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While not an issue in many contexts, it is can be an issue with our closed loop AP systems.


I just came across this article which made me think that this could be an interesting way to help us remove heavy metal build ups in our AP systems. The article doesn't cite any references (this annoys me to no end when publications do this) so can anybody dig up the real research?


If the process is as simple as drying our left-over banana peels and using them as a filter media placed somewhere in our water flow, this would be great!


My questions include:

  • Would the peels remove other materials that are beneficiary to AP?
  • Is it hazardous to our bacteria, fish, or plants? 
  • What's the filtering time frame we are talking about? 1 hour, 1 day? After a time, the peels would start to decompose, releasing the captured heavy metals.
  • What heavy metals does it remove? Copper? Lead? 


What do you think?

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Keep in mind that commercially grown bananas are heavily sprayed with pesticides.  Not such a big deal just eating the banana but the peals might be another story.

Duckweed and Azolla help with heavy metals.

Right, but we tend to feed the duckweed to our fish, so we don't have a net loss of heavy metals to the system. They would just get passed through the fish or accumulated in the flesh. Right?

Chi Ma said:

Duckweed and Azolla help with heavy metals.

You just remove it from the system.

Have a look at this site:


It is in French but you can use Google Translation. This company is specialized in water treatment...with plants. They even built a "plant's plant system" in China.


On the left side, they said that reed is the champion plant for depollution. Here is a Google translation:


The reed is the most widely used filter plant in the world to clean up the sewage, eitheras a filter or as vegetated alluvial basins planted. Carrying pure oxygen in its rhizomes, itis very effective for treating organic loads: chemical pollution (COD), organic pollution(BOD5), suspended matter ... It is also now used in phytoremediation to clean up thesludge.


If you go to, than on the left side you will see another plant called Typha. Here is a Google translation:


Typha is a very tough plant that can be used 
for the case of pollution the most desperate. She is able to decontaminate 
highly polluted wastewater to the limit of asphyxia (manure, water discharges). 
It is very efficient in circles at the edge of anoxia (low 
oxygen). It biodegrades well petroleum products, compounds 
polycicliques aromatic and chlorinated compound. It resists all: Metal 
heavy salt excess of COD, BOD5 ...


Hope this helps,


Roger Pilon

Costa Rica Aquaponics

I am curious about this too. I know in the aquarium setting you cannot just continue to add fresh water to compensate the evaporation loss, as the heavy metals build up over time and can become toxic to fish.

Assuming that you do not change out the water and just add water to replace the consumption, is it necessary to do regular partial water changes to maintain fish health in an AP system or do the plants take care of the heavy metal build up?

What do they do in the commercial setting?

This appears to be an older thread, but I'll jump in anyway...

I say keep the bananas and the duckweed.  Instead, get permission to use water hyacinth, and dispose of it properly.

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