Heavy Metals Bioremediation and Water Softening Using Ureolytic Metschnikowia Pulcherrima and Raoultella Planticola Strains

Abstract This study employed the ureolytic fungal Metschnikowia pulcherrima (29A) and bacterial Raoultella planticola (VIP) strains in Pb 2+ and Hg 2+ removal using the promising CaCO 3 bio precipitation technique. Out of fifty isolates, strains 29A and VIP were selected based on their highest ureolytic activity followed by MIC assay using 350 ppm of Pb 2+ and Hg 2+ . The maximum urease activity recorded 884 and 639 U/mL for 29A and VIP strains at 24 and 30h of incubation, respectively. Complete removal of Pb 2+ was achieved at 42h and 90h for 29A, VIP correspondingly, while Hg 2+ was totally removed at 60h and 102h for 29A, VIP respectively. Remarkable removal of Ca 2+ (>95%) was achieved by the end of the experiments, which would address the hardness problem in the water treatment process. Further, EDX, SEM and, XRD were used to characterize the remediated precipitates. EDX profiles showed characteristic peaks of C, O and, Ca 2+ besides Pb 2+ and Hg 2+ . SEM illustrated the presence of microbial imprints and calcinated cells in the remediated bioliths. However, XRD confirmed the transformation of soluble metals to insoluble forms entrapped in calcite or vaterite lattice. Such a bioremediation approach ensures the detoxification and sequestration of heavy metals in a stable and durable matrix; obstructing their leach from carbonate complex trap to the environment.