Slurry-Phase Bioremediation of Creosote and Petroleum-Contaminated Soils

Abstract

Successful bioremediation often is difficult to achieve because of complex interactions between contaminants, the soil environment, and decomposer organisms. The objective of this work was to study the extent and pattern of contaminant biodegradation during slurry-phase bioremediation of four industrially-contaminated soils (<3% contamination) to obtain further insight into the factors which may control biodegradation. Two soils (sand and silty clay) were contaminated with creosote compounds, and two soils (loam and clay loam) were contaminated with petroleum compounds. Two liter glass jars containing 300g soil and 300ml nutrient solution (300g soil and 100ml nutrient for sand), and 5% inoculum of previously bioremediated soil containing an active culture, were rotated at 3rpm at 22°C in the dark for 10 weeks. Biodegradation was monitored by measuring reductions in total dichloromethane-extractable organics (TEO), selected polycyclic aromatic hydrocarbons (PAHs), and thermal extraction GC-FID detectable component classes of contaminant compounds. Degradation of TEO over 10 weeks was most extensive in the clay soil (43%) and least in the sand soil (25%). The rate of TEO biodegradation slowed, or plateaued, in the clay soil after 2–4 weeks. Degradation of total GC-elutable compounds was 1.4- (sand) to 2.7-fold (loam) greater than TEO degradation, and a plateauing of some GC-elutable component classes occurred in most soils within 10 weeks. Plateauing of contaminant concentrations in soils was attributed to bioavailability limitations due to strong partitioning into the residual contaminant matrix. In addition, microbial competence limited biodegradation in the sand soil.