Dear editor,
Biosolids are our waste, our poo, and also all that is disposed of in the sewer.
Biosolids a.k.a sewage sludge is now commonly recycled into compost. In the last 20 years, municipalities in Canada and the U S. have switched from paying to dispose of the waste to recycling it, mixing it with sawdust and wood chips and composting and selling it to gardeners and farmers.
Biosolids are organic matter — by definition. They are used as a soil amendment. Increased organic matter improves the soil to hold more water (very good in the summer) and to increase biodiversity, fertility, and plant growth.
As a fertilizer they provide essential micronutrients (zinc, copper and iron) and much macronutrients (nitrogen, phosphorus and potassium) that increase vegetation growth and productivity.
They provide a slow release source of nutrients that can be available to the plants for years. The slow release prevents leaching of excess nutrients and minimize the contamination of ground and surface water. Biosolids suppress plant diseases and pests.
They facilitate reforestation, wetlands restoration, and habitat revitalization] by amending marginal and contaminated soils. They remediate soils contaminated by hazardous waste.
Much agricultural soil has lost half or more of its organic matter content in the age of chemical agriculture. So biosolids remediate the degraded soil and promote biodiversity and as a bonus, sequester carbon in the soil.
The Environmental Protection Agency in the U.S. estimate cost savings of more than 50 per cent over conventional remediation technologies.
There is, however, a muddle with our use of the sewer system.
If biosolids were only composted poo, there would be no problem. After all, the Chinese and most other cultures have been using humanure for thousands of years. The problem is that as well as collecting poo, the sewers drain industrial and commercial wastes and hospitals and everything else. It all goes in the mix.
And with that come all kind of synthetic molecules. Fire retardants, plasticizers, pharmaceuticals of all sorts — steroids, hormone and chemotherapy drugs, antibiotics, household products, and more.
Some of these are persistent organic pollutants which do not decompose in the wastewater treatment plant, concentrating instead in the biosolids.
Admittedly, they are normally at low concentrations but in the absence of comprehensive and independent testing of the biosolids to ensure safety and efficacy, the National Academy of Sciences in the U.S. has issued a recent warning, and the EPA no longer promotes the use of biosolids in agriculture.
There are also low levels of heavy metals in biosolids. They are well regulated, tested for each batch, and the allowable levels are quite low (in parts per million, like most pesticides).
But heavy metals are immobilized and accumulate in the soil and in the plants, raising questions about the long term effect on soil fertility and human health.
So here we are, with this conundrum. Biosolids are a wonderful way of recycling our waste but they are generally contaminated with low levels of nasty stuff.
And like the pesticides, it becomes a matter of choice. You use them because they are cheap and efficient or you avoid them like the pest.
Dr. Thierry Vrain
Courtenay
