COMPOSTING: Vermicomposting Works Its Way Into Fertilizers

David Davenport

The popular choice with farmers and gardeners worldwide, earthworms are now working their way into industrial fertilizer manufacturing.

The common earthworm, which is able to consume its weight daily in most kinds of urban waste, is being used to turn waste into high-quality organic soil. By producing pellets rich in nutrients (nitrogen, phosphorous and potassium) and organic matter, the worm's natural waste lightens and conditions soil.

The Naturba Process, developed by the French firm Sovadec, separates recyclables from organic waste, then places the organic waste in an aerobic fermentation tank. The fermentation, which heats waste to 160-170DegreesF, disinfects and sanitizes the organic matter by eliminating pathogenic germs, larvas and insects. From the fermentation tank, the waste is moved to a vermicomposter (a device that maintains temperature, aeration and moisture levels) so the earthworms can digest matter and release it into the composted material. After vermicomposting, the matter is dried by a second heating process and filtered to remove the non-composted material. After completion, the vermicompost is bagged as fertilizer (see chart).

Vermicompost has been used by gardeners for centuries and has proven to be a effective way of turning compost into fertilizer, according to Terry McGuire, deputy director of the French Technology Press Office, Chicago. Now being used on an industrial scale, the process is "the kind of technology developed in a country like France which has very limited landfill situations," he said. "The French have been making fertilizer out of compost for a long time. It's both ecological and beneficial."

The Naturba process, currently in use at a processing center in La Voulte, France, requires a full day to separate 100 tons of waste brought to the 27,000 square foot plant. Twenty-five percent of the waste is recyclable; the remaining 75 tons are placed in the fermentation tank for 36 days to reduce the weight to 50 tons by eliminating water and carbon dioxide. The waste then spends 62 days with millions of earthworms in the vermicomposting stage, where the waste is reduced to 30 tons of compost high in fertilizing value. "The process produces 25 percent of elements to recycle, 30 percent of Naturba compost and 20 percent that is stabilized," said Claude Baratier, Sovadec's export director, Montelimar, France. "Twenty-five percent of the waste is evaporated during the process."

The process does not produce liquid or gaseous pollution, and it generates steam water and carbon dioxide evaporations which are easily absorbed into the atmosphere. The final waste that is not bagged into fertilizer can be landfilled without any danger, according to Baratier.

Turning compost into fertilizer has its financial benefits too. "There's a certain amount of capital outlay to build and run the vermicomposting facility, but there are two sorts of return on investments," said McGuire. "First, there's the actual financial return. Then there's the social benefit, such as less environmental pollution and new jobs. A value can't be put on that. It's not just the cost or the price you get from the sack of compost but also the social value."

The process is best for communities with populations between 30,000 and 200,000, but is applicable to those with more than 200,000 people, said Baratier. "However," he said, "some of the drawbacks to these [larger] facilities would be increased transportation costs and pollution generated by the extra trucks."

Currently, the Naturba Process is not in being used in the United States, but Naturba Canada is working to create U.S. facilities.