Li Zh

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.

Effect of chemical and biological factors on the densification of filamentous sludge

Densification may be an alternative method for controlling sludge bulking; however, little information is available on the method. Various methods including different oxygen concentrations, surface velocities of aeration, calcium concentrations and extended starvation period were employed for triggering densification of filamentous sludge in this study. It was found that high surface velocity of aeration could effectively improve the settleability of filamentous sludge in the short term, which resulted in filamentous granulation, but could not avoid filamentous bulking even after granulation. Increase of calcium concentration could also improve the settleability by forming pigtail filaments colony in the short term, but could not trigger granulation. Extension of starvation period seems effective neither for further densification nor for granulation. Additionally, increased ovality of meshes formed by filaments was frequently associated with a dense structure of filamentous sludge. It was suggested that pigtail type of filamentous colony that thus increased the resistance to elevated shear force may encourage the densification of sludge, and two kind of densification growth patterns, i.e., granular or cluster growth pattern of filamentous sludge, were identified.