Correlation between aeration time in aerobic granular sludge reactors with the production of bioactive polysaccharides and microbial communities

Bioactive polysaccharides (PSs) as useful resources have been extracted from floc sludge, but there is limited knowledge about those from granular sludge. To address this gap, three aerobic granular sludge (AGS) reactors (R1, R2 and R3) with various operating conditions were set up for PS production (R1PS, R2PS and R3PS). Reactor operated under medium aeration time of 117 min (R2) led to the highest yield of PS (10.97 +/- 0.34 %, g/g). The carbohydrate, protein and sulphate contents for all PSs ranged between 43.2-46.4 %, 0.82-1.52 %, and 2.23-24.12 %, respectively. All PSs were mainly heterogenous heteroglycans with different degree of sulphation. Four antioxidative activities were evaluated with R1PS having the most prominent effect in scavenging DPPH, ABTS and hydroxy radicals, while R2PS had the strongest reducing power. Major microbial communities found in the reactors at the phylum level were Proteobacteria, Bacteroidota, and Firmicutes. Correlation analysis revealed the relationships among aeration time, bacteria, and polysaccharide properties. Person correlation method was used to construct two complete linked pathways (aeration time->microbiota->sludge/effluent wastewater qualities and aeration time->microbiota->PS composition->PS antioxidant property) with two cutoffs (p-value < 0.05 and R2 > 0.8), and 35 microbial genera, 3 wastewater and sludge properties (sludge particle diameter, nitrite and nitrate) and 6 polysaccharide properties (glucose, galactose, fructose, sulphate content, hydroxyl scavenging radical and reducing power) were retained. These results facilitate the understanding of the relationship between the cultivation conditions in the AGS reactors, sludge granulation, PS properties and bacterial profiles for the optimal production of PS and their application as resource of bioactive substances.