RSM has become extremely prevalent for designing, enhancing, and optimising complicated processes, as well as determining the significance of different operating variables (Mondal et al. 2019). For a set of three independent variables, namely, influent As (III) concentration, inlet flow rate, and bed depth, the most efficient CCD in RSM was employed to study their effects on the breakthrough time for fixed-bed continuous of As (III) by PETC-Fe. Table 2 lists the variables' testing limits, as well as their notation and unit in central composite design.

Table 2

Testing levels and ranges of operational parameters

FactorNameUnitsMinimumMaximumCoded lowCoded high
Influent As(III) concentration μg/L 300.00 1,500.00 −1 ↔ 300.00 +1 ↔ 1,500.00
Influent flow rate mL/min 3.00 9.00 −1 ↔ 3.00 +1 ↔ 9.00
Bed height cm 5.00 15.00 −1 ↔ 5.00 +1 ↔ 15.00
FactorNameUnitsMinimumMaximumCoded lowCoded high
Influent As(III) concentration μg/L 300.00 1,500.00 −1 ↔ 300.00 +1 ↔ 1,500.00
Influent flow rate mL/min 3.00 9.00 −1 ↔ 3.00 +1 ↔ 9.00
Bed height cm 5.00 15.00 −1 ↔ 5.00 +1 ↔ 15.00

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