Award of Merit: Creemore Membrane Sewage Treatment

Category: Water Resources

MARSHALL MACKLIN MONAGHAN

After decades of being concerned about their septic systems, cesspools, leaching beds and holding tanks, the people of Creemore in southern Ontario requested a communal sewage treatment system that would protect both the groundwater aquifer and the pristine Mad River.

After the concept of using membrane technology to treat the sewage was introduced during an environmental assessment in 1997, prime consultant Marshall Macklin Monaghan, working with R.H. Carter Architects and Terraprobe, were asked to design a treatment plant. The plant had to have a “better than a tertiary level” of treatment and be economical. The community also wanted the structure to blend into the quiet countryside.

The result is the barn-shaped Creemore sewage treatment plant, located southeast of the community in the Mad River flood plain. The plant, with its small footprint, is the first full-scale municipal membrane bioreactor for sewage in Ontario.

The process consists of an influent pumping station with an automatic fine screening system, a two-basin ZenoGem membrane technology treatment process, UV disinfection, effluent reaeration chamber and outfall to the Mad River. Phosphorus is removed by adding alum ahead of the aeration tanks. The plant includes a single basin aerobic digester equipped with a ZeeWeed Membrane system for thickening. There are also provisions for sludge storage and hauling.

Sewage is collected and pumped upstairs in the plant to the screen room, which contains two pumps (one is a standby). Each pump can move 35 litres of sewage per second. In the screen room 3-mm fine mesh screens protect the treatment membranes. A rotating screw screen is located in the main concrete channel. The screen removes the large particles from the sewage then washes them to break up and return the organic component to the treatment system. There is also a bypass channel with a manually cleaned bar screen. Ventilation, with an air monitoring and alarm system, protects the operators.

At the heart of the process are the aeration basins and digester. The incoming screened sewage is split evenly by two v-notch weirs. The sewage is mixed with air for 6 to 10 hours in two aeration tanks, during which time microorganisms consume the organic matter.

Clear effluent is drawn from the tanks through vertical tube shaped membranes hung in cassettes at one end of the tank. Unlike most sewage treatment plants, the levels in the tanks are allowed to rise and fall up to 2.4 metres to equalize the incoming flow. To maintain the system’s efficiency, some micro-organisms are periodically removed from the aeration basins, stabilized in the digester tank and then stored in the blue glass-lined steel tank located behind the plant. The stabilized biosolids are removed during the summer and spread on approved agricultural sites.

Although the tanks are hidden by the barn structure, walls on one side and one end of the building are left open to provide natural ventilation. The feature avoids the very high cost of ventilating indoor tanks.

A 300-kW diesel generator set is sized to operate the essential components of the plant in case of a power outage. “Tectum” wall board and acoustically dampened ventilation ducts deaden the noise of equipment in the blower and diesel rooms.

The plant is designed to treat 860 cubic metres of sewage per day, serving the residents of Creemore, the area’s commercial core, and the Creemore Springs Brewery. With the simple replacement of pump impellers and addition of membrane cassettes, the plant’s capacity could increase to 1,400 cubic metres per day.

Completed in November 2000 and officially opened in August last year, the plant and sewage collection system cost $7.41 million.

Name of project: Creemore Membrane Sewage Treatment Plant

Other key players: R.H. Carter Architects, Terraprobe (soils investigation) , Zenon Environmental Systems (membrane equipment process designer)