PETROLEUM HYDROCARBON REMEDIATION IN BIOPILES: OPTIMIZING AERATION AND HEATING

摘要

A full-scale ex-situ bioremediation field study was carried out at the Soil Recycling Center (GRC) operated by Deme Environmental Contractors (DEC NV) in Kallo (Belgium), to evaluate the efficiency of aeration and heating for bioremediation in biopiles. An existing cell, 57 m long and 20 m wide, was filled up to a height of 1.8 m with contaminated soil. Both the aeration system and heating system consisted of pipes placed in the concrete floor of the cell. On top of the pipes a layer of gravel was placed to protect this construction. The soil was characterized as a clayey sand (texture: 70.8% sand, 17.7 % silt, 11.5% clay), the mean soil bulk density was 1.55 ± 0.09 g cm-3 at the start and 1.57 ± 0.07 at the end of the treatment period. Initial total hydrocarbon concentration was 1898 mg kg-1dry soil. The process was monitored during time by measuring the temperature and oxygen concentration weekly at different depths in the biopile. Two types of respirometry testing were done: the transient respirometry test proposed by Hinchee et al. (1992) and a static respirometry test as described by Patterson et al. (1999). The total petroleum hydrocarbon (TPH) concentration was measured at different times and the treatment was stopped when an average concentration of 500 mg TPH kg-1 was reached. The biopile operation began late September 2001 and concluded beginning of December 2001. TPH, oxygen concentrations and temperature values showed that very heterogeneous conditions existed in the biopile. The oxygen concentrations during aeration were at atmospheric level at every depth in the biopile, suggesting that aeration was more than sufficient. Assuming that optimal bacterial activity does not need atmospheric oxygen levels, a discontinuous aeration system would be more economical. Although respiration tests showed a decrease of biological activity over time, the estimated degradation rate was low, when compared to the decrease in hydrocarbon concentration. Further research will be needed to optimize the design of a discontinuous aeration system by oxygen concentration measurements and respiration tests.