The ENA pilot test involved the injection of an organic substrate into the aquifer in order to generate favorable environmental conditions for the metabolic activity of sulfate-reducing bacteria, strictly anaerobic bacteria that, under reducing conditions, use sulfates as terminal electron acceptors for metabolic respiration reactions resulting in the formation of sulfides. In groundwater sulfides can than react with bivalent metals, such as Cd and Zn, producing metal sulfides, insoluble salts that precipitate settling in the soil.

High levels of heavy metals, such as Cadmium and Zinc, have been found in groundwater of an Industrial area. The removal of these pollutants by conventional water treatment techniques has numerous disadvantages from both environmental and economic perspectives.

In this site, after a baseline microbiological characterization, the Enhancend Natural Attenuation (ENA) technique was selected for bioremediation of metal-contaminated groundwater. The pilot test of ENA involved the injection of an organic substrate into the aquifer in order to generate favorable environmental conditions for the bacterial formation of sulfides. In groundwater sulfides can than react with bivalent metals, such as Cd and Zn, producing metal sulfides, insoluble salts that precipitate settling in the soil.