<a href=showthread.php?s=&postid=15002031#post15002031 target=_blank>Originally posted</a> by therealfatman
In review I see a mistake in what I wrote in that I should have written; As for diffusion of carbon based compounds difussion is the movement of the compounds within the fluid from an area of higher concentartion to an area of lower concentration. I do believe however that I clarified what I meant in the two following sentences.
You say:m
"In a shallow bed denitrification can and does occur and advective flow will have greater effect over a larger surface area as opposed to a greater depth with limited surface area in the bucket."
First: Define shallow sand bed.
I define shallow sand bed as two inches or less.
IMO Very, very little nitrification occurs in a shallow bed as there is too much oxygen diffusion. Adressing adjection as an effect of over lying materials is just a crap shoot argument as the variables are to vast. Sizes of rock shapes, surface textures, amount of contact with substrate etc. Does this adjection I assume also relate to water movement caused by circulation, that is pretty variable and therefore might provide no adjection at all. Dense packing of fine sand will happen I buy that. So what. That only indicates your using the wrong particle size if it is a problem.
Did you ever consider larger grains of sand as is used in Plenum type deep sand beds to increase water to the what 9" deep RDSB versus the 6" in tank deep sand bed. Your arguments are inadequate flow through the bottom layer when flows should be slow. You claim inadequate diffusion of nutrients where other people claim problems with excess nutrients, hum. I repeat there is no reason for a shortage of water movement in the depths of a properly set up RSDB. Many waste water treatment plants have shown that retention time of the influent water in a denitrification system should be around 2 hours. That is prety slow movement of water through the substrate.
There is also no need for critters to drag food or create channels. There is more than enough dissusion. Many people try to mimic a deep sand bed when setting up a RDSB, and therefore use sugar sand at depths of 9". I can believe there might be water movement shortages (maybe) under 9" of sugar sand in a bucket. There might even be a chance of a diffusion problem. I am not aware of any rules requiring a person that is setting up a RDSB create problems such as that. Are there standards or rules someone has imposed for sand particles sizes and such, or because you chose the wrong particle size and could not get your system to work that makes all RDSB systems bad. And there all bad regardless of flow/retention rates or differing diffusion rates than you must have had in your one test of a remote deep sand bed of unknown specifics other than 7" deep in a 30 gallon bin.
Perhaps you should simply make a RDSB with large sand particle size and if you think you need some sugar sand place it over a screen or some geotectile fabric.
Dr. Dean Jaubert method works quite well even without the plenum and that has been well documented. People have tried to tweak the systems through using fine sand to get more surface area for nitrification bacteria and found they then had to add digging critters because of the problems caused by the deep small particle sized sand. Now they also have nutrient build up problems and algae problems and crusting problems.
Many times people thinjk thet are advancing the sciences when they are making changes that actually in the end show a worsening of a concept. I also know of people using a plenum in their RDSB. Many people use aggregate layer seperators, many iuse larger aggregate than is used by most with in tank Deep sand beds. It is quite easy to just replace a deep sand bucket so if nutrient accumalate that is not a problem.
You are the only one I have heard from that just blatantly claims a RDSB will not work but not setting any design parameters such as particle size or such for your arguments that fllow or retention times are inadequate or that food dissusion is inadequate. Most people make alterations so as to produce results not just throw a concept out the door.
I have made many RDSB and have used many sand types and particle sizes. I have always found the systems to work but I also have small nitrate problems to begin with.
What citation on what earlier post?
I have read many articles, abstracts and full papers from many researchers and the one thing they all have in common is they conflict with each other. I have never read anything from a researcher saying a remote deep sand bed as I described will not work. They below paper is a widely accepted paper which conflicts in several major areas with reef forum disbursed opinions.
This is a nice article:
http://www2.hawaii.edu/~toonen/files/Toonen-Wee-05.pdf
The artcile noted has two parts. I've read it several times.The format is easier to read here:
http://www.advancedaquarist.com/2008/8/aafeature3
This is from the second part:
"Each sediment-based aquarium design appeared capable of handling nutrient inputs up to 0.5 mg / L / day of NH4+ - which is equivalent to a well-stocked reef aquarium. At this input level, final concentrations of ammonia, nitrite and nitrate did not differ significantly among aquaria 1) with or without plenums, 2) containing deep (9.0 cm) or shallow (2.5cm) sediments, or 3) containing coarse (2.0mm) or fine (0.2mm) mean particle sizes."
How does this support a notion that plenums, depth beyond 2.5 cms or grain size matters. It says the opposite?
Which can be found here:
http://www.advancedaquarist.com/2005/7/aafeature
Here is the prior post on advection . I thought I posted it here but it was another thread:
Advective flow is what moves water up and down through a sand bed along with dissolved organics,inorganic nutrients and particulate matter. Some diffusion also occurs.
Advection occurs due to a variation in water pressure as the flowing water encounters obstacles at the surface even as fine as a sand grain . Rocks and other obstacles in the flow can enhance it causing an upwelling. For example, in an illlustration in"The Reef Aquarium 3",Sprung and Delbeek, cite a model wherein advection over the sand bed moves the water down into the bed by only about 4 cm. When a 10cm rock is place in the flow , an upwelling occurs in the area of the rock which pulls the water down as much as 10cm.
So, whatever design you use it's about moving water and organic( for a carbon source) as well as inorganic nutrient matter and doing so at a rate strong enough to move the organic matter to the area where heterotrophic bacteria thrive while slow enough to ensure that an anoxic area is maintained.
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Tom
Yes, flow rate would effect advection( not adjection btw). In the cited model a flow rate of 10cm per second was used. For those with access to a copy of "The Reef Aquarium Vol 3", the page number is 264. All in all this refence covers a nice discussion on both advection and diffusion in aquariums.
Per your demand:"First define a sand bed"
I think of 2 inches give or take a centimeter or two when I think of a shallow bed for denitrification.
You state it is your opinion that little nitrification occurs in a shallow bed. Did you mean denitrification? If so the article you cited strongly suggests otherwise.
Again the research you noted belies grain size as much of a significant variable. Nonetheless,the original monster thread on bucket seabeds which I have read went into great detail on grain size including magnified examinations of grains. The consensus argument was for oolictic fine sand since it not only offers additional surface area but is spherical and thus less likely to pack together than more angular larger grained materials. BTW I have tried several particle sizes in the past.
Do buckets of sand work. Yes, but probably would work equally well if they were much shallower and even better if some structure was used equal to sand depth to enhance advective flow. For those with the space who want a remote deep sand bed using a larger surface area and adding structure( such as live rock) combined with a bed equal in depth to the structure employed seems like a good way to go as far as a remote bed design goes in my opinion.
Details are very important. Heterotrophic bacteria do not use inorganic carbon such as CO2 or bicarbonate.Autotrophic bacteria which nitrify do.
