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.

Non-enzymatic reduction of Cr (VI) and it's effective biosorption using heat-inactivated biomass: A fermentation waste material.

The effectiveness of heat-inactivated fungal biomass a fermentation waste of newly isolated laccase enzyme producer Leiotrametes flavida was studied for Cr (VI) removal in water and applied for Cr (VI) removal from tannery effluent. Adsorption parameters pH, biomass concentration and contact time were optimized using Box-Behnken design of response surface methodology. The adsorption process fits the Langmuir isotherm. Thermodynamic and kinetic studies showed that the process is spontaneous at ambient temperature and followed the second-order kinetics model, respectively. The values of the kinetic model indicated that the adsorption process is a combination of physisorption and chemisorption. Chromium adsorption onto the biomass was confirmed by SEM-EDAX, FTIR, XPS and XRD analysis. XPS analysis confirmed the reduction of Cr (VI) to Cr (III). The amount of chromium adsorbed was 72.38 % and 68.33 % for water and effluent, respectively. Chromium adsorbed onto biomass was desorbed at pH 9 with 1 M NaOH. Total chromium desorbed was 61.40 and 59.38 percent from water and effluent, respectively. The amount of Cr (III) in the desorbed sample was 71 and 68 percent, respectively. The heat-inactivated biomass of Leiotrametes flavida is a suitable material for efficient Cr (VI) removal and detoxification.