Water Treatment Residuals Remove Copper, Lead, and Zinc from Acidic Wastewater

Acidic sulfur-rich waste water is an environmental pollutant generated from a variety of industrial waste streams, and is a major problem that must be solved or at least controlled. The major source of such waste is acid mine drainage (AMD) that discharges from both active and closed mines and results from the weathering of sulfide minerals such as pyrite. It is usually acidic and contains a variety of contaminants—most notably high concentrations of sulfate, iron and other heavy metals. While there are several existing remediation techniques for treating heavy metal-contaminated waste water with their inherent advantages and disadvantages, this study evaluated the effectiveness of using a waste by-product—drinking water treatment residuals or WTRs—as a sorbent to remove a host of metals (copper, lead, and zinc) from standard solutions and from simulated AMD. Both the Al- and the Fe-based WTRs were able to remove ~90% to 99% of Cu, Pb, and Zn from standard solutions (initial load: 2500 mg/kg WTR). Batch experiments conducted to study the effects of pH demonstrated that pH did not have any significant effect on removal of copper or lead between pH 2 to 6, but did have a significant effect on the removal of zinc (Tukey HSD, α = 0.05). In simulated AMD, the Al-WTR was able to remove ~64% to 69% and 88% to 91% of the initial loads of copper and lead, respectively (initial load: 500 mg/kg for each), and ~34% to 50% of the initial load of zinc (5000 mg/kg). Under the same conditions, the Fe-WTR was able to remove ~54% to 56% and 84% to 88% of the initial loads of copper and lead, respectively, and 25% to 47% of zinc. Preliminary results demonstrated the effectiveness of the WTRs as a potential sorbent to treat heavy metal-contaminated acidic waste water.