Synergistic Mechanism of Modified nZVI and Citrobacter Reshaping Sludge Microbiome Drives Co-Removal of HBCD and Nutrients in Municipal Wastewater

Abstract

Hexabromocyclododecane (HBCD), a persistent and toxic brominated flame retardant, poses severe ecological and health risks due to its bioaccumulation and endocrine-disrupting effects. Effective removal from wastewater is critical to mitigate risks. Coupling functional microbes with modified nanomaterials represents a robust approach for degrading such recalcitrant organohalides. Based on the research foundation of the functional bacterial strain Citrobacter sp. Y3 and a modified nano-zero-valent iron (nZVI) coupled system, we designed and constructed a novel anaerobic continuous stirred-tank reactor (CSTR) system for the treatment of municipal wastewater in this study. HBCD-contaminated wastewater and actual domestic sewage were fed into this CSTR system. During continuous monitoring of HBCD concentration changes over 360 h, we simultaneously tracked the removal efficiencies of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD). The results demonstrated that the HBCD degradation rate reached 100% within 72 h, while the removal of other nutrients met regulatory discharge requirements. The CSTR system significantly enriched diverse functional bacterial taxa harboring multiple functional genes, including organohalide-respiring bacteria (OHRB) (rdhA/B, PecA/B), iron-reducing bacteria (IRB) (cymA, fur), and nitrogen/phosphorus-removing bacteria (hzoB, haoA, norB and pstA/B/C). Dynamic interactions (synergistic cooperation and competition) among microbial communities drove the decomposition and transformation of pollutants. To our knowledge, this study provides the first demonstration of coupling functional bacteria with modified nanomaterials in activated sludge systems.

Keywords: Hexabromocyclododecane, Municipal Wastewater, Anaerobic CSTR, Functional Genes, Synergistic Degradation