About batch processes:

onlinelibrary.wiley.com/doi/10.1002/smll.201303703/abstract

Now working in a paper on continous mode.

Yes, we have very positive results.

However, we are about to publish it, and they are not still open and validated.

I will put the links here when the acceptation arrives (let's hope so!).


Toni

Hi Toni

I was wondering if you are still continuing with this projects as you had mentioned in the webinar we back in July?

Did you find out why the iron nano particles actually resulted in 70% biogas production increase (I am not sure if it was that much, in the figure you shared fin June it looks to be a little bit less but still a lot…) and why some of the particles prepared with different stabilizer didn't show that effect at all?

Did you manage to reproduce the biogas production increase also in pilot scale (100L) and continuous mode? You mentioned you were looking for a fecal sludge treatment plant in spain to test this if possible?

Cheers and happy new year,
Dorothee

PS: Has the paper you mentioned here been accepted, would it be possible to share it or a version of it?

Links, further readings, etc:
We are in the final stage of submitting our main first results to the journal "Science". Of course, the paper includes the funding of Gates Foundation in the acknowledgements. However, the paper is still in the hands of English revisers. I would prefer to include a link when the paper is published (in Science or other journal).

For those of you interested in Toni's research, I can recommend watching this online discussion that we recorded with Toni on 1 July.
Toni's presentation starts at 2:32 into the recording (see attached file below); it is followed by questions and answers that start at 10:13 until 14:20.

I have added the Youtube link below to start at exactly the right time:



In the question session, the following was discussed:

• the role of the stabilisers (they prevent agglomeration of the iron nanoparticles) in the observed increased biogas production; as well as the possibility that enyzmatic activities are increased with the additional iron.
• I asked Toni a question about the costs: he explained that iron nanoparticles are very cheap when they are industrial grade (but expensive in the lab because here it is high grade). So he thinks that costs for adding the iron oxide nanoparticles should not be a prohibitive factor, and that the increase in biogas production (up to 70% increase in the lab) should far outweigh the additional costs of the nanoparticles.

Thank you, Toni, for your participation in this!

Good idea.

We have the methodologies ready to measure lipases, cellulases and proteases.

We will try it.

Many independent variables govern the performance of anaerobic digesters. Temperature, nutrients level, loadings, mixing, SRT, LRT, and solids recycle impact the performance of the digesters and the gas production.

Low bacterial population leads to low waste stabilization, resulting in low gas production. It is not only the question of rate of gas production, but also the percentage of methane component of the gas. Typically, 50 per cent of the methane component in the gas signifies essentially carbohydrate nature of waste.

Batch mode and continuous operation mode entails changes in the volatile acids concentration (their production by the acid-formers and, utilization by the methane-formers) and, this in turn, impact the gas production. Continuous operation of digesters, after reaching the equilibrium state, in general, give stable performance, assuming there are no wide variations in input variables.

F H Mughal

Hmm, my first guess would have been improved enymatic digestion of cellulose and lignin. A quick google search turned up that there is a (albeit negative) correlation between the concentration of iron-ions and the activity of cellulases. Maybe that is something to look further into.

A lot of questions, not enought answers.

Now we are working with real sludge, it seems that when organic matter is consumed, microorganisms look for something that can consume, in this case something that is not biodegradable under continous mode, when you are feeding esaily biodegradable organic matter.

Moreover, it is something with a high biogas potential, as it is produced very fast.
Some fat?

We are still working and try to reproduce these results to prepare a strategy in a 100-L continuous reactor.

See the final figure attached.

We will keep you informed!

Ahh, so my assumption that is is an batch process artifact was basically right, just not the explanation I offered. How economic would it be to increase the retention time in a continuous reactor to the point this effect would help at all?

Hmm... however maybe this would also help in digesting relatively low nutrient containing feedstock? Edit: That would actually a better test for your hypothesis than the one your graph seems to be based on, wouldn't it? E.g. Take already digested bioslurry, aerate it for a while, than put it back in the reactor and see if with the iron particles you can still get some more gas out of it or not.

Any suggestion why the iron nanoparticles actually have that effect? Are they acting as a sort of catalyst or as a final electron sink? Or do you suspect it is something else entirely?

The nanoparticles increase the biogas production under starving conditions, when easily biodegradable organic matter is consumed. See the picture of three controls and an anaerobic digester with nanoparticles.

We are happy!

(in the figure, scale time is in hours and R2 is the only anerobic digester with nanoparticles)

Interesting.

We suspect that S can precipitate nanoparticles, we are carrying out now experiments to confirm it with sulphate as control. We have also observed that the stabilizer used to prevent the agglomeration of nanoparticles is essential to avoid this problem, which inhibits the improvement observed in the biogas production.

See a couple of nanoparticles with one stabilizer (NP1) and one with another, in which agglomerations is not observed (NP2).

Hmm, without being an biogas expert, here is a wild guess:
Maybe that is an artifact of the batch mode, e.g. at a certain point methanogesis suppressing side products (NH4, H2S???) accumulate and prevent further methane production (and your iron nano-particles in turn bind them and prevent that), however in a continuous reactor those can escape before they cause a problem?