Revealing the behavior of perfluorooctane sulfonic acid in an aerobic granular sludge system: Fate and impact

Abstract

The biogeochemistry (i.e., migration and transformation) and impacts of perfluorooctane sulfonic acid (PFOS) in an aerobic granular sludge (AGS) system have been studied. The results suggested that PFOS removal rates under 0.1, 0.5 and 5.0 mg/L PFOS treatment were 89.23 ± 0.92 %, 71.92 ± 1.45 % and 48.15 ± 1.90 %, respectively, which was mainly attributed to the adsorption mechanism involving electrostatic, hydrophobic and ionic bridging interactions. Meanwhile, the adsorbed PFOS deteriorated sludge flocculation. Compared with the control, 0.1 mg/L PFOS treatment increased the concentration of effluent suspended solids (ESS) from 70 ± 5 to 238 ± 15 mg/L. Interestingly, the denitrification performance of the AGS improved (i.e., total nitrogen (TN) average removal rate increased from 87.05 ± 0.21 % to 96.56 ± 0.05 %), which was contrary to the outcomes for activated sludge. Further analysis showed that PFOS reduced the percentage of norank_f_norank_o_Ardenticatenales, norank_f_Sphingomonadaceae and Candidatus_Competibacter maintaining the particle stability, which led to the decrease in AGS flocculation. In addition, the relative abundance of nitrite-oxidizing bacteria Nitrospira decreased under PFOS exposure, while the total abundance of denitrifying bacteria (mainly Dechloromonas) increased. This might enhance the short-cut nitrification and denitrification capacity of the AGS system and promote the removal of TN. However, PFOS had no obvious impact on the settleability of AGS and the transformation of chemical oxygen demand (COD) and soluble phosphorus (SOP). Our findings will provide theoretical insights and practical support for risk control in the process of treating fluoride-containing wastewater.