Evaluating crab-shell chitin, lactate, and spent mushroom compost for acid mine drainage remediation in central pennsylvania

Acid mine drainage (AMD) is a major environmental consequence of mining activity. This is a recurring problem around the world, and especially in some specific areas of United States, including Pennsylvania. Remediation of AMD has three requirements: pH neutralization, reduction of sulfate concentrations, and removal of dissolved metals. The aim of this study was to evaluate the sustainable waste material, crab-shell-chitin, as a multifunctional substrate for AMD remediation. The performance of chitin was evaluated under different raw water characteristics (comparative sites test), and compared with lactate and spent mushroom compost (comparative substrates test). Sacrificial, duplicate microcosms were prepared in serum bottles containing AMD water, sediment (microbial source), and the evaluated substrate. For the comparative sites test, three microcosm sets were prepared using AMD water from three different sites within central Pennsylvania, and all were treated with crab-shell-chitin. For the comparative substrates test, the AMD source was held constant and the substrate varied between crab-shell-chitin, sodium lactate, and spent mushroom compost. Microcosms were incubated in the dark, at room temperature, and under anoxic conditions for up to 50 days. Crab-shell-chitin (ChitoRem" SC-20) increased the pH from pH 3.0 - 3.5 to near neutral in 2 - 3 days. Increases in pH were much faster in the microcosms containing chitin than with the other substrates. In microcosms containing chitin, steady alkalinity generation and acidity removal were observed at average rates of 35 and -27 mg CaCO ₃/L-d, respectively. The activity of SO ₄ ^2- reducing bacteria was evident after 7 - 9 days of incubation, with reduction rates of 11.9 - 17.8 mg SO ₄ ^2-/L-d. Similar changes in alkalinity, acidity, and SO ₄ ^2- were also observed in lactate-containing microcosms, but they only started after 27 days. No alkalinity generation or sulfate reduction activity was observed in bottles containing spent mushroom compost. Aluminum and Fe removal was observed with all substrates, but it was much faster with chitin. Chitin was the only substrate able to partially remove manganese (>73%). The results of this study indicate that crab-shell-chitin is a promising material to be used as a substrate or amendment for AMD remediation. Its slowly fermentable nature makes it a suitable electron donor source to support the activity of sulfate reducing bacteria. In addition, the rapid release of its built-in carbonate minerals effectively neutralize acidic waters and facilitate the precipitation of dissolved metals.