Hi Gang! I am very very happy to find this forum and get to discuss with you here. I have been scheming to build a digester for over a year... built and drew several prototype schemes in my spare time... this forum is just the medicine for my interest! Thanks to Bob for putting it together.
Anyway like the good folks at Piedmont, we operate a small scale biodiesel plant at a college in Pennsylvania, USA. Our main waste product in biodiesel production is crude glycerol. The glycerol is contaminated with methanol (about 25% by volume) and has a high pH. Our glycerol contains potassium as we use KOH as a catalyst for the BD reaction. Many biodieselers report that it makes good digester feedstock, and I am told that in Europe this is the main disposal route for biodiesel byproduct. In our shop we make about 24 gallons of the liquid byproduct weekly.
I have been working in conjunction with our state's Department of Envrionmental Protection to try to establish what is "Safe, Legal, and Responsible" behaviour for biodiesel production on a small scale. For example, dumping glycerol on the land or in streams is not responsible. Technically, glycerol with methanol contamination is classified as hazardous waste, because it is both ignitible and toxic. The DEP has been reluctant to allow on-farm disposal of crude biodiesel glycerol (CBG) because of this haz-waste classification.
However, if we can show a benefit to using glycerol in a digester (such as increased gas production) and can show that it does no harm (no harmful emissions, and biodegradable effluent) I think the DEP will allow this use. Many small scale biodieselers are interested in biogas digestion, but few of us have ever given it a try.
My hope in posting here, and reading on the forum is to develop a small research project that will demonstrate digestibility of CBG, and come up with a cost effective homescale unit that people can home-brew along with their biodiesel equipment. I was most pleased to see Bob's design on the Biorealis web page and can't wait to get started!
Thanks for your comments.
If you have an interest in biodiesel, the best web sites I know are:
(the forum)... drill down into the pages Biodiesel > Glycerine Byproduct to get to the glycerol discussion