Fe3+ addition for enhancing the formation and stability of aerobic granular sludge to treat low-strength wastewater

Aerobic granular sludge (AGS) has attracted great attention because of its characteristics of high pollutant degradation efficiency, less land occupation. However, the application of AGS in treating low-strength wastewater is still facing some problems, such as long period requirement for AGS formation and poor operation stability. In this study, Fe3+ was employed to enhance the AGS formation and stability. The AGS was cultured in a sequencing batch reactor (SBR) and the influent chemical oxygen demand (COD) was set at 150 mg/L. The results showed that AGS was formed rapidly within 9 days when Fe3+ was added to the influent, and the removal efficiency of COD, ammonia nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP) were 81 %, 96 %, 35 % and 33 %, respectively. However, no AGS was observed in the control group (without Fe3+) and the pollutant removal was low. The AGS's extracellular protein content was about 150 mg/g mixed liquid suspended solid concentration (MLSS) which was higher than that in the control group. On day 47, the particle size of AGS reached 669 mu m. It was found that Fe3+ could stimulate the production of tryptophan and tyrosine proteins, Amide I band, beta-exopolysaccharides. These substances are considered having a great contribution to the formation and stability of AGS. In addition, Fe3+ could stimulate the growth of Zoogloea to enhance the secretion of extracellular polymeric substance (EPS) and stimulate the growth of Pseudoxanthomonas to improve the stability of AGS. The study has provided a strategy for AGS application in low-strength wastewater treatment.