The Removal Effect of Pollutants and Components in Extracellular Polymeric Substances from Aerobic Granular Sludge in Simultaneous Removal of Organic Matter and Ammonia Nitrogen

Biological processes, such as activated sludge and granular sludge are widely used to remove organic pollutants as well as inorganic pollutants, such as metallic elements1–3, which are known to be potentially toxic, and impact the performance of biological waste treatment processes4. Granular sludge is a dense aggregate of microorganisms, minerals, and microbial produced compounds such as extracellular polymeric substances (EPS)5,6. Compared to traditional activated sludge technology, AGS as a new type of microbe auto-immobilization technology, has many advantages, such as compact structure, fast settling velocity, higher sludge concentration, and ability to withstand high organic loading7,8. Many researches mainly try to study the operating conditions9, microbiological properties10,11, physicochemical characteristics12,13, and extracellular polymeric substances of granular sludge14,15. The AGS technology is used for treating all kinds of wastewater, including organic matter, nitrogen, phosphorus, and toxic substances16–19. EPS is a complex high-molecular-weight mixture of polymers in AGS. The EPS is a network bacteria embedded20, has a significant effect on the physicochemical properties of AGS, including structure, surface charge, flocculation, settling properties, and adsorption ability; plays a crucial role in biological wastewater treatment21–23. It not only results from active bacterial secretion, but also from cell lysis and effluent molecules24. EPS is considered as an organic product with mineral cations bound. Guibaud et al.25 have showed that some mineral particles, such as manganese oxides and iron oxy-hydroxides in the EPS extract can improve the ability of the EPS binding lead or cadmium cations. However, the mineral fraction of the EPS extracts, which is too often neglected in EPS studies, can affect the physicochemical properties of EPS26. The aim of this study is to investigate the removal effect of pollutants and the components, including the organic and mineral fractions, and especially to evaluate the mineral fraction in EPS to improve the stabilization of the AGS.