Biosolids Management

Biosolids Management

GNPCC Digesters 1 and 3The two tanks on the left and in the center of the photo are digesters that produce biosolids at GNPCC

Biosolids are the solid end product of wastewater treatment in the RDN. They are a nutrient-dense organic material with a humous-like texture that is similar to compost. 

The Canadian Council of Ministers of the Environment (CCME) and the BC Ministry of Environment and Climate Change Strategy promote the use of biosolids to benefit from the high nutrient value. The Liquid Waste Management Plan also commits the RDN to beneficially using biosolids.

Award-Winning Programs

The RDN produces about 7,500 tonnes of biosolids each year. The RDN has a two-time, award-winning biosolids management program. Currently, RDN biosolids are  managed in two reuse programs:

1) Forest Fertilization Program

Through this program, biosolids can increase tree growth on nutrient-poor timberland while coordinating land use with forestry operations and recreational activities. This program manages biosolids from the Greater Nanaimo Pollution Control Centre (GNPCC) and serves as a contingency site for biosolids from the French Creek Pollution Control Centre (FCPCC).

Check out this Focus on Forest Fertilization sheet for more information.

2) Soil Fabrication Program

This program operates in partnership with Nanaimo Forest Products Ltd. to fabricate soil at the Harmac mill in Duke Point. This program also serves as a contingency site for GNPCC biosolids. 

Check out this Focus on Soil Fabrication sheet for more information.

More information on the Biosolids Management Program is provided below.

Frequently Asked Questions

Beneficial Reuse 

What are the benefits of reusing biosolids?

Beneficially using biosolids has many benefits:

  • It returns nutrients to the land. Biosolids contain nitrogen, phosphorus, potassium, and many macronutrients and micronutrients essential for healthy plant growth. Biosolids provide a sustained source of nourishment because they release nutrients over several years.
  • It increases a soil's water-holding capacity because solids have a high organic matter content. Through this it decreases run-off and soil erosion and helps plants thrive during periods of drought.
  • It offsets the use of synthetic fertilizers, which require a lot of energy to produce.
  • It helps meet carbon emission reduction targets by returning carbon back to the soil. It also helps trees grow bigger and faster which pulls even more carbon out of the atmosphere. 
How do other jurisdictions manage their biosolids?

A report of Biosolids Management Options Used in Other Jurisdictions was presented to the RDN Board on March 22, 2022.

Biosolids Production and Regulation

How are biosolids different from wastewater sludge?

Biosolids are different than sludge. Sludge is the term for solids that settle during the wastewater treatment process. Biosolids are produced by taking solids treatment a couple of steps further. 

  • Solids are stabilized at set temperatures for specific lengths of time in engineered tanks called "digesters".
  • Stabilized solids are then dewatered.

Stabilized solids can only be called "biosolids" once they meet quality standards outlined in the Provincial Organic Matter Recycling Regulation. 

What quality standards do biosolids need to meet?

Biosolids are treated to standards in the Organic Matter Recycling Regulation. 

Microorganisms: Treatment in RDN digesters kills more than 99 per cent of the microorganisms in biosolids; the rest die off naturally once they are exposed to sunlight and cooler temperatures in the soil. 

Trace elements: Trace elements can enter the wastewater collection system from residences, businesses, and stormwater runoff. Many of these trace elements are micronutrients and actually benefit plant growth, but they can be harmful in excess concentrations. Trace elements in biosolids are carefully monitored. Some trace elements are typically found at lower concentrations in biosolids than in the soils to which they are applied. 

What controls are in place to protect public health and the environment?

Public health and the environment are protected in the management of biosolids. The wastewater treatment process mimics the natural breakdown of wastes. When microorganisms "digest" the solid material, they reduce volatile organics and pathogen concentrations.

Biosolids land applications are carried out according to a Land Application Plan which must meet all requirements set out in the Organic Matter Recycling Regulation. The Land Application Plan is also provided to the Ministry of Environment and Climate Change Strategy and Island Health. 

The Land Application Plan contains details including soil quality, biosolids quality, biosolids management details, and site-specific management methods. Additional information is also gathered on nearby water features, well locations, and nearby residences.

To protect public health and the environment, we:

  • Regularly test our biosolids to ensure they meet regulatory criteria for land application
  • Restrict public access to application areas
  • Respect setback distances to water bodies, property boundaries, and public roads
  • Post signs on roads and paths advising the public that biosolids are being applied
  • Regularly monitor surface water at the site.

Forest Fertilization

Where is the Forest Fertilization Program located?

The RDN Forest Fertilization Program is located on private forest lands managed by Mosaic.

Historically, biosolids were applied to lands are approximately 12 km northwest of Nanaimo, about 1 km west of the Biggs/Doumont Road intersection, just off Weigles Road. The forest fertilization program has moved to a new site located about 8 km to the south of the Doumont site, near an area known as Blackjack Ridge, shown on this map of forest fertilization areas.

How does biosolids fertilization improve tree growth and health?

RDN biosolids are applied to nutrient-poor forest stands with rocky soils. Even though we live in a rainy climate, these forest stands are are often classified as "very dry" because of the naturally low soil organic matter and summer drought conditions. Biosolids help trees to achieve their maximum natural potential through promoting more ideal site conditions. The biosolids Forest Fertilization Project has demonstrated increases in tree growth. Trees fertilized with biosolids also appear healthier: needles and buds are longer, greener, and more numerous.

Comparison of tree growth rings before and after biosolids
Comparison of tree growth rings before and after biosolids application
Comparison of tree needles with and without biosolids application
Comparison of Douglas-fir tree branches from a stand applied with biosolids (top) and unapplied (bottom)
How are biosolids stored and applied?

Biosolids are trucked to storage sites located within the fertilization area. Biosolids storage facilities at the forest fertilization site are paved, walled on three sides, and covered during the rainy season. Once a sufficient quantity is stored, the biosolids are loaded into a specialized biosolids application vehicle. The vehicle has a large box which feeds the biosolids into a high-speed side throw fan.

The biosolids are carefully applied according to a Land Application Plan. Biosolids are applied to pre-selected application areas at a rate which supplies nutrients required by soil organisms, understory vegetation, and trees.

What do the fertilized sites look like?

Fertilized sites appear to be covered by a rich, dark topsoil material at an average depth of 1 cm.

Where are biosolids permitted to go?

The production, distribution, storage, sale and use, or land application of biosolids are strictly regulated by the Organic Matter Recycling Regulation. We regularly test our biosolids to ensure they meet regulatory criteria for land application. Biosolids land applications are restricted to:

  • Suitable forest stands
  • Suitable slopes
  • Suitable weather conditions (biosolids are not applied during heavy rain, over snow, or onto frozen ground)

Biosolids are not applied within specified setback distances from water bodies, property boundaries, and public roads. Public access is restricted in the application areas through locked gates and signage. Signage is posted at entry points and along select trails advising the public that biosolids are applied. We monitor surface water across the biosolids application site.

Will forest fertilization affect our drinking water?

Surface water

  • Biosolids are applied outside of a 30 m setback from waterbodies, meaning there is a very low risk of biosolids entering surface water.
  • The RDN forest fertilization program operates in a distinctly separate watershed from the City of Nanaimo drinking water supply area.


  • Once applied, biosolids only travel about 5-10 cm through the soil matrix, the typical length of a pencil. This means that it is very unlikely that biosolids will enter groundwater, aquifers, or well water, or travel far from where they are applied through wind or water movement.
  • Assessments carried out in 2003 and 2012 concluded that past and proposed future applications of biosolids within the Forest Fertilization Application Area will not impact groundwater quality in any of the wells located in the region.
Will access to the forest be restricted during or after biosolids applications?

The RDN's biosolids forest fertilization project is located on private land and access is restricted. Notification signs are posted at locations of biosolids fertilization.

Where else has this type of project been done?

Biosolids have been widely used in Canada, the United States, Europe, and across the world for over 70 years. In BC, the most common uses are as a feedstock in composting or soil fabrication, followed by beneficial use in agriculture, mine reclamation, and forestry. Metro Vancouver has completed forest fertilization projects throughout the province following early work in collaboration with the University of British Columbia demonstrating the potential for using biosolids as a forest fertilizer. Seattle, Washington has over 30 years of experience fertilizing forests with biosolids.

What reports are available?

Annual Summary of RDN Biosolids Management:

Information on the historic Doumont Forest Fertilization Program includes:

Surface Water

Surface water quality summaries conclude that it is unlikely that biosolids application at the forest fertilization site are having an adverse effect on surface water quality.


In 2003 and 2012, groundwater impact assessments were carried out. They concluded that past and proposed future application of biosolids within the Biosolids Application Area will not impact groundwater quality in any of the wells located in the region. This confirmed previous monitoring results from 1992 that showed biosolids had:

  • No measurable impact on ground water
  • No measurable impact on nearby surface waters
  • No detectable impact on the five nearest residential water wells.
Extensive research from the 1992 pilot project showed that trace elements introduced into the soil through biosolids applications generally do not move far below the soil surface - usually within 5-10 cm. Biosolids in the forest fertilization program are not applied over drinking water aquifers.