Due to the disorder of balance between hydraulic and substrate selective pressures,a great quantity of aerobic granules began to break down into flocculent sludge after a while of stable operation period.Powdered activated carbon(PAC) was used to regulate the hydraulic selective pressure and strengthen the stability of aerobic granules.Experimental results showed that PAC addition had great effects on the physical properties of sludge and microbial growth kinetics:PAC addition could enhance granular wet den...