Potato Peels as an Adsorbent for Heavy Metals from Aqueous Solutions: Eco-Structuring of a Green Adsorbent Operating Plackett–Burman Design

Table 2

Variables and their domains for a Plackett–Burman design (PBD) for both RPP and BPP.

Variables and their codes	Level 1 (low, −1)	Level 2 (central point, 0)	Level 3 (high, +1)
pH (pH, A, pH unit)	3	6	9
Heavy metal concentration (HMC, B, ppm)	10	105	200
Adsorbent dose (AD, C, g/L)	0.1	1.550	3.0
Contact time (CT, D, min)	5	32	60
Response “Y”	Maximum % of heavy metal removal