BIOVENTING OF DIESEL OIL-CONTAMINATED SOIL - COMPARISON OF DEGRADATION RATES IN SOIL BASED ON ACTUAL OIL CONCENTRATION AND ON RESPIROMETRICDATA

The effects of bioventing, nutrient addition and inoculation with an o il-degrading bacterium on biodegradation of diesel oil in unsaturated soil were investigated, A mesocosm system was constructed consisting o f six soil compartments each containing 6 m(3) of naturally contaminat ed soil mixed 1:1 with silica sand, resulting in a diesel oil content of approximately 2000 mg kg(-1). Biodegradation was monitored over 112 days by determining the actual diesel oil content of the soil and by respirometric tests, The best agreement between calculations of degrad ation rates based upon the two methods was in July, when venting in co mbination with nutrient addition resulted in degradation rates of 23 m g kg(-1) day(-1) based on actual oil concentration in the soil and 33 mg kg(-1) day(-1) calculated from respirometric data, In September, th ese rates decreased to 9 and 1.4 mg kg(-1) day(-1), and in October the degradation rates were 5 and 0.7 mg kg(-1) day(-1) based upon the two methods, The average ambient temperature during the respirometric tes ts was 14, 10 and 2 degrees C in July, September and October, respecti vely, The combination of venting and nutrient addition resulted in an average residual oil content of the soil of 380 mg kg(-1). Neither ven ting alone nor inoculation enhanced oil degradation. The respiratory q uotient averaged 0.40, The oil composition changed following degradati on resulting in the unresolved complex mixture constituting up to 96% of the total oil content at the end of the experimental period.