An Innovative Solar Thermal Drying Solution for Municipal Sludge in Canada

7 February 2019

6 rows of RACK20 solar collectors will be deployed in the spring of 2019 at the Thetford Mines region’s sludge treatment plant (Quebec, Canada) to dry sludge from septic tanks. they will total 446 m2 of catchment area and a power of 290 kW thermal. This project will be carried out in collaboration with several partners: in addition to the Intermunicipal Board, the management firm of the residual materials fertilizers Viridis environment will take care of several tasks at the level of the design, the management of the materials and the taking of data and the company Asisto Inc., specializing in water and environmental engineering, will also be sought for help with design and monitoring of tests. This showcase is also supported by the Créativité Québec program of the Quebec Ministry of Economy and Innovation.

In this septic sludge management project, Rackam’s solar thermal collectors will be paired with a drying bed approximately 12m by 3m in size to demonstrate drying applications for municipal sludge or applications for industrial sludge from such a solar system. Sludge from septic tanks (BFS) will therefore begin to be treated at the Thetford area (Quebec, Canada) in the summer of 2019 with this system.

This new solar thermal technology raises a lot of hope because sludge management is a problem in Quebec and around the world. Currently, the solution of many municipalities is to bring in private companies to periodically drain the aerated ponds where the sludge is stored and then transport and develop these sludges as fertilizer for the agricultural world or as filling material for degraded sites. But the cost of transportation and disposal, as well as the small number of companies offering this service, is an important constraint for the municipalities, hence the interest of drying these sludges on the spot to limit the expenses in their transport and increase their on-site processing capacity. Thermal drying solutions already exist, but often use fossil fuels.

Rackam has already tested the coupling of solar thermal collectors with a drying bed in the city of Surprise in Arizona with convincing and promising results: for drying to a dryness (percentage of dry matter) higher than our regions, the volume of sludge has been reduced from 3 to 4 times using a showcase with a power of 110kW. In our northern climates, since freeze-thaw drying beds perform very well in winter but are less efficient in summer (the season for which solar collectors are the most efficient), a solar collector system coupled with the drying bed is quite relevant. In Quebec in summer, this lower performance of standard drying beds leads to a lower dryness than the 20% minimum dryness required for recycling by agricultural application. The hybrid solution could therefore alleviate this problem. For municipal sludge, depending on the conditions, this new solution developed by Rackam and its partners could dry the sludge to more than 30% of dryness and decrease more than 8 times their volume, greatly reducing transportation costs for the municipalities.

And since the dried sludge residue after treatment will have a granular consistency, it is even possible to imagine a different outlet to the traditional spreading of this material in our fields, to develop a circular economy opportunity and partnership synergies in the field. revaluation. Indeed, for the partner Viridis environnement, recently acquired by the Quebec COOP Network, the improvement of the quality of biosolids to be recycled by solar thermal drying represents an important step forward in the marketing of quality products for fertilization of farmers’ land. The latter are more and more interested in this type of ecological and economical products. The coupling of the two technologies: freeze-thaw and solar thermal drying, will therefore offer increased performance for the same drying bed and will achieve dryness above 20% for better value and reduced transportation costs. This showcase will therefore promote this solution in our northern climates.