Controversial fertilizer: Toxic sludge turned into biosolids


Locally grown produce on sale at a farmer market.


The Canadian government promotes biosolid fertilizer as safe for humans, animals and the environment, but critics are adamant that sludge mixture being applied to Ontario farmlands is still toxic.


Sewage sludge to biosolid fertilizer

Sewage sludge is made up of everything that ends up in our sewers; human waste, runoff, landfill drainage, industrial, hospital and even radioactive waste factors into the mix.

Wastewater treatment plants remove toxins from sewage sludge and the remaining solids are then processed as fertilizers for agricultural production. The finished product is renamed biosolids.

The use of biosolids as fertilizer was developed as a solution to landfill dependency and the high costs of landfills. The mix is used for various land applications including fertilizer pellets, landfill and site remediation.

According to a 2010 review from the Canadian Council of Ministers of the Environment, Canada has few national guidelines for wastewater biosolids or best management practices for land applications.

Ontario Ministry of Agriculture and Rural Affairs (OMAFRA) regulates biosolids under the Canadian Environmental Protection Act. However, management of wastewater biosolids falls under provincial jurisdiction. As a result, provinces develop their own standards and parameters to ensure the quality of biosolids produced, used and disposed of.


Produce from Foodland Ontario.

10 provinces currently allow biosolids to be applied to agricultural lands and Ontario spreads nearly 120,000 dry tonnes of biosolids on 15,000 hectares of land each year, most of which is given away for free to farmers.

Toronto has four wastewater treatment plants, but only two plants are equipped to produce biosolids; 78 per cent of Toronto’s biosolids come from Ashbridges Bay treatment plant and 22 per cent from Highland Creek treatment plant.

According to Ashbridges Bay reports, Toronto produces approximately 195,000 tonnes of biosolids every year.

Production process of biosolids

After wastewater arrives at Toronto filtration sites, it undergoes various processing systems.

  1. Preliminary Treatment: Large debris is removed
  2. Primary Treatment: Wastewater is slowed and the solids are allowed to settle.
  3. Secondary Treatment or “activated sludge process”: Most of the liquid is removed and the effluent is sent to digester tanks. A portion of activated sludge – sludge that has been treated in a previous cycle – is added to the mixture. The activated sludge contains naturally occurring bacteria and other microorganisms that consume the dissolved organic material in the new sludge, which purifies the mixture.
  4. Aeration: The mixture passes four times through 11 step-feed aeration tanks. After settling, the mixture is removed as waste activated sludge.
  5. Thickening: Waste activated sludge is thickened using air and polymers.
  6. Anaerobic digestion: A process that reduces sludge volume and stabilizes the solids in the absence of oxygen. This process produces carbon dioxide, ammonia and methane, some of which is used as boiler fuel to heat the plant. The mixture is now called biosolids.
  7. Dewatering: Biosolids pass through centrifuges, resulting in a biosolid cake that is either sent to incinerators, landfills or undergoes further processing to create fertilizer pellets.

Highland Creek incinerates all of its biosolids while 50 per cent of the biosolids produced at Ashbridges Bay is designated for land application according to a 2010 report.

Organic farming and biosolid use

Certified organic farms are prohibited from using processed sewage sludge under the Canadian Organic Standards.

Melanie Golba, an organic farmer at Plan B Organics in Hamilton, confirmed that as an organic farm, Plan B only uses composted animal and vegetable waste.

“There are strict rules for using even manures from organically raised animals,” says Melanie. “You must follow these rules, compost temperature regimes, and set back dates between spreading and harvesting crops for human consumption.  The composting rules are very strict for organic farmers.”

Benefits of land application of biosolids

Biosolid supporters say that using biosolids reduces the environmental impact of commercial fertilizer production. They also highlight that organic matter in biosolids enhance the receiving soil. Biosolids often have high levels of nitrogen, phosphorous, copper, iron and zinc, and are seen to increase moisture retention, permeability and produce greater growth and yields.

Health effects of biosolids

Critics express significant concerns about using biosolids, citing possible risks to people living nearby, workers applying the mixture, people eating food produced from the land. Critics are concerned that the presence of low-level pathogens, heavy metals and organic pollutants found in biosolids may cause health problems. They raise concerns about the accumulation of toxins in the soil and runoff into waterways.

Many residents near properties to which biosolids have been applied complain about a range of maladies including respiratory problems, diarrhea, headaches, nausea, rashes, fatigue and pneumonia, according to a 2008 Toronto Star article.

A 2009 brief by the Canadian Institute for Environmental Law and Policy (CIELAP) reports that the quality of biosolids depends heavily on the initial quality of the wastewater; if hazardous materials are present in wastewater when it arrives at a treatment plant, the current processing methods do not ensure that such hazards will be removed. Wastewater often contains contaminants such as antibiotics, fire retardants, hormones and other endocrine disrupting substances from the manufacture and use of pharmaceuticals and personal care products.

Critics are very concerned that the levels of heavy metals are not being regulated closely enough. CIELAP reported “biosolids may be contaminated with heavy metals (also referred to as trace metals or trace elements) such as chromium, cadmium, lead and other contaminants that end up in sewage treatment plants after having been discharged into sewers as industrial waste.”

According to the Ashbridges Bay annual report, the concentrations of 11 metals are regulated in its digested sludge and the concentrations “are compared to metal concentrations regulated by The Nutrient Management Act” which the plant states is well within provincial limits.

The levels pathogens – disease-causing agents such as bacteria, viruses, prions, endotoxins and parasites – are also a concern. Guidelines do not require pathogen testing or regulation of pathogens. They also do not regulate organic contaminants such as dioxins, PCBs, pesticides, detergents, cleaning solvents, flame retardants (PBDEs), personal care products and pharmaceuticals.