Soil bioremediation

Biological treatment, whether of excavated soil or of soil and groundwater still in place, involves using micro-organisms to transform toxic chemical substances into non-toxic ones. The micro-organisms used are often bacteria, although fungi play a role in some ex situ treatments. Bioremediation of soil and groundwater involves the implementation, or at least the participation, of various processes such as diffusion and advection (which in short are often referred to as dispersion), sorption and desorption, and biodegradation. For biological soil remediation to take place, the specific micro-organisms and target compounds must be in contact to initiate the reaction. Moreover, if the number of micro-organisms is insufficient, or if they are not sufficiently active, little or no degradation will take place. Biological treatment of soil not only depends on favorable conditions for the biodegradation of pollutants, but also on the techniques operating with acceptable efficiency, speed and cost. Good process control therefore requires knowledge of soil science and process engineering.

Biological treatments have the following advantages:

• are destructive processes that avoid the transfer of pollution;

• to be among the most profitable treatments;

• have a positive impact on public opinion.

This decontamination technique is only applicable :

• only for compounds that are biodegradable, non-inhibiting and non-toxic, as some metabolites may be more toxic (to micro-organisms and to humans) and sometimes more stable than the original contaminant;

• than for in-situ applications, since the permeability of the subsoil must be greater than 10 ^–6 m/s ;

• only when the duration of treatment is not inconvenient, as it generally extends over several months or, in some cases, years.