Influence of nitrogen-poor wastewater on activated sludge aggregation and settling: Sequential responses of extracellular proteins and exopolysaccharides

Abstract

To explore the mechanism by which the degree of wastewater nitrogen deficiency affects the aggregation and sedimentation of activated sludge, the structure, aggregation, sedimentation and thermodynamic properties of activated sludge and the composition, structure and properties of extracellular polymers under different influent nitrogen contents were examined. Hydrophobicity was the main factor affecting sludge aggregation. When nitrogen was limited (C/N = 100:2), the sludge aggregation ability decreased to 38.1 ± 1.1%, but with increases in extracellular protein (PN) content (89.8% increase) and hydrophobicity, the sludge aggregation ability returned to the level in the control phase. Under nitrogen deficiency (C/N = 100:0), the PN/exopolysaccharide (PS) decreased to 1.36 ± 0.09, and the increased hydrophilicity of PS led to a decrease in sludge aggregation ability (48.5 ± 1.0%) and a loose structure, which reduced sludge settling performance. In addition, PN and PS sequentially responded to changes in influent nitrogen content and played key roles in sludge aggregation. This study clarifies the mechanism by which the degree of wastewater nitrogen deficiency affects the aggregation and sedimentation of activated sludge from the perspective of extracellular polymers (EPS), which will help promote the further application of activated sludge processes.