Effect of pH on stability of aerobic granular sludge

In order to investigate the tolerance of aerobic granular sludge(AGS) to different pH environments, the stability of AGS under different pH wastewaters (3, 4, 5, 10, 11, 12) was studied. In the acidic environment, the physical and chemical properties of AGS deteriorated(EPS decreased from 102.5 to 76.43 mg/g, SOUR decreased from 17.94 to 16.19 mg O₂/(g MLSS·h))as the pH decreased. When the pH was 3 or 4, sludge floating was observed in different degrees, and the removal efficiency also showed a downward trend. In addition to the unsatisfactory removal of ammonia nitrogen, the removal rate of other pollutants remained above 80 %. In the alkaline environment, sludge swelling also occured. As the increase of pH, the physical and chemical properties decreased (EPS rose from 93.27 to 178.45 mg/g, SOUR decreased from 6.81 to 4.30 mg O₂/(g MLSS·h)). At the same time, the removal ability of AGS for pollutants decreased sharply, and the removal rates of COD, TN and TP all dropped below 50 %.The results showed that AGS was capable to maintain stable in acidic environment, while alkaline environment had a greater inhibitory effect on AGS.