Microbially induced carbonate precipitation with Arthrobacter creatinolyticus: An eco-friendly strategy for mitigation of chromium contamination.

Chromium contamination from abandoned industrial sites and inadequately managed waste disposal areas poses substantial environmental threat. Microbially induced carbonate precipitation (MICP) has shown promising, eco-friendly solution to remediate Cr(VI) and divalent heavy metals. In this study, MICP was carried out for chromium immobilization by an ureolytic bacterium Arthrobacter creatinolyticus which is capable of reducing Cr(VI) to less toxic Cr(III) via extracellular polymeric substances (EPS) production. The efficacy of EPS driven reduction was confirmed by cellular fraction analysis. MICP carried out in aqueous solution with 100 ppm of Cr(VI) co-precipitated 82.21% of chromium with CaCO3 and the co-precipitation is positively correlated with reduction of Cr(VI). The organism was utilized to remediate chromium spiked sand and found that MICP treatment decreased the exchangeable fraction of chromium to 0.54 ±â€¯0.11% and increased the carbonate bound fraction to 26.1 ±â€¯1.15% compared to control. XRD and SEM analysis revealed that Cr(III) produced during reduction, influenced the polymorph selection of vaterite during precipitation. Evaluation of MICP to remediate Cr polluted soil sample collected from Ranipet, Tamil Nadu also showed effective immobilization of chromium. Thus, A. creatinolyticus proves to be viable option for encapsulating chromium contaminated soil via MICP process, and effectively mitigating the infiltration of Cr(VI) into groundwater and adjacent water bodies.

Valorization of tannery solid wastes for sustainable enzyme induced carbonate precipitation process.

Biocementation via enzyme induced carbonate precipitation (EICP) is an emerging ground improvement technique that utilizes urease for calcium carbonate precipitation. Usage of expensive laboratory grade chemicals in EICP hinders its implementation at field level applications. In this study, the feasibility of utilizing solid wastes generated from leather industry was investigated for EICP process. Initially, the proteinaceous fleshing waste was used as nitrogen source for production of an extracellular urease from Arthrobacter creatinolyticus MTCC 5604 followed by its subsequent use in EICP with suspended solids of tannery lime liquor, as alternative calcium source. The calcium ion solution was prepared by treating suspended solids of lime liquor with 1 N HCl. The EICP was optimum with 1000 U of urease, 1.0 M urea and 1.0 M CaCl2.2H2O for test tube experiments. Sand solidification experiments under optimal conditions with five times addition of cementation solution yielded a maximum unconfined compressive strength (UCS) of 810 kPa with laboratory grade CaCl2.2H2O and 780 kPa with calcium from lime liquor. The crystalline phases and morphology of the CaCO3 precipitate were analyzed by XRD, FTIR and SEM-EDX. The results showed the formation of more stable calcite in EICP with calcium obtained from lime liquor, while calcite and vaterite polymorphs were obtained with CaCl2.2H2O. Utilization of fleshing waste and lime liquor in EICP could reduce the pollution load and sludge formation that are generated during the pre-tanning operations of leather manufacturing. The results indicated the viability of process to achieve cost effective and sustainable biocementation for large scale applications.