. 2021 Dec 25;8(1):e08680. doi: 10.1016/j.heliyon.2021.e08680

Table 3.

Chemical characteristics of spent and unspent liquors at the artisanal tannery.

Parameter	Liming	Deliming/Bating	Spent vegetable tanning	Spent alum tawing	Spent red dye	Black dye	Ghana EPA (2016)
pH	12.95 ± 0.28	8.79 ± 0.22	6.02 ± 0.47	4.54 ± 0.83	6.36 ± 0.60	5.75 ± 0.74	6–9
BOD₅ (mg/L)	2705.3 ± 396.73	2073.4 ± 287.51	2803 ± 308.76	1445.6 ± 641.56	2709 ± 354.12	2068.8 ± 291.41	50
COD (mg/L)	17050 ± 157.20	4366.7 ± 921.65	24333 ± 654.84	2380 ± 109.23	13600 ± 157.55	6970 ± 72.10	250
BOD₅: COD	0.16 ± 0.06	0.47 ± 0.04	0.12 ± 0.02	0.61 ± 0.06	0.20 ± 0.04	0.30 ± 0.06
TN (mg/L)	115.68 ± 21.85	93.14 ± 14.45	37.18 ± 9.16	64.35 ± 55.87	38.52 ± 7.02	40.10 ± 36.77	50
NH₃–N (mg/L)	68.75 ± 7.43	48.08 ± 5.79	16.80 ± 3.38	21.38 ± 3.54	3.20 ± 0.78	4.75 ± 0.49	1
SO₄²⁺(mg/L)	355.75 ± 30.74	115.38 ± 19.56	30.14 ± 3.20	1190.7 ± 18.72	90.25 ± 3.80	10.42 ± 2.05	250
Ca²⁺ (mg/L)	18.45 ± 5.78	14.80 ± 3.61	7.26 ± 1.15	9.74 ± 2.38	5.72 ± 1.28	3.24 ± 0.26	-
Cl⁻(mg/L)	23280 ± 1636	12516 ± 151.32	751 ± 68.74	20490 ± 1270.64	795.88 ± 82.35	643.30 ± 76.55	-
Na⁺ (mg/L)	20727 ± 503.28	9510 ± 141.35	258.66 ± 36.95	14056 ± 763.75	315.20 ± 72.61	245.28 ± 45.60	-
Total Fe (mg/L)	7.58 ± 2.40	6.05 ± 2.94	2.02 ± 1.45	5.26 ± 1.72	2.95 ± 1.08	18.90 ± 5.92	10
Al³⁺ (mg/L)	5.04 ± 1.02	3.55 ± 0.75	1.28 ± 0.08	78.18 ± 10.52	0.54 ± 0.01	0.95 ± 0.15	-
Total Cr (mg/L)	0.04 ± 0.001	0.04 ± 0.002	0.04 ± 0.002	0.04 ± 0.002	0.03 ± 0.001	0.2 ± 0.01	0.5
Zn²⁺ (mg/L)	3.18 ± 0.14	5.04 ± 0.64	0.64 ± 0.26	1.54 ± 0.12	0.54 ± 0.18	0.4 ± 0.10	10