Physico-chemical characterization of selected feedstocks as co-substrates for household biogas generation in Ghana

Figures & data

Figure 1. Different feedstocks used in this study (a) Human Excreta (HE), (b) Food Leftovers (FLO), (c) Kitchen Residue (KR) and (d) Cow Dung (CD).

Table 1. Percentage composition of FLO and KR based on wet weight.

KR Components	Composition (% wet weight)	FLO Components	Composition (% wet weight)
Pawpaw peels	3.04	Rice	27.58
Watermelon peels	4.53	Cassava/Fufu	17.52
Avocado peels	3.12	Kenkey (cooked fermented corn dough)	14.66
Banana peels	2.59	Banku (cooked fermented cassava and corn dough)	12.80
Mango peels	4.00	Bread and Vegetables Sauce	4.19
Orange peels	5.87	Plantain	6.58
Pineapple peels	3.28	Kontomire (Boiled Cocoyam Leaves)	2.06
Onion peels	4.98	Gari (Cassava Flakes) and Beans	3.09
Lettuce, Cucumber, Pepper, Tomato, Carrot, Garden Eggs	8.48	Fish	0.12
Cocoyam peels	3.19	Egg	0.05
Plantain peels	12.47	Yam	11.35
Yam peels	20.91
Cassava peels	23.54

Figure 2. Setup and equipment utilized in this study (a)oven, (b) furnace, (c) potentiometric setup for alkalinity, (d) pH meter, (e) COD instruments and (f) ICP-MS.

Fig. a. Gray and greenish blue electric dryer with crucibles inside Fig.b. Closed blue and gray electric furnace. Fig c. Potentiometric setup for alkalinity determination showing a pH metre, hand with gloves using the ph metre, beaker containing some samples, burette stand and electronic stirrer. Fig d. Left to Right: pH metre placed in a white beaker with a plain 250-ml beaker containing homogenised cow dung samples placed beside it. Fig e. Hach COD HR+ (200–15000 mg/L) test vials, Hach heating device with vials placed in them and DR 3900 spectrophotometer with a single feedstock containing vial being read. Fig f. White and black ICP-MS placed in a laboratory setting.

Table 2. Physical, Chemical and Compositional Characteristics of HE, FLO, KR and CD (mean (standard deviation); n = 3).

	Analysis	HE	FLO	KR	CD
Proximate Analysis	TS (% wet weight)	11.32 (0.03)	25.65 (0.02)	9.42 (0.01)	24.71 (0.18)
	VS (% of TS)	81.02 (0.05)	96.89 (0.06)	88.59 (0.09)	85.29 (0.03)
	VS (%)	9.17 (0.02)	24.85 (0.004)	8.35 (0.02)	21.08 (0.16)
	VS/TS	0.81 (0.001)	0.97 (0.001)	0.89 (0.001)	0.85 (0)
	MC (% wet weight)	88.68 (0.03)	74.35 (0.02)	90.58 (0.01)	75.29 (0.18)
	AC (% wet weight)	2.15 (0.01)	0.80 (0.02)	1.08 (0.01)	3.63 (0.02)
Compositional Analysis	Carbohydrate (% dry weight)	NA	56.88 (0.04)	63.67 (0)	64.40 (0.02)
	Crude protein (%)	NA	19.58 (0.03)	11.82 (0.01)	12.56 (0.01)
	Crude fat (% dry weight)	NA	3.22 (0.02)	0.36 (0.01)	0.61(0.01)
Ultimate Analysis	Carbon (%)	44.92 (0.02)	46.93 (0.03)	44.03 (0.03)	52.71 (0.03)
	Hydrogen (%)	7.71 (0.02)	8.24 (0.02)	10.96 (0.04)	6.29 (0.02)
	Nitrogen (%)	5.36 (0.06)	2.12 (0.03)	1.89 (0.02)	2.01 (0.04)
	Sulphur (%)	0.32 (0.03)	0.18 (0.03)	0.33 (0.02)	0.59 (0.02)
	Oxygen (%)	39.55 (0.09)	41.73 (0.04)	41.71 (0.04)	34.76 (0.05)
	C/N	8.39 (0.09)	22.14 (0.26)	23.34 (0.25)	26.19 (0.47)

Figure 3. (a) pH, (b) Alkalinity and (c) COD levels in HE, FLO, KR and CD.

Figure 4. Phosphorus, potassium, calcium, magnesium and sodium content in HE, FLO, KR and CD.

Table 3. Micronutrient Characteristics of HE, FLO, KR and CD (mean (standard deviation); n = 3).

Analysis	HE	FLO	KR	CD
Iron, Fe (mg/L)	2.64 (0.001)	11.86 (0.004)	5.64 (0.003)	14.18 (0.001)
Nickel, Ni (mg/L)	0.34 (0.001)	0.09 (0.001)	0.06 (0.001)	1.43 (0.01)
Zinc, Zn (mg/L)	1.36 (0.001)	7.40 (0.001)	9.76 (0.005)	1.29 (0.0004)
Chromium, Cr(mg/L)	0.36 (0.001)	0.06 (0.002)	0.03 (0.001)	4.32 (0.001)
Cobalt, Co (mg/L)	0.013 (0.0003)	0.005 (0)	0.004 (0)	0.203 (0.001)
Copper, Cu (mg/L)	0.95 (0.001)	0.23 (0.001)	0.36 (0.001)	1.25 (0.01)
Cadmium, Cd (mg/L)	0.003 (0)	0.002 (0)	0.004 (0)	0.01 (0.001)
Molybdenum, Mo (mg/L)	0.58 (0.001)	0.03 (0.001)	0.02 (0.001)	3.04 (0.01)
Manganese, Mn (mg/L)	0.23 (0.0001)	0.59 (0.01)	0.39 (0.01)	1.84 (0.001)
Selenium, Se (mg/L)	0.004 (0)	0.002 (0)	0.002 (0)	0.015 (0.0001)

Table 4. Reported stimulatory and inhibitory concentrations of metals on anaerobic biomass (expanded from Romero-Güiza et al. (2016)) compared with values from this study.

Trace Element	Values from this study (mg/L)	Stimulatory Concentration (mg/L)	Inhibitory Concentration (mg/L)	References
Ca	547.50–2308.33	100<Ca<1035	300<Ca<8000	Lo et al. (2012)
Mg	17.63–543.33	<720	NR	Lo et al. (2012)
Na	588.33–4184.83	100<Ca<350	3500<Na<8000	Lo et al. (2012)
K	494.50–3390.00	<400	400<K<28934	Lo et al. (2012)
Fe	2.64–14.18	<0.3	NR	Worm et al. (2009)
Ni	0.06–1.4	0.03<Ni<27	35<Ni<1600	Arthur et al. (2022) Altaş (2009) Fermoso et al. (2009)
Zn	1.29–9.76	0.03<Zn<2	7.5<Zn<1500	Altaş (2009) Li and Fang (2007)
Cr	0.03–4.32	0.01<Cr<15	27<Cr<2500	Altaş (2009) Li and Fang (2007)
Co	0.004–0.203	0.03<Co<19	35<Co<950	Fermoso et al. (2009) Arthur et al. (2022)
Cu	0.23–1.25	0.03<Cu<2.4	12.5<Cu<350	Altaş (2009) Li and Fang (2007)
Cd	0.002–0.01	<1.6	36<Cd<3400	Altaş (2009) Li and Fang (2007)
Mo	0.02–3.04	<0.05	NR	Worm et al. (2009)
Mn	0.23–1.84	<0.027	NR	Worm et al. (2009)
Se	0.002–0.015	<0.04	NR	Worm et al. (2009)

NR means Not Reported.

Table 5. Theoretical Biogas and Bio-Methane Potential of HE, FLO, KR, and CD.

Feedstock	Molecular Formula	Product Equation	BGPTH mL/gVS	BMPTH mLCH4/gVS	CH4 (%)
HE	^C3.74 ^H7.65 ^O2.47 ^N0.38 ^S0.01	2.06CH4 + 1.67CO2 + 0.38NH3 + 0.01H2S	946.93	472.50	49.90
FLO	^C3.91 ^H8.17 ^O2.61 ^N0.15 ^S0.01	2.27CH4 + 1.64CO2 + 0.15NH3 + 0.01H2S	918.72	512.05	55.74
KR	^C3.67 ^H10.87^O2.61 ^N0.13 ^S0.01	2.49CH4 + 1.18CO2 + 0.13NH3 + 0.01H2S	864.09	563.91	65.26
CD	^C4.39 ^H6.24 ^O2.17 ^N0.14 ^S0.02	2.37CH4 + 2.02CO2 + 0.14NH3 + 0.02H2S	1058.94	552.27	52.15

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Data availability statement

Data are available within the article or its supplementary materials.