Performance enhancement by adding ferrous to a combined modified University of Cape Town and post-anoxic/aerobic-membrane bioreactor

Abstract The removal of nutrients in a combined modified University of Cape Town and post-anoxic/aerobic-membrane bioreactor (UCT-A/MBR) was investigated. Denitrifying phosphorus removal (DPR) and nitrate-dependent anaerobic ferrous oxidation (NAFO) were applied to enhance the nutrient removal performances. The results showed that NAFO with the addition of Fe(II) and DPR could promote nitrogen and phosphorus removal. The total nitrogen removal efficiency gradually increased from 71.05 ± 2.00% to 73.84 ± 1.74% and 75.70 ± 1.47% with no Fe(II) addition, addition to the post-anoxic tank, and addition to the anoxic tank, and the total phosphorus removal efficiency increased from 89.37 ± 1.91% to 95.21 ± 0.85% and 96.01 ± 1.10%, respectively. Gene sequencing was conducted, and Saprospiraceae was determined to be the dominant DPR-related bacteria, with its abundance increasing from 16.31% to 22.45% after Fe(II) addition. Additionally, the proportion of the NAFO-related bacteria Azospira increased from 0.58% to 1.91% after Fe(II) addition. The microbial succession caused by the addition of Fe(II) may have resulted in the enhanced removal performance.