# Microbially Induced Desaturation and Carbonate Precipitation through Denitrification: A Review
## 4 Potential Applications of Denitrification-Based MICP Biotechnology
### MIDP-Driven Applications
Many previous studies have demonstrated that inclusion of small amounts of gas bubbles in soil results in a decrease in the degree of saturation which significantly increases  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Liquefaction** & & & & & \\
**Mitigation** & **Mechanisms** & **Costs** & **Negative Effects** & **Limitations** & **Author and Ref** \\
**Methods** & & & & & \\ \hline \multirow{4}{*}{Desaturation} & Inclusion of a small amounts of gas in the soil can add considerable compressibility to the observation of soil with porosity 50\% is from 0.25 to 0.31/m3 of saturated soil. & The estimated cost of electron donor and acceptor for 10\% (volume of gas/volume of water) & Traditional desaturation methods, such as & \\  & & & & \\ \cline{1-1}  & Inclusion of a small amounts of gas in the soil can add considerable compressibility to the observation of soil with porosity 50\% is from 0.25 to 0.31/m3 of saturated soil. & Traditional desaturation methods, such as & \\ \cline{1-1}  & Inclusion of a small amounts of gas in the soil can add considerable compressibility to the observation of soil with porosity 50\% is from 0.25 to 0.  
the compressibility of the pore fluid, and hence the cyclic resistance of the soil can be enhanced [77; 79; 80; 81; 82; 83]. As shown in Figure 5e, a section of soil is under overall confining effective stress \(\sigma^{\prime}_{3}\). When an external load (\(\Delta\sigma\)) is applied to the soil, by [PERSON]'s effective stress principle, the change in effective stress is:  
\[\Delta\sigma^{\prime}=\Delta\sigma-\Delta\mathrm{u} \tag{10}\]  
where, \(\Delta\sigma\): change in effective stress, \(\Delta\sigma\): external load, \(\Delta\mathrm{u}\): excess pressure. The excess air pressures (\(\Delta\mathrm{u}_{\mathrm{a}}\)) and water pressures (\(\Delta\mathrm{u}_{\mathrm{w}}\)) generated in the voids are equal if the surface tension between air and water is neglected due to air being in bubble form [84]. That means when an external load is applied, air and water in the pores experience the same excess pressure \(\Delta\mathrm{u}\). \[\Delta\mathrm{u}_{\mathrm{a}}=\Delta\mathrm{u}_{\mathrm{w}}=\Delta\mathrm{u} \tag{11}\]  
where, \(\Delta\mathrm{u}_{\mathrm{a}}\): excess air pressure, \(\Delta\mathrm{u}_{\mathrm{w}}\): excess water pressure. Based on the above equations, the relationship between the excess pore water pressure (\(\Delta\mathrm{u}\)) and the external load (\(\Delta\sigma\)) is deduced by [PERSON] [85] from the formula given below:  
\[\Delta\mathrm{u}=\frac{1}{1+\frac{\mathrm{n}\left[\mathrm{SC}_{\mathrm{w}}+ \frac{(1-\mathrm{S})}{\mathrm{u}_{\mathrm{a}}}\right]}{\mathrm{C}_{\mathrm{ s}}}} \tag{12}\]  
where, \(\Delta\mathrm{u}\): excess pressure, \(\mathrm{n}\): porosity, \(\mathrm{C}_{\mathrm{w}}\): compressibility of water (\(-0\)), \(\mathrm{C}_{\mathrm{s}}\): compressibility of soil, S: the degree of saturation. Considering Equation (12), when S = 1.0, since \(\mathrm{C}_{\mathrm{w}}\) is almost 0, the excess pore water pressure \(\Delta\mathrm{u}\) becomes equal to the applied load \(\Delta\sigma\). However, when S < 1.0, the excess pore water pressure \(\Delta\mathrm{u}\) is less than the applied load (\(\Delta\sigma\)). This means that the inclusion of gas in the voids can reduce the excess pore water, thereby providing mitigation of liquefaction. Based on the aforementioned theoretical approach, and the results of previous studies reporting liquefaction mitigation, upon injecting bubbles to the saturated soil, another potential application of microbial denitrification has appeared. In this novel approach, microbial denitrification was considered as a novel bio-based method to mitigate the liquefaction of saturated sand through the microbial production of \(\mathrm{N}_{2}\) and \(\mathrm{CO}_{2}\) gases (Figure 5d-f). MICP through denitrification generates \(\mathrm{N}_{2}\) gas which in the soil environment is entrapped between the precipitated crystals or between the bound soil grains.