Carrier-based granules vs aerobic granular sludge

Carrier-based granules (CBG) are like aerobic granular sludge (AGS) in both morphology and functionality, but CBG is more easily formed and can keep a greater stability than AGS, especially under adverse conditions. In this study, a light organic nutshell (NS) was selected as the carrier, with a particle size of 200-300 μm and a density of 1211 ± 0.1 kg/m³. The study aimed to develop a single-sludge (biofilm) process as an alternative to AGS. Thus, the experiments focused on biofilm formation, performance and stability, using a selective wasting strategy by shortening the settling time. The results indicated that CBG was able to readily form on NS, which exhibited a structure resembling that of AGS. However, CBG exhibited a higher density (1028 ± 1.5 kg/m³), a larger mean particle size (853 μm) and a greater settleability (SVI₃₀=27 mL/g). Furthermore, CBG exhibited its satisfactory pollutant removal efficiencies (COD=93 %; NH₄⁺-N = 96 %; PO₄^3--P = 95 %), along with a significant SND capacity. An analysis on the microbial community revealed that CBG harbored a diverse population of bacteria capable of promoting flocculation, storing intracellular polymers and secreting substantial EPS. Furthermore, the experiment with low COD influent demonstrated a greater stability with CBG in both structure and pollutant removal compared to AGS, which was attributed to its higher EPS (especially PN) content and interfacial reactivity between microorganisms. These excellent characteristics of CBG were likely a result of the process by which sludge overcame additional stress from abrasive forces during attachment, which induced microorganisms to reduce intercellular repulsion, aggregate into a more compact and firm form, and ultimately form CBG.