Composting: Solution?

Three years ago, Dickinson College entered the world of biodiesel production in an effort to improve the college's ecological footprint and to provide its students with a hands-on education. Our production, which began with a modest 50-gallon Appleseed reactor, has flourished into a highly successful operation. In 2007, student workers produced more than 2,000 gallons of fuel for campus vehicle use. Our success, however, comes with a problem: we have been struggling to gain control of an ever-growing supply of glycerine.

Although several producers have found creative methods to decrease glycerine stockpiles, very few of these techniques are practical (not every biodiesel maker has the time or desire to craft fifty gallons of soap). That's why our college biodiesel project, with the permission of Pennsylvania's Department of Environmental Protection, decided to conduct some research.

This past fall, Matt Steiman (Dickinson's Biodiesel Production Manager and the SVO forum's "Farmer") and I began to investigate whether composting glycerine is a viable option for responsible small-scale producers. Many popular websites and books suggest that biodiesel glycerine can be composted, but despite thorough searching, we found no documentation of actual composting research. Our goal was to determine what happens biologically and chemically when biodiesel glycerine is added to compost piles. We're still in the process of researching, but we've already found some interesting answers.

We began the experiment by mixing a compost base of cow manure and hay (3:1 ratio). Next, we constructed 3 ft. by 3 ft. piles from 240 gallons of the pre-mixed base. Each pile was then mixed with either 18 gallons (the determined saturation point at which we felt the piles could take no more glycerine without runoff), 13.5 gallons, 9 gallons, or 4.5 gallons of KOH-based glycerine; two piles were left free of glycerine to serve as a control (NOTE: Prior to the experiment, our glycerine was distilled to remove methanol). Piles were then covered with Compostex compost covers to prevent runoff of glycerine into surface and ground waters. During their 12-week maturation period, the piles were turned six times and their temperatures were recorded regularly. At the end of the 12 weeks, samples of the compost were sent to the Woods End Research Laboratory in Mt. Vernon, Maine for testing.

Tests found that carbon to nitrogen ratios and potassium levels increased with the compost's glycerine concentrations, while nitrogen levels decreased. The piles with larger quantities of glycerine were found to stay hotter longer. However, there was no significant difference between the maturity of the piles at the end of the testing period.

The pH of the composts ranged from 8.97 (pile with no glycerine) to 9.71 (pile with 18 gallons of glycerine). In addition, the piles with more glycerine were dryer, denser and they supported larger colonies of a white fungal growth (this fungus is believed to consume fats).

The direct correlation between increased potassium levels with the addition of glycerine indicates that KOH-based glycerine has the potential to increase fertilizer value when added to compost. These results also suggests that NaOH-based glycerine will increase sodium content when added to compost. According to researchers at the Pennsylvania State University, excess sodium is damaging to cropping soil. It may therefore be unwise to compost NaOH-based glycerine.

Because of increased pile temperatures, adding glycerine may also help to kill pathogens and weeds in compost piles.

Research is currently being conducted to address the effect of the compost's high pH on plants. We are trying to determine whether glycerine needs to be neutralized prior to composting, or if the high pH can have a beneficial "liming ability" on acidic soils.