Sustainability evaluation for a circular maize-pig system driven by indigenous microbes: a case study in Northeast China

Figures & data

Figure 1. Technical flow chart of Yunfeng Cooperative’s Maize-Pig system.

Figure 2. System emergy flow of separated and integrated maize-pig system.

a is the separated system and b is the integrated system. Red lines are the differences between the separated and integrated maize-pig systems.

Table 1. Agricultural input and output inventory lists of separated and integrated maize-pig systems.

Items	Unit	UEV (sej/Unit)	RNF	Raw data			Emergy value (sej)
				MS	PS	IS	MS	PS	IS
Input
Sun	J	1.00E+00	^b1.00	2.95E+10	9.32E+08	3.05E+10	2.95E+10	9.32E+08	3.05E+10
Wind	J	^a7.90E+02	^b1.00	1.22E+10	3.25E+08	1.25E+10	9.63E+12	2.57E+11	9.89E+12
Rain	J	^a1.28E+04	^b1.00	6.06E+10	6.37E+08	6.12E+10	7.75E+14	8.15E+12	7.83E+14
Groundwater	kg	^a4.96E+11	0.00	0.00E+00	5.70E+04	7.00E+04	0.00E+00	2.83E+16	3.47E+16
Fertilizer (N)	g	^b4.84E+09	^b0.00	5.56E+05		0.00E+00	2.69E+15		0.00E+00
Fertilizer (P)	g	^b4.97E+09	^b0.00	2.40E+05		0.00E+00	1.19E+15		0.00E+00
Fertilizer (K)	g	^b1.40E+09	^b0.00	2.40E+05		0.00E+00	3.36E+14		0.00E+00
Pig manure	g	^c1.61E+08	^c0.80	0.00E+00		1.05E+07	0.00E+00		1.68E+15
Pesticides	g	^b4.58E+09	^b0.00	1.04E+04		0.00E+00	4.77E+13		0.00E+00
Seeds	g	^c2.55E+05	^c1.00	6.37E+04		6.37E+04	1.62E+10		1.62E+10
Vitamin premix	g	^d1.89E+10	^d0.00		3.89E+06	1.44E+06		7.34E+16	2.71E+16
Maize	J	^d2.05E+04	^d0.11		4.44E+11	3.72E+11		9.08E+15	7.61E+15
Soybean meal	J	^d9.17E+04	^d0.33		8.94E+10	1.32E+11		8.20E+15	1.21E+16
Wheat bran	J	^d8.66E+04	^d0.11		1.06E+11	4.34E+10		9.15E+15	3.76E+15
Maize straw	J	^d9.40E+04	^d0.11		0.00E+00	1.94E+11		0.00E+00	1.83E+16
Electricity	J	^c2.20E+05	^d0.09	1.61E+04	1.89E+10	2.57E+10	3.54E+09	4.17E+15	5.65E+15
Diesel	J	^c1.81E+05	^d0.00	5.96E+07	1.04E+09	4.40E+08	1.08E+13	1.88E+14	7.96E+13
Labor	J	^e6.38E+05	^d0.12	2.21E+09	8.11E+09	4.04E+09	1.41E+15	5.18E+15	2.58E+15
Coal	g	^c5.81E+04	^d0.00		2.93E+05	0.00E+00		1.70E+10	0.00E+00
Vaccine	g	^d1.89E+10	^d0.00		5.57E+03	3.00E+03		1.05E+14	5.66E+13
Disinfectants	g	^d7.47E+12	^d0.00		1.61E+03	0.00E+00		1.21E+16	0.00E+00
Construction investment	$	^e2.58E+12	^d0.12		2.07E+03	6.60E+03		5.35E+15	1.70E+16
Equipment investment	$	^e2.58E+12	^d0.12		3.17E+00	3.17E+00		8.18E+12	8.18E+12
Y							6.46E+15	1.55E+17	1.37E+17
R							9.44E+14	6.36E+15	1.23E+16
RN							5.52E+15	1.49E+17	1.19E+17
Output
Maize yield	J			2.58E+11		0.00E+00
Maize straw	J			8.52E+10		0.00E+00
Pig meat	J				3.87E+11	4.56E+11
Pig manure	J				6.21E+11	0.00E+00

UEV is unit emergy value and RNF is renewability factors. Y is the total emergy, R is renewable emergy, and R_N is nonrenewable emergy. The global emergy baseline used in this paper is 1.20 × 10²⁵ sej/yr (Brown et al. 2016a).

^aParameters reference from (Brown et al. 2016b).

^bParameters reference from (Odum 1996).

^cParameters reference from (Lan, Qin, and Lu 2002).

^dParameters reference from (Wang et al. 2015).

^eParameters reference from (Cristiano, Ulgiati, and Gonella 2021). A blank value in the table means that the system does not have this input, and 0 means that the item input of this system is 0.

Figure 3. Boundaries of systems.

a is the maize production system (MS), b is the pig rearing system (PS), and c is the integrated maize-pig system (IS).

Table 2. Normalization and weight factors of potential environmental impacts.

Impact category	Unit	Global benchmarks (kg/Unit)	Weight factors
GWP	kg CO2-eq	6869.00	0.12
AP	kg SO2-eq	52.26	0.14
EP	kg PO4-eq	1.90	0.12
AT	kg 1,4DCB-eq	4.83	0.11
HT	kg 1,4DCB-eq	197.21	0.14
ST	kg 1,4DCB-eq	6.11	0.09

Parameters reference from (Liang 2009).

Table 3. Expressions and description of the emergy indexes.

Emergy index	Unit	Expression	Description
Unit emergy value (UEV)	sej/j	UEV = (Y+ Es)/E	Measure the unit emergy value of the system
Resource use efficiency (RUE)	sej/j	RUE = (RN+Es)/E	Measure the system internal resources use efficiency
Emergy yield ratio (EYR)	NA	EYR = Y/F	Measure the ability of the system to make available local resources by investing outside resources
Environmental loading ratio (ELR)	NA	ELR = RN/R	Measure environmental pressure resulting from the system
Emergy sustainability index (ESI)	NA	ESI = EYR/ELR	Evaluate the sustainability of the system

Y is the total emergy of the system; E is the system effective energy output; F is the external feedback of the system; R is the renewable resources; R_N is the nonrenewable resources; Es is the potential environmental services, with calculation reference (Wang et al. 2015).

Table 4. Economic indices of separated systems and integrated systems.

Items	MS	IMS	PS	IPS	SS	IS
Yield (kg/UF)	1.58E+04	2.28E+04	1.91E+04	2.25E+04	3.49E+04	2.25E+04
Cost ($)	2.07E+03	3.00E+03	1.83E+04	1.91E+04	2.04E+04	1.63E+04
Income ($)	4.08E+03	7.52E+03	5.30E+04	7.58E+04	5.71E+04	8.33E+04
Profit of unit ($/UF)	2.01E+03	4.52E+03	3.47E+04	5.67E+04	3.67E+04	6.71E+04
The ratio of income to cost	1.97	2.51	2.89	3.97	2.80	5.12

Table 5. Potential environmental impacts of separated and integrated maize-pig systems.

Item	Unit	Characterization results		Normalization results		Weighted evaluation results
		SS	IS	SS	IS	SS	IS
GWP	kg CO2-eq	2.97E+05	2.96E+05	4.32E+01	4.30E+01	5.18E+00	5.16E+00
AP	kg SO2-eq	1.21E+03	5.92E+02	2.32E+01	1.13E+01	3.25E+00	1.59E+00
EU	kg PO4-eq	7.45E+02	5.91E+01	3.92E+02	3.11E+01	4.71E+01	3.73E+00
HT	kg 1,4DCB-eq	1.66E+04	2.30E+00	8.43E+01	1.17E-02	1.18E+01	1.63E-03
AT	kg 1,4DCB-eq	5.21E+03	5.27E-01	1.08E+03	1.09E-01	1.19E+02	1.20E-02
ST	kg 1,4DCB-eq	2.10E+02	6.15E-03	3.44E+01	1.01E-03	3.09E+00	9.05E-05
Total		3.21E+05	2.96E+05	1.66E+03	8.56E+01	1.89E+02	1.05E+01

Figure 4. Source and composition for the potential environmental impact of systems.

Table 6. Results of emergy indices of separated and integrated systems.

Items	MS	IMS	PS	IPS	SS	IS
EYR	1.14	1.25	1.00	1.39	1.01	1.01
ELR	5.84	0.69	18.96	8.32	17.27	6.89
ESI	0.19	1.81	0.05	0.17	0.06	0.15
RUE (sej/j)	2.41E+04	4.32E+03	4.20E+05	1.83E+05	1.47E+06	1.87E+05
UEV (sej/j)	2.77E+04	1.05E+04	4.37E+05	2.05E+05	1.48E+06	2.14E+05

Figure 5. Emergy inputs structure of economic feedback resources for systems.

Table

Abbreviation	Full name
EME	Emergy accounting
LCA	Life cycle assessment
IS	Integrated maize-pig system
SS	Separated maize and pig system
IMS	Maize production of integrated system
IPS	Pig rearing of integrated system
MS	Maize production of separated system
PS	Pig rearing of integrated system
GWP	Global warming potential
AP	Aacidification potential
EP	Eutrophication potential
AT	Freshwater aquatic ecotoxicity
HT	Human toxicity
ST	Soil ecotoxicity
UEV	Unit emergy value
RUE	Resource use efficiency
EYR	Emergy yield ratio
ELR	Environmental loading ratio
ESI	Emergy sustainability index
RMB	Renminbi
USD	U.S. dollar

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