Influence of slowly biodegradable organic matter morphology on sludge floc characteristics and microbial colony development

Slowly biodegradable organic matters play an important role in sewage treatment because of their complex structure and slow degradation. This study compared the sludge floc characteristics and microbial colony growth of different substrate forms, namely particulate (particulate starch) and dissolved (dissolved starch) slowly biodegradable organic matters, in different operational modes of a sequencing batch reactor (SBR). Results showed that dissolved starch promoted sludge floc granulation and maintained good sedimentation performance during the whole operational period, while particulate starch accumulated extracellular starch in full aerobic operation mode and the total polysaccharide content increased significantly, causing non-filamentous bulking. High-throughput sequencing results confirmed the effects of varying sludge characteristics when supplied with different starch forms, on the functional microbial community. The dominant genus in the particulate starch system was Flavobacterium, promoting the production of polysaccharides in EPS, while the dominant genus in the dissolved starch system was Kouleothrix, which plays an adsorption bridging role in sludge with larger particle sizes and maintains a good sludge sedimentation performance. PICRUSt2 analysis showed that microbes in the particulate starch system exhibited high activity in terms of nitrogen, carbon and amino acid metabolism. Here, we demonstrate a theoretical basis for the use of particulate organic matter in sewage treatment systems, providing a novel perspective on the relationship between the morphology of slowly biodegradable organic matters and sludge bulking.