A Sequencing Batch Reactor (SBR) with activated sludge was operated with synthetic wastewater containing ibuprofen (IBU) to investigate the biomass stress-responses under long-term IBU exposure. There were 3 different phases: phase I as the control without IBU for 56 days, phase II (40 days), and phase III (60 days) containing IBU at 10 and 5 mg L-1 each. The overall performance of the SBR as well as the extracellular polymeric substances (EPS) in terms of polysaccharides, proteins, and humic acid substances were estimated. Morphological parameters of microbial aggregates in the presence of IBU (phase II and phase III) were assessed by quantitative image analysis (QIA). Removal efficiencies of chemical oxygen demand (COD) and ammonium (NH4+) were significantly reduced by IBU. Loosely bound EPS (LB-EPS) decreased during phase II and phase III, and tightly bound EPS (TB-EPS) was slightly higher in phase II than phase I. TB-EPS proteins were greater in phase II, perhaps to protect microbial cells from IBU exposure. These findings provided insight into both activated sludge stress-responses and EPS composition under long-term IBU exposure. Spearman correlation showed that EPS and morphological parameters significantly affected sludge settleability and flocculation. QIA also proved to be a powerful technique in investigating dysfunctions in activated sludge under IBU exposure.
Keywords: Activated sludge; Extracellular polymeric substances; Loosely bound EPS; Quantitative image analysis; Tightly bound EPS.
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