Dosing silica to encourage diatoms as a form of nutrient control/export

[Dan_P]

Sorry about the confusion. I would say for our purposes diatoms and macro algae are about the same even though diatoms have a shell and the weight percent of nitrogen is possibly lower.

The point I was making was that you are unlikely to grow enough diatoms to make a difference without turning your system into what looks like split pea soup. And then there is the matter of harvesting diatoms.

What would be useful to know is the weight of diatoms per cc we can expect to grow in an aquarium. Then we could calculate some expected nutrient export rates forvyour idea.

OK, I dug up some numbers from

http://www.fao.org/docrep/007/y5720e/y5720e08.htm

Assuming I correctly interpretted the data table, based on a million diatom cells per cc, selecting 27 micrograms organic matter per million cells, and assuming the organic matter is 6% nitrogen, I come up with a whopping 7 ppm of nitrate consumption possibility. Even at a 100,000 diatoms per cc this is a substantial nutrient capture, if you can filter out the cells.

Diatom organic mass per million cells ug 2.7E-05
Cells/cc 1.00E+06
Mass per liter ug/l 2.7E+04
Nitrogen Content ug/l 1.62E+03
Nitrate Equivalent mg/l 7.17E+00

I love numbers.

How cloudy is water with 1 million diatoms per cc?

Dan

 

[Dan_P]

One more idea: algae, macro algae and diatoms, exude organic compounds that are metabolized by bacteria.

Question: what fraction of nitrate reduction from growing algae can be attributed to algae exudate acting like carbon dosing and beefing up bacteria growth? This could explain those cases where algae growth is too low to account for the observed nutrient reduction.

 

[SantaMonica]

why use an algae scrubber and controlled growth and harvesting of diatoms as an experiment

Well if run at the same time, you could compare which one has stronger photosynthesis (filtering). If you run them separate, then you don't get the same battle.

As for the (primarily) glucose that algae put into the water, it certainly does carbon dose, and would be another nice experiment. It has been done, but who knows where those studies might be.