Treatment of polluted sediment through sediment washing and photoelectrocatalysis

Abstract

There are significant amounts of metals and organic pollutants found in aquatic environments due to an increase in urbanization and industrialization. These contaminated sediments are usually dredged out from the depth of the water in waterways for the safety of water transport and also from stormwater sediment ponds to reinstate their original capacity for settling of suspended solids. While it used to be common practice to dispose of contaminated sediments at sea, this is now often prohibited. Landfilling serves as an alternative, yet the challenge of mass management of contaminated sediments is a rising problem due to its high cost for remediation and limited available space for dumping. This thesis aims to investigate innovative sediment remediation techniques, through sediment washing by using eco-friendly leaching agents followed by photoelectrocatalysis (PEC), to address contamination challenges in sediment from both a marina and traffic runoff. PEC combines photocatalysis and electrocatalysis to effectively degrade organic pollutants and recover metals from polluted water. The study reveals promising results, with leaching methods showing potential in reducing copper (Cu) and zinc (Zn) concentration in traffic runoff sediment, although the marina sediment presented challenges. While reductions in organotin compounds, specifically tributyltin (TBT) and polycyclic aromatic hydrocarbons (PAH), were observed in the sediments, achieving significant risk class level reductions remained elusive. Optimal leaching agent selection for metal extraction proved to be difficult, yet the potential for metal extraction from sediment was evident. PEC treatment demonstrated potential in reducing Cu and Zn concentration from the leachates, requiring further study on metal recovery and environmental risk mitigation. For organic pollutants, a combination of soap and methanol with a reduction of up to 70% of TBT emerged as an effective leaching agent, with challenges when addressing both metals and organic pollutants. PEC showed potential in organic pollutant degradation (up to 99%) in the leachates. In conclusion, this research contributes valuable insights into the complexity of sediment washing, metal extraction, and organic pollutant degradation using PEC. It emphasizes the need for further investigations and highlights the importance of considering site-specific attributes when implementing remediation approaches.