Tolerance to short-term saline shocks by aerobic granular sludge

In industrial wastewaters, rapid shifts of salinity leading to transient shocks caused damages on biological treatments. Aerobic granular sludge is a promising technology that showed its greater resistance to adverse conditions. However, the impact of short-term saline shocks on the performance of aerobic granular sludge process was not studied sufficiently. This study investigated salt-tolerance ability of aerobic granular sludge from aspects of chemical oxygen demand (COD) removal efficiency and sludge concentration under different saline shocks that shock concentration ranged from 0 to 60 gNaCl/L and shock duration was set at 6 h. The results showed that no obvious change of sludge concentration after all saline shocks. Moreover, COD removal efficiencies could revert to 90.7% and 87.5% that was near to the previous level (90.9%) in short-term recovery after 20 g/L and 40 g/L saline shocks. However, stable COD removal efficiency (73.8%) could not recover to the previous level (90.9%) after 60 g/L saline shock. These results suggest aerobic granular sludge has an excellent ability to withstand up to 40 g/L saline shock. The corresponding salt-tolerance reasons could be explained from three aspects. After 40 g/L saline shock, the specific oxygen uptake rate of aerobic granular sludge could recover to ensure biological activity. Aerobic granular sludge with the integrity coefficients of 87.6% maintained compact structure. In addition, aerobic granular sludge with relative small DNA leakage of 177.2% has advantages to diminish damage on cell structure. These results provide further insight into the application of aerobic granular sludge for saline-shock wastewater treatments.