Stability of aerobic granular sludge under low energy consumption: Optimization of granular size distribution by a novel internal component

To enhance the stability and pollutant removal performance of aerobic granular sludge (AGS), four groups of AGS reactors with mesh screens of different pore sizes (R1 is the control reactor; R2, R3, and R4 have pore sizes of 1.5, 2.5, and 3.5 mm, respectively) were established in this study. The results showed that the granular sludge in the reactor with a 2.5 mm mesh screen (R3) has the highest mixed liquor suspended solids (MLSS) value of 8.2 ± 0.2 g L−1 and the lowest sludge volume index (SVI30) value of 30 mL g−1. At the same time, the mature granular sludge in R3 had a compact structure and excellent total nitrogen (TN) removal performance (84.9 ± 1.2%), along with an optimal granule size distribution (span value of 96 ± 0.12). Analysis of the sludge microbial community showed that R3 has a higher enrichment of functional microorganisms, such as Zoogloea spp. (50.5%) and Thauera spp. (16.1%). This is beneficial for improving its intercellular adhesion and denitrification performance. The granule size distribution results indicated that R3 screened the growing granules with its appropriate mesh aperture in terms of optimizing hydraulic shear, thus inhibiting the growth of filamentous bacteria and keeping the granule size within the optimal range. This created a favorable niche for these fast-growing microorganisms, eventually forming granules with good stability and high denitrification efficiency.