its ability to hold oxygen decreases.
Not much to change here. I could add a heater to the DSB in order to reduce the oxygen content, however, that may not be very efficient. I could use the same wattage pump to run a protein skimmer.

2. Photosynthetic activity: In bright light, aquatic plants are able to produce more oxygen. I don't believe this would impact a DSB due to the depth of the sand. In addition, my ORP values increased overnight to 300+mV, and are currently 199mV just before lights out.

3. Decomposition activity: As organic material decays, microbial processes consume oxygen.
I think this one is the BIG one that is currently missing in the DSB. Based on what I've seen so far could be the most important factor. With nothing to consume the oxygen within the bed would it not just diffuse from high to low concentration until evenly distributed.

Maybe it's not low flow that causes anaerobic conditions for denitrification directly. However, the low flow causes organic matter to settle which decays and in turn consumes oxygen. As the oxygen diffuses from the water column into the bed it is consumed by decomposition resulting in anoxic/anaerobic zone below???

4. Mixing and turbulence: Wave action, waterfalls, and rapids all aerate water and increase the oxygen concentration.
Occurs in the water at the surface, and effects are probably negligible within the bed.

5. Salinity: As water becomes more salty, its ability to hold oxygen decreases.
Not much to change here

Not a expert either, just throwing stuff out there as well.........still wish I had more 5 gallon tanks and meters to work with (hint).

Will stay the course for now.

 

[ruprecht]

Hi ruprecht,

Is there a way I could obtain a sample that would prevent this. I currently place the drip tube at the bottom of the vial to avoid.

I apologize for the shortness of my answer. I had meant to finish my comment with an edit but then had forgot. A drive-by comment is the worst. I am enjoying your experiment so please keep up the good work.

Let me say that I get paid to take oxygen samples, hundreds a year, so I do have some experience. Am I a chemist? No. But I have seen first hand how variable oxygen samples can be even with apparently replicate drawing technique and subsequent titration. Am I seeing a 2ml/L difference in what I do? Hell no, if I was I'd get fired. So in retrospect I can say - I was wrong in saying that I was not surprised that with drips the samples were similar. However, the same levels of oxygen in both samples still does not surprise me. The experiment has only had a week or so to progress, denitrification may only be in its infancy at this point. Give it some time and I'll try to show some more patience by keeping my mouth shut. I look forward to seeing future results. Hopefully I'll get my system set up and get cycling myself. Look forward to hearing your opinions on my ideas.

 

[ruprecht]

I think this one is the BIG one that is currently missing in the DSB. Based on what I've seen so far could be the most important factor. With nothing to consume the oxygen within the bed would it not just diffuse from high to low concentration until evenly distributed.

Simply put, denitrifying bacteria will use dissolved carbon and dissolved oxygen to turn nitrate into nitrogen gas.

I think when you see oxygen around <0.5ml/L you'll have evidence of denitrification.

 

[TheFishMan65]

ruprecht has a good point it takes a while for the bateria to get established. Wasn't this 'new' sand? How long does it take to cycle a new tank (been too long since I did one)? I would think this would occur a little faster since a lot of bacteria are present, but maybe not since the needed bacteria are established somewhere else.

 

[bioload]

Yet another reference

Biological Oxygen Demand

 

[ruprecht]

How long does it take to cycle a new tank (been too long since I did one)?

Every tank is different. I'm looking forward to seeing how this system balances out.

Yet another reference

Biological Oxygen Demand

Take that and their Dissolved Oxygen page with a grain of salt. For instance, they say less than 4ppm DO is 'Poor Water Quality', however in the open ocean the largest assemblage of organisms on the planet live in water with that range of DO. They also say that 8-12 is 'Good', when I can't recall even seeing values that high even in the chlorophyll maximum in the open ocean or even in coastal waters for that matter.

 

[wayne in norway]

You know, the DSB in a bucket is a really great, simple design, and the principle source of water flow is well understood and modelled. Please look to the research I referred to on the first page as they have already modelled all this stuff very nicely. To say noone knows how a dsb works is just not so. You just won't find it in a lot of hobbyist material

Capn' H - I strongly disagree with the model that says that water flow thro' the sediment is controlled or dominated by biological activity. It's been measured, modelled and experimnted with and demomstrated to be a mix of something like advective flow 90%, biological effected flow 8% and simple diffusion 2%. I've seen the various quotes from Shimek and others , adn they are completely unsubstantiated as far as I can tell - he offers no support for them.

I'd also argue the top layer of a sand bed is pretty good aerobic biological filter as well. You do not need a ton of live rock to provide a bacterial media (tho' it's nice)

 

[King_Richard]

bioload:

I'm a lil confused on which method is getting tested out here?

Is it the deep sand bed in which we feed our bristle worms, pods, burrowing clams etc.... and also try to maintain an area beneath all of that where we get our collection of bacteria to grow and convert nitrates.

Is it the really deep sand bed that people are putting in buckets and running filtered water through in order to only culture the bacteria portion of the sandbed.

Or is this some other beast all together?

 

[bioload]

Hi King_Richard,

The Sand bed is a remote deep sand bed where water is flowed over the bed and returned back to the tank, similar to the DSB in a bucket. However, there is no "filtration" of the supply water being passed over the DSB, which I suspect should help to expidite the denitrification process by providing a food source.

To date (Day 18) I have yet to see a reduction in nitrate from the effluent drip within the bed. In addition, no water changes have been performed on the tank.

 

[Allmost]

Hi King_Richard,

The Sand bed is a remote deep sand bed where water is flowed over the bed and returned back to the tank, similar to the DSB in a bucket. However, there is no "filtration" of the supply water being passed over the DSB, which I suspect should help to expidite the denitrification process by providing a food source.

To date (Day 18) I have yet to see a reduction in nitrate from the effluent drip within the bed. In addition, no water changes have been performed on the tank.

so what are the nitrate readings ? although I dont agree this works same as a DSB, but if it is keeping your no3 stable, it is actually removing the newly introduced no3 to the system right ?

basically matching the input to output. and that's all we want from a DSB right ? if no3 is to increase 2 PPM a day,we want DSB to remove 2 PPM a day. so I would put no change in no3 as a positive outcome

 

[bioload]

I don’t have the exact value for nitrate using the API test kit

0-10ppm (shades of yellow)
20ppm (orange)
40-160+ (shades of red)

It is difficult to say based on the shades of red what the exact value in ppm is. That said it is possible that nitrate is increasing beyond the range of the test kit.

If there was any reduction in nitrates I would expect to see it in the drip obtained from the bed, which I have yet to observe, before any reduction in the tank takes place.

ORP is still 300mV +/- 100mV

although I dont agree this works same as a DSB – How so? What would you recommend changing.

 

[King_Richard]

From what I understand and seen it was somewhat debated already is that a typical dsb rely's on the upper 1-2" to be filled w/various life forms, pods, worms and maybe burrowing clams (believe most people call em perrywinkle's or something). All of these things are supposed to play a role in breaking down the stuff that settles on the bed to feed it deeper into the bed to feed the bacteria down there while also keeping the upper surface moving to release the gas bubble that form.

The bucket method rely's soly on the bacteria. Now I'm not as familar w/the bucket method and don't quite understand how they work all I remember from reading on em was most people were saying that you needed to filter the water going into the dsb area since the bacteria itself cannot breakdown the stuff that settles on it.

So, I think you've got a problem unless nothing is settling onto the sand bed. The only way to get around it is either add the life to it as stated above earlier, run a strong enough current to keep anything from settling on it or filter it. If you add life to it then your no longer trying to test the "bucket" method. You would then be utilizing the traditional dsb.

Also I noticed your grain size looked rather large. The benneficial bacteria is supposed to be in very low oxygen zones and the larger the grain size, the deeper the bed needs to be and I'm not sure if yours is gonna be deep enough to get a substantial amount of bacteria to make a big enough impact, just something to consider for long term use.

If I'm wrong in any of these area's please correct me, I've done alot of reading on sand beds and this is just how I've interpreted it, I have also used dsb's for some time now, just not the "bucket" method.

 

[Allmost]

I don't have the exact value for nitrate using the API test kit

0-10ppm (shades of yellow)
20ppm (orange)
40-160+ (shades of red)

It is difficult to say based on the shades of red what the exact value in ppm is. That said it is possible that nitrate is increasing beyond the range of the test kit.

If there was any reduction in nitrates I would expect to see it in the drip obtained from the bed, which I have yet to observe, before any reduction in the tank takes place.

ORP is still 300mV +/- 100mV

although I dont agree this works same as a DSB "“ How so? What would you recommend changing.

I said how so I dont see this as DSB,

but I still dont have any better design.
I have no doubt on DSB working when set up properly.

I have seen it work on all my 4 tanks, and all other 17 I have set up and maintain lol