Long Chain Fatty Acid-Induced Flotation of Anaerobic Granular Sludge and its Critical Factor: Retention of External Bubbles

Abstract

Overloading long-chain fatty acids (LCFAs) induce sludge flotation, biomass loss, and instability in anaerobic reactors. There exists a direct correlation between sludge flotation and the generation and release of gaseous products. However, current investigations into the causes of LCFA-induced sludge flotation have primarily focused on internal gas retention within the sludge, while overlooking the influence of external bubbles. This study demonstrates that the retention of external bubbles on the sludge surface is the critical factor in LCFA-induced flotation. This paper explores the connections between sludge surface properties, sludge characteristics, and external bubble entrapment, employing Spearman's rank correlation coefficient (Rs) to analyze the correlation between sludge flotation potential (SFP) and these characteristics. The findings indicate that LCFA induces (i) increased hydrophobicity, roughness and porosity, (ii) decreased density and mechanical strength, (iii) reduced EPS content and increased PN/PS, (v) decreased microbial activity and acetate accumulation., all of which contribute to sludge flotation.

Keywords: Long-chain fatty acids, anaerobic granular sludge, Sludge flotation, Sludge characteristics