The HRT for the UASB and I-BAFs is gradually reduced from 40
(start-up), 20 (127–160 d), and 15 (161–183 d) to 12 h (184–252 d)
during the entire operation period. However, the COD removal is
observed to be stable in the proposed system in spite of shorting
HRT, indicating that the HRT reduction has no significant effect on
COD removal efficiency in this study.