TRURO, Nova Scotia – The problem with garbage and sewage is that there is too much of it in one place. Spread it around and the nuisance becomes a valuable commodity.
That’s what several researchers told a national meeting of agrologists here recently. Sewage sludge, paper plant waste, left over construction materials and residue from coal-fired power plants can all be used to improve soil. But the circumstance must be right and the application done properly.
Calvin Chong, of the Horticulture Research Institute of Ontario at the University of Guelph, said Canada produces 20.3 million tonnes of refuse and recyclable material annually.
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In Ontario, 17 percent of the material is recycled, five percent is incinerated and 77 percent winds up in landfills.
Concerned about growing landfill sites, municipalities are starting to charge hefty fees for dumping and provincial governments are passing legislation requiring as much as 50 percent reductions in waste by the turn of the century. This has prompted many businesses to approach Chong to find uses for their waste. He has found success using sludge, paper and other material as a potting mix for nursery plants.
In one case, Chong was asked to find a use for spent compost from an Ottawa-area mushroom grower. The compost had high levels of soluble salts, so high that it appeared to be toxic to plants.
“We hypothesized that too much of the spent compost, especially in the fresh, unleached state, would be detrimental to container-grown nursery crops,” he said. “Observations from trials indicated otherwise. A wide assortment of woody nursery crops thrived in six-litre containers filled with compost-amended media.”
With just one watering, the salts (chloride, potassium sulfates, calcium and sodium) leached out. In fact, the brief stress caused by the salts seemed to make the plants grow faster than in a bark mixture.
Limestone alternative
A byproduct from so called “clean coal” electricity generating plants can be used as an alternative to limestone. Coal is burned with calcitic limestone that absorbs some hazardous emissions. The byproduct is one third coal ash, one third gypsum and one third calcitic limestone.
The material is high in boron content, which is bad for most plants but an essential micronutrient in alfalfa.
The material is similar to Portland cement. It can be sprayed on alfalfa or poured in perpetually wet dairy yards to provide a dry pad.
Mel Webber, of Water Technology International Corp. in Burlington, Ont., said municipal sewage sludge, the muddy solids remaining after sewage has been treated, contains significant amounts of nitrogen, phosphorus and organic matter that are valuable to agriculture. But there are fears about disease-causing bacteria and viruses and heavy metals contaminating the soil. There are also concerns about smell.
However, Webber’s research has found that if applied in appropriate quantities, there appears to be no build up of harmful metals. And there has been no documented case of disease transmitted to humans from land treated with sewage. If the sludge is injected into the soil, smell is not a problem, he said . The procedure has been so successful around Guelph that when a project began in the Ottawa area, there was a rush of farmers eager to have their fields treated, he said.
