What to Do With Your Glycerin Layer
What is the glycerin layer (aka "glycerin")?
Glycerin is the byproduct left over after the biodiesel reaction process is complete. In a BioPro™ 190, at the end of the two-step reaction process, there will be 50 gallons of biodiesel in the main tank resting above 10-12 gallons of glycerin. (In the BioPro™ 380, this will be 100 gallons of biodiesel atop 20-24 gallons of glycerin).
This glycerin is usually dark brown and has a thicker viscosity than reacted biodiesel which is usually a honey brown color. Before moving to the wash cycle, your glycerin must be drained out of the tank at the ball valve and captured in a separate container.
What do I do with my glycerin?
There are many options:
- Recover your methanol from the glycerin and make raw soap with The De-methylation Trio.
- Make soap (and an online biodiesel soap-making book).
- Feed your glycerol to cattle: Feeding glycerin to ruminants; Glycerin as a potential feed ingredient for dairy cattle; Glycerol, a byproduct of the biodiesel industry, in livestock feeds, Glycerin confirmed as a feasible foodstuff for cattle.
- Take it to a sewage treatment plant where they have an “anaerobic digester”. Though they probably won't pay you for it, they do welcome the stuff.
- Use it as a composting agent. See the Dickinson College study.
- Use it as a dust suppressant.
- Burn it.
Note: There are things you should not do with your glycerin. You should never dump it into a stream or down the drain. Glycerin will kill fish and other aquatic creatures due to its high BOD (Biological Oxygen Demand) rate.
Frequently asked questions
How much glycerin does a BioPro 190 or BioPro 380 batch produce?
A BioPro 190 batch typically leaves 10 to 12 gallons of glycerin beneath 50 gallons of biodiesel at the end of the two-step reaction. A BioPro 380 batch produces about 20 to 24 gallons of glycerin beneath 100 gallons of biodiesel.
Plan for a separate container of that size to capture the glycerin, along with a way to use or dispose of it responsibly.
How do I tell the glycerin layer apart from biodiesel and when do I drain it?
Glycerin settles to the bottom of the tank and is usually dark brown and noticeably thicker, while reacted biodiesel above it is typically a lighter honey-brown color. The glycerin must be drained through the ball valve at the bottom of the tank into a separate container before the wash cycle starts.
In a standard BioPro 190 this happens about 24 hours after the process begins, or about 8 hours in a 190EX. Draining is the only hands-on step mid-process and takes under 5 minutes.
What can I do with glycerin left over from making biodiesel?
Crude glycerin has several practical uses. Common options include:
- Recovering the methanol from it and making raw soap
- Feeding it to cattle as a feed ingredient
- Taking it to a sewage treatment plant with an anaerobic digester
- Using it as a composting agent or dust suppressant
- Burning it
Research the rules and best practices for your chosen use, especially for livestock feed.
Can biodiesel glycerin be poured down the drain or dumped outdoors?
No. Never pour glycerin down a drain or dump it into a stream. It has a high biological oxygen demand (BOD), meaning it consumes the dissolved oxygen that fish and other aquatic life need, and it can kill them.
Instead, send it to a facility that can digest it, such as a sewage treatment plant with an anaerobic digester, or put it to a beneficial use such as soap making, composting, or dust suppression.
Does the glycerin layer from a BioPro contain methanol?
Yes, crude glycerin drained from the reactor carries some of the excess methanol used in the reaction, which is why recovering methanol from glycerin is one of the recommended options for handling it. Recovering it lets you reuse the methanol and leaves a safer glycerin product for soap making and similar uses.
Because methanol is toxic and flammable, handle freshly drained glycerin with gloves and eye protection, keep it away from ignition sources, and store it in a closed, labeled container.
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