A new residuals management process at a water treatment plant in Alberta is designed to improve the environment for fish and for recreational boaters on the Red Deer River.

The city of Red Deer operates a surface water treatment plant (40 mgd design, 12 mgd average) for 101,000 city residents and several neighboring communities. It draws water from the river and uses the Actiflo rapid-settling clarification system (Veolia Water Technologies). 

For years the clarifier blowdown, consisting mainly of solids removed from the raw water along with some aluminum sulfate and sand from the clarification process, was discharged to the river through a stormwater outfall. There was nothing unsafe about the residuals, but the discharge created a visible plume in the river.  

In spring 2022 Red Deer began operating a process that thickens and dewaters the residuals, which are then landfilled. The water going back into the river is now much cleaner than the raw water that was taken out. 

The new Residuals Management Facility that houses the process won a 2021 Envision Bronze Award from the Institute for Sustainable Infrastructure because it was designed and built with numerous energy-saving and sustainability-enhancing features.

“Regulators asked us to look at options to improve the quality of this waste stream,” says Kingsford Amoah, a city environmental planning engineer and the project manager. “It was not required, but it’s the right thing to do.

“With the high solids content, the discharge had an impact on fish habitat, and the plume made people not want to go boating on that side of the river. It was also a proactive step, because it is only a matter of time before treatment of residuals becomes a regulatory requirement.”

Old plant razed

The RMF was built on the site of the city’s first water treatment plant, which was replaced in 1983 by a new plant next door. The old plant and a sludge dewatering facility were demolished to make room for the RMF.

The new facility houses storage tanks for the thickened clarifier blowdown and supernatant, a polymer system (Veolia), a thickener system (Ecodyne), centrifuges (Andritz) and a bin-handling system (Schwing Bioset) for transporting the solids to the landfill. The dewatered residuals are not considered suitable for land application. The clarifier blowdown is stored in the water treatment plant before being moved to the RMF.

The design capacity of the RMF is 1.6 mgd; the average flow is about half that. Amoah expects the facility’s impact to be the most obvious in spring, when snowmelt makes the river water especially turbid. “Snowmelt brings in a lot of organics,” says Amoah. “The quality of the raw water is poor.” Big storms also increase the raw water turbidity and increase the volume of residuals from the clarification process.

The energy-saving features in RMF include a heat exchanger for the HVAC system that uses exhaust air to preheat air being drawn in for ventilation. Others include enhanced insulation in the roof, use of window light where possible and motion sensors for lighting control. Software for monitoring RMF operations connects with the SCADA system and helps monitor energy use. The building uses about 24% less electricity than similar facilities. 

Noise control

Another design factor in the Envision award was mitigation of noise and vibration, a high priority because the RMF is within a few hundred yards of various light industrial, commercial and multifamily residential developments. Studies of a similar facility indicated that noise from the RMF might exceed recommended levels for those neighbors.

To reduce noise, power levels in the HVAC system were adjusted and acoustic liners were used in the ductwork. In the centrifuge room, the concrete floor was separated from the outer walls to reduce noise and vibrations. Groundwater management was another factor in the award: monitoring wells were included because some contaminated soil was found on the site. 

The outfall for the treated clarifier blowdown is a pipe nearly 100 yards long that discharges the water at midstream. Since the water has been cleaned, it would be acceptable to discharge on the surface or on the riverbank as before, but Amoah says the new outfall allows better mixing and dispersion. The treated water can run continuously through the outfall, or can be stored in tanks for use as construction water or for irrigation of parks.

Good decision-making

The water treatment plant uses a multistage process that includes clarification, filtration, chlorine and UV disinfection, fluoridation, pH stabilization and chloramination. Other residuals from the plant, such as filter backwash, are discharged to the sewer system.  

Construction of the RMF began in 2019 and was completed earlier this year. In announcing the Envision Bronze award Melissa Peneycad, managing director of the Institute for Sustainable Infrastructure, praised Red Deer for using the Envision guidelines both for planning and construction and long-term operations and maintenance decisions. 

In particular, the designers followed the city’s policy of encouraging staff to consider the environmental impacts of infrastructure and to develop environmentally sound operating procedures. They also required bidders to observe sustainability principles.