Through a joint research venture initiated in 1994 ANC and ARC evaluated composting as a technique for development of a range of higher value products for commercial applications. Composting equipment designed and built in Alberta was chosen to process the raw sludge and generate a substrate that could be modified to meet market demand for growth media and soil enhancement products. The main objectives of the project included:

  • operational compost production,
  • compost characterization and comparison,
  • plant growth trials, and
  • product registration under the Canadian Food Inspection Agency Fertilizer Act.


Compost was produced at the ANC mill site through a system design based on a pilot facility at Olds College.  Sludge passed through several conditioning bunkers and tunnels which allowed filtered heated air to pass through the material for over 56 days to create a stabilized, mature odour free product which could be bagged and stored.  A total of 4 compost runs were completed, and a complete characterization was completed for the feedstock sludge and final compost product for each run.

ANC Compo-Mix

The composted sludge was labelled “Compo-Mix” and advertised as a versatile organic product derived from composted newsprint mill process streams.  These streams consist of small pulp fibers (primarily sludge) and biological (secondary) sludge which is a byproduct of the activated sludge effluent treatment process.  Compo-Mix was designated a soil supplement which increased organic matter content, water holding capacity, drainage, and improved soil structure.

ANC Compo Mix Characterization

The compost product was evaluated by ARC laboratories and Nor-West Labs which allowed greenhouse growers to make a direct comparison of Compo-Mix to products commonly used.  

Plant Growth Trials

Plant growth trials were conducted with Compo-Mix and included an assessment of the germination and performance of garden cress, cucumber, faba bean, golden bean, lettuce, radish, geranium, fuchsia, and tomato by commercial greenhouse growers and ARC.

  • Germination rates in Compo-Mix ranged from 86% to 98% for the different species which was equivalent to or greater than the values for commercial potting mixes.
  • During the initial 4 to 6 weeks of the trial, growth in the Compo-Mix was similar to the commercial products however, subsequent growth in the compost treatments was significantly better.
  • The data indicated that the compost product had no obvious limiting properties and was suitable for a use as a plant growth medium.

Grower Feedback

  • Growers preferred to use soilless planting mixes and saw potential in the composted sludge product
  • Growers liked the “recycle” angle of sludge composing, saving trees, and reducing landfill use
  • Growers wanted a product that promoted porosity, aeration, and moisture retention which are factors critical to good root development
  • Growers unanimously indicated that they would welcome a better product of consistent quality that is readily available, competitively priced, and produced in Alberta


  • Promotes excellent root development
  • Porous
  • Dries evenly – important especially  during lower light conditions (fall, winter)
  • Drains well
  • Good particle size for transplants


  • Draining and drying out faster can result in higher costs associated with more watering and potentially loss of nutrients
  • Material is too coarse for bedding plants
  • Compost may potentially hold moisture too long and exclude air causing poor survival of root cuttings (ex. Fig root cuttings)

Product Marketing and Economics

  • Most growers prefer a blended product that is ready for use as compared to a product that they have to blend. Some growers have blending facilities (larger operations) whereas others do not.
  • Variable product distribution mechanisms were investigated and evaluated including, compressed bales, loose fill bags, refillable bags, compressed plastic bag (bale), large bulk bags, and truckloads of material.  Preferences were dependant on the size and capabilities of the growing operations
  • All growers recommended producing a limited size of product line.
  • All growers were interested in the potential to have jiffy pots, seedling trays, planter pots etc., produced from the compost and/or raw sludge to replace the predominantly plastic products currently being used.
  • For retail sale it was recommended a bag size that was easily manageable and potentially adding things like carrying handles and using bags less prone to punctures or ripping to minimize the loss of material often associated with bales of peat or potting mix.

Requirements for Proceeding with Composting Sludge

  • Determine the optimal start up period considering growing season and market demand.
  • Proceed with a detailed engineering study.
  • Conduct additional pilot runs using screw pressed material.
  • Engage a consulting firm that specializes in the composting field to review the project for possible omissions and risk assessment of trace contaminants in comparison to competitive products.
  • Develop a strong marketing plan to create a sales start up curve and designate an individual or group to aid in promoting the product to growers.
  • Supply product to nurseries for evaluation and enhancing of consumer acceptance.
  • Promote product by attending horticultural shows and on location booths/displays at greenhouse/nursery operations.  Plants grown in the product provide excellent justification for product use. Educating others regarding product availability, consistent quality, and weed free nature is important.
  • Explore additional potential markets (i.e., bark, peat, topsoil, and potting mix replacements or the general public, landscapers, nurseries, golf courses, and public agencies).