Passive remediation of acid mine drainage using crab shell chitin

Streams contaminated by acid mine drainage (AMD) are complex environmental systems which require biological, chemical, and physical treatment steps for thorough remediation. In this work, a novel concept for treating AMD was investigated, in which the biological reduction of acidity, chemical enhancement of alkalinity, and physical sorption of metals occurred simultaneously using one multifunctional substrate: chitin from crab shells. Sacrificial microcosm tests were conducted to evaluate the ability of chitinous material from crab shells to reduce acidity and dissolved metals concentrations in AMD water collected from Kittanning Run in Altoona, Pennsylvania. In the presence of SC-20 grade crab shell chitin, pH increased from 3.21 to 6.79, acidity decreased from 192 to -114 mg/L, and alkalinity increased from 0 to 235 mg/L, in just 9 days. Corresponding to this increase in pH, dissolved iron and aluminum concentrations were reduced by more than 99% and manganese concentrations were reduced by 81%. In addition, sulfate concentrations were observed to decrease from 489 to 303 mg/L, confirming the activity of sulfate reducing bacteria. Physical adsorption of iron to chitin, chemical precipitation of aluminum hydroxide (Al(OH)(3)), and biologically induced manganese sulfide (MnS) precipitation were the likely mechanisms of dissolved metals removal in this system. The results of this work demonstrate for the first time the effectiveness of chitin as an alternative substrate for AMD treatment.