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1. Interception: wastewater collects in an interceptor.
2. Screening: coarse and fine screens remove large debris and grit from wastewater.
3. Desilting: silt is removed from the water.
4. Settling and degreasing: sludge, water and grease (scum) are separated in a decanter.
5. Aeration: air and bacteria from recirculated sludge are injected into the aeration tank to decontaminate the water.
6. Secondary decantation: the water is decanted again. Once treated, it is discharged into the river (nos 7 and 8). The sludge is removed from the water and treated in preparation for use in farming (nos 6A to 6D).
   1. Sludge thickening: sludge is thickened through gravity.
   2. Sludge digestion: anaerobic digestion of the sludge produces methane. This gas is captured to heat the buildings and dry the sludge.
   3. Drying and granulation: some of the dehydrated sludge is dried into pellets.
   4. Agricultural use: biosolids (dehydrated sludge and pellets) are used for farming.
7. Service water: some of the water is treated with chlorine and used to cool and clean the equipment.
8. Natural environment: the water is disinfected with UV rays before being discharged into the river.

For additional information about water management in Gatineau, go to Gestion de l'eau (French only).

Use of sludge

Solids extracted from the wastewater (sludge) generates biogas (methane), which is used to help heat the wastewater treatment buildings and supply the sludge drying plant (located on the same site as the wastewater treatment plant).

As indicated above, solids are transferred to the drying plant to be transformed into pellets. Those pellets are then distributed to farms where they are used as fertilizer. Since January 1, 2017, no municipal sludge has gone to a landfill site, even though this is permitted.

For additional information about the use of municipal sludge, you can consult the frequently asked questions page of Quebec's ministère de l'Environnement et de la Lutte contre les changements climatiques (French only).