Environmentally friendly laboratory-scale remediation of PAH-contaminated soil by using pressurized hot water extraction coupled with pressurized hot water oxidation

Abstract

Water is an alternative solvent and reaction medium to many conventional organic solvents. In pressurized hot water extraction (PHWE) and pressurized hot water oxidation (PHWO) the altered physico-chemical properties of heated and pressurized water are exploited for the treatment of wastes in solid and liquid states. On-line coupled PHWE and PHWO equipment was used to extract polyaromatic hydrocarbons (PAHs) from a soil sample and then to destruct them with potassium persulfate as oxidant. In PHWE experiments, study was made of the effects of flow direction and flow rate in the extraction vessel on the recovery of PAHs. Compared with Soxhlet extraction, PHWE gave better recoveries overall. In PHWE–PHWO, temperature, flow rate (reaction time) and oxidant concentration affected the conversion of the PAHs. It was important that temperature was high enough and reaction time long enough for effective oxidation. These parameters had thus to be chosen carefully for optimal results. Under optimized conditions almost 100% PAH conversions were obtained, and also a clear reduction in total organic carbon content of the effluent was evident. However, some organics remained in the effluent after the procedure, and a considerable amount of sulfate was released in water. Further treatment of the effluent is thus required as a final step.