|Free Water Surface Constructed Wetlands|
Constructed wetlands are essentially a horizontal flow, submerged trickling filters built to treat and remove contaminants from water utilizing the same principals and multiple mechanisms as natural wetlands. They are a series of shallow ponds that have a vast surface area comprised of plant material, living and dead, which are heavily colonized by microbial, invertebrate, and vertebrate populations. They purify the water that flows through them including persistent organic pollutants such as DDT, pharmaceuticals, personal care products and endocrine disrupting compounds (hormones).
Constructed wetlands differ from natural wetlands in that they do not have short circuits through them and being intensively planted at construction they develop the desired diversity of plants and associated organisms rapidly. They are very inhospitable places for human enteric bacteria. Their life span can exceed a century. So long as they are undisturbed they are a sink for heavy metals and carbon. (Temperate latitude constructed wetlands have been demonstrated to sequester more carbon dioxide that tropical rain forests due to the latter extreme nutrient deficiency.)
Compared to conventional treatment methods, they tend to be simple, inexpensive, and environmentally friendly. They utilize a far smaller ecological footprint than other advanced wastewater treatment mechanisms. Capital costs approximate those of municipal recreational parklands, and operational and maintenance costs that can be ten per cent of that of an advanced physio-chemical treatment plant. Unlike conventional engineered treatment plants, the ancillary benefits such as parkland, education, wildlife habitat, groundwater recharge, temperature amelioration, storm water attenuation, and a number of other benefits can exceed the wastewater treatment values.
Free Water Constructed Wetland at Lighthouse Pub, Port Renfrew, BC.
Constructed wetlands have multiple pathways for contaminant removal. An incomplete list:
An example of a free water constructed wetland in Prince George, BC
Another example of a free Water Constructed Wetland at Arcata Marsh and Wildlife Sanctuary, Arcata, California
Constructed wetlands may be used to treat water from many different sources:
Free Water Constructed Wetland at Lighthouse Pub, Port Renfrew, BC
Municipal/commercial/residential/industrial wastewater can be effectively treated with free water surface constructed wetlands, which are suitable for a wide variety of fairly dilute wastewater flows. They are the least expensive to build, however, they occupy the most land area.
Landfill Leachate is a result of precipitation flowing through solid wastes, leaching harmful substances, possibly for many decades even after closure. Landfill leachate is a complex and ever-changing wastewater stream that can be comprised of some of the most ecologically troublesome substances known such as heavy metals, high ammonia levels, and virtually any other of society’s discarded chemicals. Free Water Surface Constructed Wetlands are largely passive processes that are powered by sunlight. The inherently sustainable processes employ biomimicry to remove virtually all inimical substances producing water that is biochemically indistinguishable from a natural wetland. Potential for long-term sustainability and significant cost savings are attractive features of this eco-technology.
The following pictures are of the Free Water Constructed Wetland at Knockholt Landfill, Region of Bulckley/Nechako, located near Houston, BC. The senior designer for the project was Curt Kerns, president of WetlandsPacific.
Construction August 2007
Planting September 2007
Note: The local moose have been enjoying the wetland, the city is attempting to dissuade their interest.