ISOLATION AND FUNCTIONAL EXPLORATION OF POTENTIAL CHROMIUM-UTILIZING BACTERIA FOR BIOREMEDIATION AND BIOMINERALIZATION APPLICATIONS: INSIGHTS INTO HEXAVALENT CHROMIUM REDUCTION IN CEMENT INDUSTRY SOIL

Abstract

Hexavalent chromium [Cr (VI)] pollution is a serious environmental problem linked to many industrial processes, especially cement production, tanning, electroplating, pigment production and metal processing. The trivalent chromium [Cr (III)] that occurs naturally in raw materials can be converted to more harmful Cr(VI) in the high temperature clinker production process used in the cement industry. Consequently, cement dust, slurry, contaminated soil and wastewater may be significant sources of chromium pollution. Cr(VI) is highly soluble and mobile, persists in the environment, is carcinogenic, and highly impacts soil microbial diversity, plant growth, aquatic ecosystems, groundwater quality and human health. Of the currently available treatment techniques, conventional physicochemical techniques have several drawbacks, such as expensive treatment cost, incomplete detoxification and production of secondary pollutants, which makes sustainable biological techniques required. This study aimed to explore the microbial chromium bioremediation and biomineralization from the cement industry-associated environments in an integrated way. The soil collected from the cement industry was used for isolating and functional screening of bacteria that can withstand the stress of heavy metals. The isolates were tested on chromium-amended media to assess the tolerance and adaptation of these isolates to Chromium. Microbial detoxification of hexavalent chromium is important because bacteria that resist chromium may transform the chromium to the less mobile and less toxic trivalent chromium using various mechanisms, including enzymatic reduction, biosorption, efflux-mediated resistance, and extracellular sequestration and precipitation-associated immobilization. Further study of the urease-associated biomineralization potential of the chromium adapted isolates was conducted in the presence of varying concentrations of urea. The urease-producing bacteria convert urea to carbonate ions and ammonia, raising the pH in the area and favouring calcium carbonate precipitation. The microbially induced calcium carbonate precipitation process (MICP) can be used in crack repair, surface protection, coatings, paints and self-healing cementitious materials. A functional basis for the identification of the isolates that may be useful for both chromium bioremediation and biomineralization-based material systems is obtained by the combined screening of chromium tolerance and urease activity. Overall, the research contributes to the development of sustainable microbial treatments for environments contaminated with chromium in industries and self-healing building materials.