Degradation of extracellular polymeric substances (EPS) extracted from activated sludge by low-concentration ozonation

Reaction mechanisms between ozone and extracellular polymeric substances (EPS) can be the key of understanding the improvements in microbial aggregates properties by low-concentration ozonation. In this study, EPS are extracted from activated sludge and treated continuously by ozone gas at 270 +/- 41 ppm. The reaction between ozone and EPS was investigated by observation of EPS component concentrations, functional groups and molecular weight distributions using UV-Vis spectrometry, excitation-emission matrix fluorescence spectroscopy (EEM), high performance size-exclusion chromatography (HPSEC) and gas chromatography-mass spectrometry (GC MS). In a 12-hour-ozonation experiment, significant ozone consumption was observed in the first 4 h and protein concentration in EPS solution was reduced by 30 +/- 12%. However, the polysaccharides concentration only had a slightly decrease at the end of the ozonation process. UV Vis spectra and EEM spectra results suggest that ozone removed protein and fluorescent matters (SMP and tryptophan-like aromatic protein) rapidly by attacking specific amino acid residues on polypeptide chain. After ozonation, the molecular weight of polysaccharide and protein dropped by 4 orders of magnitude according to HPSEC results. TOC concentration of EPS solution was reduced by 13 +/- 2% after ozonation. The loss in TOC could be explained by the observation of volatile organic compounds such as carboxylic acids, aldehydes and ketones in the off gas detected by GC MS. The results in this study can provide a better understanding towards the mechanisms of improvements in activated sludge properties by ozonation. (C) 2015 Elsevier Ltd. All rights reserved.