Effects of salinity on the morphological characteristics of aerobic granules

Saline wastewater is ubiquitous in industries. The present study reports the effects of salinity on the morphological properties of aerobic granules. Within a wide range of salinity from 1% to 5%, good aerobic granules were successively cultured in sequencing batch reactors (SBRs). It was found by scanning electron microscope (SEM) analysis that the granular surface turned to be smoother and more regular with increase of salinity, and under lower salinity (1%) the microbe was cocci-dominated, while under higher salinity (5%) the microbe was filaments-dominated. As a result of size distribution analysis, the granules were found to grow faster, larger and with a wider size spectrum under higher salinity. However, the porosities of the granules under the salinity of 1%, 2.5% and 5% were 0.90, 0.89 and 0.82, respectively, indicating that higher salinity may result in more compact granules. It can be concluded from this study that formation of large and compact granules is possible under salinity as high as 5% and filamentous microorganisms did not necessary lead to sludge bulking and granule breakage.