Optimization of Bio-Foamed Concrete Brick Strength via Bacteria Based Self-Healing and Bio-Sequestration of CO2

This research aimed to optimize the compressive strength of bio-foamed concrete brick (B-FCB) via a combination of the natural sequestration of CO2 and the bio-reaction of B. tequilensis enzymes. The experiments were guided by two optimization methods, namely, 2k factorial and response surface methodology (RSM). The 2k factorial analysis was carried out to screen the important factors; then, RSM analysis was performed to optimize the compressive strength of B-FCB. Four factors, namely, density (D), B. tequilensis concentration (B), temperature (T), and CO2 concentration, were selectively varied during the study. The optimum compressive strength of B-FCB was 8.22 MPa, as deduced from the following conditions: 10% CO2, 3 × 107 cell/mL of B, 27 °C of T and 1800 kg/m3 of D after 28 days. The use of B. tequilensis in B-FCB improved the compressive strength by 35.5% compared to the foamed concrete brick (FCB) after 28 days. A microstructure analysis by scanning electronic microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction analysis (XRD) reflected the changes in chemical element levels and calcium carbonate (CaCO3) precipitation in the B-FCB pores. This was due to the B. tequilensis surface reactions of carbonic anhydrase (CA) and urease enzyme with calcium in cement and sequestered CO2 during the curing time.

Mechanism and Characteristics of CH4/CO2/H2O Adsorption in Lignite Molecules

Adsorption characteristics of coalbed methane (CBM) are significant to investigate the absorption of coal, shale, and porous media. In particular, adsorption characteristics of CH4, CO2, and H2O play an important role in predicting CBM output and geologic sequestration potentials of CO2 in research fields of CO2-enhanced CBM recovery (CO2-ECBM) and sequestration of CO2. In this work, adsorption characteristics of CH4, CO2, and H2O in lignite molecules were simulated through the grand canonical Monte Carlo (GCMC) method and molecular dynamics (MD) method. Research results demonstrated that given the same temperature and pressure, the ultimate adsorption capacity of lignite per unit to H2O is the highest, followed by those of CO2 and CH4 successively. All isothermal adsorption curves conform to the “I-type” characteristics. In the saturated molecular configuration, gas molecules show different distribution patterns at two sides of the lignite molecule chain. Lignite has typical physical adsorption to CH4 and CO2, with adsorption energy provided by nonbonding energy. However, lignite has both physical adsorption and chemical adsorption to H2O, with adsorption energy provided by both nonbonding energy and hydrogen bond energy. High temperature is against adsorption of CH4, CO2, and H2O. Temperature might inhibit adsorption of gas molecules. Research conclusions lay foundations for the exploitation and development of CBM and relevant studies on sequestration of CO2.