Substrate Particle size and DSB

[MikeS]

Hi all...

Been doing a LOT of reading on plenums and DSB's in preperation for my tank switch....and a question popped into my head... :idea: Looking for some thoughts on this...

Ok...I'm switching from a DSB to a plenum with a coarse substrate with high flow. The main reason is to remove the reliance on "bugs" to facilitate diffusion into the substrate. Here's my question...if the larger particle size and increased flow will reduce the reliance on bugs for diffusion...is a plenum under this type of substrate really necessary? Or would a DSB of similar large particle size and high tank flow acheive the same end? Exactly what advantage would a plenum under such a substrate have over a similar substrate without one? (I think I know the answer, just want to hear what you all think... )

MikeS

 

[NaH2O]

Mike - I think a plenum is a good idea - you will have diffusion and processes going on....just not relying on the bugs to move the wastes down. Without the plenum, what would happen when the byproducts hit the bottom of the tank? Also, are you still going to plumb the plenum space to occasional removal?

 

[MikeS]

Nikki...yes the plenum will be plumbed for occasional removal, but more cruedly than the wasting plenum we discussed here...

Ok...plenum or no plenum...the plenum itself does not directly aid in diffusion (although I believe there is a bit of osmotic stuff going there with it vs. without, and there is obvioulsy the lack of substrate resistance to diffusion in the lower depths of the bed when using a plenum)...so bugs shouldn't be a factor either way...the flow and substrate size should facilitate similar diffuation rates into the bed with or without the plenum...does that make sense?

MikeS

 

[mojoreef]

Ahh this is the question you wanted me to look at.
Good question and the answer is yeas the plenum section under the gravel is very important. When you put the plenum down and you cover it with screens you are creating a block for the large amount of diffusion you are getting in the above areas. Go back to the basic principles. WHat you are trying to do is to get more control over keeping the areobic zone viable and controlling the growth of the anerobic zone. To control the areobic zone you are using alot of flow and larger particles to allow that oxygenated water to penetrate into the rubble to keep it oxygenated with out relying on bugs to do it. In the same breathe you need to create an enviroment for the denitrifing bacteria to populate and function. the barriers that you put up once laidened with biofilm and bacteria along with organics will do that for ya and still keep the bacteria types at hands length. The plumbing that you are installing is just an added bonus of being able to reduce end product build up.
BUT remember rubble will want to trap all detritus, so good flow and properly directed flow is critical to keeping the vast majority of the detritus/food in the water column, thus only allowing a smaller percentage of the detritus to end up having to be processed. This is in direct conflict of a dsb where you cant have the flow to do that as you will have sand storms, thus the percentage is opposite, so instead of the detritus/food being available to the corals and then being removed it becomes food for the sand. Makes for a well feed sand bed, but takes a very very viable food source from the inhabitants.


Mike

 

[MikeS]

Thanks....

That was basically my understanding of the advantage of a plenum under the substrate...in addition, some research cite an area of anoxic rather than anerobic condition exisiting in a properly set up plenum substrate where "high energy" bacteria live that are extremely effcient at nitrate removal thrive...supposedly this zone is much smaller in a DSB, if present at all...

MikeS

 

[wave98]

Mojoreef and MikeS:

I just registered and this is only my second post. I got here thru a plenum wasting link and i am interested in pursuing the development of that sandbed option. While plenum wasting has not become popular or common yet, niether has it been experimented with very much in comparison to the more highly debated sandbed options, at least as far as i have been able to find thus far. Can you help me find a currently active discussion on this topic, as I find more potential in this approach than the limited and hotly debated alternatives.

 

[MikeS]

Hello and welcome to RF...we have a lenghty thread here on the design of a wasting plenum...
http://www.reeffrontiers.com/forums/showthread.php?t=2931

Mine will not be as intricate as this one, but it will be designed to allow me to draw off it from time to time as necessary...

MikeS

 

[wave98]

MikeS:

According to Goemans and Gamble it is the Anoxic zone that supports faculative bacteria and nitrate reduction, and not the anaerobic zone, albiet contrary to popular belief. The authors consider the anearobic zone to be a source of nasties and claim that the plenum "extends" the anoxic zone deeper into the bed.

Now bear with me here Mike 'cause I'm getting to the good part. The authors make it clear that they do not like the anaerobic zone, and would eliminate it completely if they could, but, their whole thing is to "extend the anoxic zone with the 4"depth, the 2-4mm grade, and of course the plenum space.

It is the function of the plenum space that they never really explain. I have carefully read the entire "ungodly-lengthy" and painful details that they represent in their "New Wave" CDrom version, and still they really never specify a function for the plenum "space" itself.

So here it is, and remember now, that Goemans and Gamble are adamantly opposed to any kind of "plenum wasting". :idea: The function of the plenum space is to allow an "unavoidable" anaerobic area, but , to have it in an area which is "almost" devoid of any surface area for bacteria to live on, and hence the reduction of the anaerobic activity which they( the authors )
abhor.

That is the difference that the space makes, and I don't buy into mojoreef's explanation about a diffusion block. ( He is a wonderful and knowledge man too, by the way IMHO )

This is how the "they" extend the anoxic zone deeper into the bed!


Personally, I am pursuing "plenum-wasting", until I learn otherwise, although I'm leaning towards the small volume high frequency type. At least I have a properly designed plenum in my tank for that purpose, and I would like to stay "up to date" with you and others on this subject to see what we can learn and how we can benefit from it.

With your larger grade 3-5mm and the additional depth 6" you have your deeper gradient, however you may lose a lot in surface area. What do you think?

Good luck on your new tank Wave98

 

[MikeS]

Good post Wave 98...sorry for the late reply, I've been out of town and have not been able to give time for a worthy reply since I've been back...

All your points are well taken, and worth further disucssion IMO...

I posted the question about the void space created by the plenum for the exact same reason you stated, there isn't a real clear explanation out there as to why it is necessary. The more I read, the more I think the answer lies somewhere between your explanation and mojo's....

You mentioned their fear of the anerobic zone and promotion of an anoxic zone. The biggest problem with an anerobic zone is ammonification. (which, as I understand, also can occur in an anoxic zone, dependent upon what is happening in the tank biologically and chemically speaking). I'm sure you are familiar with it...ammonia interferes with denitification, creating ammonium instead of free nitrogen gas. This is supposedly prevelent in an anerobic environment, which is why they fear it. The plenum, as mojo stated, creates a barrier that helps contain this environment.

On surface area playing a role in it...sure, a defiante point, but I think it is secondary. The plenum space has less surface area for bacteria growth, but it also, and equally importantly, provides a barrier against diffusion.

As for particle size and surface area, Goemans and Gamble have this to say about surface area...

Regrettably the concept of advective transport is less likely to aid diffusion in aquarium substrates, especially where very fine grain material is used. We have often heard that the best sand is very fine sand. And that's because when there are more sand grains there's greater total surface area, therefore more microbes. Even though that's true, it's of no value when one thinks of overall system balance. Small grains pack together very tightly and the space between them, porewater, is greatly reduced. When that happens, anoxic conditions (defined in previous writings and above) are restricted to an extremely shallow depth just below the upper oxic area.

and this to say about particle size....

Coarser sediments, i.e., above .5 mm, have higher, more useful permeabilities. In the wild, water flow around, near and at these grain size sediments (advection) can penetrate somewhat and dominate over diffusion as the transport process for solutes in porewater close to the bulk water-sediment interface. And, with higher current flows the supply of oxygen for organic matter decomposition can easily be met by porewater advection and the sediments can stay oxic (and low in carbon) even if they have the same input of organic matter as a muddy sediment.

So I feel that the trade off in surface area vs. diffusion is well worth it in my more coarse substrate...

On wasting...Here is my fear...if you are constantly drawing water off the plenum, you will be increasing the rate at which detritus builds up in the substrate and plenum vs. normal diffusion, thus increasing the potential for ammonification to occur....

MikeS

 

[mojoreef]

Howdy Wave

According to Goemans and Gamble it is the Anoxic zone that supports faculative bacteria and nitrate reduction, and not the anaerobic zone, albiet contrary to popular belief. The authors consider the anearobic zone to be a source of nasties and claim that the plenum "extends" the anoxic zone deeper into the bed.

The anaerobic zone is just a transisional zone between areobic and anoxic, I dont see how anyone could not have this zone?? where talking percentage of oxygen.

Anyway what is the nasty thing about a anaerobic zone that they fear??


Mike

 

[wave98]

Thanks MikeS:

I thought maybe you guys went to Hawaii and just stayed there! :lol:

You know, this is starting to sound like a discussion. Kind of scary, huh?

You, Mojo and many others here know w-a-a-y-y more than I do about this, and I appreciate your help and response.

Advection > horizontal movement of a mass of air. ( Webster's ) I assume that they mean water flow just below the surface that is transferred from flow that is just above the surface. Ok, I think I've got that part.

So, advection makes flow in the substrate, "close" to the surface, which is variable based on amount and direction of flow above the surface, along with the particle size. Your 3-5mm size is going to allow a "deeper" advection gradient, but deeper than what, and how much deeper?

Well, we don't know "how deep is deep", or "how close is close". I'll take a wild guess here and say maybe 1/4" depth of advection flow at Goeman's 2-4mm grain size with fairly high horizontal flow, and maybe 1/2" in a particilar area where the flow is directed at the substrate.

If we compare your 4mm avg. to Goeman's 3mm avg. then using the square function you get 80% deeper, or using the cubic function you get 140% deeper. So you might get down to 5/8" and even 1 1/4" in some areas, of "advection flow".

Now diffusion is going to take over. I'll admit that I don't understand diffusion very well. Maybe you could point me towards some good articles on that subject. I have not seen much of anything. There are a lot of widely varying opinions about it's depth for a particular grain size, and this is exactly where you're at with with your new tank and setup.

On wasting, I think I'd prefer to get away from calling it "continuous", and start calling it high frequency. As in HFPW. Oh my god, a new anacronym!:shock: What I envision is exactly along the lines of what LDRHawke was doing some time back, with a little( or a lot ) more experimentation on wasting frequency and volume, as well as substrate size and depth.

I asked LDRHawke to chime in with some of his previous results, but he has not responded yet. His original scheme was one pint, 3 times a day. On my 20 gal. of actual water, with a footprint of 265 sq. in., that would be 9/64" of "forced" advection "downflow" that would occur at a 100 gph flow rate for 4.5 seconds once every eight hours.

That would be about 7/16" per day which may or may not be a bit high. This is where wasting frequency and volume along with grain size and depth come in. It seems to me that this would extend both the aerobic and anoxic zones to some degree, and reduce the anearobic zone as well through wasting.

I don't know the rate at which diffusion occurs, or how it goes up and down at the same time either for that matter. Downflow that is equal to or greater than the upward diffusion rate may or may not be an advantage. this is something that needs to be found out.

It doesn't seem though, that the diffusion rates that we currently have in our substrates are somehow already perfect, either by accident or even by "mother nature", so HFPW gives us some control in this area. I or we need to find out how much control is beneficial here. At least with a properly designed "wasting plenum" in place we can make adjutments as we learn more about what depths the chemical and biological processes are taking place.

Once we do , frequency and volume can be adjusted to accomodate various grain sizes and depth.

On detritus removal, it is my current preference to use high flow( I'm at 20 X volume ) smaller grain size and skimming to keep detritus out of the substrate to begin with, at least most of the animal poop kind. Wasting at an appropriate frequency will force advection through the upper layer, and allow the use of smaller grain size at the surface( the aerobic zone ) for the purpose of rejecting detritus. Larger substrate could be utilized below that to aid in diffusion, if deemed appropriate.

Thanks again Wave98

 

[wave98]

Mojoreef:

According to Goemans and Gamble, it is first "aerobic" at or near the surface, then "anoxic" ( low oxygen ), and then below that is anearobic ( No oxygen ).

Anoxic is a transitional zone between aerobic and anearobic.

They were the first that I know of to discuss the existence of the "anoxic" zone as far as I know, and may have even "coined" the word.

Almost all tanks have all of these zones, unless they have a very large substrate and very shallow depth.

The "nasty" is in the unoxygenated zone regardless of what it is called, and hydrogen sulfide is the worst of many. I'm sure you know a lot more about that than I do.

I'm glad to see that we've got that active discussion on plenum wasting going that we had discussed previously. Maybe you could help us get some of information from LDRHawke's previous installation and what it was that did not work out well enough for him. Wave98

edit: ooPS - - - See the last post from MikeS

 

[mojoreef]

According to Goemans and Gamble, it is first "aerobic" at or near the surface, then "anoxic" ( low oxygen ), and then below that is anearobic ( No oxygen ).

No its a play on words Wave. anoxic and anaerobic are pretty much the same thing. Anoxic mens with out oxygen, anaerobic zone means an area that critters (anerobes) live with out oxygen. So an easy way to look at it would just be either areobic or with out oxygen.

They were the first that I know of to discuss the existence of the "anoxic" zone as far as I know, and may have even "coined" the word.

hehehe

Almost all tanks have all of these zones, unless they have a very large substrate and very shallow depth.

all tanks have them even if they dont have substraights.

The "nasty" is in the unoxygenated zone regardless of what it is called, and hydrogen sulfide is the worst of many. I'm sure you know a lot more about that than I do.

Sure that is true, but the problem is that Nitrate reducers only live in the same place as them. So its kind of a dammed if you do and dammed if you dont.
This thread has some good potencal, I think we need to just strip away some of the mis-givings here so we can advance it.


MIke

 

[mojoreef]

Ok lets lay some stuff down here so we are all on the same page and then we can take it further and see how the plenum wasting system might work or not..
First thing in looking at how the system works bacterially. We have to look at the baccteria system as a multi branched system, not just a system with one bacterial strain sitting on top of another.
The first bacterial strains that we are looking at are nitrifing bacteria, these are the ones that take ammonia or amonium and convert it to nitrite and then to nitrate. Thes bacteria occur everywhere in the tank, on the glass, rock, sand and in the water column, even on a peice of food or poop floating in the water.
From here we are looking at nitrate reducing bacteria. Now these bacteria perfer oxygen for respiration, but have the ability to use nitrate in its place when it is gone. Thes bacteria also occur on the same places as the nitrifing bacteria, BUT also can occur in locations that are oxygen void. So we can have them on or IN peices of food, waste, or in oxygen voided areas. They are faculative.
From their we go into bacteria that can only live with out the presence of oxygen and would die if exposed to it. In this area we are going to have the sulfer reducing, methagenes, metal reducing and a host of others.

Ok now some other quickies. Bacteria can just jump on something and begin to eat it. They need to create an enzyme and liquify the product and then they go to town. So where ever we see bacterial activity we are going to see a build up of these materials. Incorporated in this material is also the biproducts and so on. We call this biofilm, bacteria call it an home. With in this soup they can travel at ease, eat, reproduce and control tthe enviromental conditions. This is very inportant to the concept of diffusion, as it stops diffusion in fine substraights.
An example of how bacterial use it in our reefs. A peice of food hits the water to feed the fish, before the fish even touches it the bacteria,nitrifiers and nitrate reducers get to it and envelop it. Once inside the fish the process doesnt stop, the bacterial are with in the fish doing thier job. the fish poops out waste and the bacteria continue the processes. As they create more enzymes and bioflim they have now changed the dynamic enviroment of that peice of waste, now thier is an area devoid of oxygen with in the waste and nitrate reducing bacteria are at work, and thus the process continues. Now pictures how many times the enviroments change and how often with in our tanks, What happens when the peice hits the sand??
Anyway we have to give the bacteria more credit then we do. They have the ability to create enviroments, control thier surroundings and so on. Now we have to throw nitch bacterial strains into the picture. An example of a nitch bacteria in our tanks would be like this. Say the substraight or what ever gets an detectable level of ammonia with in it. Well in this case the the nitrate reducers cant use thier enzyme, and thus can do anything. Well another bacteria takes over and instead of turning nitrate into gas, it converts nitrate to ammonium and then sends it back up the chain to be reduced again (cycling). Or thier is another bacterial strain that lives in oxygenated water and can turn ammonia straight into gas.

Anyway just some things to keep in ind as we go here


Mike

 

[wave98]

High oxygen, low oxygen, and no oxygen.

Nitrification, denitrification, and hydrogen sulfide etc.

It looks like we might have to include live rock now in "substrate". Maybe even fish too! :lol:

Predominantly:

nitrification > high

Denitrification > in the middle

Nasties > farther down

But how much farther down?

So, for Plenum wasting, whether it be high or low frquency, once we get the frequency and volume coordinated with the grain size and bed depth, well have something that is helping us. This will likely require further investigation and some experimentation.

Of course, it is "the nasties" that predominate "somewhere farther down" that we hope to remove from the system to some degree by wasting. At what rate we can "waste and remove" while maintaining and extending the high and low oxygen zones is the area that we need to address here, along with the obligatory grain size and depth consideration.

There is no reason to believe that a wasting plenum is a cureall, or that it would necessarily eliminate or be in competition with other equipment and or methods, at least not any more than a DSB. If it can remove compounds that have been contributing to to poor water quality ,or to eventual tank crashes in some cases, then we will have made some progress.

We will be able to keep many of the substrate dwelling creatures that are so interesting to watch and culture , along with a more natural and appealing bottom condition, with reduced concern about toxic compound build-up.This hopefully would be worth the effort.

Mojo - - are we on the same page yet? Wave98

 

[mojoreef]

Were getting thier Wave, were getting thier.

If sulfur is your worry or one of the points then we might be in trouble. both aerobes (Beggiatoa, Sulfolobus, Thiobacillus, Thiothrix) and anaerobes (Thiospirillum, Thiocapsa, Chromatium, Chlorobium, Prosthecocloris) oxidize sulfide to sulfur and then oxidize it to sulfate, usually in cooperative sequences. So it happens both low and high in any substriaght. Sulfide oxidizes spontaneously in the presence of oxygen at neutral pH, microbes that use it as an energy source are generally anaerobic (Thiomicrospira) or acidophilic (Thiobacillus ferrooxidans, Thermothrix); both Thiomicrospira and Thermothrix use nitrate as their terminal electron acceptor. Couple that and the fact that nitrification, denitrification, the sulfur cycle, the iron cycle and so on and so on can happen anywhere in, on or around the substraight its going to be a hard one to control.
Now in say that do we really need to control it?? is a sulfide zone really that big of a problem?? IN all my years in the hobby I have only heard of a very few peple having and issue with it. In most cases when talking about the limitations or build up of any substraight system its more to do with end product detritus and Phosphates. Basically the things that the substraight has no method for dealling with. SO is that wat we want to remove or deal with??


Mike

 

[wave98]

My interest in pursuing a "wasting plenum", or any kind of substrate for that matter, is twofold. Firstly, I am particularly endeared of pearly jaw fish, "goby-shrimp" symbiosis, and the habits of many other predominantly substrate dwelling creatures.

Secondly, if there is anything in the water column, or in the substrate, that either collects, or is processed, in the substrate, I would like to utilize that substrate in any fashion available that either releases smaller quantities back into the water column( for improved real time water quality ), or can be removed directly through "wasting", for the same reason, and to "help to" avoid the eventual tank crashes that so many people are concerned about.

Most people, in recent years have been concerned about various "nasties" that are concentrated in what is often considered to be a chemical sink( whether it be DSB or Plenum ). My interest is in determining what grain size, bed depth, flow volumes and frequency, that are most conducive to converting the "chemical sink" into a "chemical drain".

Improved "Natural Nitrate Reduction" is the first objective, while "wasting" of whatever else we can rid the tank of, is the second. If we can't substantially affect the build-up of phosphate by this method, then we will just have to rely on detritus suspension by proper flow( and surface grain size ), with skimming and phosphate removal media.

Controlling phosphates introduction into the system is a big factor, and calcification schemes that reduce it's input will help a lot, along with care in feeding methods.

Where do we go from here? - - Wave98

 

[mojoreef]

Wave any substraight, or even the proper enviroment will encourage denitrification. Of coarse how effective it is become a function of how many bacteria we can get into play.
So in other words we are going to get either denitrification or putting it into cycle with any substraight used. So lets leave that one on the shelf as an easy one.
From reading your posts it looks like you have good knowledge of diffusion or at least a plan/thoughts on what you are looking for. Why dont you share those with us?

good conversation by the way


Mike

 

[wave98]

Mojo:

What I'm looking for is one post "up". What my "plan is", is 7 posts "up". Beyond that it is still a matter of particle size and bed depth, as stated, and in the case of wasting It is also frequency and volume. Do read post #11 above, as this describes in great detail the starting point for wasting volume and frequency, as well as the downflow rate or "forced advection" rate that would result.

We do need to determine what downflow rate or distance will allow the zones to spread downward somewhat, but not so far as to overly extend the nitrification zone, or to begin wasting the the low oxygen level zone where faculative bacteria and denitirfication are prevelant.

Goemans and Gamble believe that the low oxygen level denitrification zone extends to 4" deep in their plenum system with their recommended substrate grade and 4" depth.

I don't know if I'm convinced of that or not, and I haven't found anything like a concensus anywhere regarding effective diffusion depths in DSB's either. Can you point toward some particularly relevant articles? I've read a lot of what is in the resource library here at RF, but I certianly haven't made it thru all of the WWM links and RC links.

I just thought you might have some favorites for me to go "wallow" in. Maybe we can get more bacteria "into play" and improve the effeciency.

Thanks again - - Wave98