Simultaneously removal of PAHs from contaminated soil and effluent by integrating soil washing and advanced oxidation processes in a continuous system: Water saving, optimization and scale up modeling

Abstract

Every year a large amount of clean water turns into contaminated effluent by soil washing (SW) process. The release of this effluent has become a growing environmental threat. In this study, a sustainable approach was developed for effective removal of PAHs from contaminated soil and the effluent by integrating SW and advanced oxidation processes (AOPs) in a continuous system. In the constructed continuous system, first small amount of clean water passed through the contaminated soil to remove PAHs. Then, the polluted effluent was treated by a quick AOPs and recycled for SW processes again and again until a complete removal of PHE be achieved. The performance of the continuous system was optimized and compared with batch system (no circulation) at lab scale. In addition, a scale up modeling was developed to predict the performance of continuous system at large scale. According to the results, under the optimum conditions: Tween 80 (TW80) = 6 g/L, ultrasonic = 160 kW, UV = 30 W, O3 = 5 g/h and TiO2 = 2 g/m2, the final PHE degradation efficiency of 98 % and 94 % were achieved by the continuous and batch systems after 130 and 185 min, respectively. The continuous system used 5 times less water volume than the batch system but resulted in better PAHs degradation. The scale up modeling revealed at large scale (100 kg soil), the continuous system could decrease the energy consumption and the required washing solution (water + TW80) up to 50 % and 80 %, respectively in comparison to the batch system. This work suggests a promising and practical approach for contaminated soil remediation without producing polluted water.