(Perma)Culture and Sanity
Wastewater Treatment and Constructed Wetlands Part One
Water Pouring Into Cistern From Garage Rooftop in Gentle Rain.
Pros and Cons of Constructed Wetlands For Wastewater Treatment
Benefits Of Constructed Wetlands
- Constructed wetlands are relatively inexpensive to construct and operate, and easy to maintain.
- Constructed wetlands provide effective, reliable and ecologically sound wastewater treatment.
- Constructed wetlands can tolerate both great and small volumes of water and varying contaminant levels.
- Wetlands-treated water is clean and can be reused for productive purposes—in fact the constructed wetland treatment process itself can incorporate productive uses.
- Constructed wetlands can be aesthetically pleasing and provide habitat for wildlife and human enjoyment. Some cities, such as Beaumont, Texas, have even created constructed wetlands for treating municipal sewage that double as city parks.
You can't get anything clean without getting something else dirty.
Disadvantages Of Constructed Wetlands
- Depending on design, constructed wetlands may require a larger land area than a conventional facility. However, as mentioned before, the extra land can be used productively for purposes besides simply treating wastewater—unlike conventional sewage treatment plants.
- Constructed wetlands can, if improperly designed and implemented, expose the odor of the waste stream (too thin a soil layer over the canals, running the canals down too steep a slope, etc.). Properly designed and built, however, constructed wetlands are odor-free.
- A constructed wetland's biological processes are not well understood and therefore in theory are unpredictable. In practice they are simple and very stable when properly designed and installed (sufficient capacity, adequate length of treatment canals, protection from storm flooding and deep freezing, correct use of both anaerobic and aerobic stages).
- While nutrients are changed to harmless forms year-round by wetland bacteria, actual nutrient removal takes place mainly during the growing seasons as this nutrient removal is accomplished by actively-growing plants' roots. This problem can be partially or completely solved, at least on a small scale, by running the waste stream through a greenhouse where 'waste' nutrients can be absorbed and productively used year-round, or by storing the endpoint water in large, shallow ponds where algae can remove nutrients year-round.
- In climates with cold winters, bacteria and plants living in the constructed wetland's soil die back. Not only does this slow or stop nutrient removal during hard freezes, but there can be susbtantial nutrient releases as the organisms previously removing and storing nutrients die in winter and release their own nutrients back into the system. In large enough systems (city-wide, for instance), this sudden nutrient release can impact local streams the same way the original effluent would have (though for a shorter period of time, and during the dormant season).
As this series on Constructed Wetland Wastewater Treatment continues, we'll discuss each of these issues in detail, as well as other aspects of the function, design and implementation of constructed wetlands.
Issues surrounding how to clean polluted water, and how to keep it clean in the first place!
Removing metals and other persistent pollutants from wastewater streams using constructed wetlands.
A description of the working parts of a constructed wetland wastewater treatment system, describing their biological functions and variations.
Reprinted from (Perma) Culture and Sanity Website