ASSESSING MINERALIZATION RATES OF PETROLEUM-HYDROCARBONS IN SOILS IN RELATION TO ENVIRONMENTAL-FACTORS AND EXPERIMENTAL SCALE

Mineralization rates of non-volatile petroleum hydrocarbons (HCs) in f ive different oil-contaminated soils with initial HC contents ranging from 0.1 to 13 g kg(-1) are estimated as a function of environmental f actors. The aim of the study is threefold, (i) to study the relevance of environmental factors that may influence the mineralization rate, ( ii) to compare mineralization rates estimated in two experiments at di fferent scales, after standardizing them to environmental reference co nditions, (iii) to evaluate the CO2 production rate as a measure for t he mineralization rate of HCs. Experiments were performed at laborator y scale (30-50 cm(3) soil volume) in closed-jars under constant enviro nmental conditions and in lysimeters (0.81 m(3) soil volume) under dyn amic climatic and hydrological conditions. A biodegradation model, cou pled to transport models for soil heat, water, and gas dynamics is emp loyed for data interpretation. The transport models are used to simula te the environmental conditions that influence the mineralization rate in the non-steady lysimeter experiments. The results show that temper ature, O-2 concentration and HC content have an effect on the minerali zation rates. Water content could not be identified as a direct govern ing environmental factor. However, an indirect effect of water content is that it influences the effective gas diffusion coefficient in soil s. The CO2 production rate seems to be a good quantity to express the mineralization rate of HCs for HC contents > 1 g kg(-1). Measured CO2 production rates standardized to reference conditions are similar for the two different experimental scales. This demonstrates that the usag e of biodegradation rates obtained in the laboratory to predict the bi odegradation rates under field conditions is sound, as long as the dif ferences in environmental conditions have been taken into account.