testing feedstock

[spiritrancho]

After reading the post here about minidigesters I decided to make several and test the various feedstocks I have available for suitability. I have adapted the design to materials at hand. One of the disadvantages of making biodiesel is the amount of waste products accumlated.
The control digester is simply rabbit droppings with wasted feed and bedding(bermuda grass) and covered with liquid drains from my composting toilet. This in a 5 gallon bucket with lid, heated in water by aqurium heater, and connected to a rising gas collector. After two days I have gas pressure.
The first experiment is with using the same hay and poop with the the slurry liquid composed of half urine drained from the rabbit catch pans and the water used to wash those pans. The other half of the slurry liquid is waste vegetable oil from french fry foods. This is the cruddy stuff left in the bottom of a collection basin. I have a couple of hundred gallons of this stuff. I started this yesterday and am heating it with a light bulb under the digester. I simplified my digester disign by cutting two plastic oil continers and fitting togeather to give a floating dome arrangement.
The third test rig will be for spilled alfalfa hay goat poop and glycerol. Glyceraol is a byproduct of the transestifercation process of making oil into biodiesel. It contains soaps, potassium hydroxide, and some methanol. Again I have several hundred gallons on hand. If it fails I will try distilling off the methanol before digesting, which is a pain.
Here is a question....How best to test the gas to see if it is methane. I suppose you just light it, but is that safe with a cubic foot of the stuff at the end of the plastic tube?
Another question....somewhere I read that using lots of fodder and bedding would work best in a batch system. Is that because of the undigestible solids forming a hard scum? Would the Biorealis design handle that feed stock without frequent cleaning?
Finally any comments or suggestions on my testing set up or feedstock?

[Bob]

Very cool experimenting! Keep us informed.

Here is a question....How best to test the gas to see if it is methane. I suppose you just light it, but is that safe with a cubic foot of the stuff at the end of the plastic tube?

There are a couple of things you can do to make it safer. Use a real burner (e.g. a bunsen burner), and don't connect it directly to the digester. Connect it through a water trap to prevent backflash.

Another question....somewhere I read that using lots of fodder and bedding would work best in a batch system. Is that because of the undigestible solids forming a hard scum? Would the Biorealis design handle that feed stock without frequent cleaning?

I think the main reason would be that the fibrous material does not pump easily. No, the Biorealis design would not work well with it.

[spiritrancho]

Thanks for responding, Bob. Yesterday I tested the papercrete adjitator to see if it would chop up the hay as well as it does paper. No way. I shall have to shred the hay first thru a leaf shredder.
I went ahead and mixed up the batch with glycerol from biodiesel production (contains methanol and soaps) and some cruddy oil from used cooking oil collection. For a starter I used liquid drains from my biolet toilet. Still needed more liquid so I used water from the cleaning rabbit pans. Each of those liquids were in about equal proportions. None of the lititure give any idea of the C/N of the oil or glycerol so I am shooting in the dark. I am digesting in a 55 gal drum with a 30 gal. plastic trash can as a rising gas dome. I have wrapped corrigated green house plastic around the drum as insulation and solar gain, am using a fish tank heater for supplemental heat. The batch ended up at 80 deg F. I will test PH today.
CAn anyone give me an idea about the C/N of the waste french fry oil sediments or the biodiesel by product?