Carbon-Based Technologies for Remediating Polychlorinated Biphenyls in Contaminated Sediment
Polychlorinated biphenyls (PCBs) are persistent hydrophobic compounds that are present widely in the environment. Due to poorly maintained hazardous waste sites, electrical equipment leakage, and illegal disposal, compounds like PCBs were deposited in sediments present in bays and estuaries. PCBs continuously partition into the overlying water posing a long-term exposure risk to the environment and human health. This dissertation demonstrates the efficacy of carbon-based materials in reducing the partitioning of PCBs from sediment to the water column and analyzes their efficiency for managing PCBs in sediment in the Houston Ship Channel and Galveston Bay System (HSC-GBS) using the Environmental Fluid Dynamics Code (EFDC) water quality model. Both existing carbon-based materials [activated carbon (AC), black carbon (BC)] and emerging nanomaterials [graphene (GE), graphene oxide (GO), carbon nanotube (CNT)] were tested to determine their efficacy to bind PCBs in sediment. The comparison between the sorbents was accomplished by examining their distribution coefficient (Ks). The magnitude of Ks provides an idea about the bioavailable fraction of PCBs in the system; the higher the Ks, the greater the strength of sorption by the sorbent and therefore, the lower the PCB bioavailability. The EFDC model grid was developed for the HSC-GBS and the Toxics module was used to simulate the fate and transport of five PCB congeners (PCB-1, PCB-3, PCB-11, PCB-17, and PCB-25). Model sensitivity was examined and the model was most sensitive to sediment PCB concentrations and partitioning properties. Results from the sorption experiment indicated that CNT performed the best overall followed by AC, BC, GO and GE. Results indicated that the Ks value for CNT was 1.16, 1.15, 1.13 and 1.04 log units greater than GE, GO, BC, and AC. The EFDC results showed a significant dependence between the change in organic carbon in sediment and the partitioning coefficients in the sediment bed, against the concentration of PCBs in the water column. Modeling results also demonstrated that there was an average reduction of 35% in the concentrations in the HSC-GBS when carbon-based materials were added to sediment.