Treatment of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in stormwater using polishing columns with biochar and granular activated carbon

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) and Polychlorinated Biphenyls (PCBs) are recalcitrant organic pollutants often detected in stormwater. Various stormwater control measures (SCMs) can remove PAHs and PCBs by filtration, adsorption, and biodegradation. However, dissolved PAHs and PCBs remain present in the treated outflow of SCMs. To provide further treatment, two types of biochar (biochar A and biochar B), a granular activated carbon (GAC), and a regenerated GAC (RAC) were tested in a column study with synthetic stormwater containing PAHs and PCBs in low concentrations. Results showed that PAH concentrations were reduced by 98.2-99.8% (range: <limit of quantification (LOQ) - 1.89 ?g/L), while PCB concentrations were reduced by 86.0-97.9% (range: <LOQ - 0.7 ?g/L). The extraction of PCBs from the media showed that >62% of the PCBs accumulated at the first third of the column due to adsorption onto the black carbon material thus providing information for management. The difference in treatment performances of different PAHs and PCBs may be caused by the molecular structure of the contaminants. Lifetime calculations indicated that biochar had lifetimes >36-51 years, while GAC and RAC showed lifetimes longer than 147 and 206 years, respectively, based on predicted precipitation for scaled up designs. The results showed that biochar and activated carbons can be efficient adsorbents for stormwater polishing treatment. With consideration of efficiency, sustainability and cost, RAC is recommended for polishing treatment of dissolved PAHs and PCBs.