Understanding role and mechanisms of zero-valent iron (ZVI) in activated sludge responses under glyphosate exposure

Abstract

The activated sludge and ZVI-amended activated sludge were applied to explore the responses of activated sludge system under glyphosate exposing, as well as the roles of ZVI. The results revealed that glyphosate negatively impacted the activated sludge, whereas the presence of ZVI mitigated these effects, as evident from stable COD removal efficiency. The underlying mechanism involves the promotion of EPS secretion, particularly proteins, which leads to an improved relative hydrophobicity, ultimately enhancing sludge settling performance. Besides, the ZVI-amended activated sludge system effectively removed glyphosate (55.89 %) through mechanisms involving ZVI function, sludge adsorption, and biological metabolism. In contrast, the removal efficiency in the activated sludge system alone was lower (35.11 %). ZVI shaped the sludge characteristics and microbial communities of the activated sludge, resulting in variations in glyphosate removal efficiency and pathways. Under the presence of ZVI, sludge with higher relative hydrophobicity removed only 2.88 % of hydrophilic glyphosate by biological adsorption, but accounted for 11.38 % in individual activated sludge system. Compared with sludge adsorption, ZVI posed increase of glyphosate biodegradation from 23.72 % (control system) to 35.11 % by shaping microbial community (enrich degradable glyphosate bacteria from 22.14 % to 47.55 %). Overall, this research provides valuable insights into the role of ZVI in the response of activated sludge to glyphosate exposure, highlighting the potential of ZVI-coupled activated sludge for treating glyphosate-contaminated wastewater.