From manure to electricity, fertilizer

Spencer Bennett holds up a quart bottle of what he believes is the ''finest liquid fertilizer'' ever produced for the home garden and for houseplants. Its significance, however, goes beyond what it can do in the garden. ''Before it got here,'' says Mr. Bennett, ''the fertilizer in this bottle produced enough electricity to light a 60-watt bulb for 40 minutes.''

The fertilizer is ''Liquid Cow,'' actually an odorless byproduct of several New England operations that convert cow manure into a form of natural gas called methane, which is then used to produce electricity. The Foster family of Middlebury, Vt., for example, converts what was once a waste problem on its dairy farm into $100 worth of electricity a day (sold to a local utility) and thousands of gallons of the high-quality liquid fertilizer.

The process takes manure and digests or composts it anaerobically (without oxygen) to produce the methane. The remaining slurry is separated into the liquid fertilizer and a fine material that looks, feels, and acts like milled peat moss.

Methane production is now quite common in India and China where there are more than 7 million units, but it is still rarely talked about here in the United States, despite the decade-long urgings on the subject by Mother Earth News magazine and some experimental work at Cornell University.

Mr. Bennett and his partner, Bill Hadley, are hoping to change all that with a project the Department of Energy (DOE) lists among the top 20 it has helped fund and which is also attracting overseas interest.

Hadley and Bennett, partners in a construction company specializing in farm projects, wanted to make some meaningful contribution to energy conservation. Both men had grown up on dairy farms and so were aware of the immense benefits if the energy content of a waste product, such as manure, could be satisfactorily tapped.

The two had no doubts they would succeed in turning manure into methane. In fact, they did so more efficiently than the DOE officials believed possible. What came as a complete surprise to the two partners was the quality fertilizer that also resulted. It is much superior to manure in its untreated form.

Not long after the first digester was set up (Hadley and Bennett have four in operation), the farmer involved reported taller stands of corn in the fields where the slurry was spread compared to conventionally manured fields. At harvest time this superiority translated into ears that were 4 inches longer.

When you take something from manure you might expect it to be a less effective fertilizer, but this is not the case with methane digestion. Closer study showed that while methane production taps the energy available in manure, it leaves the NPK (nitrogen, phosphorous, potassium) content, along with the micronutrients, largely unused, but in altered form. The nitrogen in the digested manure is more water-soluble. While some nitrogen in conventional manure is invariably lost to the atmosphere in the form of ammonia gas, almost none of the slurry's is lost this way.

Further tests at greenhouses continued to prove the value of the byproduct. Joe Ventrillio of the Monroe Gardens Center, Monroe, Conn., was originally reluctant to use the new product. Now he is among its most enthusiastic promoters.

A spin-drying action separates the solids from the liquids in the slurry, resulting in a substance like peat moss and the liquid manure, which is available in its pure form or fortified with 5-10-5 fertilizer.

Spencer Bennett sees the day when manures everywhere will be treated this way. It represents a fantastic resource, he says, not a major waste-handling problem. Indeed, according to his figures, each cow in America could produce 4, 000 gallons of top-rate fertilizer and 10,000 hours of electrically powered light each year. And milk? Oh, yes, that too.

For information on the liquid fertilizers or on the prospects for establishing similar treatment plants in your area, get in touch with Hadley & Bennett Inc., PO Box 517, Henniker, N.H. 03242.