# A Review on the Importance of Microbial Biopolymers Such as Xanthan Gum to Improve Soil Properties
## 3 Bioclogging Technique
### Bioclogging as Solution in Geotechnical Engineering  
The integration of engineering, microbiological and ecological studies is required to implement biological methods to improve the mechanical properties of soils, and bioclogging has an important role in this solution. Bioclogging involves the use of microorganisms, especially the ones that produce polysaccharides, which results in a positive correlation between the microbial biomass produced and the stability of soil [5; 15].  
Since the 1990s, some studies have attempted to use bioclogging tests to reduce soil permeability and diminish soil erosion [9]. Many water-insoluble polymers and gel formers of bacterial origin are produced by industry; these materials still only have limited use due to the cost involved and limited knowledge [11; 14].  
Consequently, laboratory tests have been carried out to identify the microbial groups that can be used for bioclogging. [PERSON] et al. [2] have shown that cultures of nitrifying and oligotrophic bacteria can be used for this purpose. The culture of autotrophic nitrifying bacteria grown in sand with dissolved ammonium produces microbial polysaccharides from the ammonium and from CO\({}_{2}\) in the air, which can reduce the hydraulic conductivity of the sand by about \(10^{-4}\) m/s to \(10^{-6}\) m/s. In the case of oligotrophic heterotrophic bacteria, they were grown in the sand with a low glucose concentration and produced polysaccharides that were also capable of reducing hydraulic conductivity in the same order [2; 8]. Some of the main different applications of bioclogging are presented in Table 2, showing their wide range, as well as some of the mechanisms and essential conditions for effective bioclogging [16; 17].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Group of microorganisms** & **Bioclogging’s Mechanism** & **Essential Conditions** & **Potential Geotechnical Applications** \\ \hline Algae and cyanobacteria & Formation of impermeable biomass layer & Penetration of light and presence of nutrients & Reduction in water infiltration \\ \hline Aerobic and facultative & & & \\ anaerobic slime-production bacteria & Production of slime in soil & Presence of oxygen and medium with ratio of C:N \(>\) 20 & Avoidance of cover for soil \\ \hline Nitrifying bacteria & Production of slime in soil & Presence of ammonium and oxygen in soil & Reduction in drain channel \\ \hline Sulphate-reducing bacteria & Production of undissolved sulfides of metals & Anaerobic conditions, presence of sulfate and a source of carbon in the soil & Formation of grout curtains to reduce the migration of heavy metals. \\ \hline Ammonifying bacteria & Formation of undissolved metals carbonates in the soil due to an increase in pH and release of CO\({}_{2}\) & Presence of urea and dissolved metal salt & Prevention of piping of earth dams and dikes. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Potential applications of bioclogging in Geotechnical Engineering (based on [PERSON] et al. [2]).  
A study by [PERSON] et al. [26] also claims that bioclogging can be used in industry to reduce fluid flow, improve oil recovery from reservoirs and repair cracks in concrete [16]. Bioclogging, as well as biocmentation, is a technique that has several features and has the potential to grow even more due to all the advantages presented in its use. What cannot be forgotten is the fact that it is a technique directly linked to the type of biopolymer used, so it is always necessary to choose the most appropriate type for the expected target [18].