Constructed wetlands for the remediation of blast furnace slag leachates
Abstract
Air-cooled blast-furnace slag (BFS), a by-product of iron production, is recycled and often used as fill material for roads and other transportation structures. The use of this material in poorly drained areas can produce a greenish leachate, with high pH, elevated sulfate and dissolved solids concentrations, and hydrogen sulfide odor. The occurrence of this leachate from BFS used as fill on I-65 in Northwest Indiana, has resulted in the Indiana Department of Transportation’s (INDOT) remedial action. The overall objective of this dissertation research was to explore the use of constructed wetlands to biologically and chemically eliminate the contamination properties of this leachate. Column, greenhouse, and field scale studies were used to investigate the use of media, plant combinations, and operating conditions to reduce total sulfur, high pH, and other contaminants. A laboratory shaker study was conducted to evaluate the leachate from slag and chemical constituents of BFS leachate. The laboratory shaker study confirms that anoxic conditions are required to produce the green color of the leachate, as elevated sulfate concentrations were observed when the suspensions were oxidized. The column and greenhouse studies indicate that treatment systems utilizing organic media (peat and mushroom compost) were more effective for reducing pH, total dissolved solids (TDS), sulfate, and total sulfur. Mushroom compost, amended with zero valent iron (ZVI) and operated with a residence time of 14 days, was the most effective matrix for the removal of sulfate (67%) and total sulfur (72%). The greenhouse study shows the ability of macrophytes to lower pH, but they also transport oxygen to the root zone, oxidizing sulfur species. The field scale wetland indicates that reduction of sulfate, metals, TDS, and buffering of pH, can be achieved by the abiotic and biotic processes of the engineered system, under low flow conditions and with long residence times. The use of constructed wetlands is a viable, cost effective treatment option for this problem. Moreover, the use of organic biofilters, utilizing anaerobic conditions, sulfate-reducing bacteria (SRB), and ZVI, may prove to be the most effective for treating BFS leachate and other sources of elevated sulfur and TDS pollution.
Degree
Ph.D.
Advisors
Banks, Purdue University.
Subject Area
Civil engineering|Environmental engineering
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