Report ENVR206 – Constructed Wetlands

ENVR206B – Constructed Wetlands for Remediation Purposes

Stefan Martensson C03347318
Definition:
Constructed wetlands are artificially built marshes built to treat human wastewater and stormwater. They have four key components:
• Wastewater
• Soil and drainage materials (such as pipes and gravel)
• Plants (both above and below the water)
• Micro-organisms
Constructed wetlands for hydrocarbon removal. The project was by accident invented when environmental technologists observed that natural wetlands reduced the mobility and concentration of the hydrocarbons. They asked if an artificial wetland would have the same effect and if so, be economically viable. Due to the expensive nature of air stripping (the common method to remove hydrocarbons today), finding a more economical way for treating contaminated water is important, especially with the heavy gas and oil operations in Alberta and Saskatchewan.
It’s more than 10years ago (1997) this project was started, and the question the research was aiming to answer are:
• At what rates could the constructed wetland handle the contaminated water and how much would the hydrocarbons biodegrade, if at all?
• How effective would planted vegetation, versus gravel, be at removing hydrocarbons?
• How well would the system work under summer and winter conditions?
WHAT WERE THE RESULTS?
The removal of hydrocarbon was 100% in summer and in winter the first two years of the project. In the winters they used subsurface aeration. In spring and late fall, without aeration, treatment efficiency fell to 50%, although the remaining hydrocarbons were removed by natural processes along the outflow channel. It was later discovered that oxygen was needed to be added to the water before it entered the wetland to stimulate the biodegradation processes. The main factor in removal of the hydrocarbons in the wetlands was mainly through volatilization and to a lesser extent through biodegradation and dilution. At the initial phases of the project the plant root systems were not established enough but even later research found that the roots did not have a significant uptake of the hydrocarbon compounds such as benzene, toluene and xylene. The concluded that constructed wetlands in the gas and oil industry remediation process they didn’t necessarily needed to maintain and establish plants in them. The overall preliminary indication was that an artificial wetland treatment system would have similar capital cost but lower operating costs than air stripping and other conventional methods. This study was conducted in 2002 and I tried to find follow up studies but unfortunately didn’t find any.
Sources:
http://en.wikipedia.org/wiki/Constructed_wetland
http://www.constructedwetlands.org/
http://www.epa.gov/OWOW/wetlands/pdf/hand.pdf
http://findarticles.com/p/articles/mi_qa5406/is_200207/ai_n21318866/

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