For the slurry concentrations (dilutions): ... dilution ratios are harder to find. Do you come upon these numbers in the literature or are these from your own experiance?
Actually both. I assume that the moisture content numbers given in the literature (including values given in the sources referenced above and built into the calculations) are average values for fresh manure as it leaves the animal (assuming the animal in question does not have diarrhea on the day the sample was taken, etc
).
But in actual practice, moisture content has far more to do with collection method, i.e. whether it is dry scraped from the barn floor, flushed into a gutter with a water hose, or dry cow pies collected from a pasture by rural peasants, etc. Same thing with human feces. If pumped from a water flush toilet (even a < 1 liter/flush model) there is no need to add additional water for dilution. But if collected from a dry toilet with urine separation, there is.
So, basically the goal has been to add water as required to make a slurry that is easily pourable and pumpable without clogging pumps and pipes. Along that line, I have come across literature sources that describe a 6-8% slurry as being the consistency of thick cream.
That said, I have been working (so far only on paper) on a high-solids design that uses digester supernatant as dilutant to make a pumpable slurry. This has several advantages, including smaller tank size (obviously), but also lower and simpler heating requirements (less volume exchanged), and pre-mixing of bacteria with incoming raw waste in a fixed media environment.
Also Another question: Do you find that most farms store their manure first in another area, or do they directly dilute it and add it to the digester fresh from the fields or pits? in other words, does the Manure normally need to be stored between land pickup and loading to the digester?
I don't know the answer to that. My own direct experience is limited to smaller scale systems, but reviewing sources such as
USEPA agSTAR program and looking through their demonstration projects I find various systems in use, and don't know if one method is predominant. I would guess that it depends on size of herd, and other site specific conditions.
