Uncover the secret of the stability and interfacial Gibbs free energy of aerobic granular sludge

Interfacial Gibbs free energy (IGFE) as a thermodynamic indicator characterize the stability of the natural system. For aerobic granular sludge (AGS), how IGFE determines the stability of sludge remains to be determined. The Gibbs free energy change at the AGS-water interface (Delta G(sw)(a)) and AGS interfaces (Delta G(s)(c)) were selected as the main interfacial thermodynamic factors. Results indicated that the stable AGS was guaranteed with Delta G(s)(c) at the range of -31 to - 46 J m(-)(2). Pearson correlation coefficients between Delta G(sw)(a)/Delta G(s)(c) and relative hydrophobicity, water content, SVI30, integrity coefficient were -0.9, 0.8, 0.85, and 0.84, which illustrated that the IGFE could be a more comprehensive thermodynamic indicator. Microbial community and EPS analysis verified the importance of denitrifiers, Amide III, protein-like substances for AGS stability. This work offers a new insight into the development of AGS stability based on IGFE.