DSB Heresy

[ldrhawke]

Greetings all,

I going to build my CPW\DSB\Coil-Denitrator and install it within the next 2 weeks.

Just a question regarding the flow through with denitrification systems. How much is the flow?

And with the design I was thinking of having +-3-5 drain holes drilled at diffrent points in the plenum to extract the water from, the reason being is that it would take water from various places inthe plenum and would move the water more evenly down through the plenum and not have fresh water move through the DSB at only one point.

Does this sound like it will be worth it as I will be running a constant flow through 2 of the drain holes and a wasting for a couple of seconds from the other drain holes.

And input welcome.

Thanks

I have commented on Coil-Denitrator before. If you figure how big it will have to be to get adequate throughput, you will see it doesn't make a lot of sense. Have a small one that just drips a drop a second will not have adequate capacity.

I have not found nitrates to be an issue with CPW. In fact it is probably improving the the nitrification process in the sand bed by feeding it and making it more effective.

I am not following you hole drilling concept. Just drill 1/32" holes about every 3" along the side of the pipe and it will work fine. You don't need to sequence or partition the CPW.

 

[ldrhawke]

it would be interesting and relatively easy to retrofit UGF plates to form a plenum with a valve to drain the water from underneath. Perhaps it would be an easier and/or cheaper way to achieve similar results.

A conventional UGF has far too much open space and it would be difficult to keep it from short circuiting. Building a plenum the way I recommended is cheap and easy.

 

[ldrhawke]

Hi John, How long did you let your substrate cycle before you started your controlled wasting? Do you have a proposed formula for hole spacing for a given area? Do you stir or level out your substrate at any time to insure even flow? And lastly, Would you say that your skimmer has increased output, decreased output, or stayed about the same as before the cpw system was implemented?

Thank you for your time.

Go through the normal nitrification cycle and then start wasting through the CPW system. The whole idea of the plenum design I recommend is to reduce the amount of shorting circuiting when you have different substrate levels and resistance to flow. If you build it as I recommend you address that potential problem.

Skimmer output......I really can say. My skimmer must be a female. It is not predictable, I never know when it will skim or not skim.

Also, I have modified my 3" by 24" PM skimmer. It was designed to make all it bubbles using only a venturi injector. I have modified my PM added a EuroReef SEDRA KSP3500 needle wheel impeller pump to recirculate in the PM and improve it's performance. It works much better now.

 

[ldrhawke]

I've been busy with business, sorry for the delayed responses. I have learned a lot over the last year and my preconceptions of what it takes to have a reef system have dramatically changed.

Let me state again, CPW is only a tool to improve upon and make you system more stable. The idea is to keep nitrates and phosphate at zero in a reef system......everyone system is unique and has different loading on the biological processing capacity of the tank.

The loading on the biological system will vary all the time. Fish and coral grow and increase the loading. Any method that helps to keep nitrates and phosphates at or near zero should be used, or at least be available to be use, when things get out of balance. How close to zero you need to be will depend upon what you are keeping in your tank.

We introduce the nitrates and phosphates when we feed the system. Over half of the nitrate and phosphates the fish eat go back into the water in solution and not as a solid. Even if you collect all the solids and remove them, you have solved less than half your problem. A skimmer removes a lot of what remains and a stable biological filter will hopefully handle the rest. If it doesn't you may need polyfilter and chemical treatment to polish the small balance if you are keeping more delicate coral.

Despite the often imposed myth, a DSB does not add phosphates. It is a biological filter that may start to store excess phosphates when it cannot biologically process them, which can become a problem, if it reaches it storage limit. If they start to be recycle back into the system they cause havoc. CPW helps to keep this from being a problem by removing the waste were phosphates concentrate and maybe are partially going back into solution. CPW helps to feed both the anoxic and oxic bacteria and makes the substrate a more effective biological filter.

It is difficult to use water changes alone to keep your tank from starting to slowly build phosphates or maintaining the chemistry. Read this well written article. http://www.reefs.org/library/article/t_brightbill_wc.html

As you can see by this article and the math, you need an effective biological treatment process taking place in the tank in conjunction with good maintenance. I believe a DSB using CPW adds to and improves on biological filtration process to help keep nitrates low and hold waste phosphates were they are concentrating.

There is no way even 10 to 20 % or more weekly water changes will keep a slow build up of waste from becoming a problem sooner or later if you don't have other methods to reduce them. I believe in a BB system, with the reduced biological filtration surface area, you will always have a nitrate problem and water changes alone will not solve the problem. Depending on the coral you keep that may not be a problem. BB tanks with a large quantity of live rock and low fish loads will have less of a nitrate problem, but it could still slowly build. You may think everything is fine and all of a sudden SPS or delicate coral start to die, and a death spiral can occur.

In short, there is no simple answer in keeping a reef system, other than knowing what to do maintain the water quality. And that will vary with every system and the best maintained system can have pollution creep up on it if you don't respond when it starts to occur.

 

[goby1]

It was mentioned earlier in the thread that as a possibly better alternative to the pipes/32nd inch holes/cloth idea, one could support some egg-crate or similar device, cover it with a filter cloth, and then fill in several inches of sand on top. The removal of fluid would come about by means of half in pvc sections, that were drilled at intervals along their lengths. It was stated that this was a "horrible" (or something like that) idea, because of "short-circuiting." Well I think it's a better idea. Skip the pvc sections at that. Just have one drain from, well, anywhere within the plenum. I don't believe that there will be significantly higher flow through the sand, while draining, in regions that are in close proximity to the drain opening. The resistance provided by the sand layer is much larger than that of the water from one side of the plenum to the other, especially if fine sand is used. Thus, while removing waste from the region, the pressure gradient across the thickness of the sand will be much larger than that from one side of the plenum to the other, through the water, which means that the gradient across the thickness of the sand will not vary from one side of the plenum to the other. This means that the flow throught he sand will be even across the bottom of the tank. With this in mind, I advocate the system as outlined by whoever it was, sans the pvc pipes. I also think that finer sand would serve the system better, due to the higher resistence and the much larger amount of surface area. A continuous drip from this system would work well, as to further minimize pressure drop from one side of the plenum to the other.

 

[darrellh]

Goby1,

Welcome to the ReefCentral forum.

I agree with everything you stated, but you're overlooking one additional problem that will occur over time. Initially the pressure gradient thru the sand bed will be uniform, but as different regions of the bed begin to clog, the flow thru these regions will have reduced flow. This sets up a vicious cycle where the regions with less flow begin to clog even more. You're correct in stating that the pressure gradient at the plenum/sand boundary will be uniform, its just that the pressure gradient thru the sand bed itself won't stay uniform.

The idea of placing small holes throughout the plenum/sand boundary (pvc pipes) is that even though the sand bed will still have regions that clog more than others, at least there won't be any large areas near the plenum surface that end up with little or no flow. This assumes of course that the little holes themselves don't clog.

As ldrhawke explained a couple of times, the problem with a continuous drip is that doesn't develop hardly any pressure differential anywhere which means the flow can short circuit to the path of least resistance. Using high pressure surges instead will force the flow to spread across all of the holes more evenly.

Darrell

 

[goby1]

Thanks for the kind welcome! I believe we are at the mercy of the clogging to some extent. However, the feed back will be negative as opposed to positive, I might guess. As regions in the SB begin to offer a higher resistance (not ence like in my post before), there will be less flow and hence less clogging particles that pass through (or try). I'm not so sure about this however. I am much more sure about the placement of the drain, in how it's location is insignificant. Even with pockets of "clogged" sand, the fact that the SB presents a much higher resistance than the plenum means that the vast majority of the pressure will be dropped across the SB, not through the water in the plenum. Consider an electrical analogy. Two copper cylinders, say an inch thick, lined up end to end, with an inch or so gap between. One cylinder represents the plenum, the other the main tank volume. In the gap are several resistors of varying values, which represent various pathways through the SB. It won't matter where you place the leads of a power supply on the copper cylinders if you are concerned about the current through the individual resistors. This is because most of the potential that the power supply is attempting to offer to the circuit, well, it's all dropped across the resistors. This analogy attempts to demonstrate that the drain location doesn't matter. In terms of clogging, one would have to consider a change in resistance as a function of potential. I would expect that the resistance offered by regions in the sand bed would increase somewhere along the lines of the square of the velocity, so in fact a large differential in pressure across the entire system would cause a dispropotionate amount of flow through the unclogged regions. A better understanding of our problem could be gleaned if we knew more about the nature of the clogging, especially the size of the regions they represent. It would also be of interest to know the diffusion constant for the various"waste" species an nitrates in the water-SB matrix. We could then tune the removal rate and sand bed depth to optimum values. I don't understand the aerobic/anaerobic biological stuff at all well enough to devise an appropriate model. Cheers, Goby1

 

[goby1]

Ah yes, so the velocity^2 argument attempts to demonstrate that a slow drip would result in a more even flow rate throughout the SB. G1

 

[ldrhawke]

Thank you Darrell, concisely stated.

G1,

I too often often compare the Laws of Fluid Dynamics and electricity when trying to convey my thoughts. But, the comparative analogy between Ohm's and Kirchoff's Law's between those of Newton, Navier, Stokes, Euler, and Bernoulli only go so far before they have a tendency to break down. Then if you throw on top of that the dynamics of the biology and chemistry of life in trying to maintain a reef tank it becomes a rather elusive moving target that is difficult to fit into a mathematical equation. ........ I continually stand in awe when I look at the Tanks of The Month on RC and I applaud and envy those that have succeeded.

For all intense purpose what you describe is an across the counter UGF that can be purchased at your nearest PETCO. Applying the dripping concept to a UGF has been tried by many in the past with no measurable success for the reasons I have tried to explain before. If you think you have discovered a way to make it work, it is easy enough to do. I suggest building one that way to satisfy your beliefs.

 

[goby1]

Ok, I have the tendency to want to trust you, but I need more theoretical analysis... the long pipe with 1/4 inch riser analogy seems to me to be described in electrical fashion, along with "Short circuiting." I'd like to know how it is demonstrated that flow is more even through the sandbed at greater overall rates, and that the location and orifice sizes of the discharge system effect the flow pattern. I really don't think this was done in this thread with other than (don't have the right word here) explanations. Perhaps you could explain using the Navier-Stokes Equation? I am really interested in this problem as establishing long-term steady-state nutrient export is my next reef task. Thanks, G1

 

[Shoestring Reefer]

I would expect that the resistance offered by regions in the sand bed would increase somewhere along the lines of the square of the velocity

It always does.:thumbsup:

so in fact a large differential in pressure across the entire system would cause a dispropotionate amount of flow through the unclogged regions.

Yes, that's known to happen in filters. For example, if you have a furnace or large air conditioner with one of those big rectangular air filters, you can try this experiment: Place a piece of fabric over PART of the filter, on the back side, so air must go through the filter before it goes through the fabric. You may have to glue the edges of the fabric to get a good seal. Run the furnace for the winter (or the A/C for the summer) and then examine your filter. The area of the filter in front of the fabric will be less dirty than the rest of the filter, even though air passed through the filter before the fabric. The reason is that the restriction caused by the fabric caused less flow to go through that part of the filter than the rest. There is no reason to believe the same results (higher proportional flow through less-clogged areas) would not occure in a clogging sand bed.

It would be nice to think that the clogged areas would actually see more flow than unclogged areas, but that's just not realistic. If it was, each fire truck would have one hose with a sponge over the nozzle, just for extra range.

Flowing water prefers to take the path of least resistance, just like electricity. That's why water generally flows downhill.

If you want to eliminate clogging, maby try a coarser substrait.

 

[Shoestring Reefer]

But, the comparative analogy between Ohm's and Kirchoff's Law's between those of Newton, Navier, Stokes, Euler, and Bernoulli only go so far before they have a tendency to break down.

I believe Darcy would apply a bit more. Darcy

I'm surprised you didn't mention him; I'm sure you studied his work while getting your engineering degree; also, did you not consider his work when you developed your commercial waste-processing system? Perhapse his work does not apply to air; I admit my focus is geared to hydraulics, so I'm not sure.

"This paper describes the scientific principles of Darcyââ"šÂ¬Ã¢"žÂ¢s law and hydraulic resistance as they relate to the in-ground dispersal of onsite wastewater effluent." (Quoted from link, below)
In-Ground Dispersal of Wastewater Effluent: The Science of Getting Water into the Ground

Perhapse the above link is relevent to the discussion.

 

[ldrhawke]

Ok, I have the tendency to want to trust you, but I need more theoretical analysis... the long pipe with 1/4 inch riser analogy seems to me to be described in electrical fashion, along with "Short circuiting." I'd like to know how it is demonstrated that flow is more even through the sandbed at greater overall rates, and that the location and orifice sizes of the discharge system effect the flow pattern. I really don't think this was done in this thread with other than (don't have the right word here) explanations. Perhaps you could explain using the Navier-Stokes Equation? I am really interested in this problem as establishing long-term steady-state nutrient export is my next reef task. Thanks, G1

You don't even need the Navier-Stokes Equation. Let me give another simple analogy to why and how the CPW design works compared to a conventional UGF.

It's like comparing the the systems needed to aircondition a multi-room home to that of what is required to airconditioning a single room travel trailer.

With single room travel trailer a window AC unit will suffice.

If you tried a single window AC unit in a home you would have some rather uncomfortable rooms.

Instead you impart energy by using a central distribution fan and then use a plenum and ducts and wall vents going into every room that impart an artificial pressure drop to even the air flow to all the various rooms so they are all uniformly cooled or heated.

The CPW piping works like a homes central AC system in reverse using the tanks head pressure and an artificial pressure drop to more uniformly remove the fluid A conventional UGF is more like the window AC unit.

 

[Shoestring Reefer]

You don't even need the Navier-Stokes Equation.

I agree. It's a little too fundamental, and the (Flow^2) X (Sum of Resistances) = (Pressure Drop) relationship will probably do.

 

[Shoestring Reefer]

Perhaps you could explain using the Navier-Stokes Equation? I am really interested in this problem as establishing long-term steady-state nutrient export is my next reef task. Thanks, G1

You asked before I posted Darcy links; perhapse this site will be handy for you:

Darcy/Idelchik Calculator

I have not used it yet. It appears you can input bed info and get flow rated based in dP. For example, you can input two bed characteristics like sand and clay, and compare flows for a given dP; then, compare those same beds with a higher dP. Then, you can compare the flow differences between the low-dP cases and the high-dP cases.

 

[joseph1336]

ldrhawke,

Great idea! I am going to try your CPW system on my new 250 gal L-shaped tank.

The 1/32" holes: Are they drilled on both sides of the pipe(As in drilled through from one side of the pipe to the other - across the diameter of the pipe?)

Also, my tank is 36 inches high does this have any effect on the size of the holes or distance between the holes.

Do you think the cpvc is better?

The L shaped tank is approx 50" on each viewing side, any ideas on the grid system, as far as combining the two grids?

Thanks for your time. Participants like you make this a truly interesting and informative website.

 

[JHemdal]

ADSB

ADSB

Hi,

I think what you are describing is what I call an "Active Deep Sand Bed". In my opinion, moving small amounts of water out of the plenum is not so much to be removing polluted water, but to cause a slight flow gradient through the bed so you aren't relying on passive diffusion. A peristaltic pump would work for moving the water.

jHemdal

 

[werew]

I'm trying this on my tank... its a small tank but I cannot think of a better way to drain off small amounts of water to perform water changes.

I'll calculate how much volume the plenum takes up and drain 30-50% of that volume per day or every other day and make adjustments as I see fit.

My larger custom tank will utilize this setup as well... if it doesn't work or I feel it's causing problems (highly unlikely to happen IMHO), i'll just plug off the drain tubes.

 

[docjay]

ldrhawke,
Where did you find a 1/32" drill bit? The smallest Home Depot carries is 1/16". I going to use your system in my next set up.

Jay

 

[ldrhawke]

ldrhawke,
Where did you find a 1/32" drill bit? The smallest Home Depot carries is 1/16". I going to use your system in my next set up.

Jay

If your drill about a total of 40 ( 1/16") holes that will flow abour 2 gpm. That will work fine.

In a large tank 150 G plus tank, you my want to double the number of holes and flow rate.