Cracks are the main cause for structural failure. One way to circumvent costly manual maintenance and repair is to incorporate an autonomous self-healing mechanism in concrete. This study exploited the potential to apply calcite-precipitating bacteria as a crack-healing agent in concrete. These bacteria were prepared in different cell concentrations and incorporated in the concrete mix. Compressive strength tests were performed at the stage of 28th day of curing. The effects of different cell concentrations of Bacillus sphaericus on concrete, reducing the crack, were studied. We used mortar cubes with 30mL of bacteria/mortar cube and sequentially increased up to 50mL (10, 20, 30, 40 and 50mL) in the ratio of mortar cubes in 1:6. The concrete grade used for the study was M25. At last, we had made concrete blocks of size 150×150×150 mm with concrete of grade M25. For those blocks, the compressive strength and non-destructive tests such as, rebound hammer and ultrasonic pulse velocity tests were performed. The results obtained in the work are that the compressive strength of blocks of size 150×150×150 mm is good when compared to control concrete. When load is applied to control concrete, the crack gets developed earlier and when bacterial concrete is used, the crack does not develop at an early stage.

Arthrobacter sp. Sphe3 and Bacillus sphaericus cells were used for Cu(II) biosorption. The effect of contact time, biosorbent dose, equilibrium pH, temperature and the presence of other ions on the efficiency of the process were extensively studied. Optimum pH value and biomass concentration were determined at 5.0 and 1.0 g/l, whereas contact time was found to be 5 and 10 min for Arthrobacter sp. Sphe3 and Bacillus sphaericus biomass, respectively. Equilibrium data fitted very well to Freundlich model (R ²â€‰= 0.996, n = 2.325, K f = 8.141) using Arthrobacter sp. Sphe3. In the case of B. sphaericus, a Langmuir adsorption model [R ²â€‰= 0.996, Q ₘₐₓ = 51.54 mg-Cu(II)/g] showed to better describe the results. Potentiometric titration and Fourier transform infrared (FTIR) spectroscopy showed that amine, carboxyl and phosphate groups participate in Cu(II)-binding. The calculated thermodynamic parameters indicated the spontaneous and feasible nature of Cu(II) biosorption on both biosorbents. Selectivity of Cu(II) biosorption was examined in binary and multi-ions systems with various anions and cations which are commonly found in municipal and industrial wastewater. A specificity towards Cu(II) was observed in binary mixtures with Cl⁻, CO ₃ ⁻² , NO ₃ ⁻ , SO ₄ ⁻² , PO ₄ ⁻³ , Mg+² and Ca+², and As(V) with the maximum uptake capacity remaining constant even at high competitive ion’s concentrations of 200 mg/l. Desorption studies showed that Cu(II) could be completely desorbed from Cu(II)-loaded Arthrobacter strain Sphe3 and B. sphaericus biomass using 1.0 and 0.8 M HCl, respectively, and both bacterial species could be effectively reused up to five cycles, making their application in wastewater detoxification more attractive.