It's better to use digestate from another working digester as inoculum, because of the presence of a broad microbial community. We used degassed sludge from an anaerobic mesophilic digester of a wastewater treatment plant (WWTP). Make sure the incoculum is completely degassed!

If you want to use cow dung as a substrate, you have to use the fresh material. As biogas and methane yield are normally expressed in LN kg-1 ODM, determine the ODM content of a subsample of your cow dung.

It is better to not use the same substrate as a feedstock and as an inoculum because to know the produced biogas from the feedstock you need to subtracted the produced biogas from the inoculum. On the other hand, it is better to use fresh manure than dried it to obtain more biogas production.

Hi

What is the volume of the digester?

What are the objective of the project? Are you doing a research? Besides cow dung, do you have any other substrate?

The reason for those questions is mainly that, if you are doing research, you can always have cow dung as the inoculum but could do a separate batch reactor that uses only the cow dung and this will be the "control" upon which the other batches can be compared.

If you are producing biogas for actual usage at a household then you can use cow dung as the substrate without drying. So, my understanding of your context will help in giving you the proper advice.

Good luck

Koenraad Van Meerbeek advised that the inoculum to be used is completely degassed; which I understand is incubating at the temperature that will be used for the anaerobic digestion. I intend to use cow dung as an inoculum for anaerobic digestion of food waste but after degassing the fresh cow dung for 2wks, I still have a VS concentration of 93% while that of the food waste is 97%.( all based on the % wet weight). Can I still use the dung this way as an inoculum? if it can be used, what will be the substrate to inoculum ratio?