Performance, Sludge Characteristics, and the Microbial Community Dynamics of Bulking Sludge Under Different Nitrogen and Phosphorus Imbalances

Abstract

In this paper, the performance, characteristics of the bulking sludge, and the variations in the microbial community (including the bulking bacteria) under different nitrogen and phosphorus imbalances were compared, using high-throughput sequencing (16S rRNA) and the high performance liquid chromatography (HPLC) technology. The results showed that after seeding bulking sludge in the A/O process and operating for a period of time, the sludge settleability of the nitrogen limitation alone reactor (RN) could recover to normal[sludge volume index (SVI)<150 mL·g-1], while the SVI of the phosphorus limitation alone reactor (RP) improved slightly; the control reactor (R0, C/N/P=100/5/1) exhibited the highest SVI index (SVI=1496 mL·g-1), followed by the reactor of simultaneous nitrogen and phosphorus limitations (RNP). Under normal nutritional conditions, Pearson correlation analysis showed a significant negative correlation between the lipopolysaccharide (LPS) relative content (LPS/MLVSS) and the settleability of bulking sludge (r=-0.625, P<0.05), while under nutrient limitation conditions, LPS showed high accuracy in reflecting the biomass of the activated sludge. Thiothrix was the dominant bulking bacteria in all the reactors. PCoA analysis showed that the migration of the community in the reactors experienced nitrogen limitation (RNP, RN) changes greatly during the stages Ⅱ and Ⅲ, while RDA analysis showed that the correlation of Thiothrix with the settling performance and oxygen consumption rate was significant.