The Oil Drum

AD can be used with various farming operations, but it is more compatible with some manure management systems than others. Total solids content is a very important parameter and different manure management systems produce waste at very different solids contents. I've added a figure to the story on this point (under The Benefits of Anaerobic Digestion) because I don't know how to put graphics in comments.

Essentially, there are different digester designs (covered lagoon - unheated and so not applicable to northern climates - complete mix and plug flow), each of which works with a different total solids content. Raw manure is excreted with a total solids contents of 8-25% depending on type of animal. For swine the figure would typically be 9.2-10%, for beef cattle 11.6-13.0%, for dairy cattle 11.6-12.5%, and for caged laying hens 25%. Manure can be diluted by process waters, misters, spilled drinking water or washing water, or it can be thickened by air drying or the addition of bedding materials. When designing a digester, all water in the manure-handling system and all processes affecting the total solids content of the resulting manure must be accounted for in order to choose the appropriate digester technology.

Flushed manure with less than 3% solids cannot be processed to produce energy in the heated digesters necessary in the Canadian climate. Complete mix digesters are suitable for slurry-based manure management systems, which result in manure with a total solids concentration of 3-10%. Plug flow digesters are used where the manure to be handled has a higher solids content, typically 11-13%, than for the complete mix design. Plug flow digesters are suitable for use on dairy farms as long as they do not use flush systems, but not for swine operations as the total solids content of swine manure is insufficient for this method of handling.