Biosolids Management

Biosolids Management

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

Municipal wastewater treatment produces treated effluent, biogas, and solids. Each product can be reused for a beneficial outcome and a smaller discharge to the environment, similar to how recycling and composting can divert solids waste from the landfill. The solids produced during wastewater treatment in the RDN are stabilized in engineered tanks called digesters. The stabilized solids become "biosolids" once they meet quality criteria outlined in the Provincial Organic Matter Recycling Regulation. 

The Canadian Council of Ministers of the Environment and the Ministry of Environment and Climate Change Strategy encourage local governments to reuse biosolids to benefit from the high nutrient value. With this consideration, the RDN Liquid Waste Management Plan commits to beneficially using biosolids. 

Award Winning Programs

The RDN produces about 7,000 tonnes of biosolids each year in their award-winning biosolids management program. Currently, RDN biosolids are managed in two programs:

1) Soil Fabrication Program

This program operates in partnership with Nanaimo Forest Products Ltd. at the Harmac Pacific (Harmac) kraft mill site in Nanaimo. There, Harmac mixes RDN biosolids, Harmac wood waste, and mineral soil to fabricate a beneficial soil product. 

2) Forest Fertilization Program

This program operates in partnership with TimberWest Forest Company (TimberWest) and Mosaic Forest Management Corporation (Mosaic) and the Nanaimo Mountain Bike Club. Through this partnership, biosolids can increase tree growth on nutrient-poor timberland. Additionally, biosolids application activities are successfully coordinated with forestry operations and recreational activities.

The RDN Forest Fertilization Program is on private forest lands approximately 12 km northwest of Nanaimo, about 1 km west of the Biggs/Doumont Road intersection, just off Weigles Road. The land is an operational forest Managed by Mosaic.

The agreements between the parties formalize the RDN's biosolids forest fertilization program and the Nanaimo Mountain Bike Club's recreational activities on private forest land, thereby also improving communication and safety, and maximizing the benefits for all three parties.

More information on the Biosolids Forest Fertilization Program is provided below.

Frequently Asked Questions


What are the benefits of beneficially using biosolids?

Beneficially using biosolids has many benefits:

  • It is consistent with the RDN Liquid Waste Management Plan.
  • It keeps biosolids from being disposed of at the Regional Landfill and helps the RDN meet its waste diversion targets set out in the RDN Solid Waste Management Plan.
  • It returns nutrients to the land. Biosolids contain nitrogen, phosphorus, potassium, and many macronutrients and micronutrients essential for healthy plant growth.
  • 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.
  • It provides a sustained source of nourishment because biosolids release nutrients over several years.

Forest Fertilization Basics

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 classed 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 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.

Health and the Environment

Are there any public health risks from biosolids?

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.

Will forest fertilization affect my well water?

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.

Ongoing surface water monitoring reveals that water quality at the biosolids fertilization site remains within a range which is typical of background water quality. Research performed by Vancouver Island University has shown that trace elements introduced into the soil as a result of biosolids fertilization generally do not move far below the soil surface, usually within 5 to 10 cm, similar to results from many other studies. To assure the safety of water supplies, biosolids applications occur only on suitable slopes and at least 30 m from any watercourse.

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 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.

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.

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.