Biosolids Management

Biosolids are the materials resulting from the treatment of sewage sludge at a wastewater treatment facility. They contain essential plant nutrients and organic matter and are a beneficial resource that is used for fertilizer and soil amendment.

The Ashbridges Bay Treatment Plant processes about 40,000 dry tonnes of biosolids each year, which includes biosolids transferred from the Humber Treatment Plant and the North Toronto Treatment Plant. The Highland Creek Treatment Plant incinerates about 10,000 dry tonnes of biosolids each year.

The City manages biosolids through the following methods:

  • environmental
    • land application for agricultural and other uses
    • pelletization to create fertilizer
    • chemical stabilization to create fertilizer product and landfill cover or to reduce acidity in soil
  • incineration
  • landfill

We remove nutrients from the soil when we harvest and consume food. Land application of biosolids returns these nutrients to the soil.

Biosolids, like animal manure, contain several nutrients and organic matter that are beneficial for crop growth. They enhance soil and improve its ability to retain water. They also reduce the need and production costs for commercial fertilizers. Numerous studies have shown that biosolids land application is safe and has significant benefits.

Biosolids can be used on:

  • agricultural land
  • forest land and at tree nurseries
  • strip mines to help reclaim and vegetate the land

In 2025, 39 per cent of the City’s biosolids were used in land application.

The Ashbridges Bay Treatment Plant has a facility that produces pellets from biosolids, which can be used as fertilizer.

  • Biosolids are heated to evaporate water content, producing a material that is 90 per cent solids or greater.
  • The high temperatures destroy pathogens (harmful microorganisms), making the pellets a registered fertilizer product.
  • The finished pellets are dust-free, low-odour and two to four millimetres in size that can be stored for long periods of time.
  • The reduction in mass and volume cuts down on transportation and storage costs.

In 2025, 37 per cent of the City’s biosolids were made into pellets.

During chemical stabilization, biosolids are mixed with chemical agents to reduce acidity, destroy pathogens and minimize odour.

The most common form of chemical stabilization is alkaline stabilization. The process consists of:

  • mixing biosolids with lime and controlling pathogen levels by increasing the temperature and lowering the acidity
  • converting biosolids into an alkaline soil conditioner for use as a fertilizer product, landfill cover or to reduce acidity in soil

In 2025, 23 per cent of the City’s biosolids were treated using chemical stabilization.

Highland Creek Treatment Plant is the only City wastewater treatment plant that incinerates all its biosolids.

The emissions are tested annually and are well below the regulatory limits.

Biosolids can be disposed of in landfills.

In 2025, one per cent of the City’s biosolids were brought to landfills as a temporary measure during critical repairs to the pelletizer equipment.
Date modified: June 19, 2026