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 glucosebased 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.