Assessment of ecofriendly carbon capture using Bacillus subtilis induced calcium carbonate precipitation with focus on applications mechanisms and cost efficiency

Abstract

This work focuses on exploiting the naturally occurring microbial calcium carbonate precipitation catalyzed by microbial consortia within lakes and oceans biogeochemistry for carbon dioxide removal from atmosphere. In this work, Bacillus subtilis OQ119616 was used for carbon dioxide sequestration in equi-molar concentrations into Bacillus-induced calcium carbonate precipitation (BICCP). As this process requires alkaline media, urea degradation by urease and nitrogen fixation were traced. BICCP has been formed from calcium salts in the following order: chloride > nitrate > acetate > citrate. However, conversion efficiency percentage (CE%) of calcium salts to CaCO₃ exhibited a different attitude of citrate > acetate > chloride > nitrate. Calcium citrate is excluded from consideration. Acetate, however, is the most efficient salt; it significantly exhibited the highest CE%, with the least cost and highest economic feasibility. The wide range in quantities, efficiency and feasibility indicates the importance of the salt anion in BICCP. In addition, BICCP exhibited applicability in healing concrete cracks, improving field capacity of sand soil and the subsequently improved seed germination of Vicia faba. BICCP was also accompanied by adsorption of heavy metals as partial purging of waste/sewage water for hygiene/reuse. Bacillus subtilis exhibited the ability to perform MICP, utilizing various calcium salts in the following order: chloride > acetate > nitrate > citrate. However, acetate is the most efficient salt of calcium to be converted to calcium carbonate precipitate by B. subtilis, as it exhibited the highest conversion efficiency percentage (g/g %), with the least cost and highest economic feasibility. Carbon dioxide removal (CDR) occurs at simultaneous equity to CaCO₃ precipitation at mole/mole ratios. Economic feasibility (US$/m³) showed that BICCP may be applicable in CDR for cleansing carbon dioxide inside closed systems and for environmental safety. The bacterially induced CaCO₃ proved successful applicability in improving the field capacity of sand soil and growth of V. faba, healing concrete cracks and sorption of heavy metals for depolluting sewage/wastewater for hygiene reuse. BICCP could repair concrete cracks of 1-2 mm wide in 7 days by 210 * 10⁶ cells/mL. Adsorption of heavy metals (Pd, Zn, Cd and Cu) for partial removal of contaminants in/from waste/sewage water for hygiene reuse.

Keywords: Bacillus subtilis; BICCP; Calcium carbonate; Carbon capture; Crack healing; Mineral sorption; Nitrogenase; Urease; Water holding capacity.

Fig. 1

Phylogenetic tree on the basis of patterns and genetic relationship of the case-studied Bacillus subtilis OQ119616. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.

Fig. 2

Growth of Bacillus subtilis as optical density (O.D._660 nm) was followed over a period of 5 days at minimal medium supplemented with four levels of four calcium salts (a: acetate, b: citrate, c: chloride, and d: nitrate). Cultures started at 0-time with O.D._660 nm of 0.2A accounting to 21 × 10⁷ cells/mL. Data are means ± SE, n = 3. At each day, means with different letters are significantly differ at P ≤ 0.05 according to Duncan’s test.

Fig. 3

Protein content of Bacillus subtilis (mg.ml^-1) was followed over a period of 5 days at minimal medium supplemented with four levels of four calcium salts (a: acetate, b: citrate, c: chloride and d: nitrate). Cultures started at 0-time with O.D._660 nm of 0.2A accounting to 21 × 10⁷ cells/mL. Statistical analysis as shown in Fig.  2.

Fig. 4

Calcium carbonate precipitation by Bacillus subtilis(g/L) after growth for 30 days in minimal medium supplemented with four levels of four calcium salts (citrate “Ci” acetate “Ac”, nitrate “N” and chloride “Cl”) (a); development of calcium carbonate precipitation over time of 30 days at successively increasing concentrations of CaCl₂ (b); Scanning electron micrographs (SEM) showing shapes and morphogenesis of calcium carbonate precipitations produced by Bacillus subtilis at the provided calcium salts (c) [4cCi, 4cAc, 4cN and 4cCl for citrate, acetate, nitrate, and chloride, respectively]; (d) transmission electron micrographs (TEM) showing nanoparticles of calcium carbonate precipitations produced by Bacillus subtilis at the provided calcium chloride and viability of bacterial cells in calcium carbonate precipitates (e1-4) and.

Fig. 4

Calcium carbonate precipitation by Bacillus subtilis(g/L) after growth for 30 days in minimal medium supplemented with four levels of four calcium salts (citrate “Ci” acetate “Ac”, nitrate “N” and chloride “Cl”) (a); development of calcium carbonate precipitation over time of 30 days at successively increasing concentrations of CaCl₂ (b); Scanning electron micrographs (SEM) showing shapes and morphogenesis of calcium carbonate precipitations produced by Bacillus subtilis at the provided calcium salts (c) [4cCi, 4cAc, 4cN and 4cCl for citrate, acetate, nitrate, and chloride, respectively]; (d) transmission electron micrographs (TEM) showing nanoparticles of calcium carbonate precipitations produced by Bacillus subtilis at the provided calcium chloride and viability of bacterial cells in calcium carbonate precipitates (e1-4) and.

Fig. 5

XRD pattern of Calcium Carbonate (A): acetate, (B): citrate, (C): chloride, (D): nitrate. X-ray diffraction patterns of calcite CaCO₃, vaterite CaCO₃ and aragonite CaCO₃ polymorphs obtained by biomineralization of Bacillus subtilis culture after 5 days of exposure.

Fig. 6

ΔpH changes relative to pH 7.1 (control) (a), relationship between acetate concentrations and pH, ammonia and CaCO₃ produced (b),

Fig. 7

Ammonia content of Bacillus subtilis cultures assessed over a period of 5 days at minimal medium supplemented with four levels of four salts of calcium (a: acetate, b: citrate, c: chloride and d: nitrate). Cultures started at 0-time with O.D._660 nm of 0.2A accounting to 21 × 10⁷ cells/mL. Statistical analysis as shown in Fig. 2.

Fig. 8

Urease activity of Bacillus subtilis was assessed as ammonia over a period of 5 days at minimal medium supplemented with four levels of four salts of calcium (a: acetate, b: citrate. c: chloride and d: nitrate). Cultures started at 0-time with O.D._660 nm of 0.2A accounting to 21 × 10⁷ cells/mL. Statistical analysis as shown in Fig. 2.

Fig. 9

Nitrogenase activity of Bacillus subtilis was assessed as ammonia over a period of 5 days at minimal medium supplemented with four levels of four salts of calcium (a: acetate, b: citrate, c: chloride and d: nitrate). Cultures started at 0-time with O.D._660 nm of 0.2A accounting to 21 × 10⁷ cells/mL. Statistical analysis as shown in Fig. 2.

Fig. 10

Conversion efficiency percentage (CE%) of the given calcium salts to calcium carbonate formed (a); Economic feasibility 1 (EF1) of BICCP in CDR as (moles CO₂ fixed/Kg salt given (b); Economic feasibility 2 (EF2) of BICCP in CDR as moles CO₂ fixed/ US$ (c1); Economic feasibility 3 (EF3) of BICCP in CDR as US$c/m³ atmosphere (c2).

Fig. 11

Concrete cracks healing by BICCP; progression of cracks healing is demonstrated as paces in figure (a–e); developed cracks (a), added healing cocktail (b), healing progress (c & d), healed cracks.