The widespread use of perfluorooctanoic acid (PFOA) has rendered its frequent detection in wastewater. The tolerance and recovery of aerobic granular sludge (AGS) to PFOA were investigated in short-term (Phase Ⅰ) and long-term (Phase Ⅱ, operation strategy adjustment: shortening aeration time and prolonging anaerobic and anoxic time). Results showed that in Phase Ⅰ, the performance of R2 reactor (0.05 mg/L PFOA) was slightly negatively affected, while 0.5 and 2.0 mg/L PFOA in R3 and R4 reactors significantly damaged the key enzyme activities of AGS, leading to deterioration of nutrients removal. TN and TP removal efficiencies decreased correspondingly from 79.32% to 78.41% on day 0 to 74.66% and 74.14% in R2 and 68.57% and 67.80% in R3 and 56.94% and 57.47% in R4 on day 7, respectively. In Phase Ⅱ, the key enzyme activities of AGS were obviously renewed dependent on operation strategy adjustment and AGS self-regulation. The performance of AGS in R2 (continuously dosing 0.05 mg/L PFOA) and R4 (stopping dosing PFOA) recovered quite good, while the long-term adverse effects of 0.5 mg/L PFOA on AGS in R3 were still more difficult to be alleviated. In end of Phase Ⅱ (69-97days), the average TN and TP removal efficiencies correspondingly reached 83.31% and 82.09% in R1 (control), 80.67% and 79.62% in R2, 76.38% and 74.27% in R3, and 79.01% and 78.25% in R4, respectively. Further analysis revealed that the effect of PFOA on proteins in extracellular polymeric substances (EPS) was greater than that on polysaccharides. Specifically, short-term dosage of PFOA mainly affected loosely bound EPS, while long-term dosage of PFOA affected tightly bound EPS. Although AGS is severely inhibited by short exposure to 2.0 mg/L PFOA (in R4), after the operation strategy adjustment, EPS content decreased, nutrient and oxygen transport channels of AGS were re-established, which contributed to the recovery of AGS.
Keywords: Aerobic granular sludge; Extracellular polymeric substances; Operation strategy adjustment; Perfluorooctanoic acid; Sludge recovery.
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