The small town of Field, British Columbia, once a stop for trains on their way over the continental divide, now welcomes tourists in the thousands as part of Canada’s Yoho National Park. And with those tourists comes an increase in waste.
When the town of 300 needed to build a new facility to handle the waste, Parks Canada reviewed the latest in advanced treatment technology and opted for a membrane bioreactor system. The newly installed MBR plant quickly became a prized facility for the town. The plant’s operators recognized that to keep their new state-of-the-art equipment running smoothly, they’d need to protect the MBR with fine screens.
Field’s effluent can be best characterized as variable. In the summer months, tourists use Field as a pit stop, putting a large demand on the wastewater treatment plant, while during the subzero, mid-winter period, usage falls dramatically due to the small numbers of permanent residents in Field. With low temperatures and short sewer lines there is little natural breakdown in organic solids before entry to the treatment plant. Also, the low flow and long residence times in lift station sumps means the solids settle, creating a significant variation in solids concentration from the standard 300 ppm.
To handle the highly variable influent, the facility looked to JWC Environmental to provide protection as advanced as their MBR equipment. They settled on an IPEC rotary screen and an IPEC screenings washer/compactor.
The rotary screen was fitted with 800-micron (opening size) stainless steel mesh for the primary separation. The high porosity allows for a high hydraulic process rate in a compact physical size. A special in-feed header on the screen comfortably handles both the high flow and the low flow/high solids concentration conditions efficiently, while maintaining the required separation. The rotary screen also processes the highly concentrated compactor pressate that is reintroduced by a separate pump system. The screen is self-cleaning, which allows hands-free operation.
The solids from the rotary screen, which include all the typical nonbiodegradable matter mixed with a much higher than normal biodegradable faction (fecal, tissue), are accepted by the PLT press. The screened organic components are effectively broken up and returned to the plant for further biological processing, while the remaining inorganic solids are discharged, in compacted form, to a bagging device. The bagging device includes an 80-meter-long plastic tube that allows for practical isolation of the rejected solids.
The IPEC screen and press combination is designed to continuously protect the membranes. In yearly inspections of the bioreactor in Field, no contaminants have been detected.
Location: Field, British Columbia, Canada
WWTP Capacity: 105,000 gpd
Screen System Capacity: 400 gpm
Feed System: Dual pump lift station
Engineer: Associated Engineers Calgary, AB
Contractor: Nason Contracting Group Edmonton, AB
Commission Date: April 2004