The majority of methane producer is not acetoclastic methanogen but hydrogenotropic methanogen. Does it mean something is going wrong during the anaerobic digestion?
How many anaerobic digestion models are nowadays being recognized beside ADM1?
Dear Aqil,
Excellent question!
ADM1 is a generic and recognized model for anaerobic digestion. Kinetic parameters are proposed for each trophic group involved, together with the respective amount of biomass. BUT assessing the actual amount of each trophic group and related kinetic parameters can only be made through experiments such as yours.
So, to my opinion, ADM1 is appropriate, but you need to tune the kinetic parameters differently in order to get the right balance between acetoclastic and hydrogenotrophic methanogens.
Doesn't it also depend on your substrate and the other parameters used? For instance, we use seaweed (different species mix) to produce methane by AD and my 454 pyro results are very different from what i've seen from other published papers but most of them are known for methane production but aren't the same as the dominant ones in others papers! Also if your biomass is rich in polyphenols it could be inhibitory for the usual microbes!
This is a quite common situation when you have some kind of inhibition episodes. Hydrogenotrophic methanogens are usually more resistant to toxicity and inhibition than acetoclastic methanogens. When you treat not common substrates that can contain potential inhibitors like heavy metals or aromatic organics, you need to study how the system behaves previously to apply any kinetic model. Sometimes adding a simple non-competitive inhibitory term is enough for having good fitting and then you could use directly ADM-1 parameters (the so-called modified-ADM1 models).
There are a lot of alternative anaerobic models, but ADM1 was precisely designed to generalize the anaerobic digestion process, so a simple modification of this model is more desirable rather than the use of a completely new model (especially for direct implementation in real cases).
What was AD process- continuous or batch? If continuous CSTR maybe you took sample of bacterial association from earlier stages (it is very hard to take only fully digested biomass). If batch process, maybe you stopped it to early. Quantity and quality of bacterial association is changing every time. ADM1 is based on general consumptions of right process. In practice some differences will be.
How would Trace Metals dosing affect the microbial community diversity?
My digester is batch culture, but I sampled few time over the course of digestion process. The results are all similar where the hydrogenotropic was dominant over acetoclastic.
A review paper stated quite extreme statement that in totality, two-thirds of methane are obtained from the acetoclastic methanogenesis pathway and one-third from hydrogenotrophic methanogenesis pathway according to anaerobic digestion model 1 (ADM1). This is misleading since reports were based on anaerobic digestion of waste water and sewage sludge with very low organic content (Manyi-Loh et al, 2013)
What do you think about this statement?
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