Investigation of the degradation of pentachlorophenol in sandy soil via low-temperature pyrolysis

Thermal treatments are the primary technologies used to simultaneously remove high-concentrations of pentachlorophenol (PCP) and polychlorinated dibenzo dioxins/furans (PCDD/Fs) from contaminated soils such as the An-Shun soil, Taiwan. However, the high cost of energy required and the potential formation of dioxins during the incineration/combustion of PCP have limited their applications. In this study, an investigation of PCP pyrolysis in sandy soil at a relatively low temperature range (200-400°C) was conducted. Temperature and heating time required to achieve the maximum removal efficiency of PCP and its byproducts from soil were investigated. Additionally, primary pathways leading to PCP removal from sandy soil were studied. The experimental results showed that a significant portion of PCP (>90%) and its byproducts were removed from the soil at 350°C with a treatment time of 40 min. The PCP decay rate constant increased exponentially from 0.20 min(-1) to 1.98 min(-1) as the operating temperature was increased from 200°C to 400°C. While pyrolysis and desorption are the main degradation pathways, detection of lower chlorinated phenols in the gas/soil indicates that dechlorination of PCP occurs during the degradation process. Low levels of PCDD/Fs were detected in the soil/gas during the pyrolysis of PCP-contaminated soils.