Emergy Evaluation of the Urban Solid Waste Handling in Liaoning Province, China

1. Introduction

2. Methodology

2.1. Description of the Present Urban Solid Treatment System in Liaoning

Liaoning is located in the southern part of China’s Northeast. Its nominal GDP for 2011 was 2.20 trillion yuan (ca. US$348 billion), making it the 7th largest in China (out of 31 provinces). After years of institutional and structural reforms, Liaoning Province abolished its Municipal Sanitation Bureau in 2000. The governmental function of sanitation work has also been incorporated into the Municipal Administration Commission. Currently, Liaoning residential garbage management agencies mainly consist of four departments: Municipal Administration Commission, Sanitation Service Centers at the district and county levels, Sanitation Management Departments at the district and county levels under the Municipal Administration Commission and Municipal Professional Sanitation Operating Units. The Municipal Administration Commission includes the Department of City Appearance Environmental Management, Public Institutions and the Department of Sanitation Facilities Management.

In 2011, the domestic waste treatment plants were initially developed to treat about 1.01 Mt per day generated by 16,585,459 inhabitants. Usually, the household urban waste is packed in plastic bags and left in waste containers, from which the waste is taken by a collection team (official manual collection and special trucks for compaction, as well as unofficial scavengers collecting recyclable materials. The formal waste collection system is formed. Some researchers have pointed out that the informal recycling of waste by scavengers not only constrains profits of the formal system, but also pollutes the environment if toxic substances leak when waste is not properly disposed of [32]. After collection, the waste can be handled in conventional ways in simple landfills (without leachate/sewage disposal systems), sanitary landfills, or incineration. Figure 1 shows that while the major amount of USW in Liaoning (80.5% in wet weight) is taken to simple landfills and sanitary landfills, only 7.5% is incinerated (45% by fluidized bed incineration and 55% by grate furnace incineration). Additionally, only 6.9% rather than 13.5% of the total USW is being effectively recycled (including biotic and abiotic materials).

Figure 1. Flowchart of urban solid waste destinations in Liaoning.

2.3. Evaluating the Impacts of Emissions

2.3.1. Quantifying Ecological Services

The treatment processes of three different kinds for pollutant discharges (i.e., airborne, waterborne and solid waste) that characterize urban systems are used to reduce discharges of pollutants into the environment and increase energy and materials recovery (reduce, reuse and recycle). After the waste treatment process, pollutants will be diluted or abated in order to decrease the concentration and potential harm to an acceptable level.

Many pollutant discharges after treatment are rendered harmless due to services provided by the ecosystem which dilute or abate the pollutant discharges to an acceptable concentration or state. The emergy value of these ecological services may be calculated from knowledge of the concentration and nature of the emissions, and the transformity conducted by the relevant ecological services. For example, the emergy required to dilute nitrogen dioxide in air may be determined with information about the concentration of the emissions, the acceptable or the background dilution concentration, and the dilution provided by wind.

Ecological services for diluting airborne and waterborne pollutants can be calculated as follows [26]:

$$M_{air/water}=d\times \left(\frac{W^{*}}{c}\right)$$

(1)

where M_air/water is the mass of dilution air/water needed; d is the air/water density; W^* is the annual amount of a given emitted pollutant after treatment; and c is the acceptable concentration from agreed regulations. The mass of air needed depends on meteorological conditions, including wind speed and stability. Using the “acceptable concentration” assumes that some pollution is acceptable. Instead, if the background concentration were used for “c”, this would have implied a pollution down to a level that is more or less the level before the industrial era. Many more environmental services would be needed than actually available, thus placing a constraint on the acceptability of emissions: no emissions that cannot be absorbed or abated by the environment. Once the dilution mass is known, the energy value of required environmental services is determined, by calculating the kinetic energy of the dilution air or the chemical energy of dilution water:

$${R_{w.air}}^{*}=N_{Kinetic}\times {tr}_{air}=\frac{1}{2}\times {M_{air}}^{*}\times v^2\times {tr}_{air}$$

(2)

$${R_{w.water}}^{*}=N_{Chem.}\times {tr}_{water}={M_{air}}^{*}\times \rho \times {tr}_{water}$$

(3)

$${R_w}^{*}=\text{Max}\left({R_{w.air,i}}^{*}\right)+\text{Max}\left({R_{w.water,i}}^{*}\right)$$

(4)

where N_Kinetic is the kinetic energy of air; v is average wind speed; tr_air is the transformity of wind; N_Chem. is the chemical energy of water; tr_water is the transformity of water; and ρ is the thermal value coefficient.

It is worth mentioning that this method is proposed without considering—for the sake of simplicity—the diffusion and the chemistry of atmosphere and water and there is a latent premise used in this analysis that the available dilution air/water is enough (which may not be true and would place a limit to the emissions, as said above).

2.3.2. Quantifying Ecological and Economic Losses

A number of methods have been developed in previous studies for assessing the environmental impact of emissions. It would be one step ahead to integrate such methods within a procedure capable of describing and quantifying the actual damage to populations or assets in emergy terms, i.e., in terms of lost biosphere work. Examples of such natural capital and human capital losses are, for example, the decreased biodiversity due to pollution or ecosystem simplification or the economic losses related to damages to human health, land occupation and degradation, damage to human-made assets, among others.

Many environmental impact assessment methods have been integrated into the LCA software (such as SimPRO, GaBi). In this study, a preliminary damage assessment of losses is performed according to the framework of the Eco-Indicator 99 assessment method [37]. Such methods, like all end-point life cycle impact assessment methods, suffers from very large uncertainties intrinsically embodied in its procedure for assessment of final impacts. Yet, it provides a preliminary—although uncertain—estimate of impacts to be used in the calculation procedure of total emergy investment. Damages to natural capital are expressed as the Potentially Disappeared Fraction (PDF) of species in the affected ecosystem, while damages to human health are expressed as Disability Adjusted Life Years (DALY), according to refs [37,38,39]. Six kinds of environmental impacts are listed in Table 1, which include carcinogenic effects on humans, respiratory effects on humans caused by organic substances, respiratory effects on humans caused by inorganic substances, damages to human health caused by climate change, damage to ecosystem quality caused by ecotoxic emissions, and damage to ecosystem quality caused by the combined effect of acidification and eutrophication.

Using concepts from E.I. 99 (PDF and DALY) to quantify a process impact on ecosystems and human health has the advantage that the assessment relies on damages that can, in principle, be measured or statistically calculated. Unfortunately, the available data in these ecological models are restricted to Europe (in most cases to The Netherlands) and their application to assess other countries requires adjustments [30] and calls for urgent database improvement. Moreover, the dose-response relationship considered in the Eco-indicator-99 is linear instead of logistic [39]. The latter characteristics suggest the method can only be applied to slow changes of pollutants concentration and are not suitable for large emissions fluctuations like environmental accidents.

The impact of emissions on human health can be viewed as an additional indirect demand for resource investment. Human resources (considering all their complexity: life quality, education, know-how, culture, social values and structures, hierarchical roles, etc.) can be considered as a local slowly renewable storage that is irreversibly lost due to the polluting production and use processes. Societies support the wealth and relations of their components in order to provide shared benefits. When such wealth and relations are lost, the investment is lost and such a loss must be charged to the process calling for changes and innovation. The emergy loss can be calculated as:

$${L_{w,1}}^{*}={\displaystyle \sum m_i^{*}\times {\text{DALY}}_i\times {\tau }_H}$$

(5)

Here, ${L_{w,1}}^{*}$ is the emergy loss in support of the human resource affected, i refers to the i-th pollutant, m^* is the mass of chemicals released, DALY is its E.I. 99 impact factor and τH is the unit emergy allocated to the human resource per year, calculated as τ_H = total annual emergy/population. The rationale here is that it takes resources to develop the given expertise or work ability and societal organization. When it is lost, new resources must be invested for replacement (not to talk of the value of the individual in itself, that is not quantifiable in physical terms).

Table 1. List of emissions and environmental impacts based on a hierarchist perspective.

Table 1. List of emissions and environmental impacts based on a hierarchist perspective.

Impact category	CAS no.	Group	Initial emission	Unit	1# DALY	2# DALY	3# DALY	4# DALY	5# PDF*m2*yr	6# PDF*m2*yr
Carbon dioxide (CO2)	124-38-9	inorganic	air	kg	-	-	-	2.10 × 10−7	-	-
Carbon Monoxide (CO)	630-08-0	inorganic	air	kg	-	-	-	-	-	-
Nitrogen oxides (as NOx)	11104-93-1	inorganic	air	kg	-	-	8.87 × 10−5	-	-	5.71
Sulphur dioxide (SO2)	7446-09-5	inorganic	air	kg	-	-	5.46 × 10−5	-	-	1.04
Dust (PM10)	-	inorganic	air	kg	-	-	3.75 × 10−4	-	-	-
Dinitrogen oxide (N2O)	10024-97-2	inorganic	air	kg	-	-	-	6.90 × 10−5	-	-
Methane (CH4)	74-82-8	nonaromatic (alkane)	air	kg	-	1.28 × 10−8	-	4.40 × 10−6	-	-
Mercury (II) ion	14302-87-5	metal	fresh water	kg	-	-	-	-	1.97 × 102	-
Cadmium (II) ion	22537-48-0	metal	fresh water	kg	7.12 × 10−2	-	-	-	4.80 × 102	-
Chromium (III) ion	16065-83-1	metal	fresh water	kg	3.43 × 10−1	-	-	-	-	-
Lead (II) ion	14280-50-3	metal	fresh water	kg	-	-	-	-	7.39	-
Arsenic (V) ion	17428-41-0	metal	fresh water	kg	6.57 × 10−2	-	-	-	1.14 × 101	-
Volatile phenol	108-95-2	aromatic	fresh water	kg	1.05 × 10−5	-	-	-	-	-
Cyanide	-	aromatic	fresh water	kg	4.16 × 10−5	-	-	-	-	-
Chemical oxygen demand (COD)	-	organic	fresh water	kg	-	-	-	-	-	-
Oil	-	organic	fresh water	kg	2.29 × 10−4	-	-	-	-	-
NH4-N	14798-03-9	inorganic	fresh water	kg	-	-	-	-	-	-

Notes: 1# Carcinogenic effects on humans; 2# Respiratory effects on humans caused by organic substances; 3# Respiratory effects on humans caused by inorganic substances; 4# Damages to human health caused by climate change; 5# Damage to Ecosystem Quality caused by ecotoxic emissions; 6# Damage to Ecosystem Quality caused by the combined effect of acidification and eutrophication.

PDF is the acronym for Potentially Disappeared Fraction of Species (Eco-Indicator 99 [37]). Such effects can be quantified as the emergy of the loss of local ecological resources, under the same rationale discussed above for the human resource:

$${L_{w,2}}^{*}={\displaystyle \sum m_i^{*}\times \text{PDF}{\left(\%\right)}_i\times E_{Bio}}$$

(6)

Here ${L_{w,2}}^{*}$ is the emergy equivalent of impact of a given emission on urban natural resource, while PDF(%) is the fraction potentially affected, measured as PDF × m² × yr × kg⁻¹. A damage of one in E.I. 99 means all species disappear from one m² during one year, or 10% of all species disappear from 10 m² during one year, etc. E_Bio is the unit emergy stored in the biological resource (seJ × m⁻¹ × yr⁻¹), which is presented as the emergy of local wilderness, farming, forestry, animal husbandry or fishery production.

As previously noted, additional emergy loss L_w,j should also be included to also account for pollution-induced damage to the city assets (e.g., facades of buildings, corrosion of monuments, etc.) according to reference [25]. This is not, however, included in the present study due to lack of sufficient data.

Finally, damage associated to solid waste generation can be measured by land occupation for landfill and disposal. This may be converted to emergy via the emergy/area ratio (upper bound, average emergy density of economic activities) or even via the emergy intensity of soil formation (lower bound, average environmental intensity). Thus the related emergy loss (L_w,3) can be obtained using the total occupied land area multiplied by the economic or environmental emergy intensity of such an area (choice depends on the area of the investigated system).

It is worth mention that not all the environmental impacts (such as climate change) occur at a local scale. As we live in a highly globalized world, economies of scale and comparative advantages exist in certain areas, which makes emissions “ownership” more complex. The multiple spatial scales between the environment and human socioeconomic systems can most easily be understood by modeling the world system as a whole. Simply trying to seek a single global solution that is implemented by national governmental units because of global impacts is far from satisfactory. The essential role of smaller-scale effects must be recognized. In this sense, under the “reciprocity” condition that the non-local environmental background value is not considered, we only focus on the local damage in this study.

3. Results

3.1. Emergy Flows

Emergy flow system diagram of four urban domestic waste treatment systems is shown in Figure 2, and emergy analysis results are listed in Table 2, Table 3, Table 4 and Table 5. For the current landfills in Liaoning, it was found out that more than 95.86% of fuel/goods input emergy came from diesel input (for transporting solid waste), and about 3.33% came from electricity inputs (mainly using for leachate disposal). There is a similar input proportion for sanitary landfills. 92.17% and 3.39% of input emergy came from diesel and electricity input, and about 4.44% came from sulfuric acid and chemical cleaners used for leachate disposal.

Figure 2. Emergy flow system diagram of four urban domestic waste treatment systems: (a) sanitary landfills; (b) fluidized bed incineration; (c) grate type incineration; (d) current landfills.

Table 2. The emergy analysis table of sanitary landfills.

Table 2. The emergy analysis table of sanitary landfills.

Category	Items	Basic data	Per Unit	Transformity (seJ/unit)	Reference	Solar emergy (seJ/t-waste)
Rw*	Oxygen involved in combustion processes	2.15 × 108	J/t-waste	4.14 × 105	[41]	8.88 × 1013
G	Diesel (transportation)	5.62 × 107	J/t-waste	1.11 × 105	After [42]	6.22 × 1012
	Electricity (transportation)	5.18 × 104	J/t-waste	1.74 × 105	After [42]	9.04 × 109
	Diesel (landfill)	3.47 × 106	J/t-waste	1.11 × 105	After [42]	3.84 × 1011
	Electricity (landfill)	1.34 × 106	J/t-waste	1.74 × 105	After [42]	2.33 × 1011
	Electricity (Leachate disposal)	0.00	J/t-waste	1.74 × 105	After [42]	0.00
	Sulfuric acid (Leachate disposal)	2.00 × 10−2	kg/t-waste	2.65 × 1012	[43]	5.30 × 1010
	Chemical cleaners (Leachate disposal)	1.00 × 10−1	kg/t-waste	2.65 × 1012	[43]	2.65 × 1011
F	Maintenance cost and services	5.65	$/t	1.13 × 1012	Country Emergy/$ ratio	6.38 × 1012
Output	Electricity	2.46 × 107	J/t-waste	1.74 × 105	After [42]	4.28 × 1012
Transportation	NMVCOC	1.36 × 10−2	kg/t-waste
	CO	1.50 × 10−2	kg/t-waste
	NOx	4.39 × 10−2	kg/t-waste
	CO2	4.14 × 10−2	kg/t-waste
	SO2	9.28 × 10−4	kg/t-waste
LFG emission	CH4	1.83 × 101	kg/t-waste
	CO2	3.35 × 101	kg/t-waste
	H2S	1.30 × 10−1	kg/t-waste
	NH3	6.00 × 10−2	kg/t-waste
	CO	5.00 × 10−2	kg/t-waste
Electricity generation	CO2	8.20 × 101	kg/t-waste
	NOx	1.70 × 10−1	kg/t-waste
	SO2	9.00 × 10−2	kg/t-waste
Leachate	COD	3.00	kg/t-waste
	TOC	9.00 × 10−1	kg/t-waste
	SS	7.50 × 10−2	kg/t-waste
	NH3-N	3.00 × 10−2	kg/t-waste

Table 3. The emergy analysis table of fluidized bed incineration.

Table 3. The emergy analysis table of fluidized bed incineration.

Category	Items	Basic data	Per Unit	Transformity (seJ/unit)	Reference	Solar emergy (seJ/t-waste)
Rw*	Oxygen involved in combustion processes	9.85 × 1011	J/t-waste	4.14 × 105	[41]	4.08 × 1017
G	Diesel (transportation)	6.78 × 107	J/t-waste	1.11 × 105	After [42]	7.50 × 1012
	Electricity (transportion)	5.18 × 105	J/t-waste	1.74 × 105	After [42]	9.04 × 1010
	electricity (pretreatment)	1.44 × 106	J/t-waste	1.74 × 105	After [42]	2.51 × 1011
	limestone	1.00	kg/t-waste	1.02 × 1010	After [44]	1.02 × 1010
	Electricity (incineration)	1.13 × 106	J/t-waste	1.74 × 105	After [42]	1.97 × 1011
	Diesel (Ignition)	6.91 × 107	J/t-waste	1.11 × 105	After [42]	7.64 × 1012
	Oxidizer (Coal)	2.90 × 108	J/t-waste	6.69 × 104	After [17]	1.94 × 1013
	Lotion (flue gas treatment)	5.00 × 10−2	kg/t-waste	2.65 × 1012	[43]	1.33 × 1011
	Electricity (flue gas treatment)	7.20 × 105	J/t-waste	1.74 × 105	After [42]	1.26 × 1011
	DTC-dithiocarbamate (ash treatment)	3.00 × 10−2	kg/t-waste	2.65 × 1012	[43]	7.95 × 1010
	Cement (ash treatment)	5.58 × 101	kg/t-waste	1.04 × 109	[45]	5.82 × 1010
	Electricity (ash treatment)	7.56 × 105	J/t-waste	1.74 × 105	After [42]	1.32 × 1011
F	Maintenance cost and services	6.24	$/t	1.13 × 1012	Country Emergy/$ ratio	7.05 × 1012
Output	Electricity	2.04 × 108	J/t-waste	1.74 × 105	After [42]	3.56 × 1013
	Slag	1.66 × 102	kg/t-waste	2.70 × 1012	[18]	4.47 × 1014
Flue gas discharge	CO2	1.26 × 103	kg/t-waste
	CO	7.11 × 10−1	kg/t-waste
	SO2	7.56 × 10−1	kg/t-waste
	NOx	6.86 × 10−1	kg/t-waste
Incineration	HCL	9.39 × 10−2	kg/t-waste
	PCDDs/PCDFs	1.50 × 10−10	kg/t-waste
	PM10	1.64 × 10−1	kg/t-waste
	NMVOC	1.77 × 10−2	kg/t-waste
	CO	1.95 × 10−2	kg/t-waste
Transportation	NOx	1.22 × 10−1	kg/t-waste
	CO2	5.45	kg/t-waste
	SO2	2.58 × 10−3	kg/t-waste

Table 4. The emergy analysis table of grate type incineration.

Table 4. The emergy analysis table of grate type incineration.

Category	Items	Basic data	Per Unit	Transformity (seJ/unit)	Reference	Solar emergy (seJ/t-waste)
Rw*	Oxygen involved in combustion processes	4.56 × 1011	J/t-waste	4.14 × 105	[41]	1.89 × 1017
G	Diesel (transportation)	6.91 × 107	J/t-waste	1.11 × 105	After [42]	7.64 × 1012
	Electricity (incineration)	1.13 × 106	J/t-waste	1.74 × 105	After [42]	1.97 × 1011
	Diesel (incineration)	1.45 × 108	J/t-waste	1.11 × 105	After [42]	1.60 × 1013
	Activated carbon (flue gas treatment)	7.20	kg/t-waste	2.65 × 1012	[43]	1.91 × 1013
	Electricity (flue gas treatment)	7.20 × 105	J/t-waste	1.74 × 105	After [42]	1.26 × 1011
	Diesel (flue gas treatment)	8.48 × 105	J/t-waste	1.11 × 105	After [42]	9.38 × 1010
	Lotion (flue gas treatment)	5.00 × 10−2	kg/t-waste	2.65 × 1012	[43]	1.33 × 1011
	DTC-dithiocarbamate (ash treatment)	3.00 × 10−2	kg/t-waste	2.65 × 1012	[43]	7.95 × 1010
	Cement (ash treatment)	5.58 × 101	kg/t-waste	1.04 × 109	[45]	5.82 × 1010
F	Maintenance cost and services	7.49	$/t	1.13 × 1012	Country Emergy/$ ratio	8.46 × 1012
Output	Electricity	8.25 × 107	J/t-waste	1.74 × 105	After [42]	1.44 × 1013
	Slag	2.57 × 102	kg/t-waste	2.70 × 1012	[18]	6.94 × 1014
Flue gas discharge	CO2	6.34 × 102	kg/t-waste
	CO	3.80 × 10−1	kg/t-waste
	SO2	4.26 × 10−1	kg/t-waste
	NOx	1.19	kg/t-waste
	HCL	1.12 × 10−1	kg/t-waste
	PM10	7.70 × 10−2	kg/t-waste
Transportation	NMVOC	1.62 × 10−2	kg/t-waste
	CO	1.79 × 10−2	kg/t-waste
	NOx	5.30 × 10−2	kg/t-waste
	CO2	5.01	kg/t-waste
	SO2	1.12 × 10−3	kg/t-waste

Table 5. The emergy analysis table of current landfills.

Table 5. The emergy analysis table of current landfills.

Category	Items	Basic data	Per Unit	Transformity (seJ/unit)	Reference	Solar emergy (seJ/t-waste)
Rw*	Air	-
G	Diesel (transportation)	5.62 × 107	J/t-waste	1.11 × 105	After [42]	6.22 × 1012
	Electricity (transportation)	9.96 × 104	J/t-waste	1.74 × 105	After [42]	1.74 × 1010
	Diesel (landfill)	8.31 × 105	kg/t-waste	1.11 × 105	After [42]	9.19 × 1010
	Electricity (Leachate disposal)	1.16 × 106	kwh/t-waste	1.74 × 105	After [42]	2.02 × 1011
	Sulfuric acid (Leachate disposal)	2.00 × 10−2	kg/t-waste	2.65 × 1012	[43]	5.30 × 1010
F	Maintenance cost and services	3.17	$/t-waste	1.13 × 1012	Country Emergy/$ ratio	3.59 × 1012
LFG emission	CH4	2.93 × 101	kg/t-waste
	CO2	5.44 × 101	kg/t-waste
	H2S	2.00 × 10−1	kg/t-waste
	NH3	1.00 × 10−1	kg/t-waste
	CO	8.00 × 10−2	kg/t-waste
Transportation	NMVOC	1.36 × 10−2	kg/t-waste
	CO	1.50 × 10−2	kg/t-waste
	NOx	4.39 × 10−2	kg/t-waste
	CO2	4.14	kg/t-waste
	SO2	9.28 × 10−4	kg/t-waste
Leachate	CODcr	2.43	kg/t-waste
	NH3-N	2.63 × 10−2	kg/t-waste
	SS	7.70 × 10−2	kg/t-waste

Compared with the two incineration systems, fluidized bed incineration process mainly needed diesel input (42.51%) and other emergy input (55.26%), which included coals as the oxidizer and DTC-dithiocarbamate and cements for ash treatment. For grate type incineration, 54.65% of input emergy came from diesel input (mainly for incineration), and about 44.60% came from activated carbon input (for flue gas treatment) and DTC-dithiocarbamate and cement used for ash treatment.

The emergy-based treatment costs are significantly different. Current landfills without leachate disposal system is the least expensive (1.022 × 10¹³ seJ/t-waste), followed by the sanitary landfills system (1.35 × 10¹³ seJ/t-waste). Two incineration systems seem to require more emergy inputs. For fluidized bed incineration process, 4.27 × 10¹³ seJ are used for treating 1t waste. It is much higher in grate type incineration (5.19 × 10¹³ seJ/t-waste). Therefore, if ecological service and emission’s impacts are not considered, the current landfill system shows promise for urban solid disposal based on the evolution of thermoeconomics.

3.2. Emission Impacts

Emission impacts are shown in Table 6. Our study will deal with the harmful emissions for the human health and ecosystem. Air emissions from both urban production and use include SO₂, dust, NO_x and CH₄ (respiratory disorders), CO₂, N₂O and CH₄ (climate change). Data about CO₂, N₂O and CH₄ are calculated as greenhouse gases released at local and global scales, based on direct and indirect energy consumption. The ecological losses caused by water emissions were not considered due to a lack of the corresponding coefficients. For sanitary landfill systems, the value of emission impacts on human health was 3.82 × 10¹⁵ seJ/t-waste, which mainly came from the damages to human health resulting from CH₄-caused climate change (62.54%), CO₂ (18.87%, climate change) and NO_x (14.74%, respiratory effects on humans caused by inorganic substances). The ecosystem loss mainly came from the damage to Ecosystem Quality caused by the combined effect of NO_x and SO₂’s acidification and eutrophication. The emission impacts of incineration systems were much higher than those of the landfill systems. The human health losses are 1.31 × 10¹⁶ seJ/t-waste and 8.81 × 10¹⁵ seJ/t-waste in fluidized bed incineration system and grate type incineration system respectively. The largest contributor was the damages to human health resulting from CO₂-caused climate change (60.38% and 45.29%). The ecosystem losses were mainly caused by NO_x’s acidification and eutrophication. The results also indicate that the human health losses caused by the harmful air emissions are ranked in this order: fluidized bed incineration > grate type incineration > current landfills > sanitary landfills, while the ecosystem losses are ranked: grate type incineration > fluidized bed incineration > sanitary landfills > current landfills. The changes of ordination are caused by the increased NO_x release of the extra treatment processes (such as electricity generation), which created a damage to ecosystem quality caused by the combined effect of acidification and eutrophication.

Table 6. Emergy analysis table of emissions’ impacts (Unit: seJ/t-waste).

Table 6. Emergy analysis table of emissions’ impacts (Unit: seJ/t-waste).

Impact category	Sanitary landfills		Fluidized bed incineration		Grate type incineration		Current landfills
	DALY Lw,1	PDF Lw,2	DALY Lw,1	PDF Lw,2	DALY Lw,1	PDF Lw,2	DALY Lw,1	PDF Lw,2
CO2	7.21 × 1014	-	7.91 × 1015	-	3.99 × 1015	-	3.65 × 1014	-
CO	0.00	-	0.00	-	0.00	-	0.00	-
NOx	5.63 × 1014	2.42 × 1015	2.13 × 1015	9.14 × 1015	3.27 × 1015	1.41 × 1016	1.16 × 1014	4.97 × 1014
SO2	1.47 × 1014	1.87 × 1014	1.23 × 1015	1.56 × 1015	6.92 × 1014	8.81 × 1014	1.50 × 1012	1.91 × 1012
TSP	0.00	-	1.83 × 1015	-	8.57 × 1014	-	0.00	-
N2O	0.00	-	0.00	-	0.00	-	0.00	-
CH4	2.39 × 1015	-	0.00	-	0.00	-	3.83 × 1015	-

The emergy loss associated with land occupation can be used as a measure of the environmental impact of discharged solid waste. On the basis of this, household solid waste would occupy 0.27 m²/t. The results in Table 7 show that the land occupations of the landfill systems were 3.23 × 10¹⁵ seJ/t-waste. Most of ecological services came from air environment service needed to offer oxygen involved in combustion processes. The maximum usage was 4.08 × 10¹⁷ seJ/t-waste in fluidized bed incineration system, which is twice as much as the usage in grate type incineration. Meanwhile, the grate type incineration system could produce 7.08 × 10¹⁴ seJ electricity with less than 1t solid waste, while the fluidized bed incineration system ranked a distant second with 4.83 × 10¹⁴ seJ/t-waste.

The results show that the total emergy usages of the four systems without considering economic and ecological losses are ranked in this order: grate type incineration (5.19 × 10¹³ seJ/t-waste) > fluidized bed incineration (4.27 × 10¹³ seJ/t-waste) > current landfills (2.92 × 10¹³ seJ/t-waste) > sanitary landfills (1.35 × 10¹³ seJ/t-waste). After considering the impacts of emissions, the total emergy usages are: sanitary landfills (3.87 × 10¹⁶ seJ/t-waste) > current landfills (3.71 × 10¹⁶ seJ/t-waste) > grate type incineration (2.39 × 10¹⁶ seJ/t-waste) > fluidized bed incineration (2.38 × 10¹⁶ seJ/t-waste). And the electricity yield ratios (Y/U) are ranked: grate type incineration (2.96%) > fluidized bed incineration (2.03%) > sanitary landfills (0.01%) > current landfills (0.00%). The results suggest that sanitary landfills, as one of the most economical waste treatment techniques, is only cost-effective in regions where land is suitable for landfilling. If the land is scarce (high emergy density) due to geographical constraints, the attractiveness of incineration is increasing. Notable among them is grate type incineration with high electricity yield ratio and low environmental impacts.

Table 7. The values of the four waste disposal methods’ emergy based indicators (Unit: seJ/t-waste).

Table 7. The values of the four waste disposal methods’ emergy based indicators (Unit: seJ/t-waste).

Category	Equation	Sanitary landfills	Fluidized bed incineration	Grate type incineration	Current landfills
Rw*	-	8.88 × 1013	4.08 × 1017	1.89 × 1017	0.00
G	-	7.16 × 1012	3.56 × 1013	4.34 × 1013	6.58 × 1012
F	-	6.38 × 1012	7.05 × 1012	8.46 × 1012	2.26 × 1013
Y	-	4.28 × 1012	4.83 × 1014	7.08 × 1014	0.00
Lw,1*	Lw,1*=∑mi* × DALYi × τH	3.82 × 1015	1.31 × 1016	8.81 × 1015	4.31 × 1015
Lw,2*	Lw,2*=∑mi* × PDF(%)i × EBio	2.61 × 1015	1.07 × 1016	1.50 × 1016	4.99 × 1014
Lw,3	-	3.23 × 1016	-	-	3.23 × 1016
U	G + F + Lw,1* + Lw,2* + Lw,3	3.87 × 1016	2.38 × 1016	2.39 × 1016	3.71 × 1016

4. Discussion

Table 8. The recommended legal framework of the residential garbage management in Liaoning.

5. Conclusions

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