Dear all,
Currently, we are trying to produce hydrogen and methane by anaerobic digestion of biodiesel waste (glycerin) at thermophilic temperature (55 °C/ 131 °F). However, as soon as temperature reaches 50 °C/ 122 °F all biomass is completely washed-out of the system.
Does anyone have an idea why this happens? Glycerin thermal decomposition should only happen at much higher temperatures.
Thank you :)
I suppose that your biomass is not thermophilic and when temperature reaches 50 oC, the biomass is killed by heat.
Best regards
Vit
Dear VIt,
Thank you for your answer.
The biomass really came from a thermophilic AD reactor. It works well when is fed with whey and other substrates. The problem is really the glycerin...
Best regards,
Giovanna.
nothing special, glycerol will follow (be subject of) a faster degradation.
Hi Giovanna:
thanks for your explanation. Please, what is the concentration of glycerin in your substrate?
Thanks
Vit
Ciao Giovanna
I agree with Vit's reply, I believe your thermophilic biomass is not adapted to glycerin which has antimicrobial properties (says some articles https://jglobal.jst.go.jp/en/detail?JGLOBAL_ID=201502216204681506). I believe you could lower your OLR and start with very small loading rates to make your consortia adapted to glycerin at thermophilic range. Did you pretreated your consortia/inoculum with heat or chemical shock for Dark fermentation? If its the case (dark fermentative bacteria gets shock twice increasing the lag phase), then make your inoculum adapted to low concentration/dose/load of glycerin and gradually increase the OLR.
Hope this helps!
Regards
Anish
an additional view to misunderstandings, glycerol if heated above 55+100 C will start degrading, this is what distillation is to be done under vacuum
Dear Vit,
Thank you for your answer! The concentration of glycerin in our substrate was 1000 mg/L at first and then it was increased to 5000 mg/L.
Dear Anish,
Thank you very much for your answer! It is the first time that I have heard the glycerin might have antimicrobial properties.
We started the reactor with a very low glycerin concentration (1000 mg/L), but I will follow your advice and Vit's and try an even milder condition for a longer period. We have tried an inoculum pretreatment (heat shock treatment) and it was even worse :'D
Best regards,
Giovanna.
Just remember glycerin is an alcohol too. And as some literature suggest, it can be "toxic" against microbes. When used at 50 degrees, its "alcohol-toxic" nature could be increased against non adapted microbes. Have you tried co-substrates?
e.g. feeding glycerin together with whey, and increase the glycerin concentration stepwise?
Dear Juan,
Thank you for your answer. Yes, the use of co-substrates is going to happen in further phases of the hydrogen project. For methane production, we were able to generate some biogas when we co-digested glycerin and molasses, but even so it was difficult.
Glycerol is quite toxic which acts as anti-microbes therefore. At a high temperature there toxicity mightbe high.
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