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 encourage local governments to beneficially reuse 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 7,000 tonnes of biosolids each year. The RDN has a two-time, award-winning biosolids management program. Currently, RDN biosolids are beneficially managed in two 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 the majority of Greater Nanaimo Pollution Control Centre (GNPCC) biosolids.

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 manages the majority of FCPCC biosolids and serves as a contingency site for GNPCC biosolids. 

More information on the Biosolids Management Program is provided below.

Frequently Asked Questions

Beneficial Reuse and Waste Diversion

How do biosolids reduce the discharge of waste to the environment or landfill?

When biosolids are reused, it means that less material is going into the oceans as effluent and into our landfill as garbage. Diverting biosolids from the Regional Landfill is in line with the waste diversion targets set out in the RDN Solid Waste Management Plan and the goals set in the RDN Liquid Waste Management Plan.

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?

The Province of BC has created an infographic to compare different uses of biosolids including non-beneficial alternatives such as landfilling. Common uses include:

  • Forest fertilization
  • Soil fabrication
  • Compost production
  • Agriculture
  • Land reclamation.

The Capital Regional District also published a Beneficial Reuse of Biosolids Jurisdictional Review on their website. 

What are some beneficial reuse alternatives?

The Province of BC has published a comparison of biosolids management options. In this review, they compared land application, incineration (with waste to energy), pyrolysis, gasification, and landfill options. Land application resulted in the strongest net benefit. 

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 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 that align with the US Environmental Protection Agency's standards for biosolids, which were developed with the aim of protecting human and environmental health. Biosolids treatment through aerobic or anaerobic digestion kills most of the microorganisms in biosolids; the rest die off naturally once they are exposed to sunlight and cooler temperatures in the soil. However, since biosolids are not pasteurized, there is a small risk associated with getting biosolids in one's eyes or mouth, just as there would be for other animal manures.

Trace elements in biosolids are carefully monitored to ensure the biosolids remain compliant with the Organic Matter Recycling Regulation. Trace elements enter the wastewater collection system from residences, businesses, and storm water runoff. Many of these trace elements are micronutrients and actually benefit plant growth, but they can be harmful in excess concentrations. Some trace elements are typically found at lower concentrations in biosolids than in the soils they are applied to. In BC as in many other jurisdictions, trace elements are monitored in biosolids; however, unlike many other jurisdictions, in BC they are also monitored in the soil.

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 micro-organisms "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 have been applied to lands are approximately 12 km northwest of Nanaimo, about 1 km west of the Biggs/Doumont Road intersection, just off Weigles Road. Over time, this site will be used less frequently.

The forest fertilization program is transitioning to a new site located about 8 km to the south of the Doumont site, near an area known as Blackjack Ridge.

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 of 80% over 18 years. 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. The RDN has an agreement with the Nanaimo Mountain Bike Club to coordinate land use. As a result, Club members and other mountain bikers are granted access to specified biking areas at the property. Outside those areas which are dedicated to mountain biking, 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.

Research and Studies

Are annual biosolids management reports available?

Yes, the RDN shares its annual Biosolids Management Summary.

What reports on surface water quality and biosolids application is available?

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.

What research on groundwater and biosolids application is available?

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 groundwater
  • No measurable impact on nearby surface waters
  • No detectable impact on the five nearest residential water wells

Extensive research from the 1992 biosolids 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 this project are not applied over drinking water aquifers.

What are the past VIU research projects about biosolids application?

The private forest lands used in the Forest Fertilization Program were formerly leased to Vancouver Island University, a past participating partner in the Biosolids Forest Fertilization Program. As such they conducted a number of research project on biosolids.

1992 - 1994 GVRD / VIU Operational Research Project - This joint research project focused on the movement of biosolids in ground and surface waters. Local residential wells were also monitored.
1992 - 2017 VIU Growth and Yield Research Project - 14 growth and yield plots were monitored regularly. Results show the long term effects that biosolids applications have on growth and yield of coniferous trees.
1998 - 2017 VIU /Ministry of Forests Biosolids Research and Demonstration Project - This research site was established in a recently-harvested area. The effect of biosolids applications on growth rates and wood quality of coniferous trees was tracked. Vegetation measurements, which are taken every three years, show that biosolids applications have greatly increased tree growth rates.
2012 - 2017 VIU / RDN Carbon Sequestration Research Project - This project focused on recently-established forest plantations, with the goals of determining:

  • How biosolids applications in both high and low nutrient sites affect the survival, growth and productivity of Douglas-fir and competing vegetation.
  • How biosolids applications affect the forest's development and its nutritional status over time.
  • How these changes affect the carbon balance of the plantations, i.e. the amount of carbon that will be stored in soil and vegetation over time.