Passive multi-unit field-pilot for acid mine drainage remediation: Performance and environmental assessment of post-treatment solid waste.

This study evaluated the performance of a passive multi-unit field-pilot operating for 16 months to treat acid mine drainage (AMD) from a coal mine in Colombia Andean Paramo. The multi-unit field-pilot involved a combination of a pre-treatment unit (550 L) filled with dispersed alkaline substrate (DAS), and six passive biochemical reactors (PBRs; 220 L) under two configurations: open (PBRs-A) and closed (PBRs-B) to the atmosphere. The AMD quality was 1200 ± 91 mg L-1 Fe, 38.0 ± 1.3 mg L-1 Mn, 8.5 ± 1.6 mg L-1 Zn, and 3200 ± 183.8 mg L-1 SO42-, at pH 2.8. The input and output effluents were monitored to establish AMD remediation. Physicochemical stability of the post-treatment solids, including metals (Fe2+, Zn2+, and Mn2+) and sulfates for environmental contamination from reactive mixture post-treatment, was also assessed. The passive multi-unit field-pilot achieved a total removal of 74% SO42-, 63% Fe2+, and 48% Mn2+ with the line of PBRs-A, and 91% SO42-, 80% Fe2+, and 66% Mn2+ with the line of PBRs-B, as well as 99% removal for Zn2+ without significant differences (p < 0.05) between the two lines. The study of the physicochemical stability of the post-treatment solids showed they can produce acidic leachates that could release large quantities of Fe and Mn, if they are disposed in oxidizing conditions; contact with water or any other leaching solutions must be avoided. Therefore, these post-treatment solids cannot be disposed of in a municipal landfill. The differences in configuration between PBRs, open or closed to the atmosphere, induced changes in the performance of the passive multi-unit field-pilot during AMD remediation.

Whey as an Alternative Nutrient Medium for Growth of Sporosarcina pasteurii and Its Effect on CaCO3 Polymorphism and Fly Ash Bioconsolidation.

Whey in large quantities can cause environmental problems when discarded, because it reduces dissolved oxygen and aquatic life. Nonetheless, it could be used as an easily available and economical alternative to reduce culture medium costs in microbially induced calcium carbonate precipitation (MICP). In this work, a native Sporosarcina pasteurii was isolated and then cultured by using different proportions of whey (W) in nutrient broth (NB). The solids were characterized by XRD, FT-IR, TGA, and SEM. The potential applications in bioconsolidation were also studied. Whey concentration was directly related to CaCO3 production. Higher whey concentrations reduced calcium carbonate purity to nearly 80%. All experiments showed calcite and vaterite fractions, where a whey increment in the media increased calcite content and decreased vaterite content, causing a decrease in crystal size. MICP improved compressive strength (CS) in sand and fly ash. The best CS results were obtained by fly ash treated with 25 W-75 NB (37.2 kPa) and sand with 75 W-25 NB (32.1 kPa). Whey changed crystal polymorphism in biogenic CaCO3 production. Material bioconsolidation depends on the CaCO3 polymorph, thus fly ash was effectively bioconsolidated by crystallization of vaterite and sand by crystallization of calcite.