Incorporation of Optical Density into the Blending Design for a Biocement Solution

Abstract

The engineering practices for applying the microbial precipitation of carbonates require a design of the blending biocement solution (BCS). The BCS is usually blended with concentrated strains NO-A10, reaction media, such as urea and CaCl2, and a solvent, i.e., water or seawater. To characterize the BCS, the unknown microbial characteristics, such as the cell viability, are complex factors. Therefore, the optical density (OD) was redefined as Rcv OD*, in which OD* was the tentative OD of the BCS used and Rcv was the conversion rate concerning the cell viability. To determine Rcv values, a standard precipitation curve based on the precipitation rate at 24 h was determined. It was found that the curve was expressed by λ1 OD+ λ2 OD2, in which λ1 and λ2 were 8.46 M and −17.633 M, respectively. With this, the Rcv and OD values of unknown BCS were estimated from the results of precipitation tests using arbitrary OD* values. By extending the testing time, the second order term of OD or OD* was negligible. Accordingly, the precipitation amount is expressed as 8.46 OD, in which the OD can be estimated by precipitation tests using arbitrary OD* values of BCSs. Unless the Ca2+ value is dominant, the optimum blending of BCS can be determined by OD. Thus, it is concluded that the blending design of BCS is achieved using 8.46 OD, or 8.46 Rcv OD*, and the standard precipitation curve was defined in this study.

Inhibited and Retarded Behavior by Ca2+ and Ca2+/OD Loading Rate on Ureolytic Bacteria in MICP Process

“…Thus, Ca 2+ /OD ratio should be a good parameter to describe the properties and behavior concerning Ca 2+ and microbes for the MICP process. The overloading effects observed by Fukue et al [16] can be associated with a critical Ca 2+ /OD ratio as the condition for the inhibition and retardation of MICP.…”

“…Then, Lai et al [14] focused on the retardation effects due to high Ca 2+ , while Cui et al [15] suggested that high urease activity is important for decreasing inhibition or retardation. On the other hand, it was found that the overload of Ca 2+ /OD caused the inhibition and retardation of MICP [16].…”

“…In the MICP technology, the numbers of alive cells to be used can be one of the most crucial factors which govern the carbonate precipitation process [16]. The cell viability presents the quantity of urease, which influences the total urease activity.…”

“…The urease activity governs the decomposition rate of urea in water. As a result, the carbonate precipitation induced can be influenced by the cell viability [15][16][17][18]. A sufficient viability of cell results in the full precipitation of carbonate under the concentration of Ca 2+ was provided, and relatively low viability may result in the retarded reaction.…”

“…However, there is a way to change this from a disadvantage to an advantage. By using the OD value, this can be achieved by defining the following relationships [16]:…”