Depending on bead longevity, packed bed systems with a 50 m 3 •d -1 treatment capacity would have a tailored reactor size between 33-100 m 3 , a much smaller footprint than fluidized bed designs (i.e., 161-297 m 3 ) for similar levels of COD removal. This is mainly attributed to the difference in the optimal HRT between the reactor types -6.5-20 hours for packed beds compared to 2.8-5.0 days for fluidized beds.