Characterization of sulfate-reducing bacteria anaerobic sludge granulation enhanced by chitosan

Two laboratory-scale up-flow anaerobic sludge granules reactors were operated as control reactor (R1) and chitosan (CTS) addition reactor (R2) to investigate the effect of the addition of CTS on the granulation process of sulfate-reducing bacteria (SRB) anaerobic sludge. Granular sludge with the diameter greater than 0.5 mm was selected to calculate the granulation percentage, and the remaining sludge was considered as flocculent sludge in this paper. The results showed that the granulation percentage in the two reactors were stabilized to 47.3% and 64.2%, respectively. The sizes of sludge granules in R2 were mainly between 0.5 and 1.5 mm with the average pore diameter of 91.6 nm and the porosity of 57.1% while the granules in the same particle size in R1 were 41.5 nm and 46.1%, respectively. It demonstrated that CTS was an appropriate additive which can enhance the formation of SRB granule sludge with better pore structure. The granular sludge with CTS exhibited excellent physical performance and more extracellular polymeric substances, especially for protein (PN). In addition, computational fluid dynamics (CFD) simulation was conducted to illustrate the hydrodynamic characteristics of granules with Kozeny-Carman model. With a higher porosity, the permeability of the granules fed with CTS was considerably increased. Moreover, the model also indicated that the permeability and convection changed significantly with Reynolds numbers (Re) of the external flow field for a given type of the porous structure.