Optimization and Modeling of Cr (VI) Removal from Tannery Wastewater onto Activated Carbon Prepared from Coffee Husk and Sulfuric Acid (H₂SO₄) as Activating Agent by Using Central Composite Design (CCD)

Table 9

Operational costs to treat 1000 mL solution by using 2 g adsorbent.

Raw Material Used
	Dose (g)	Cost (ETB)	Rate (ETB to $ US)	Cost ($)
Coffee husk	10	7	0.01945	0.1362
Chemicals used
	Volume (mL)	Cost (ETB)	Rate (ETB to $ US)	Cost ($)
Sulfuric acid	100 (98.3%)	61.476	0.01945	1.196
HCl	100 (38%)	10.28	0.01945	0.2
Mass (g)
K2Cr2O7	5 (power)	0.771	0.01945	0.015
NaOH	10 (solid pellet)	6.01	0.01945	0.117
Power consumption
	KW.hr
During stringing	0.1	1		0.0195
Total cost		86.545		1.6837