Between encapsulated systems, packed bed systems tended to have higher predictions of rCOD but were usually subjected to higher LC and higher CI per tonne COD removed than a comparable fluidized bed system. Increasing total HRT from 1 day to 4 days or above generally led to higher cost and impacts per tonne COD removed, with the increase in rCOD overshadowed by the quickly rising cost and impacts from the construction and O&M of a larger reactor (Figure ). Between 1-day and 2-day HRTs, the implication was more nuanced. For example, increasing the HRT of a single-stage UASB system from 1 day to 2 days reduced the CI per tonne COD removed but raised the LC. For a single-stage fluidized bed system, however, a 2-day HRT could have both lower cost and lower impacts because further reducing HRT to 1 day was detrimental to COD removal performance.