Synergistic effects of prokaryotes and oxidants in rapid sand filters treatment of groundwater versus surface water: Purification efficacy, stability and associated mechanisms

Effective elimination of manganese (Mn) and ammonium (NH4+-N) from drinking water is still challenging. Utilizing oxidants to improve the simultaneous removals of Mn and NH4+-N from rapid sand filter (RSF) systems has been extensively studied. However, the prokaryotes containing in the water geochemical properties greatly affected the RSF performance. In this study, groundwater and micro-polluted surface water were used to compare with/without potassium permanganate (KMnO4) assistant on the contaminants removals and system stability. Results showed that KMnO4 reduced the start-up period of RSF for treating groundwater and surface water to 20 and 41 days, respectively, with excellent Mn removal rates (>97%). The relative abundance of efficient ammonia-oxidizing bacteria (Nitrospira) in RSF treated groundwater without KMnO4 was higher than that in RSFs treated micro-polluted surface water or with KMnO4, resulting in a higher NH4+-N removal rate of the former (similar to 57%). Notably, KMnO4 and prokaryotes synergistically contributed to the amorphous structure, mixed phases (buserite, MnO2 and birnessite) and mixed-valence Mn system of active manganese oxides (MnOx), whose abundant oxygen vacancies and highly reactive Mn(III) favored the autocatalytic oxidation of Mn, while NH4+-N removal relied more on bacteria actions. Additionally, prokaryotes enriched the bacterial community diversity, leading to a more stable RSF system when facing hydraulic loading shock. This paper provided new insight into the synergistic effect of KMnO4 and prokaryotes on Mn and NH4+-N eliminations in RSFs and was helpful for practical applications.

Automated summary

The study demonstrated that the addition of potassium permanganate (KMnO4) significantly reduced the start-up period for treating groundwater and surface water in RSF systems, enhancing manganese removal rates. Prokaryotes played a crucial role in system performance and NH4+-N removal, enriching bacterial community diversity and improving RSF stability when facing hydraulic loading shock. The synergistic effect of KMnO4 and prokaryotes provided new insights into manganese and ammonium elimination in RSF systems, beneficial for practical applications.