Effects of feeding mode on the formation and stability of aerobic granular sludge under combined antibiotic stress

Abstract

Aerobic granular sludge (AGS) is a promising technology for wastewater treatment due to its high biomass retention, nutrient removal, and resistance to toxic substances. However, the formation and stability of AGS are affected by various factors, such as feeding mode and antibiotic stress. This study investigated how three feeding modes, namely anaerobic plug-flow (APM), anaerobic mixed-flow (AMM), and aerobic feeding mode (AFM), influenced AGS formation and stability under exposure to a mixture of tetracycline, sulfamethoxazole, ofloxacin, and roxithromycin. The results showed that only APM and AMM achieved granulation within 40 d, while AFM failed to form AGS within 90 d due to the low shear force that led to a different composition and structure of extracellular polymeric substances and a high potential barrier calculated by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The average granules diameters of APM (896.6 μm) were larger than that of AMM (519.4 μm), and the results of ultrasonic crushing experiment and XDLVO calculation showed that the structural stability of APM was slightly stronger. However, AMM outperformed APM and AFM in terms of total phosphorus removal, antibiotic removal, and long-term operational stability under low temperature conditions. Illumina MiSeq sequencing and qPCR results revealed that typical biofilm formers (Sediminibacterium and env.OPS_17) contributed to the stability of AGS and increased phosphorus accumulating organisms’ genes abundance ensured the high TP removal in AMM. This study offers valuable insights into the effects of diverse feeding modes on aerobic granulation and stability under combined antibiotic stress and suggests that AMM is a promising mode for enhancing AGS performance and resilience in wastewater treatment applications.