Occurrence and fate of substituted polycyclic aromatic compounds in petrochemical refinery and coking wastewater treatment plants

Substituted polycyclic aromatic compounds (PACs) are an emerging class of contaminants in industrial wastewater, yet their occurrence and fate remain unknown. This study investigates the presence of 30 alkylated PACs and 14 heterocyclic PACs in wastewater and sludge from two different industrial facilities: a steel mill and a petrochemical refinery. Through a 3-day field sampling campaign, we collected industrial sludge and wastewater samples and characterized the occurrence of substituted PACs through a validated state-of-the-art gas chromatography - tandem mass spectrometric technique. Standard wastewater quality indicators were also determined to assess the effectiveness of existing treatment methods in removing substituted PACs. Principal component analysis revealed that the occurrence of substituted PACs and the standard wastewater quality indicators varied depending on the partitioning of PACs in wastewater or sludge media. In the biological treatment step at the petrochemical refinery, the influent contained three times more substituted PACs than at the steel mill. However, the sludge at the refinery held up to 15 % less substituted PACs than the steel mill. The biological treatment step at the petrochemical refinery demonstrated complete mineralization of substituted PACs through biodegradation, while the steel mill treatment plant primarily relied on sludge biosorption for PAC removal. This study could identify the differences in the effectiveness of treatment methods adopted by steel mill and petrochemical refinery in removing substituted PACs. • More substituted PACs dominate final effluent than parent PAHs of both industries. • Dissolved air flotation increased dissolved PACs in refinery wastewater treatment. • Substituted PACs correlate with TS and TOC, suggesting particulate adsorption. • Substituted PACs removed via biosorption at steel mill; biodegradation at refinery.