Case study: Constructed wetland treats wastewater and adds green space in Loyalist Township, ON

The Amherstview Water Pollution Control Plan Constructed Wetland in Loyalist Township, ON, is the 2020 winner in the water category of FCM’s Sustainable Communities Awards.

The Corporation of Loyalist Township, ON, uses a series of in-line lagoons to provide tertiary treatment at the Amherstview Water Pollution Control Plant (WPCP). However, algae growth in these systems meant the final effluent had high pH levels that were not compliant with environmental standards. To address the issue in a sustainable way, the Township built a wetland to decrease the pH levels of the waste stream effluent through natural processes.

Passive, natural treatment chosen over mechanical options

At the Amherstview water treatment facility, wastewater is treated with a mechanical aeration process before passing through three lagoons that provide passive disinfection. In the summer months, excessive algal growth in the lagoons leads to elevated pH levels. While UV irradiation or chlorination/dechlorination processes could be used to address the situation, the Township had a previous study, conducted in collaboration with the Civil Engineering department at Queen’s University, that showed a natural wetland was a viable, sustainable and cost-effective alternative to attenuating pH.

Local plant used to mimic nature’s own processes

The constructed wetland was designed to fit within the footprint of the final disinfection lagoon. To replicate natural processes that had been shown to reduce the pH level of the effluent, the project team selected cattails, a locally available plant, as the primary vegetation for the wetland. The first year the wetland was completed, it consistently kept final effluent pH levels below the maximum limit of 9.5, and frequently met the water treatment facility’s objective of 9.0. In its second year, effluent met the objective more often and it is expected that, as the vegetation matures, the constructed wetland will become more effecting and this objective will be met more regularly.

Wetland benefits the environment, residents and the Township budget

In addition to attenuating pH levels, other benefits of the constructed wetland can be investigated in the future, such as the removal of E. coli and elimination of pharmaceuticals and personal care products from waste streams. Studies have shown that constructed wetlands can remove up to 90% of the endocrine-disrupting chemicals from pharmaceuticals and personal care products, and the configuration of the Amherstview wetland will allow for further research in this emerging field. The wetland allows more access to green space for residents, as well as waterfowl and shore birds. The Kingston Field Naturalists have monitored birds in the wetland, and several tours have been organized for schools and public groups.

The project has also realized economic benefits for the community, with the capital costs of the constructed wetland coming in at about half of the cost of a UV disinfection system. UV systems also have high energy consumption and require frequent maintenance, whereas the constructed wetland is expected to have very low operating costs over its useful life.

Design team learned the value of involving operations staff early on

The project team faced problems with the hydraulics of the system and the structural integrity of the wetland berms. This meant the flow of water through the constructed wetland could not be controlled and the system had to be taken out of commission until the problem could be addressed. Input from plant operators resulted in the development of a simple yet effective flow control structure that solved the hydraulic issues and accomplished the project goals. The situation illustrated the importance of involving operations staff early in the design phase of the project.