Table 3.

Physical and chemical biochar properties, comparative literature values and international guidelines.

Parameter	Unit	N-BC	N-CBC	W-BC	W-CBC	Ugandaa	Ethiopiab	IBIc	EBCd	EUe	USEPAf
Sample size		12	1	12	1
Volatile matter	[%]	20.3 $\pm$ 4.0	21.1	14.2 $\pm$ 2.5	13.3	6.7–26.1
Fixed carbon	[%]	34.1 $\pm$ 3.9	28.6	17.2 $\pm$ 5.2	6.1	18.8–23.3
Ash	[%]	45.6 $\pm$ 4.2	50.3	60.8 $\pm$ 5.5	80.6	54.5–73.8
HHV	[MJ/kg]	14.9 $\pm$ 0.9	13.9	9.7 $\pm$ 1.5	4.9	8.8–12.4
pH	[ ]	10.5 $\pm$ 0.5	9.4	10.8 $\pm$ 1.2	12	9.1–11.2	8.23
CaCO3-equ.	[%]	13.8 $\pm$ 2.7	16.9	20.1 $\pm$ 2.8	23.7
Ca	[g/kg]	56.4 $\pm$ 3.9	63.3	89.4 $\pm$ 11.5	103.4		32.8
Mg	[g/kg]	7.8 $\pm$ 0.7	8.9	9.6 $\pm$ 1.7	12		28.9
K total	[g/kg]	8.1 $\pm$ 0.8	8.1	11.7 $\pm$ 1.9	8.8		8.21
K available	[% of total]	77.7 $\pm$ 2.9	78.3	71.9 $\pm$ 9.4	58.1
P total	[g/kg]	1.2 $\pm$ 0.2	1.7	2.2 $\pm$ 0.6	2.2	31–42	42.7
P available	[% of total]	61.0 $\pm$ 6.4	52.1	53.7 $\pm$ 12.1	41.5	75.3–98.3
Cd	[mg/kg]	13.5 $\pm$ 2.7	15.1	12.4 $\pm$ 2.0	15.5		1.23	1.4–39	1.5	20–40	85
Cr	[mg/kg]	56.1 $\pm$ 5.8	92	54.3 $\pm$ 16.5	98.6	113.7–194.2	39.5	93–1200	90		3000
Cu	[mg/kg]	463.0 $\pm$ 61.1	541.1	310.3 $\pm$ 37.0	370.7	81.8–113.2	214	143–6000	100	1000–1750	4300
Ni	[mg/kg]	122.7 $\pm$ 37.1	100.3	164.1 $\pm$ 48.8	184.9	57.4–96.5	84.4	47–420	50	300–400	420
Pb	[mg/kg]	395.3 $\pm$ 57.9	552.9	241.7 $\pm$ 50.9	311.9	<5–21.5	502	121–300	150	750–1200	840
Zn	[mg/kg]	1516.9 $\pm$ 209.1	2173.2	1072.9 $\pm$ 326.9	1385.2	872.9–1116	28400	416–7400	400	2500–4000	7500

^a(Gold et al., 2018).

^b(Woldetsadik et al., 2016).

^cMaximum thresholds for biochar (IBI, 2015).

^dBasic quality biochar (EBC, 2019).

^eLimit values in sludge for use in agriculture (EEC, 1986).

^fCeiling concentrations for biosolids applied to land (Walker et al., 1994).