Wetlands are areas of land that are saturated with water for part or all of the year. They have unique types of plants and soil, and support an amazing variety of wildlife. Constructed wetlands (CWs) are engineered wetlands that “mimic the simultaneous physical, chemical, and biological processes occurring in natural wetlands for wastewater treatment purposes.”[1] By leveraging these processes that occur in natural wetlands, CWs can be used to treat municipal wastewater.
Recommended Practices
Professional guidance. Constructed wetlands, for the purpose of wastewater treatment, require professional guidance in their design and implementation. They may be vertical flow constructed wetlands (VFCW), surface flow constructed wetlands (SFCW), horizontal sub-surface flow constructed wetlands (HSSFCW), hybrid constructed wetlands and may involve other technologies, such as biochar, microbial fuel cells (MFC) or Phospholock to remove phosphorus. The quality of the effluent (water leaving the treatment wetland) from these CWs is impacted by plant types, filter media, arrangement of the treatment systems and bed configuration.[2]
Design for inputs. The type of constructed wetland, any additional technologies it includes, hydraulic retention time and even the specific plants contained in the system must be designed to address incoming pollutants to be removed. These can include nutrients (nitrogen, phosphorus), suspended solids, pathogens (bacteria, protozoa, helminths and viruses), household chemicals, pharmaceuticals and personal care products (PCPP), heavy metals and pesticides – all of which can be significantly treated/removed by CWs.
Design for climate. Seek expert advice on the implementation of this example of NBS for the local climatic conditions. Sub-surface flow systems, because they are insulated from cold air during winter, are likely to be more suitable to Canadian conditions.[3]
Monitoring. Water quality monitoring of outputs versus inputs is important to measure the efficacy of wastewater treatment and to ensure adaptive management can improve gaps in treatment if identified. For example, one study in Manitoba found that CWs were effective in treating wastewater with one gap: antibiotic resistant genes (ARGs). “Additional studies would be beneficial to determine whether upgrades to extend retention time or alter plant community structure within the wetland would optimize removal of micropollutants and ARGs to fully characterize the utility of these systems on the Canadian Prairies.”[4]
Project Considerations
Constructed wetlands for wastewater treatment can be complex to design and take several years to establish a fully developed root zone, so communities that implement this example of NBS should plan for additional wastewater treatment as the CW matures.[5] Since CWs are built ecosystems that are intended to perform specific functions, “purposeful manipulation is a key engineering factor that has to be incorporated into design and operation”[6] in order for the systems to succeed.
Design considerations for CWs for this purpose include[7]:
- Climatic conditions
- Topography
- Geological structure
- Availability of land needed
- Current and projected wastewater volume and flow
- Effluent quality laws
- Effluent reuse options (if applicable)
- Effluent receiving waterbody
- Total costs
Because of the prevalence of conventional wastewater treatment facilities, “in terms of public acceptance and a general shift towards community based wastewater treatment practices, a perceived risk (associated with CWs) is as damning as any actual risk of deleterious substance breakthrough.”[8] As such, extensive public education campaigns on the design, efficacy and planned monitoring may be beneficial in communities looking to begin treating wastewater with wetlands.
The Business Side
CWs for wastewater treatment can provide long-term sustainability as they provide “ecosystem services that are highly valued but low cost, are fueled directly by solar radiation, are self-adaptive and low maintenance, and are sources for value added residuals.”[9] They are energy-efficient and can be a “cost-effective option when compared to a traditional treatment process.”[10] In the implementation of this NBS, municipalities will need to budget for up-front expenses associated with design and construction of the CW, supplementary treatment as the CW matures into its optimal function, monitoring and maintenance.
The Nature Side
Wastewater wetlands provide a wide variety of ecological benefits, the primary one being water filtration and removal of nutrients, pathogens and other contaminants from sewage. Municipal wastewater contains many contaminants that are harmful to aquatic life. By implementing effective constructed wastewater wetlands, communities can reduce the risk to aquatic life and downstream water quality for other users. The plants in wastewater wetlands can also provide carbon sequestration. Depending on whether contaminants are removed by adsorption or through microbial or photo-degradation, plants may need to be disposed of safely if they contain adsorbed contaminants such as heavy metals. CWs also provide biodiversity and habitat, and flood attenuation values.
The Community Side
Healthy wetlands can add aesthetic value to neighbourhoods as well as recreational opportunities such as birdwatching and other wildlife viewing. They help to moderate temperature in cities, mitigating the urban heat island effect. Wetlands also provide educational opportunities for children and adults alike. Wetlands used for wastewater treatment can be leveraged for education on the value of wetlands and the remarkable ecosystem services they provide. Adding natural spaces such as wetlands has a positive impact on human health and a positive effect on real estate value and marketability.
[1], [2], [10] Ghimire, U., Nandimandalam, H., Martinez-Guerra, E., & Gnaneswar Gude, V. 2019. Wetlands for wastewater treatment. Water Environment Research 91(10).
[3] Werker, A. G., Dougherty, J.M., McHenry, J. L., & Van Loon, W.A. 2001. Treatment variability for wetland wastewater treatment design in cold climates. Ecological Engineering 19(1-11).
[4] Anderson1, J. C., Carlson, J. C., Low, J. E., Challis, J. K., Wong, C. S., Knapp, C. W., & Hanson, M. L. 2013. Performance of a constructed wetland in Grand Marais, Manitoba, Canada: Removal of nutrients, pharmaceuticals, and antibiotic resistance genes from municipal wastewater. Chemistry Central Journal 7:54.
[5], [6], [8], [9] Werker, A. G., Dougherty, J.M., McHenry, J. L., & Van Loon, W.A. 2001. Treatment variability for wetland wastewater treatment design in cold climates. Ecological Engineering 19(1-11).
[7] Stephanakis, A. I. 2016. Constructed Wetlands: Description and Benefits of an Eco-Tech Water Treatment System. Impact of Water Pollution on Human Health and Environmental Sustainability (pp.281-303). IGI Global.
Anderson1, J. C., Carlson, J. C., Low, J. E., Challis, J. K., Wong, C. S., Knapp, C. W., & Hanson, M. L. 2013. Performance of a constructed wetland in Grand Marais, Manitoba, Canada: Removal of nutrients, pharmaceuticals, and antibiotic resistance genes from municipal wastewater. Chemistry Central Journal 7:54.
Ghimire, U., Nandimandalam, H., Martinez-Guerra, E., & Gnaneswar Gude, V. 2019. Wetlands for wastewater treatment. Water Environment Research 91(10).
Stephanakis, A. I. 2016. Constructed Wetlands: Description and Benefits of an Eco-Tech Water Treatment System. Impact of Water Pollution on Human Health and Environmental Sustainability (pp.281-303). IGI Global.
Werker, A. G., Dougherty, J.M., McHenry, J. L., & Van Loon, W.A. 2001. Treatment variability for wetland wastewater treatment design in cold climates. Ecological Engineering 19(1-11).