Increased human activities, weathering of building materials and atmospheric deposition contribute heavy metals such as lead, copper, zinc, and cadmium to urban runoff. Bioretention is a green infrastructure as well as a best management practice used to improve the quality of stormwater runoff in addition to reduce its quantity. This stormwater management practice is gaining popularity in commercial development because it can easily be sited in the required natural areas of places such as parking lot medians and streetscapes.
The goal of this research was to evaluate the suitability of bottom ash as a replacement for sand in bioretention media by studying the effect of the bottom ash on the removal and retention of heavy metals. The effect of vegetation on heavy metal removal efficiency of bioretention was also considered. To achieve our objective, a 50:50 ash and wood fines mix was compared to a control of 50:50 sand and wood fines for pollutant removal effectiveness. The 50:50 mixture of incinerator bottom ash and wood fines was chosen because it satisfied drainage requirements of at least 2 feet per day. Eighteen columns were constructed of 8-inch diameter PVC pipe and filled with 18 inches of media. Twelve of the 18 columns were planted with switchgrass; the remaining columns were left unplanted. With synthetic rainwater prepared in a laboratory setting, the columns were subjected to dosing. Its composition was based on samples of local rainwater and published literature. The contaminants examined were copper, lead, zinc, iron, nickel, cadmium, and chromium.
Prominent levels of heavy metals were present in the stormwater, but the levels decreased over time for all growth media. The concentration of heavy metals were affected by the type of growth media. The experimental media retained mean lead concentration of 11.2% but the control media leached 29%. Lower mean concentration of zinc, iron, and cadmium were leached from the experimental media (-39%, -5,910%, -2%, respectively) than control media (-57%, -44,758%, -11%, respectively). Overall, vegetation had no effect on metal retention for the first two sampling dates, but had a greater effect thereafter with higher retention for copper, lead, zinc, and iron. This study revealed that media, rather than vegetation, had a greater effect on heavy metals retention. The results suggest incinerator bottom ash has the potential to be a valuable bioretention media for urban planners seeking to protect urban surface water quality due to its excellent infiltration rate, plant suitability, and heavy metal content below water quality standards.
|Advisor:||Morgan, Susan M.|
|Commitee:||Fries, Ryan N., Zhou, Jianpeng|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 52/05M(E), Masters Abstracts International|
|Subjects:||Civil engineering, Environmental engineering|
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