Mobilisation of bacteria in soils by electro-osmosis.

A prerequisite for effective bioremediation of contaminated soil is the presence of microorganisms able to degrade the contaminants. If such microorganisms are absent initially, dissemination of bacteria and nutrients becomes necessary; this is a challenge, especially in dense soils. We studied the feasibility of disseminating bacteria by electro-osmosis in three different soil types; garden soil, fine sand, and clay. We tested migration velocities in a horizontal gel electrophoresis setup and used microcosms specially designed with electrodes in order to simulate field conditions. When an electric current is applied, the bacteria co-migrate with water to the cathode. Results were compared to those of controls without electricity, showing that electro-osmosis stimulates bacterial spreading even in low-permeability soil such as clay, although the migration velocity was lower than in the other soils tested. In fine sand, the bacteria migrated ca. 1 cm h(-1), in garden soil ca. 0.6 cm h(-1), and in clay ca. 0.1 cm h(-1). Phenol served as a growth substrate in the microcosm tests; it appeared to improve the migration of bacteria and the number of recoverable bacteria in most tests. In clay, a moisture gradient formed, which is a factor to consider in designing field applications.