Performances of bio-Fenton SBRs under different hydraulic retention times and magnetite dosages

In our previous study, a bio-Fenton sequencing batch reactor (SBR) demonstrated enhanced removal of the antibiotic sulfamethoxazole (SMX) through bio-Fenton reactions facilitated by microbially produced H 2 O 2 and magnetite redox cycling. This study examined the performances and dominant microbial species in bio-Fenton SBRs with hydraulic retention times (HRT) of 12 to 0.5 days and magnetite dosages of 0, 1, and 3 g/L. Results show that the bio-Fenton SBR with 1 g/L magnetite (SBR1) enhanced COD and SMX removal, as well as nitrification and denitrification rates, at HRTs of 1–2 days. SMX removal reached 100 % in SBR1, which was 40–50 % higher than in SBRs with 0 or 3 g/L magnetite. Enhanced SMX removal was attributed to the increased microbial H 2 O 2 production observed in sludge flocs and the subsequent ·OHs generation during aerobic periods. Magnetite as the heterogeneous catalyst for bio-Fenton reaction was reduced and oxidized through the identified iron-reducing bacteria ( Dechloromonas ) and bio-Fenton reaction, respectively. Increased nitrification and denitrification rates were attributed to the enrichment of nitrifiers ( Nitrosomonas and Nitrospira ) and denitrifying bacteria ( Thiobacillus ), respectively, with shorter HRT. Further kinetic studies are required for precisely evaluating and optimizing the performance of a bio-Fenton SBR. • HRT had different effects on SMX, COD, and nutrients removals. • 100 % removal of SMX in bio-Fenton SBR with 1 g/L magnetite at HRTs of 2 and 1 day • In situ H 2 O 2 and the subsequent ·OHs production enabled effective SMX removal. • bio-Fenton reaction occurred within the magnetite-sludge flocs. • Magnetite addition enriched bacteria involved in iron redox and nutrients removal.