During anaerobic digestion of low C/N substrates, the digestion system often faces ammonia inhibition. Biochar has been widely used to relieve ammonia inhibition. Although biochar has a high specific surface area, its ability to adsorb ammonia nitrogen is still limited (10-100 mg/g). Therefore, the adsorption effect may not be the main reason for ammonia nitrogen to alleviate ammonia inhibition.
Dear Cai Yafan,
In my opinion, although ammonia adsorption is one of the mechanisms that helps dealing with high ammonia concentration but it is not the only one. Biochar is rich in carbon and can provide a readily accessible carbon source for the microorganisms and balance the C/N ratio. In addition, because of its high surface area, biofilm can grow on biochar. Biofilms are generally more resistant to unfavorable environmental conditions in comparison to planktonic cells.
Biochar is an electrically conductive material. Therefore, I think that the mechanism of resistance to inhibition by ammonia is largely associated with the inclusion of alternative pathways of methanogenesis along the pathway of direct interspecies electron transfer (DIET).
This is a good question. Are there any peer reviewed papers that prove biochar improves AD in low C/N reactors, and what are the dosages used? I struggle to find clear numbers that prove such effect. At the same time, if there are such studies, are they carried out against robust controls and comparing with other alternatives? such as zeolites, etc,? I have tried biochar for ammonia adsorption and got no significant effect at all. I am honestly interested in finding what needs to be done to get a result. With biogas production did not get any effect at all. It is wrong to suggest biochar is readily available carbon when it is otherwise being offered as a way to fix carbon in soils ;)
Edgar Blanco , There are indeed some papers demonstrating the role of biochar in low-C/N fermentation systems. For example, "Impacts of different biochar types on the anaerobic digestion of sewage sludge". The amount of biochar used is generally 2-40g/L. Compared with conmmon fermentation systems, the mechanism of biochar in nitrogen-rich fermentation systems may be more complicated. It is indeed a good idea to use zeolite as a control group to explore the contribution of biochar adsorption.
Edgar Blanco , There are indeed some papers demonstrating the role of biochar in low-C/N fermentation systems. For example, "Impacts of different biochar types on the anaerobic digestion of sewage sludge". The amount of biochar used is generally 2-40g/L. Compared with conmmon fermentation systems, the mechanism of biochar in nitrogen-rich fermentation systems may be more complicated. It is indeed a good idea to use zeolite as a control group to explore the contribution of biochar adsorption.
Edgar Blanco , There are indeed some papers demonstrating the role of biochar in low-C/N fermentation systems. For example, "Impacts of different biochar types on the anaerobic digestion of sewage sludge". The amount of biochar used is generally 2-40g/L. Compared with conmmon fermentation systems, the mechanism of biochar in nitrogen-rich fermentation systems may be more complicated. It is indeed a good idea to use zeolite as a control group to explore the contribution of biochar adsorption.
Thank you Yafan. Given the very low density of biochar, a dosage of 40 kg per ton would be an issue to any process and probably cause mechanical issues in practice apart from the financial implications (Opex). Is anyone applying it at full-scale? And is it financially sustainable?
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