# Fire-Induced Changes in Soil and Implications on Soil Sorption Capacity and Remediation Methods
## 4 Fire-Induced Changes in Soil and Choice of Soil Remediation Technologies
### Biological Remediation Methods
#### 4.3.2 Bioremediation  
Bioremediation involves the use of microorganisms to alter contaminant migration or transformation in the soil environment through extracellular complexation, precipitation, oxidation-reduction reaction and intracellular accumulation [135; 152]. Though these methods are mainly used to treat soils contaminated with organic pollutants, they have also been successfully used to treat soils contaminated with heavy metals [135; 152]. Biodegradation is a natural process occurring in most contaminated environments and is often referred to as natural attenuation. The natural rate of this process is very slow, and so the contaminated environment is usually enhanced to improve its natural attenuation capacity. Methods of enhancements could be in situ (bioventing, biostimulation, bioaugmentation) or ex situ (biopilling, landfarming and bioreactor) [153; 154]. Bioremediation methods like bioventing, which require the presence of autochthonous population of microorganisms capable of breaking down the contaminants in the soil [153; 154], would be ineffective on fire-affected soils, because most if not all of these microorganisms would have been eliminated by the fire. Biostimulation involves addition of nutrients to the contaminated site to improve the metabolic activities of indigenous microorganisms, thereby accelerating the rate of degradation of contaminants [155]. Biodegradation of contaminants by soil microbes is limited by nutrients, pH, temperature, moisture, oxygen, soil properties and contaminant presence. Improving these conditions in the soil environment would improve the rate of contaminant degradation and transformation by microbes in the soil environment. Biostimulation also requires the presence of autochthonous microorganisms at the contaminated site. It has been used to treat organic soil pollutants including polyaromatic hydrocarbons, non-halogenated volatile organic compounds, and petroleum in soils and aquifers but has been rarely used in the remediation of heavy metal-contaminated soil [156]. On its own, it may not be suitable as a remediation method for fire-affected soils, where the population of microorganisms would have been drastically reduced by the fire. However, if combined with bioaugmentation to ensure the presence of suitable microorganisms to act on the contaminant, biostimulation could be effective on fire-affected soils. Bioaugmentation of the soil involves the introduction of microorganisms capable of degrading the contaminant of concern in the contaminated environment to enhance natural attenuation at the site [153]. A major challenge with this method would be the establishment of the inoculated bacteria at the site, especially if it is not adapted to the new environment. Considering that this method does not rely on autochthonous microorganisms, it could be used to treat fire-affected soils after they have been biostimulated. Fire events also destroy soil organic matter from which most microbes derive the necessary energy. To ensure the survival of the inoculated microbes in the contaminated soil, soil conditions would have to be optimized by providing the necessary pH and nutrient levels that support their growth. Biopilling is an ex situ bioremediation technique that could also be used to treat fire-affected soil. In biopilling, contaminated soils are excavated after which, nutrients are added, followed by aeration to enhance microbial activities [153; 157]. The involvement of excavation in this method implies it is practical when the volume of contaminated soil is small. Another ex situ remediation method involves using a bioreactor in which contaminated samples are fed. The reaction conditions in the bioreactor are manipulated to optimize bioremediation time. According to [PERSON] et al. [153], process parameters in the bioreactor including temperature, pH, agitation and aeration rates, substrate and inoculum concentration, nutrient content can be easily controlled to enhance bioremediation through bioreactors.