The Region of Niagara spent the last two years investigating an innovative idea to use recycled glass in bioretention stormwater systems. If successful, this would create a secondary market for recycled glass, and provide an alternative source of the sand component in engineered bio-soil. The project was first detailed in a 2018 blog post, “Development of an Alternative Glass Market: Bio-Soil from Recycled Glass“.
Bioretention uses natural features to manage stormwater
Bioretention is a stormwater infiltration practice that treats runoff from paved areas by using the natural properties of soil and vegetation to remove contaminants. Other names commonly used for these types of practices includes rain gardens, bioswales, dry swales, stormwater planters and biofilters.
The ultimate goal of stormwater management is to maintain the health of streams, lakes and aquatic life as well as provide opportunities for human uses of water by mitigating the effects of urban development. To achieve this goal, stormwater management strives to maintain the natural hydrologic cycle, prevent an increased risk of flooding, reduce undesirable stream erosion, and protect water quality.
Tipping fees impact net costs of recycled glass sand
An economic analysis was completed to determine the net cost of producing the recycled glass sand. Three main variables impacted the financial outcomes: tip fees applied for the glass feedstock received; residual waste disposal costs; and the sales price for the glass sand. The cost of processing was constant in all scenarios. The resulting revenue varied between a net loss of $40 per tonne, to a positive result of $10 per tonne. This wide variation of cost is impacted primarily on the tipping fees applied for the glass received. It also illustrates the need to be exceptionally diligent in controlling costs during the manufacturing process of the glass sand.
Current demand for bioremediation media, such as recycled glass sand, is estimated to be as high as nearly 8,000 tonnes per year. The potential for the use of recycled glass sand in place of concrete sand is significant, however, concrete sand is inexpensive in comparison. Another factor impacting the economics of this option is the incoming quality of the mixed broken glass. Typical Ontario Material Recovery Facility (MRF) glass contamination rates are up to 20 per cent. If MRFs can reduce the contamination rate and install better glass clean-up systems, this could bring the product yield up to 70 per cent and the residue rate down to 30 per cent, thereby improving the economic result.
Bioretention systems as an alternative glass market?
The final report, “Investigating the Use of Recycled Glass for Storm Water Management“, outlines that bioretention system installations in Ontario are growing, but implementation is not regulated and therefore use and construction are based on best practice guidance put forward by stakeholders associated with stormwater control. New markets for materials such as recycled glass sand need to be developed and this study has helped to demonstrate innovation in its infancy.
The use of recycled glass sand in both the production of bioretention media and in the water storage reservoir allows for the replacement of a natural product that does not need to be consumed.
Final Project Findings:
The cost of production of glass sand is currently more
Currently, the cost of concrete sand used in a bioretention facility is less than the cost of the production of recycled glass sand. This would be of concern to an owner or developer of a project since the least costly components are generally used. For recycled glass sand to gain a foothold in the market, the cost differential must be narrowed. Two of the most significant factors to examine are a reduction in the contamination prior to processing and the tipping fee at the processing plant.
Glass fines must be removed
Glass fines consist of glass that is smaller than 80 mesh. At the outset of the project, it was anticipated that the glass fines would be usable. As the project developed, however, this was not found to be the case due to the need for the sand to be consistent with the CSA Group standard W200-18, which specifies the need to use particle sizing in the glass sand that meets the requirements of concrete sand. This effectively excludes the glass fines, leaving it to be destined for the landfill unless another useful diversion opportunity is discovered. Niagara Region’s contracted operator, Niagara Recycling, is researching alternate uses for this material.
Contamination levels affect cost of production
The amount of contamination found within the feedstock glass needs to be reduced before the best economic picture for the production cost can be achieved. If contamination can be reduced to 5 or 10 per cent, then the economics improve as demonstrated in the analysis.
Green procurement policies encourage a circular economy
Recommendations moving forward for other municipalities interested in developing a market for the use of recycled glass sand include the development of green procurement policies and amendments to municipal purchasing by-laws to contribute to a sustainable environment and encourage a circular economy. Where feasible and without significantly affecting the intended use or quality of products or services, municipalities can endeavor to include specifications which contain the maximum level of post-consumer recyclable content.
The provincial government is moving forward with the creation of guidelines for better control of urban stormwater runoff. Municipalities can promote this by enacting changes in their standard specifications for works that occur under their control.