Properly Treated, Human Biosolids Are Good Fertilizer
October 31, 2000
by Dennis T. Avery
THE BridgeNews FORUM: Viewpoints on farming, farm policy and related agricultural issues.
CHURCHVILLE, Va.--Chinese peasants and today's organic farmers have long shared an important idea: We can't afford to waste our wastes.
Today, that includes "biosolids"--residue from sewage treatment plants. Some of my neighbors are nervous about living near fields where biosolids are being applied.
Oddly enough, they seem totally secure about the idea of living next to an organic farm. Yet the use of biosolids is far safer for neighbors, workers and consumers than is organic farming.
For centuries, China has had "sustainable" agriculture, using human wastes to fertilize its rice paddies. The Chinese had no other source of nitrogen for their crops, and no better way to deal with huge amounts of human waste.
Modern sewage treatment produces millions of tons a year of what we call biosolids. Industrial plants, such as milk and other food-processing plants, produce additional millions of tons.
We can process these biological residues into safe forms, and use them as valuable soil conditioners on farmland and forests. Or we can waste them, using up lots of valuable landfill space. Incineration is even more expensive than putting waste in landfills and adds more greenhouse gases to the atmosphere.
Biosolids contain essential such plant nutrients as nitrogen and phosphorous. They also contain organic matter, the single most important component of the world's most important substance, topsoil. Virtually all the life on this planet ultimately depends on topsoil converting sunlight into plants and trees.
Our livestock and poultry farms also produce hundreds of millions of tons of manure a year. Properly handled, animal manure is just as valuable as biosolids.
Mainstream farmers use it mainly on feed crops. They use chemical fertilizer on food crops because it doesn't carry the risk of pathogenic bacteria.
Organic farmers refuse to use chemical fertilizers, so they feel they must put manure on food crops. It's the bacteria that make organic farming more dangerous for its workers and neighbors.
Modern societies can also afford to make their wastes much safer to land-apply than China's night soil. Organic farmers usually compost their manure by stacking it in piles for some months and letting the natural heat of fermentation kill bacteria.
Biosolids are treated still more intensively. They're typically put into a sealed digester and composted at much higher temperatures than most organic farmers achieve. They're also checked before land application to make sure the pathogens are killed, which is not true for organic farms.
Recently, health authorities retested some biosolids that had allegedly caused flu-like symptoms among workers spreading them. The biosolids were found to be as safe as the garden dirt in my backyard, with none of the pathogenic bacteria that attack humans (salmonella, shigella, E. coli, etc.).
This indicates there was no residual biological activity from the sewage sludge. In fact, the high concentrations of environmental fungi and bacteria in the biosolids re-emphasized how good the biosolids are for soil microorganisms.
While no food crops can be harvested from land that has received biosolids for 12 to 38 months (limits enforced by individual states), organic farmers have only a voluntary commitment to wait three months before harvesting food from fields where they have spread raw manure.
This disparity, three months instead of 12 to 38 months, exists even though most organic farmers use cattle manure, which is the major reservoir of the most virulent new bacterial threat in our food, E. coli O157:H7.
Researchers at the Department of Agriculture say they have found O157 on every cattle farm and ranch they've tested, even extensive cattle ranches in western Canada. Infections from this bacterium are primarily associated with undercooked hamburger, but this strain has also been found on vegetables and fruits. It can kill even healthy people and often leaves its survivors with damage to internal organs such as the liver and the kidneys.
The Centers for Disease Control say America is getting at least 25,000 of these cases a year, and about 250 deaths. There are no known deaths from pesticide residues or biosolids.
Isn't it time we made organic food production as safe as our use of biosolids?
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Dennis T. Avery is based in Churchville, VA, and is director of the Hudson Institute's Center for Global Food Issues.