Cobalt Constructed Wetland
Purpose of the Project
A Sewer Works Project was implemented in 1994 to provide sewage treatment for the Town of Cobalt.
A thorough environmental assessment of sewage treatment alternatives was undertaken. The alternative preferred by Town residents and as a result of the environmental assessment was a constructed wetland.
Accordingly, the Town sought and received provincial approval to design and operate a constructed wetland. Approval was granted and the constructed wetland was commissioned in December 2000. As a condition of approval the Town is undertaking a five year research program to demonstrate the effectiveness of this technology even under extreme northern Ontario climatic conditions.
The following pages provide some basic information on the Cobalt Constructed Wetland. If you wish more detailed technical information, please go to the last page for contact information
Following you will find information on:
Constructed Wetland Technology
- CCW Location and Access
- Cobalt Constructed Wetland (CCW) Design and Layout
- On-going CCW Research and Treatment Performance
- Ecological Co-Benefits of the CCW
Cobalt Constructed Wetland – Cell 3
Constructed Wetland Technology
Wetlands are described as nature's kidneys because they naturally function as filtering systems in the landscape. Principal processes in wetland systems include sedimentation, filtration, adsorption, chemical precipitation, decomposition and degradation of material by microorganisms. These ecosystems are being used as templates to design and construct wetlands that have enhanced treatment capabilities for managing municipal wastewater.
Ontario was a pioneer in the development of this technology beginning in the early 1980’s. Since then, the science of constructed wetland treatment technology has advanced considerably and is now used throughout the world. Constructed wetlands are particularly suited for small-scale applications such as treating sewage from small, rural communities, storm water treatment, runoff from large farming operations and some industrial waste waters including acid mine drainage. Constructed wetlands are an ideal technology for these types of applications due to their low cost of construction, operation and maintenance in relation to other wastewater treatment alternatives. In addition, constructed wetlands utilize natural processes, creating low energy requirements and offering important habitat features for vegetation and wildlife. In brief, constructed wetlands are an excellent example of sustainable development being put into practice.
Cobalt Constructed Wetland Location and Access
The constructed wetland is located adjacent to Sasaginaga Creek east of downtown Cobalt. The following map shows its location and the best means to access the site.
Parts of the wetland are fenced off for public safety reasons but the remainder of the site is accessible. Gravel paths have been constructed on the berms which enclose the wetland. These paths are ideal to walk along and to observe the wetland and the diversity of plants and animals that inhabit the site.
For various reasons, entry into the actual wetland area is prohibited. Sewage from the Town of Cobalt enters the west end of the wetland and flows easterly to the outlet. The treated effluent is released into Sasaginaga Creek.
The wetland consist of three basic treatment components:
- Grit channel/Grinder
- Maintenance Forebay (U-shaped as shown below)
- Three wetland cells (shown below)
Grit channel/Grinder
The raw sewage first passes through the grit channel and then a grinder. These are contained in the small building located at the inflow to the facility. The grit channel removes sand and other non-biodegradable and rapidly settling solids. The grinder pulverizes any solids in the sewage into small particles. Doing so greatly enhances the biodegradation process and prevents the buildup of large solids in the upper part of the wetland.
Maintenance Forebay
The sewage is then discharged to the maintenance forebay. This area is fenced off but can be observed from outside the fence. The maintenance forebay is designed to collect non-biodegradable solids (e.g., plastics) and rapidly settling solids. The maintenance forebay is cleaned out each spring. This is the only operation that the Town of Cobalt must regularly perform to keep the system operating smoothly.
Wetland Cells
The CCW is based on a free-water surface flow technology. Free-water surface flow constructed wetlands are comparable to natural open-water marshes. The wastewater flows at low velocity through the wetland vegetation. The water depth in the wetland cells is carefully controlled and increases slightly downstream. The average depth ranges from 15 to 25 cm in depth. This shallow depth ensures adequate oxygen exchange and a high rate of contact between the wastewater and the microfilms on the vegetation and the sediments. These microfilms are colonies of "waste-eating" bacteria and are the primary means by which a high level of water quality is achieved.
The wetland consists of three wastewater units called cells. The cells operate in series with Cell #1 flowing into Cell #2 and Cell #2 into Cell #3. Each cell is further divided into channels. The channels are formed by baffles that run across each cell. These baffles force the wastewater to follow a serpentine pattern. In doing so, short-circuiting is avoided and maximum contact between the wastewater and the microfilm colonies is assured. The wetland cells are connected by inlet and outlet pipes and are completely surrounded by vegetated berms. A single weir at the outlet of Cell #3 controls water levels throughout the wetland.
CCW Wetland Cells – water flows in a serpentine fashion from left to right
On-going CCW Research and Treatment Performance
The CCW was designed to operate year round in the cold northern climate. The CCW is the first constructed wetland facility to treat raw municipal sewage in Canada. For these reasons, conditional approval was granted for a five-year period. A key condition of approval was that a research program be put in place to monitor treatment performance.
Based on the first two years of research results, the CCW has generally exceeded the forecast treatment performance although some minor adjustments to the operation are being tested to see if treatment performance can be improved even more.
Water quality samples are taken on a regular basis through out the wetland. Water quality parameters being monitored include biological oxygen demand (BOD5), total suspended solids (TSS), total phosphorus, various nitrogen compounds, pathogens and heavy metals.
The following graphs depict the treatment performance of the wetland for two of the sample parameters - BOD5 and TSS. The first graph in each respective case shows the amount of BOD5 and TSS which is loaded in the water as it comes into the wetland (influent), while the second graph depicts the amount of BOD5 and TSS which exists in the water (effluent) after it travels through the three treatment cells of the CCW. Notice in both cases how the loading BOD5 and TSS is almost always less than that of their objective targets.
Monthly Loading of BOD5 in Influent
Monthly Loading of BOD5 in Effluent
Monthly Loading of TSS in Influent
Monthly Loading of TSS in Effluent
Ecological Co-Benefits of the CCW
An important co-benefit of constructed wetlands is the wildlife habitat that is created in the process. Wetlands support a diversity of plant and animals species.
As part of the five-year research program, plant and animals inhabiting the wetland are regularly surveyed. Species of wildlife that may be seen and/or heard in and around the CCW include: Common Name
| Scientific Name | | Mallard duck | Anas platyrhynchos | | American black duck | Anas rubripes | | Northern Shoveler | Anas clypeata | | Blue-winged Teal | Anas discors | | Green-winged Teal | Anas crecca | | American widgeon | Anas americana | | Hooded merganser | Lophodytes cucullatus | | Lesser Scaup | Aythya marila | | Canada goose | Branta canadensis | | Ring-billed gull | Larus delawarensis | | American Bittern | Botaurus lentiginosus | | Killdeer | Charadrius vociferus | | Greater yellowlegs | Tringa melanoleuca | | Lesser yellowlegs | Tringa flavipes | | Spotted sandpiper | Actitis macularia | | Solitary sandpiper | Tringa solitaria | | Great Blue heron | Ardea herodias | | Snipe | Gallinago gallinago | | American crow | Corvus americanus | | Sharp-shinned hawk | Accipiter striatus | | Cliff swallow | Hirundo pyrrhonota | | Red-winged blackbird | Agelaius phoeniceus | | American pipit | Anthus rubescens | | Sparrow sp. | Melospiza sp. | | Snow bunting | Plectrophenax nivalis | | Horned lark | Eremophila alpestris | Downy woodpecker
| Picoides pubescens
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