Bacteria-assisted phytoremediation to cure soils and groundwater contaminated with organics

Abstract

Trees can pump 200 liters of groundwater per day and in this way attract high amounts of contaminants. This process is completely solar powered. Moreover, some of these trees such as poplar and willow are phreatophytic, meaning their roots always reach the groundwater, even on e.g. 10 m depth. Organics can be degraded by plants and their associated bacteria. The plant itself often has different strategies to cope with organics (going from sequestration, transformation to degradation). The plant-associated bacteria are from nature present allover (on and inside) the plant. Next to the well known pathogenic bacteria, beneficial bacteria are ubiquitous. These bacteria can promote plant growth and development and might even be able to degrade the organic contaminants. They are localized in the plant’s transport system (xylem vessels), which can act as a catalyst to degrade the contaminants. In case of natural phytoremediation, the degradation capacity remains uncontrolled. The degradation efficiency is affected by the plant species as well as by the present microorganisms. If degradation fails, plants might suffer from phytotoxicity and volatile contaminants can be transported from the soil and groundwater through the leaves to the atmosphere. In order to ensure an efficient degradation, bacteria with the appropriate characteristics are enriched inside the plant by means of inoculation. The ideal bacteria to inoculate are bacteria that are capable of degrading the desired contaminant, are living in the rhizosphere and/or inside the plant and have plant growth promoting traits. In case of bacteria-assisted phytoremediation, all trees are provided with a drainage tube in their rooting zone when they are planted. In this way the trees can be enriched with these ideal bacteria by adding them through the drainage tube. Evapotranspiration measurements guarantee there are no significant amounts of contaminants transported to the atmosphere.