Influences of the recalcitrant organic compound oleic acid on the floc characteristics and microbial community of activated sludge

The present study aims to investigate the impacts of a typical recalcitrant organic compound, namely oleic acid, on the floc characteristics of activated sludge, including extracellular polymeric substances (EPS) and polyhydroxyalkanoates (PHA) under different operation modes of a sequencing batch reactor (SBR). In addition, the morphological structure, sludge settling performance, and microbial community structure were further compared with those under a treatment system based on glucose as a substrate. The results showed comparatively lower EPS concentrations under the oleic acid-based SBR system than those observed under the glucose-based treatment system, particularly the polysaccharides (PS) contents of EPS. Furthermore, the oleic acid compound resulted in comparatively reduced PHA concentrations. The oleic acid-based SBR system revealed a better settling performance than that of the glucose control group, showing maximum sludge volume index (SVI) values of 170 and 633 mL/g, respectively. Indeed, the oleic acid-based SBR system inhibited the formation of filamentous sludge bulking. The obtained high-throughput sequencing results demonstrated the reduction effect of the recalcitrant oleic acid organic compound on the sludge microbial abundance and diversity. However, the relative abundance showed Mycobacterium a temporal increase over the experiment, reaching up to 16.66 % and, consequently, becoming the dominant microbial species. These findings provide a theoretical basis for the addition of recalcitrant biodegradable organic compounds to influents of actual wastewater treatment plants, outlining the impact of oleic acid on sludge floc characteristics.