Determination of the level of hexavalent, trivalent, and total chromium in the discharged effluent of Bahir Dar tannery using ICP-OES and UV–Visible spectrometry

Figures & data

Table 1. The operating conditions of ICP-OES

Parameter	Condition
Power	1100 W
Nebulizer flow rate	0.65 L/min
Nebulization pressure	1.75 bar
Pump speed	20 rpm
Plasma flow	15 L/min
Auxiliary flow	0 L/min
Sheath flow	0.2 L/min
Wavelength	267.716 nm

Figure 1. Plot of ICP-OES emission intensity versus total chromium concentration (C_T = 0.0, 0.2, 0.8, 3.2, 6.4, and 12.8 ppm).

Table 2. Summary of the average total chromium concentration (Cr_T) in samples collected from two sites around Bahir Dar tannery using the ICP-OES

Site	Calculated concentration/ppm			* CrT ± SD (ppm)
	1st	2nd	3rd
Before treatment	82.375	82.410	82.415	82.40 ± 0.20
After treatment	3.020	2.941	2.908	2.96 ± 0.06

* Mean of triplicate measurements, SD = standard deviation

Figure 2. Plot of UV–Vis absorbance versus chromium (VI) concentration (0.00, 0.01, 0.05, 0.25, 0.75, and 1.25 ppm).

Table 3. Summary of the average Cr(VI) concentration in samples collected from the two sampling sites in Bahir Dar tannery

Site	Calculated concentration/ppm			*Cr(VI) ± SD (ppm)
	1st	2nd	3rd
Before treatment	0.195	0.171	0.181	0.18 ± 0.01
After treatment	0.099	0.065	0.076	0.08 ± 0.02

*Mean of triplicate measurements

Table 4. Summary of the average Cr(III) concentration in the discharged effluent of Bahir Dar tannery collected from the two sites

Site	CrT (ppm)	Cr(VI) (ppm)	Cr(III) (ppm)
Before treatment After treatment	82.40 ± 0.20 2.96 ± 0.06	0.18 ± 0.01 0.08 ± 0.002	82.22 ± 0.19 2.88 ± 0.05

Table 5. The maximum allowed concentration of chromium species that could be discharged to surface water after treatment according to different countries and WHO guidelines

	Chromium species
Country	CrT	Cr(III)	Cr(VI)	References
WHO limit	–	–	0.05–0.06	(WHO, 1996)
Europe general	2	–	0.2	(WHO, 1996)
Brazil	–	1	0.1	(Quevauviller, Marrier, & Griepink, 1995)
USPS	–	0.5	0.1	(Hossain, Kumita, Michigami, Islam, & Mori, 2005)
Ethiopia	2	–	0.1	(EEPA, 2003)
Italy	2	–	0.2	(Jakov, 2005)
India	2	–	0.1	(Jakov, 2005)
France	1.5	–	0.1	(Jakov, 2005)
Tunisia		0.5	0.01	(Jakov, 2005)
Bahir Dar Tannery	2.96	2.88	0.08	Present study

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