Enhancing nitrogen removal efficiency for anammox granular sludge at low temperature by fulvic acids from different sources

Abstract

The stable and efficient operation of the anaerobic ammonia oxidation (anammox) process in mainstream wastewater treatment at low temperatures still faces significant challenges. In this study, the effect of mineral fulvic acid (MFA) and biochemical fulvic acid (BFA) on the nitrogen removal efficiency of the anammox reactor at low temperature (20 °C) was investigated. The results demonstrated that both MFA and BFA could improve the nitrogen removal performance of the anammox reactor, with MFA exhibiting a more pronounced promotional effect than BFA. At concentrations of 30 mg total organic carbon (TOC)/L for both MFA and BFA, the nitrogen removal rate (NRR) increased by 26.68 % and 21.93 %, respectively. MFA and BFA stimulated the secretion of extracellular polymeric substances (EPS), preventing the disintegration of granular sludge at low temperatures, with a notable increase in the particle size of granular sludge, especially at high concentrations of MFA. Moreover, serving as electron shuttles, MFA demonstrated superior electron transfer ability compared to BFA, significantly enhancing the metabolic activity of anammox bacteria (AnAOB) under low temperatures. In addition, compared with BFA, MFA exhibited the potential to promote the growth of Candidatus_Kuenenia, offering a beneficial contribution to improving the nitrogen removal performance of the anammox reactor at low temperatures.