BIODEGRADATION OF NO-2 DIESEL FUEL IN THE VADOSE ZONE - A SOIL COLUMN STUDY

Packed soil columns were used to simulate and investigate in situ biological remediation of soil contaminated with diesel fuel. We investigated and evaluated several operating strategies, including continuous flooding of the column soil with nutrient solution, and periodic operating cycles consisting of flooding followed by draining and aeration. The objectives were (a) to determine the extent of diesel fuel degradation in soil columns under four operating conditions (biologically inhibited control; continuous saturation with nitrogen and phosphorus amendments; periodic operation, consisting of flooding with nitrogen and phosphorus, followed by draining and forced aeration; and periodic operation, consisting of flooding with nitrogen, phosphorus, and calcium and magnesium amendments, followed by draining and forced aeration); (b) to evaluate CO2 production and oxygen consumption as indicators of biodegradation; (c) to monitor hydraulic conductivity under different operating strategies; and (d) to examine the system requirements for nitrogen and phosphorus. Our results showed that periodic operation promoted higher rates of biodegradation of diesel fuel in soil and minimized the use of water containing nutrient amendments, and consequently the possible need to collect and treat such water. We believe that monitoring CO2 and O-2 levels in situ may provide a means of optimizing the timing of flooding and aeration events to increase degradation rates. Results of this laboratory study will aid in improving the design and operation of field-scale bioremediation systems.