What is in-situ bioremediation?
In-situ bioremediation refers to treatment of contaminated soil in place, without the need for excavation. As with ex-situ bioremediation, it uses natural biological processes to permanently degrade contaminants and is very cost effective compared to alternative soil remediation methods. Since there is no soil excavation involved, there is minimal site disruption and plumes of contamination present underneath buildings can also be treated.
Organic contaminants persist in the subsurface because environmental conditions are not suitable for the microbial activity that results in biochemical degradation. By understanding the biological principles under which these contaminants are degraded we can optimise environmental conditions for maximum rate of site remediation.
Biostimulation vs bioaugmentation
Biostimulation involves adding nutrients such as nitrogen and phosphorus, as well as oxygen and other electron acceptors to stimulate the existing soil microbial population into multiplying and degrading the contaminants of concern. On the other hand bioaugmentation is the introduction of large numbers of specific laboratory grown microorganisms selected for their ability to degrade certain chemical contaminants such as petroleum hydrocarbons. Although this may appear to be a good idea, in practice it can be difficult to establish introduced microorganisms in large enough numbers to make a significant difference in the rate of in-situ bioremediation. This is often due to inability to compete with the natural microbial population already present, or inability to thrive under site specific conditions of pH, soil type and so on.
Bioventing is a term used for the process of aerating soils to stimulate in-situ biological activity and promote bioremediation. At its simplest it involves blowing air into, or drawing air through, the unsaturated zone through injection boreholes to increase subsurface oxygen levels and hence promote aerobic bioremediation. It is often the most cost-effective and efficient technology available for vadose zone remediation of hydrocarbon contaminated sites.
Biosparging is a method of in-situ bioremediation of groundwater and soil within the saturated zone by injecting air into the groundwater to increase dissolved oxygen levels. Biosparging can be used to reduce concentrations of organic contaminants such as petroleum hydrocarbons that are dissolved in groundwater, adsorbed to soil below the water table, and within the capillary fringe. When volatile contaminants are present, biosparging is often combined with soil vapour extraction. The vapour extraction system creates a negative pressure in the vadose zone through a series of extraction wells that control the vapour plume migration.
Oxygen release compounds
Introduction of oxygen release compounds is another approach to enhancing aerobic bioremediation in the saturated zone. Commonly used compounds include calcium peroxide, magnesium peroxide and proprietary oxygen-releasing compounds. This technique can be used to address source areas or entire plumes.
Oxygen release compounds are usually introduced into the saturated zone in slurry or solid form. This can be done in several ways:
- Injecting as a slurry using direct push drilling (e.g., Geoprobe).
- Placing the compounds into drilled boreholes or excavations.
- Mixing oxygen release compounds with contaminated soil and then using the mixture as backfill.
- Suspending oxygen release compounds contained in "socks" in groundwater monitoring wells.
Aerobic vs anaerobic bioremediation
Although the majority of commonly found organic contaminants such as petroleum compounds degrade best in an aerobic environment, i.e., use oxygen as an electron acceptor, some contaminants require anaerobic conditions. Usually bacteria, these microorganisms can use alternative electron acceptors such as nitrate, sulphate and other organic substrates.
Injecting proprietary remediation products such as DCL-Biosolv is particularly effective for the in-situ anaerobic bioremediation of chlorinated solvents such as perchloroethene and trichloroethene.
Telluric Land Remediation has been undertaking in-situ bioremediation since the 1990s and has successfully completed a large number of contracts throughout the UK. We will design, build and install a system that is optimised for your site taking into account local geology, contaminant types and concentrations, and any on-going site operational activities.
Case studies of land remediation projects using in-situ anaerobic bioremediation for the treatment of trichloroethene and in-situ aerobic bioremediation for treating petroleum hydrocarbons can be viewed by following the links.
Typical contaminants that are amenable to treatment by in-situ bioremediation include, for example:
- Petroleum hydrocarbons
- Lubricating oils
- Polycyclic aromatic hydrocarbons
- Phenols and cresols
- Chlorinated solvents
In-situ bioremediation case studies
- Permeable Reactive Barrier for Tetrachloroethene
- In-Situ Bioremediation on a Manufacturing Site
- Land Remediation Following Domestic Heating Oil Spill
- Bioremediation on a Housing Development Site
- In-Situ Bioremediation Using DCL Biosolv
- Contaminated Land Remediation on a Housing Development
- Groundwater Remediation for Oil and Trichloroethene Contamination
- Remediation of a Contaminated Playing Field
- Groundwater Remediation for Trichloroethene Contamination