I'm embarking on a series of jar tests to find out what type of residuals are going to result, when this is varied. I should know more next week.

 

But, I ran a series of BOD's on the settled aqueous layer of a test batch I made. The highest dilution - 5 microliters in a 300 ml bottle, -"whited out."

That corresponds to a BOD of at least 480,000 mg/l O2.

I've never seen a value that high.

 

Dedalus Environmental Homepage

 

I don't know exactly what the biodiesel process was/is, or at what point they pulled this by-product, but for what it's worth, this is the BOD we have measured on the by-product.

G

First off, if you are interested in what's involved in bio-diesel production, take a look at:

http://biodiesel.infopop.cc/eve/forums

It's rare that I've seen such a heartening display of shade tree ingenuity than is demonstrated on this board.

Briefly: there are two processes. Alkaline catalyzed transesterification, and acid catalyzed transesterification/direct esterification.

In the first, that I briefly described above, the sodium hydroxide serves two purposes. It catalyzes the glyceride ---> methyl ester transesterification reaction, and it ties up free fatty acids (FFA's) as soap. A two fold molar excess of MeOH is used.  

The second uses, generally, sulfuric acid as a catalyst.  Because of "product inhibition" (water is a by product of direct esterification) a 5 - 10 fold molar excess of MeOH is used. This process is far more tolerant of poor quality feedstocks than the first described.

It was not clear to me, in the post quoted above, whether methanol recovery was carried out. I did not do it on the sample from my (whited out) BOD test. This is customary in both processes. When this operation is performed, the BOD should decline, sharply.

Wastes from the acid process will contain less glycerol, depending on the FFA concentration of the feedstock. However, there will be lots of sulfates, which it's my understanding, you municipal people don't like.

Wastes from the alkaline process will have negligible sulfates, but more soaps; salts of fatty acids. My understanding is that you municipal people don't like those too much, either. How much you get depends on the quality of the feedstock.

I'm doing some experiments to see if the FFA's can be separated from substandard feedstock so that it may be processed via the alkaline catalyzed method; later, recovered FFA's could be transformed via the acid process. Perhaps, HCl could be used instead of H2SO4.

In the works: tests to determine whether glycerol could be used on-site to generate bio-gas. Studies I've seen indicate that acetogenic fermentation must precede methanogenic fermentation. And, that this process works best if there is a lot of more conventional feed, like manure, and the glycerol is spiked in at moderate concentrations.

In short, I'm still learning. This technology is going to experience explosive growth in the next ten years, as petroleum supplies dwindle. The people on top of these waste handling problems will be the winners, and I aim to be one of them.