South Sewage Treatment Plant (SSTP)

At the City of Castlegar’s South Sewage Treatment Plant (SSTP), wastewater first passes through the headworks (consisting of screens to remove garbage and large solids), a vortex and classifier to remove grit, and a flow measuring device.

Wastewater then travels to the equalization (EQ) basin, which functions to provide more consistent flows throughout the day. From the EQ basin, wastewater is pumped into the biological reactor. This is a series of tanks where microorganisms break down waste.

In simple terms, incoming waste (a carbon source) becomes food for the bacterial organisms (sludge) in the biological reactor. The sludge is then periodically wasted to the digester and further processed and dewatered in Geotubes, before being trucked off-site to a biosolids handling facility. Meanwhile, the treated water goes through ultraviolet light (UV) disinfection before final discharge to the river.

Biosolids Management & the Geotube System (SSTP)

Currently, the plant is equipped with a Geotube system for sludge dewatering. Wastewater at the plant is treated by a population of microorganisms that consume the waste and nutrients in the water. A small percentage of the total sludge in the system must be extracted each day to maintain the desired population of microorganisms. This waste sludge is processed through Geotubes, large porous tubes that trap the solids while the water drains out and is returned to the start of the treatment process. Once the Geotube is at full capacity, the biosolids are excavated out and trucked off-site to a processing facility.

Previously, the SSTP used open-air sludge drying ponds to manage biosolids; however, long-standing operational and odour issues, along with further restraints on how much material could be stored in each pond, required the City to find an alternative management solution suitable for the site. The City installed Geotubes in 2024 to manage biosolids. When the Geotube bags are opened for removal and transport, odours can temporarily increase as the material is mixed and handled. Unfortunately, the Geotube system isn’t working as effectively as expected to manage biosolids or control odours. Staff are working with technical experts to improve performance and are exploring the viability of other biosolids dewatering solutions, which could help reduce odours.