Cobalt Constructed Wetland
The Constructed Wetlands project was undertaken in 1994 after a thorough environmental assessment of alternatives to treat wastewater for the Town of Cobalt.
Accordingly, the Town sought and received provincial approval to design and operate a constructed wetland, which was commissioned in December 2000. As a condition of approval the Town conducted research to evaluate the effectiveness of this technology even under extreme northern Ontario climatic conditions.
The technology has proven to be very effective and efficient, comparable and even surpassing standards of conventional wastewater treatment plants.
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.
Wastewater from the Town of Cobalt enters the west end of the wetland and flows easterly to the outlet. The treated effluent is deemed as clear as what would be produced through a conventional waste water treatment facility.
Based on research to date, the Cobalt Constructed Wetlands 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.
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 include:
American black duck
Technical aspects of the Cobalt Constructed Wetlands
The wetland consist of three basic treatment components:
• Grit channel/Grinder
• Maintenance Forebay (U-shaped as shown below)
• Three wetland cells (shown below)
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.
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.
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 throughout 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