Trace element solution

I had an excellent call with Kamal from NYU last night. He suggested that we didn’t need the multi-mineral pill at all. When he looked at the


micronutrients solution based on the formulation by Rabaey and colleagues [39]

it appeared to only contain ions that we had already added in powder form. If anyone (@NarcisP?) can get hold of a copy of


[39] K. Rabaey, W. Ossieur, M. Verhaege, W. Verstraete, Continuous microbial fuel cells convert carbohydrates to electricity, Water Sci. Technol. 52 (2005) 515–523.

It could be really useful to confirm exactly which (if any) micronutrients we need to add.

Otherwise, I'd suggest we look at AI tools to help us with our Journal research like [Semantic Scholar]( and [Research Rabbit](

@Martin I found a copy on ResearchGate - (you don’t have to create an account, just click on “Download full-text” and cancel the sign-up popup.

@“Gerrit”#p134 Well done, and I’ve found the relevant portion: “To all influents, 1ml of a trace element solution was added, containing per litre: FeSO4.7H2O 1g; ZnCl2 70mg; MnCl2·4H2O 100 mg; H3BO3 6 mg; CaCl2·6H2O 130 mg; CuCl2·2H2O 2 mg; NiCl2·6H2O 24 mg; Na2Mo4·2H2O 36 mg; CoCl2·6H2O 238 mg.” - other than the calcium chloride, these weren’t the chemicals we added in solid form.

Next step would be to find the easiest way to get a food grade version of this that doesn't require everyone to source 9 different chemicals, but that also dissolves nicely (unlike my vegan multivitamin pill) and ideally doesn't turn everything orange...

@“Martin”#1 Yeast extract? Or filtered and sterilized seawater?

@“Gerrit”#p141 I think they’d use yeast extract as a carbon and energy source, so we’d end up with much more than Hydrogen Oxidising Bacteria.

Seawater extract is a nice idea - I'll ask a friend who's working on zero-waste desalination if they have a relatively easy way of extracting all bar the sodium chloride & bromate. With typical seawater we'd end up producing sodium hypochlorite (bleach) and bromate.

While multiminerals are not as common as multivitamins, they do exist. I’ve been thinking that we probably want a multimineral in capsule form, as tablets have bulking agents and anti-caking agents. And then I discovered that you can also get them in liquid form, e.g. Nutrisorb Trace Minerals.

For capsules, I found a [multi mineral veggie capsule]( and a [multi-mineral complex capsule](

@“Gerrit”#p174 I like the idea of a water based liquid (just like Rabaey’s) so I checked out the Nutrisorb Trace Minerals ingredients:

  • 1. Purified Water,
  • 2. Sodium Borate,
  • 3. Preservative (Citric Acid),
  • 4. Chromium Chloride,
  • 5. Manganese Sulphate,
  • 6. Sodium Molybdate,
  • 7. Sodium Selenite.
  • So, when compared with [Rabaey et al]( they are missing:

  • 1. iron,
  • 2. zinc,
  • 3. calcium,
  • 4. copper,
  • 5. nickel &
  • 6. cobalt.
  • And add:

  • 1. citric acid,
  • 2. chromium &
  • 3. selenium.
  • @“Gerrit”#p174 capsules are also a great idea. The multi mineral veggie capsule's you found contain:

  • 1. Calcium (as DimaCal Di-calcium Malate, TRAACS Calcium Bisglycinate Chelate) 100 mg
  • 3. Iodine (as Potassium Iodide) 75 ug
  • 4. Magnesium (as Albion Di-Magnesium Malate, TRAACS Magnesium Bisglycinate Chelate) 100 mg
  • 5. Zinc (as TRAACS Zinc Bisglycinate Chelate) 7.5 mg
  • 6. Selenium (as Albion Selenium Glycinate Complex) 35 ug
  • 7. Copper (as TRAACS Copper Bisglycinate Chelate) 1 mg
  • 8. Manganese (as TRAACS Manganese Bisglycinate Chelate) 1 mg
  • 9. Chromium (as TRAACS Chromium Nicotinate Glycinate Chelate) 60 ug
  • 10. Molybdenum (as TRAACS Molybdenum Glycinate Chelate) 37.5 ug
  • 11. Potassium (as Albion Potassium Glycinate Complex) 42.5 mg
  • 12. Boron (as Albion Bororganic Glycine) 1.5 mg
  • 13. Vanadium (as TRAACS Vanadium Nicotinate Glycinate Chelate) 50 ug
  • So they are missing:

  • 1. iron,
  • 2. nickel,
  • 3. cobalt,
  • 4. sodium,
  • 5. sulphate,
  • 6. chloride (good)
  • And add:

  • 1. iodine (may be bactericidal),
  • 2. magnesium,
  • 3. selenium,
  • 4. chromium (may also be bactericidal),
  • 5. potassium,
  • 6. malate (potential carbon and energy source),
  • 7. glycinate (potential nitrogen, carbon and energy source)
  • 8. gluconate (potential carbon and energy source)
  • 9. niacin (potential nitrogen, carbon and energy source)
  • @“Gerrit”#p174 multi-mineral complex capsules contain:

  • 1. Coral Calcium 180 mg
  • 2. Magnesium Gluconate 150 mg
  • 3. Potassium Gluconate 150 mg
  • 4. Zinc Gluconate 10 mg
  • 5. Bamboo Extract (75% Silica) 10 mg
  • 6. Manganese Citrate 5 mg
  • 7. Copper Gluconate 2 mg
  • 8. Boron Citrate 2 mg
  • 9. Sodium Molybdate (Molybdenum) 500 ug
  • 10. Iodine (as Potassium Iodide) providing 220 ug elemental Iodine
  • 11. Selenium 100 ug
  • 12. Chromium Picolinate 100 ug
  • So they are missing:

  • 1. iron,
  • 2. calcium,
  • 3. nickel,
  • 4. cobalt,
  • 5. sulphate,
  • 6. chloride (good)
  • And add

  • 1. silica
  • 2. potassium
  • 3. iodine (may be bactericidal),
  • 4. selenium,
  • 5. chromium (may be bactericidal),
  • 6. citrate (potential carbon and energy source)
  • 7. gluconate (potential carbon and energy source)
  • 8. picolinate (potential nitrogen, carbon and energy source)
  • Do we need to match Rabaey et al exactly, or is it possible that there is a multi-mineral on the market that is “good enough”?

    @“Gerrit”#p178 Brilliant question, and the answer of course is no, we don’t need to match exactly. But how do we know which elements are optional?

    At a 20ml volume I'd say that chemicals are cheap and time is expensive, so my instinct would be to start with something we know works, then remove elements we suspect (or hope) may not be needed.


    remove elements we suspect (or hope) may not be needed.

    That sounds time consuming :) But yeah, if our intent is to reproduce the experiments from Pous et al exactly, then we should start there. I was thinking we could look to see what trace element solutions are used for similar HOB experiments, and where they overlap.

    What I mean is if we skip three elements and see no growth we have no useful data. We have no idea what prevented growth. If we replicate someone else’s work with the only difference being our bioreactor we at least know it wasn’t the lack of a certain trace mineral that killed it. That seems like the fastest route to success.

    We absolutely could attempt to copy any other HOB experiment. My preference for Pous et al, is that if we see no growth, Narcís will have a better chance of seeing where we went wrong & is more likely to be willing to take a look than someone who doesn't know us.

    The closest of the three you have sourced may be the [multi mineral veggie capsule]( as we have sodium and sulphate in our 'meso-nutrient' solution and we'd really rather avoid chlorine (as it will electrolyse to form bleach and kill the bugs). So if you add iron nickel and cobalt you at least should have all the elements they want. You then just need to hope that things like iodine and chromium aren't inhibitory and all the organics (which you wouldn't normally have in trace nutrients) don't mean that a non-HOB proliferates and makes one of the other nutrients rate limiting.

    I'm wondering if a cheaper mineral pill, less bioavailable to humans (avoiding the organics), may be better for the HOBs. I tried enlisting AI:
    Gemini hallucinated a [few products]( that I couldn't find for sale anywhere, the ones it suggested that I could find seemed no better than those above.
    Copilot gave me Sanatogen A-Z multivitamin & a [fertiliser]( that it warned is not intended for human consumption.

    As you have two pioreactors, a really useful experiment would be to run one as per Pous et al and run a second with your mineral capsules.

    @Gerrit & I have been doing a little background work on this. We haven’t yet managed to find a food grade source of the Rabaey et al micronutrients, but @Gerrit found Onyxmet who can sell enough of each of the 9 components to make 42L of the micronutrient solution for £53.50.

    I'm reaching out to some industry contacts to see if anyone can source food grade equivalents. If you know anyone who may be able to help out, let us know.

    If we draw a blank I'd suggest that our approach is for one of us to purchase the chemicals from Onyxmet, then package up enough dry chemical for others to make 2L (allowing for wastage). We can then:

    1. try enrichment cultures with this non-food-grade media,

    2. develop an easily available food-grade solution,

    3. then start the enrichment culture with it from scratch.

    Multus just came up in a funding conversation. Perhaps we should reach out to them about jointly developing a micro nutrient solution?

    I was looking through the Waag BioHack Academy archives and they have a trace mineral solution recipe. They mention using water conditioners from aquarium stores as an alternative source of trace minerals, which I thought was interesting. Turns out you can buy it in tablet form:

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    Also, I went looking through the DSMZ list of organisms, and most HOB strains they have use “Trace element solution SL-6”:

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    I’m just wondering if one of the reasons that external electrolysis results in higher growth rates is that in-situ electrolysis results in a little HOCl formation from the trace minerals. The HOCl would most likely kill as many HOB as it came in contact with until it was consumed. I wonder how much impact there would be using a non-standard trace mineral solution that had fully beneficial anions…?

    @NarcisP have you contemplated avoiding Cl2 in your trace nutrients?

    HOCl generation can occur when high chlorides concentrations are present in the medium. To avoid this reaction to occur: 1) Use Platinized titanium as anode, 2) Avoid chloride addition to the medium. Trace minerals are not specially relevant due to its low content. Macronutrients (N, P) are the key. Specially, avoid ammonium chloride, you can use other ammonium salts (e.g., ammonium sulphate) or urea (synthetically produced and widely used as fertilizer).

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    I was looking for food-grade sources of boron and noticed that these boron capsules use sodium borate (borax). I’m having a really hard time finding a food-grade source of boric acid (H3BO3), so maybe borax (Na2B4O7.10H2O) is the way to go?

    According to this borax supplier in the US there is only technical grade borax, which is not approved for food or beverage use. But, since it’s non-synthetic and mined as a mineral salt, it’s possible to find nutritional suppliers using food grade containers and packaging methods for borax.