Table 4 Coded levels for four variables framed by the Central Composite Design.

From: Enhanced anaerobically digested swine wastewater treatment by the composite of polyaluminum chloride (PAC) and Bacillus megatherium G106 derived EPS

Factors

Codes

Codes levels

−1

0

1

EPS (mg/L)

x 1

10

20

30

PAC (g/L)

x 2

10

15

20

pH

x 3

5.5

7.5

9.5

Agitation speed (r/min)

x 4

100

200

300

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