The goal is to remove H2S from a gas stream. Not interested in a pure, axenic, commercial culture at all, but rather in an open, mixed microbial culture able to work under non sterile conditions.
Is WWTP sludge a good source? If so, which kind of selection/enrichment procedures do you recommend?
Which food/nutrient demands can you advise for that?
Which reactor / growth configurations do you recommend?
Thanks.
I think you want sulfide-oxidizing bacteria, which can be found in aerobic and anaerobic environments. You might be able to get some in wastewater, another option is from a biologically active community like pond mud. You could also create a Winogradsky column and get a high inoculum of sulfur-oxidizing bacteria from that.
The enrichment process would be dependent on which types of sulfide-oxidizer you want. Most are chemolithotrophic, so in this case, I would supply them with ample carbon dioxide and H2S. Some may want oxygen as well, but likely at low concentrations. Others might also be organotrophic and require organic material as opposed to light. Again, concentrations of these gases are specific to the type of sulfur bacteria you want. In the case of phototrophic bacteria, you will want to give them light as they use that as their energy source.
Media-wise, you will want to give them some autotrophic media source without carbon to encourage the autotrophic organisms to grow. Some sort of microalgae media should be fine. If you want organotrophs, you can throw in a carbon source.
Reactor wise, you would want something you could do gas-fermentation with ideally. A bubble reactor works well for this. You will need it to be able to withstand this acidic gas stream, so something glass would be ideal. For starters, you can make a simple bioreactor using a glass bottle and put in holes for gas in and gas out.
I suggest reading up more on sulfide-oxidizing bacteria, specifically purple bacteria, and green-sulfur bacteria. There may be other types out there, but I think that deciding what type of bacteria you want to use will be vital.
Dear Matthew B Paddock ,
Thank you for you kind and prompt reply. Indeed very useful. If you don’t mind, I’d go further into your advices:
A chemolithotrophic consortium sounds more feasible to me as it would not require light or a substantial C source other than CO2. Again, I’m not interested in a pure culture, which may be more effective but also much more sensitive to operating shocks. Therefore, a get-the-job-done solution (i.e. grow, remove H2S from biogas, not CH4) would be appropriate for such an exploratory study :)
But then you refer “Media-wise, you will want to give them some autotrophic media source without carbon to encourage the autotrophic organisms (…)” In a chemolithotrophic option, I would simply supply them with CO2, H2S and some nutrient media, in order to suppress auto- and organotrophics, right?
By the way, I have found elsewhere in recent papers to provide a thiosulfate-based medium for enrichment purposes, do you agree?
Both your suggestions of green and purple bacteria are supposedly autotrophic, am I wrong? But I’d like to avoid setting up a phototrophic process by now.
A Winogradsky column sounds cool, while also it seems to me a bit time-consuming and especially non-selective enrichment process. I heard (from non-scientific soundbites) that a good sulfide oxidizing culture could be retrievable from a starch effluent treatment process. At least, I agree your suggestion to get a good starting culture from pond mud or a municipal WWTP sludge and then enrich with S-based media, thiosulfate for instance.
In a chemolithotrophic option, would you recommend a mixture of both aerobic and anaerobic sludge for enrichment? And would I provide some O2? I keep in mind that if I would provide oxygen I also would provide conditions for sulfuric acid generation rather that elemental S, which is an additional issue in the liquid media and reactor materials.
Reactor stuff is not a major issue by not, though its design is linked with the bioprocess I want to set up. I though in a simple column with the fixed bed, with recirculating liquid media bottom-top and a gas diffuser at the bottom.
Many thanks again!
Flavio
Flávio C Silva
So for media, there exists alot of media recipes for autotrophic organisms. Typically they have Nitrogen and phosphate as the macronutrients and then a variety of micronutrients with no carbon source. You are correct in your assumptions about the media.
Thiosulfate might work well. I do not know too much specifically about enrichment methods specifically for this case, but it would be worth trying if others have had success.
Yes, they autotrophic, but in this case photoautotrophic. I do not know too much about the chemoautotrophic sulfur-oxidizing bacteria as the phototrophs are much better studied, but if you do not want to add light, then selecting for them wont help.
A mix might be interesting to try. I do not know enough about oxygen for cs, but I would assume some are at least microaerobic. If you add O2, I would keep it below atmospheric concentrations. You might be able to do some tests to see which works best for your consortium.
That reactor sounds solid.
Best of luck.
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