A novel protease-immobilized carbon catalyst for the effective fragmentation of proteins in high-TDS wastewater generated in tanneries: Spectral and electrochemical studies

The aim of this study was to degrade proteins in high-total dissolved solids (TDS)-containing wastewater produced during the soaking process in tanneries (tannery-TDS wastewater) using a halotolerant protease-assisted nanoporous carbon catalyst (STPNPAC). A halotolerant protease was obtained from the halophile, Lysinibacillus macroides, using animal fleshing as the substrate. The protease was immobilized using ethylene diamine (EDA)/glutaraldehyde functionalized nanoporous activated carbon (EGNPAC). The optimum conditions for the immobilization of protease were determined as time (120 min), pH (6), protease concentration (575-600 U/g), EGNPAC size, salinity, and temperature (30 °C). The immobilization was confirmed by FTIR, TGA-DSC, SEM, and XRD analyses. The adsorption kinetics was consistent with a pseudo first order rate constant of 1.43 × 10^-2 min^-1. The thermodynamic parameters (ΔG, ΔH, and ΔS) confirmed the effective immobilization of the protease onto EGNPAC. STPNAPC was found to efficiently degrade the proteins in tannery-TDS wastewater, with a complete fragmentation time of 90 min at pH 6 and 30 °C. Accordingly, the protein fragmentation was confirmed by UV-visible and UV-fluorescence spectroscopy, ESI-mass spectrometric analysis and circular dichroic studies. The formation of protein hydrolysates was confirmed by cyclic voltammetry and electrical impedance studies. BOD₅: COD value, 0.426 of treated tannery-TDS wastewater may favor sequential biological treatment processes.

Regeneration of wastewater contaminated by cationic dye by nanoporous activated carbon produced from agriculture waste shells

The discharge of organic dye into environment is the threat to hydrosphere and biosphere. On the other hands, the agriculture solid wastes such walnut and almond shells pose serious pollutions in lithosphere and atmosphere when burned. The aim of present investigation is to fabricate microporous activated carbon from agriculture waste shells by microwave irradiation as efficient adsorbent to overcome these problems. Firstly, zinc chloride was impregnated into milled shell particles, 300 μm, by conventional and microwave-assisted techniques and then the dry precursors were heated in the closed and open ceramic vessels in air and nitrogen atmospheres. The experimental investigation was carried out to understand the roles of different fabrication factors such as shell particle size, catalyst impregnation ratio, microwave power, carbonization temperature, and atmosphere on cationic dye removal from wastewater. The mentioned factors efficiently affect the dye removal onto obtained activated carbon. The increase in the microwave power up to 600 W could effectively increase the dye removal. However, the higher powers inversely affect the removal efficiency. The equilibrium data were well fitted by Langmuir equation with high linear regression coefficients in which the maximum adsorption capacities of activated carbon produced by walnut and almond shells were determined to be 98 and 114 mg/g, respectively. The most prominent advantage of activated carbon produced from almond shell is lower content of catalyst employed in impregnation stage. Although the larger particles of solid waste were applied, the spongy nature with average pore diameter of 2.4 nm is the unique characteristic of activated carbon fabricated from almond shell which improves the performance of adsorbent in wastewater treatment.