Investigation of measurement methods and characterization of zeta potential for aerobic granular sludge

A measurement protocol and characterization of zeta potential for aerobic granules were investigated. The homogenization at 8000 rpm for 1.5 min was a good pretreatment method to break big aerobic granules into fine particles for directly measuring the zeta potential. There was no obvious variation of zeta potential for sludge concentration in the range of 0.1–8.0 g TSS/l. For mature aerobic granules, the zeta potential of fine particles after homogenization, LB-EPS, TB-EPS, and residual sludge after EPS extraction had different values of −10.2 mV, −10.7 mV, −18.2 mV, and −30.0 mV, respectively. The low and similar zeta potential features of fine particles after homogenization and LB-EPS suggested that LB-EPS should be a more important component than TB-EPS in influencing the electrochemical properties of the sludge. During the aerobic granulation process, the zeta potential of fine particles decreased gradually from –19.5 mV to −10.0 to −12.0 mV finally. The decrease of zeta potential might be a necessary condition for the formation and stability of aerobic granules.