SELECTIVE BIOAUGMENTATION OF DIESEL-CONTAMINATED SOIL AND GROUNDWATER

摘要

In 1991 a diesel fuel spill from an above ground water storage tank resulted in over 23,000 cubic meters of soil groundwater contamination at an electric power facility in Vega Baja, Puerto Rico. Soil pollution was present in both saturated and non-saturated zones. Restoration of these and similar events can be accomplished through biological means. In this case biodegradation of diesel was accomplished using in-situ bioremediation techniques. First, biostimulation in non-saturated zones was carried out by injecting air and nutrients periodically into the soil through multiple wells. Due to oxygen limitation in saturated zones a nitrate solution was injected along with nutrients to provide an alternate electron acceptor. Monitoring methods included measurements of pH, conductivity, total heterotrophs and concentration of nitrate, nitrite, sulfite, ammonia, iron, and phosphate. Nitrate concentration never surpassed the established limits of contamination suggesting bacterial activity under denitrifying conditions in the saturated zone. Furthermore, bioaugmentation was employed as a complementary strategy in areas of extreme contamination. Indigenous bacteria were grown ex-situ under denitrifying conditions and then inoculated in hot spot areas. After one year of treatment, TPH revealed a decrease in diesel concentration to cleanup standards in nearly 85% of total affected area. Both, biostimulation and selective bioaugmentation were proven to be efficient in the restoration of this site.