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Bioreactors for Soil and Sediment Remediation

Bioremediation methods are being increasingly used to clean up contaminated soils and sediments. In many applications they can be cost effective compared to other alternatives such as thermal or physical chemical treatment methods. The bioremediation of soils and sediments can be either accomplished by in situ methods where these materials are treated in place without disturbing the site, or ex situ techniques where the materials are excavated and treated in a separate reactor. In this paper only the ex situ techniques will be discussed. In the ex situ treatment process the soils/sediments are excavated (or removed from the site) and placed in reactors where they are biodegraded in presence of nutrients (N, P, ‘e’ acceptors, cometabolites, etc.) under controlled environmental and mixing conditions. In general, the ex situ process is faster than the in situ process and a more thorough treatment of the soil/sediment can be accomplished. The disadvantages of ex situ processes include site disturbance and removal of soil/ sediment during which workers could be exposed to contaminants if proper precautions are not taken and increased costs. However, the increased costs should be weighed against shorter time of treatment and a more thorough treatment by these processes. The soil/sediment could be placed back at the site after treatment provided regulatory requirements were met. Most of the existing literature on bioremediation deals with contaminated soils rather than sediments. However, it is expected that the research information dealing with the contaminated soils will be in almost all cases applicable also to the sediments. In this presentation the literature information presented are for contaminated soils but they will most likely be applicable also to the contaminated sediments.