Microbially induced calcium carbonate precipitation is a method for the protection of cement-based materials. This paper deals with the strength characteristics of microbial cement mortars, which are treated by the Enterobacter sp.FJ 973550 microorganism in different calcium sources (calcium hydroxide, calcium acetate, calcium chloride and calcium oxide). The crystalline phases of calcium carbonate crystal formation and the surface morphology of cement mortar are investigated by X-ray diffraction and scanning electron microscopy. Microbial cement mortar specimens treated in calcium hydroxide source show higher compressive strength (,29%) and tensile strength (,47%) compared to control specimens. Surface treatment of specimens with bacteria resulted in an approximately 56% decrease in water absorption and increased the resistance to water and hazard material penetration. This biological surface treatment shows promising prospects for increasing strength and durability aspects of cement mortar specimens.

The method of microbial mineral plugging in porous media is common in nature. Physical and biochemical properties of calcium carbonate (CaCO 3 ) precipitation induced by Enterobacter and Serratia microorganisms into cement mortar specimens are studied and analysed. X-ray diffraction is used to identify the calcium carbonate crystal as calcite, vaterite, aragonite. Scanning electron microscopy (SEM) is used to verify the formations of white precipitation (calcium carbonate) in the microbial cement mortars. The improvement of strength in the concrete/cement mortar base is attributable to the formation of calcium carbonate, which fills the pores between the cement sand matrices. In the present study a noteworthy enhancement of compressive strength of 44% is observed in the biocuring Enterobactertreated specimen relative to control. This method of implanting semi-solid mixtures onto the surface of the cement paste specimens shows significant effects such as decrease of permeability and capillary water penetration.

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The current paper makes obvious the elimination of chromium(VI) ion, from wastewater via adsorption technique with activated carbon generated from Manilkara zapota tree (MZTWAC). Preliminarily MZTWAC has undergone characterization studies which uncovered the suitability of MZTWAC to expel chromium(VI) from aqueous solution. Batch adsorption experimentation was premeditated with the competence of central composite design (CCD) and it was executed. Response surface methodology (RSM) was the key optimization software to appraise the adsorptive chattels of MZTWAC engaged in removing chromium(VI) ion in aqueous solution which explored the interactions flanked between four expounding variables explicitly initial concentration of chromium(VI) ion, pH of the solution, MZTWAC dose and time of exposure, and contact time. The response variable that was concentrated in the study was adsorption capacity. It was deduced a polynomial in quadratic equation was documented amid the adsorption capacity and variables influencing the adsorption with R 2 = 0.9792 which was projected as the best suit for the adsorption process. ANOVA that is expanded as analysis of variance judged the connotation of adsorption process variables. 0.2 g of MZTWAC dosage has removed 87.629% chromium(VI) from aqueous solution. The enhancement of adsorption process reclined on the attainment of maximum adsorption capacity which further depends on the optimization of variables under consideration. This criterion was accomplished by the desirability function optimizing the process variables.