USING A WASTE BY-PRODUCT TO REMOVE METALS FROM CONTAMINATED SHIPYARD STORMWATER

Metals contamination is a significant problem in many industrial sites—especially in shipyards, where metals are used in many of the shipbuilding processes. While there are a wide variety of remediation techniques, this study evaluates the effectiveness of using a waste by-product—drinking water treatment residuals or WTRs—as a sorbent to remove several metals (aluminum, copper, lead, and zinc) from stormwater runoff generated in industrial sites. The WTRs can be obtained free of charge from drinking-water treatment plants, and they have already been shown to have a high capacity for removing other contaminants from water—such as arsenic, chromium, and phosphate. Two WTRs were used in a packed bed reactor experiment (one Fe and one Al based) to evaluate the adsorption/desorption kinetics of metals with the WTRs. Both WTRs showed a capacity to adsorb large amounts of various metals. In the studies involving stock solutions of the metals in simulated stormwater, both WTRs were able to remove more than 99% out of the initial loads of aluminum, lead, and zinc (1150 µg/L, 27 µg/L, 72 µg/L, respectively) after 24 hours at a ratio of 1:5 (g WTR: mL solution). Under these same conditions, the Fe-WTR was able to adsorb approximately 98% of the initial Fe load (1439 µg/L), and both WTRs showed effectiveness in removing copper from solution (79 - 88% for the Al-WTR, ~75% for the Fe-WTR at an initial load of 72 µg/L). Different environmental factors such as pH, competing ions, reaction times, and solid:solution ratios were also evaluated to determine their effects on metal sorption capacity and kinetics. Overall, results for both the Fe and the Al-WTRs demonstrated their ability to remove a host of metals from shipyard stormwater which could lead to possible development of a new remediation method.