Tuesday, December 15, 2009
a brief description of how landfills + constructed wetland work:
About 32.5% of the trash is either recycled or composted, 12.5% is burned, and the rest, 55% is buried in landfills, however, the amount of trash buried in landfills has doubled since 1960.
What landfills generally are is a carefully designed structure built into or on top of the ground where garbage is then isolated from it's surrounding environments. The most common method is the used of a bottom liner and then daily coverings of soil to prevent flying garbage or raiding of pests, but because space is a precious commodity, many companies are now experimenting with tarps or spray on paper or cement emulsions.
There are generally 2 common types of liner, the sanitary landfill uses a clay liner and the municipal solid waste landfill uses a synthetic or plastic liner to isolate garbage from the environment. The purpose of the liner is to isolate it from groundwater so that the contents above will be kept drive and not in contact with air. Under these conditions, the decomposition process will slow, almost preserving the waste.
A: Recycling Centres
B: Scale House
C: Access roads
D: Sanitary Landfill-
E: Municipal Solid
F: New Cell Prep
G: Cell Being Filled
H: Storm Drainage
J: Methane Vent
K: Methane Piper
L: Methane Station
M: Monitoring Pipe
N: Run-off Collection
O: Storm Water
P: Storm Water Pipe
Q: To City Water
B: Compacted Clay
C: Plastic Liner
D: Leachate Collection Pipe
E: Geotextile Mat
G: Drainage Layer
H: Soil Layer
I: Oil Cells
J: New Cells
K: Leachate Pond
The cross-section drawing shows the structure of a typical municipal solid waste landfill and the arrows indicate the flow of leachate.
The basic parts of this system are:
- C - bottom liner that separates leachate from groundwater
- I + J - cells, both old and new where garbage is stored within the landfill
- D - Leachate collection system that collects water that has percolated through the landfill
- Storm water drainage that collects rainwater
- Methane collection system that collects the gas that is formed during the breakdown process.
- and lastly, the covering or cap that seals off the top of the landfill.
Storm water drainage that collects rainwater
Leachate pond that collects contaminants
The Leachate pond is then tested for chemicals: organic chemicals, pH, calcium, magnesium, iron, sulfate and chloride, are just some common chemicals they test for. After the testing, the water can be treated like any other sewage or wastewater and can happen insitu or exsitu. A method to reduce the volume of leachate water can be to recirculate it, making it more concentrated, but this poses a problem with the increase in concentration and possibly contamination.
It is also important to implement a methane collection system to collect the anaerobic byproducts, which is methane gas, during the natural landfill break down process in absence of oxygen. The reason for this is to prevent methane from exploding or burning, therefore a series of pipes embedded in the landfill is used to collect this gas, and in some cases, it is collected for natural energy, burned, or vented. Methane gas would then still be produced for a number of years after the landfill is capped, making it an ideal way of generating renewable energy.
The capping process is the last portion of the landfill where it will be covered permanently with a polyethylene cap and then 2 feet of compacted soil. Vegetation is then planted to prevent erosion and generally consists of shallow penetrating root type plants, such as kudzu and grass.
In my thesis, the constructed wetland acts as the leachate pond where the leachates will drain into the wetland for remediation.
Constructed wetlands are wastewater treatment systems composed of one or more treatment cells in a built and partially controlled environment. There are generally two types of wetlands, free water surface and vegetated submerged bed. For the wetland portion of the project, the thesis will utilize the free water surface method. Where free water surface constructed wetlands closely resemble natural wetlands in appearance and function, with a combination of open-water areas, emergent vegetation, varying water depth, and other typical wetland features. The components of this system include berms to enclose treatment cells, inlet structure that regulate and distribute influent wastewater evenly for optimum treatment, various combinations of open-water areas and fully vegetated surface areas, and outlet structures that allow adjustment of water levels within the treatment cell.
A Vegetated submerged bed wetlands consist of gravel beds that may be planted with wetland vegetation. A typical system also contain berms and inlet and outlet structures for regulation and distribution of wastewater flow. The vegetated submerged bed are not dependent on wetland vegetation for treatment performance and also do not require open-water areas. However, the success of the previous system is in view of the fact that the performance of constructed wetlands depends heavily on the ecological functions that are similar to those of natural wetlands, which are based largely on interactions within plant communities.
Freudenrich, Craig. “How Landfills Work”, How Stuff Works, 2000, 14 Dec. 2009 http://science.howstuffworks.com/landfill6.htm
“Municipal Solid Waste”, United States Environmental Protection Agency, 13 Nov. 2008, 14 Dec. 2009 http://www.epa.gov/garbage/facts.htm info
United States. United States Environmental Protection Agency. Manual: Constructed Wetlands Treatment of Municipal Wastewaters. Cincinnati, Ohio: Office of Research and Development, 2000
1-5: Freudenrich, Craig. “How Landfills Work”, How Stuff Works, 2000, 14 Dec. 2009 http://science.howstuffworks.com/landfill6.htm
7-8: United States. United States Environmental Protection Agency. Manual: Constructed Wetlands Treatment of Municipal Wastewaters. Cincinnati, Ohio: Office of Research and Development, 2000