Removal of Heavy Metals from Acid Mine Drainage with Lab-Scale Constructed Wetlands Filled with Oyster Shells

Abstract

The present study investigated the applicability of constructed wetlands (CWs) filled with oyster shells (OSs) for removing heavy metals from acid mine drainage (AMD). Lab-scale CWs consisted of columns (ID 12.5 cm, H 50 cm) packed with OSs or limestone, which were left unplanted or planted with cattails. Synthetic and real AMD containing 7.3 mg/L of Zn, 38.0 mg/L of Fe, and other minerals (pH = 4.0) were fed to the CWs (1 L/column) under a hydraulic retention time of 7 days in a sequencing batch mode. The effluent pH values of the CWs reached 6.9–8.3. Results show that OSs with high CaCO3 contents had higher neutralizing capability for AMD than limestone had. During 7 months of operation, all CWs were highly effective for removing Zn (88.6–99.2%); Fe (98.7–99.7%); and Cd, Cu, Pb, As, and Mn (48.2–98.9%) from both real and synthetic AMD. The mass balance in the CWs indicated accumulation in OSs or limestone as a main pathway for removing heavy metals, representing 44.8–99.3% of all metals, followed by biomass (8.8–29.9%) in the planted CWs. Other processes examined for this study only played a minor role in removing heavy metals. The higher metal treatment performance of OS CWs demonstrated the value of this aquaculture byproduct as a CW substrate.

Shell Waste Management and Utilization: Mitigating Organic Pollution and Enhancing Sustainability

“…In a constructed wetlands study, both oyster shells and limestone had high AMD neutralization potential during a 7-month operation. Accumulation in the substrates was a principal pathway for removing heavy metals [57]. Therefore, the recycling of waste bivalve shells as substrates in constructed wetlands for AMD treatment might encourage the reduced usage of natural minerals such as limestone.…”

Blue Circular Economy—Reuse and Valorization of Bivalve Shells: The Case of Algarve, Portugal

“…Shells are often considered nuisance waste rather than a valuable commodity, resulting in them being dumped in landfills or incinerated. Promoting the circularity of this waste is crucial to achieving environmental, economic, and socio-cultural benefits [25], beyond researching solutions for this waste, which can be applied across various sectors including construction, cosmetics manufacturing, artificial stone production, food supplement production, insulation material in thermal renders, agriculture, livestock farming, soil recovery, water and effluent treatment, as well as animal feed formulation [16,[26][27][28][29][30][31][32][33][34]. The tradition of using oysters in civil construction dates back to ancient times, since the 16th century, rooted in the history of coastal regions, where the local population benefited from local resources for construction needs [35].…”