[Digestion] Digestion Digest, Vol 2, Issue 8

[David Fulford]

Dear Carolyn, Ahmet and listers,

Anaerobic digesters seem to work better on mixed feeds than on single 
feedstocks. A mix of chicken and cattle has more advantages than 
problems. The cattle dung provides all the right bacteria, while chicken 
dung provides extra nitrogen and a richer feed (cattle are just too 
efficient at using all the foodstuffs in the grass they eat, so cattle 
dung is not the most productive of feedstocks). If other materials, such 
as waste food, are added, the gas production per kg of feed can be much 
higher. Mixed feeds also encourage a wider range of bacteria to develop 
within the digester, which gives greater stability for the system.

A danger of mixed feeds is that some materials need to be ground up, 
otherwise they can block the pipework. Chicken feathers and carcasses 
often end up in the dung, and they need to be chopped up. This is also 
true of food wastes. Even cattle dung can cause problems, as other 
materials can end up in the digester. If the dung is scraped up from the 
ground, it can contain stones and earth which can block pipes and fill 
up the digester. Cattle often eat stones to help in their digestion and 
these end up in the bottom of the digester and can cause problems in 
feed grinders.

I hope this answers people's questions,

David Fulford

Carolyn Henri wrote:
> I am also interested in the question posed by Ahmet Musluoglu regarding 
> experiences mixing cow and chicken manure during digestion.  I'd like to 
> know: 1) are there existing, operating digesters that regularly use this 
> manure mix?  If so, where? 2) what are the challenges in combining 
> cow/chicken manure?  3) Are there advantages to this mix?  Didn't want this 
> topic to get lost in the pile.
> Thanks,
> Carolyn Henri
> **************************************************
> Carolyn J. Henri, Ph.D.
> Project Manager
> Stanwood Bio-Energy Producers
> Methane Digester Feasibility Project
>
> Resource Consulting Service, LLC
> 4805 Belvedere Ave.
> Everett, WA 98203
> Phone: (425) 290-3181
> Fax: (425) 290-7678
> Cell: 425-308-1634
> E-mail: Carolyn at ResourceConsulting.us
> ****************************************************
>
>