The Treatment of Municipal Solid Waste in Cambodia, Thailand and Vietnam: An Environmental and Technological Analysis of Current and Future Scenarios

Abstract

The population growth of South-Asian countries is contributing significantly to the escalating volume of municipal solid waste (MSW). Presently, waste management in this region predominantly relies on landfilling, necessitating a shift towards a more sustainable paradigm. To address this imperative, this study explores the feasibility of extending the European-based waste management system for treating MSW in Cambodia, Thailand, and Vietnam. Assuming as current scenario the direct disposal in landfill, the environmental and technical performances of five other proposed scenarios based on the following technologies were assessed: mechanical–biological treatment; incineration; their combination; mechanical recycling; composting and anaerobic digestion. As expected, all alternative technologies showed potential for improving the current scenario. However, from an environmental point of view, incineration of mixed MSW emerged as the sole option that yielded a discernible environmental benefit for all the countries involved in the study (achieving a carbon footprint of about −0.111 t-CO₂-Eq./FU). Recycling-based scenarios achieved higher benefits for Thailand and Vietnam (−0.145 and −0.186 t-CO₂-Eq./FU, respectively), but not Cambodia (0.072 t-CO₂-Eq./FU) due to the lack of valuable materials to recycle. Technical findings showed how separate collection remains the system generating the least amount of waste for disposal (about 0.185 t), having a synergic effect on the combined approach of mechanical–biological treatment and incineration, which boasts the highest specific energy yield (about 0.339 and 1.183 kW/t, for electric and thermal energy, respectively). These results underscore the imperative to extend the analysis to the economic domain, combining diverse criteria to identify the most sustainable solution.

1. Introduction

The management of municipal solid waste (MSW) is a critical issue in developing countries, where urbanization, population growth, and economic development have led to increased waste generation [1]. The lack of effective MSW infrastructure, technology, and funding in many developing countries is the main reason for this increasing pressure on society [2]. As a consequence, in several developing countries, the inefficiency of governments, MSW management authorities, and treatment facilities has resulted in unsustainable and hazardous waste disposal practices, such as open dumping and burning [3], which pose significant environmental and health risks to communities [4]. In particular, concerning open burning of MSW, a recent study has pointed out how among 18 main hazard–pathway–receptor combinations, seven were scored as having high harm potential and six as medium/high [5]. On the other hand, the main drawbacks associated with open landfilling of MSW are related to underground water pollution due to the leaching of substances of concern, odor pollution from the deposition of MSW, and marine pollution from any potential runoff [6].

Despite the challenges, developing countries have a unique opportunity to adopt sustainable and innovative waste management strategies that can mitigate the negative impacts of waste on the environment and public health, while also generating economic and social benefits [7]. Effective MSW management can contribute to climate change mitigation, resource conservation, and job creation, while also promoting public participation, awareness, and education [8].

In this context, the development and implementation of a comprehensive MSW management system that integrates waste reduction, reuse, recycling, and safe disposal practices are crucial for sustainable urban development in developing countries [9,10]. This requires a multidisciplinary approach that involves government, private sector, civil society, and international organizations working together to address the complex and interrelated issues of waste management in developing countries [11].

On the other hand, developing countries face significant challenges in identifying a suitable and appropriate MSW management system. Indeed, the best combination of a source reduction approach, treatment technologies, and material and/or energy recovery is not unique and it strictly depends on various factors such as availability of funds, local conditions, and waste characteristics. For instance, the most sustainable MSW management system in Tanzania from a social, economic, and environmental point of view could be the one that provides composting for organic waste, recycling for plastic, paper, glass and metals waste, while the remaining waste, 20.25% of the total, would go to sanitary and/or bioreactor landfills [12]. In contrast, incineration of MSW in Chile would be a more sustainable option than landfill with gas flaring or gas energy recovery, savings 11.3% GHG emissions and 21.8% particulate matter compared to the current one [13]. In Brazil, MSW incineration did not show significant benefits over sanitary landfilling, due to limitations in energy utilization and the low-carbon background electricity [14]. In particular, in the city of Sao Paulo, the highest environmental sustainability among different MSW management systems was achieved by the one with the highest separate collection rates, based on recyclables recovery and anaerobic digestion of organic waste [15].

It is worth noting that context specificities can highly influence the performance of MSW management systems, which have not been widely studied in southern Asian countries. Hence, the aim of this work was to assess from the environmental and technical points of view the performance of different EU-based MSW treatment schemes for three Asian countries, namely Cambodia, Thailand, and Vietnam. The focus was placed at first on mixed MSW collection, which is by far the most common scheme in these countries. Not considering the current issues faced by these countries in sustaining a proper MSW separate collection scheme, the investigation was extended to the possibility of adopting a separate collection scheme for materials recycling. Considering the scope, the carbon footprint of each scenario proposed was calculated as well as a composite technical indicator for materials recycled, energy recovered, and waste disposed in landfill.

2. Materials and Methods

2.1. Framework of the Study

The three countries (Cambodia, Thailand, and Vietnam) considered in the study are characterized by a growing population (in 2022, about 17, 70, and 98 million, respectively) and a tropical monsoon climate. In 2016, the amount of MSW produced by Cambodia, Thailand, and Vietnam was 1,159,859, 27,268,302, and 11,562,740 tons, respectively, the main part of which was composed of organic waste (about 40–50%) [16]. Since disposal of MSW in landfills is the predominant solution, the current MSW management system has a significant impact on the environment.

The assessment boundaries of this work comprised the treatment and disposal of MSW in Cambodia, Thailand, and Vietnam, excluding collection and transportation. To enable a comparative analysis between the countries, a functional unit (FU) of 1 ton/y of MSW was considered.

Table 1. Composition, proximate, and ultimate characterization of MSW from Cambodia, Thailand, and Vietnam.

MSW Fraction	Cambodia 1	Thailand 2	Vietnam 3	Proximate Analysis [%]			Ultimate Analysis [%]					Ref. *
				Combustible	Water	Ash	C	H	O	N	S
Food waste	46.2%	39.7%	47.8%	18%	78%	4%	47%	7%	42%	3.8%	0.1%	[17]
Yard waste	3.6%	2.6%	8.9%	56%	35%	9%	39%	5%	41%	10%	1%	[18]
Paper	7.1%	12.2%	19.7%	70%	20%	10%	44%	6%	49%	0.2%	0.02%	[17]
Flexible plastic	14.8%	24.7%	8.0%	74%	17%	9%	74%	11%	11%	0%	0%	[17]
Rigid plastic	6.5%	6.3%	4.9%	74%	17%	9%	74%	11%	11%	0%	0%	[17]
Metals	1.0%	3.5%	1.2%	0%	0%	100%
Textiles	8.1%	4.1%	4.3%	92%	3%	5%	58%	5%	36%	1%	0%	[19]
Glass	1.0%	4.7%	1.9%	0%	0%	100%
Wood	7.1%	1.0%	1.7%	60.3%	18%	22%	52%	7%	40%	1%	0%	[20]
Inert	4.5%	1.1%	1.6%	0%	0%	100%

¹ Values reported for Cambodia are the average of [21] and [22]; ² values reported for Thailand are the average of [23] and [24]; ³ values reported for Vietnam are the average of [25] and [26]. * The values reported in table have been adapted from the respective references.

presents the MSW composition in Cambodia, Thailand, and Vietnam classified into the following categories: organic waste (food and yard waste), paper, plastic (flexible and rigid), metals, textiles, glass, wood, and inert. Table 1 also summarizes the proximate and ultimate analysis of each category.

2.2. Scenario Description

Six waste management scenarios have been considered in the study: one representing the current MSW management (base scenario) and five scenarios presenting different treatment proposals to manage MSW. Each scenario was assessed for the context of Cambodia, Thailand, and Vietnam by varying the MSW composition that characterized each country (Table 1).

The first scenario (S0) represented the existing MSW management option based on the disposal in landfill of all collected waste. For the scope, a basic MSW sanitary landfill was considered, assuming no biogas recovery for energy production.

Scenario 1 (S1) focused on the incineration of all MSW FU in a specific plant for energy recovery. It was assumed that the MSW incineration plant generated electric and thermal energy through a combined heat and power (CHP) system, supplying the electricity and hot water from the MSW combustion to public facilities or households around the plant [27]. The incinerator scale was calculated dividing the FU by the number of working days of the incinerator plant. The amount of ash produced during the process was assumed to be disposed of in a specific landfill site for inert waste.

Scenario 2 (S2) considered MSW pretreatment through mechanical–biological treatment (MBT) before disposal in landfill. The entire amount of waste was sent to an MBT plant and then landfilled. Concerning the MBT technologies, there is a wide variety of schemes and layouts with different yields and performances [28]. In this case, an aerobic MBT plant with 7-day processing with temperature and oxygen control was considered. This treatment allows degradation of the easily biodegradable fractions of MSW, obtaining a dry and stable residual output [29]. For this scenario, at the end of the MBT process, the whole output was disposed of in the same landfill as described in S0.

Scenario 3 (S3) combined the two treatment technologies presented in S1 and S2, considering a system composed of MBT followed by incineration. In this scenario, the MSW was first pre-treated in the MBT plant (as described in S2) and the processed waste in output was sorted in a dry-fraction stream (mainly composed of plastic, paper, and textiles) and in a stabilized one (mainly composed of degraded organic waste). The first stream was sent to the incineration plant (as described in S1), while the stabilized stream was disposed of in MSW landfill (as described in S0).

Scenarios 4 and 5 (S4 and S5, respectively) were created assuming the introduction of a separate collection system, in which collected waste was then recycled through specific technologies. The MSW FU was divided in a separate collected stream and in a residual mixed one. The separated collected stream was composed of five separated streams for the following fractions: organic waste (food and yard waste), paper, plastic (flexible and rigid), metals, and glass. Each separately collected material had a specific diversion factor (as explained in Section 2.3.4.) according to the user separate collection rate, estimating the amount of waste diverted from the mixed collection to the separate one. Dry fractions (paper, plastic, metals, and glass) were mechanically recovered into new raw materials in an appropriate recycling plant. Organic waste was treated through a composting (S4) and combined anaerobic digestion (AD)-composting scheme (S5). Composting was characterized by an oxygen- and temperature-controlled aerobic degradation, producing compost for agricultural use. AD was assumed to work in wet and mesophilic conditions, producing biogas that was combusted in a CHP for energy recovery. The output from AD was sent to a further composting system. The composting and AD plant scales were calculated dividing the inlet waste by the respective number of working days of the plants. The residual fraction was treated according to the scheme described in S3.

The proposed scenarios are summarized in Figure 1.

2.3. Techno-Environmental Analysis

2.3.1. Incineration Setting

The incineration process was modelled in accordance with [17], as explained below. For each waste category input to the plant, the lower heating value was calculated: for food waste we used Steuer’s equation (Equation (1)), while for the remaining categories Equation (2) was adopted.

$${LHV}_i=4.184\times \left\{8100\times \left(\%C-\frac{3}{8}\%O\right)+5700\times \frac{3}{8}\%O+\mathrm{34,500}\times \left(\%H-\frac{\%O}{16}\right)+2500\times \%S-600\times \left(9\times \%H+\%w\right)\right\}$$

(1)

$${LHV}_i=4.184\times \left(4500\times \%f-600\times \%w\right)$$

(2)

where LHV_i = lower heating value [kJ/kg]; %C = weight percentage of carbon [%]; %O = weight percentage of oxygen [%]; %H = weight percentage of hydrogen [%]; %S = weight percentage of sulfur [%]; %w = weight percentage of water [%]; %f = weight percentage of combustible content [%].

The electric and thermal energy produced from the MSW incineration were calculated through Equation (3). The calculation was based on the LHV obtained from Equations (1) and (2), assuming an electric and thermal energy efficiency of 20% and 85%, respectively [17].

$$E_{el/th}={LHV}_i\times \frac{1000}{3600\times 24}\times S_{Inc}\times \eta$$

(3)

where E_el = electric energy produced from MSW combustion [kW]; E_th = electric energy produced from MSW combustion [kW]; LHV_i = average lower heating value of the MSW input to incineration plant [kJ/kg]; S_Inc = scale of the incinerator treatment [t/d]; η = electric (20%) or thermal (85%) energy efficiency of the CHP system [%].

The amount of ash A_out produced from the incineration was calculated considering the ash content (as reported in Table 1) of each fraction input in the process, as expressed in Equation (4):

$$A_{out}={MSW}_{in}\times \sum _{i=1}^n{\%Fin}_i\times {\%Ash}_i$$

(4)

where MSW_in = amount of MSW input to the incineration plant [t]; %Fin_i = percentage of the i MSW fraction of the MSW input to the incineration plant; %Ash_i = ash content of the i MSW fraction of the MSW input to the incineration plant; n = number of MSW fraction = 10 (food waste; yard waste; paper; flexible plastic; rigid plastic; metals; textiles; glass; wood; inert).

The carbon footprint of the MSW incineration process (CF_Inc) was obtained by evaluating the contribution of the processes that cause environmental burden (B_i) or credit (C_i), as shown in Equation (5).

$${CF}_{Inc}=B_1+B_2+B_3-C_1-C_2$$

(5)

where CF_Inc = carbon footprint of the whole incineration process [t-CO₂-Eq./FU]; B₁ = equivalent CO₂ emission from waste incineration [t-CO₂-Eq./FU]; B₂ = equivalent CO₂ emission from energy consumption of the incineration plant during operation [t-CO₂-Eq./FU]; B₃ = equivalent CO₂ emission converting the N₂O generated during waste incineration [t-CO₂-Eq./FU]; C₁ = equivalent CO₂ emission reduced by electric energy generation [t-CO₂-Eq./FU]; C₂ = equivalent CO₂ emission reduced by thermal energy use [t-CO₂-Eq./FU].

Each member of Equation (5) is calculated according to the methodology explained in [17], as noted below. B₁ was calculated following Equation (6), considering only plastic (flexible and rigid) and textiles. Paper, wood, food, and yard waste categories were excluded because they are carbon neutral, while metals, glass, and inert waste were excluded as well since they are incombustible.

$$B_1={MSW}_{in}\times \left({\gamma }_p+{\gamma }_t\right)\times \frac{{\gamma }_p\times {\gamma }_{pc}+{\gamma }_t\times {\gamma }_{tc}}{{\gamma }_p+{\gamma }_t}\times \frac{{\gamma }_p\times {\%C}_p\times {\gamma }_{pc}+{\gamma }_t\times {\%C}_t\times {\gamma }_{tc}}{{\gamma }_p\times {\gamma }_{pc}+{\gamma }_t\times {\gamma }_{tc}}\times \frac{44}{12}$$

(6)

where γ_p = plastic (flexible and rigid) fraction of MSW input [%]; γ_t = textile fraction of MSW input [%]; γ_pc = percentage of combustible content of plastic (flexible and rigid) fraction in MSW input [%]; γ_tc = percentage of combustible content of textile fraction in MSW input [%]; %C_p = weight percentage of carbon in plastic (flexible and rigid) fraction in MSW input [%]; %C_t = weight percentage of carbon in textile fraction in MSW input [%].

B₂ was calculated following Equation (7), assuming an energy consumption of the incineration plant equal to 140 kWh/t [17].

$$B_2=\frac{140\times {MSW}_{in}\times F_e}{1000}$$

(7)

where F_e = electric power emission factor = 0.512 [kg-CO₂-Eq./kWh].

B₃ was calculated following Equation (8), assuming that NO_x emissions were 0.017% of the MSW incinerated and that 1.54% of these emissions were N₂O [17].

$$B_3=0.017\%\times {MSW}_{in}\times 1.54\%\times F_{N2O}$$

(8)

where F_N2O = N₂O to CO₂ warming conversion factor = 265 [t-CO₂/t-N₂O] [30].

The environmental credits C₁ and C₂ were calculated following Equations (9) and (10), assuming that the heat supply was 60% of the power generated by the incineration plant and all the heat was supplied.

$$C_1=\frac{E_{el}\times 24\times d\times F_e}{1000}$$

(9)

$$C_2=\frac{E_{th}\times 24\times d\times \frac{3600}{1000}\times 0.6}{V_k\times \frac{F_k}{1000}}$$

(10)

where d = number of working days = 280 [days]; V_k = kerosene calorific value = 36.49 [MJ/L]; F_k = kerosene emission factor = 2.489 [kg-CO₂-Eq./L] [17].

2.3.2. Mechanical–Biological Treatment Setting

The MBT facility was modelled according to the degradation scheme explained in [31]. At the end of the process, the inlet MSW had a weight reduction of 25.93%: the different fractions were calculated assuming a weight reduction of only paper and textiles (30% and 20% respectively), while the food waste and yard waste categories were obtained as a difference. The screening process separating dry and wet fraction was modelled assuming a sorting efficiency of each category [31], as summarized in

Table 2. Sorting efficiency for each MSW category of dry and wet fraction at the end of the MBT process [31].

Category	Dry Stream	Wet Stream
Food waste	2%	98%
Yard waste	2%	98%
Paper	50%	50%
Plastic (flexible and rigid)	71%	29%
Metals	60%	40%
Textiles	75%	25%
Glass	4%	96%
Wood	56%	44%
Inert	4%	96%

.

The carbon footprint of MBT (CF_MBT) can be obtained using Equation (5), which is explained in the previous section. However, the equation can be summarized to the single factor of B₂ (as shown in Equation (7)), assuming the energy consumption of the MBT plant as 30 kWh/t (primary data). The CO₂-Eq. emissions obtained from the decomposition of organic material derived from biomass sources (e.g., food waste, wood, etc.) were not included in the calculation because the carbon was of biogenic origin [32].

2.3.3. Landfill Setting

The uncontrolled emission of landfill gas to the air from the decomposition of degradable MSW fractions is the main landfill-related impact. The main issue in the operation of municipal waste landfills is the emission of two gases (CH₄ and CO₂), which are also the basic greenhouse gases [33]. In order to estimate the potential CH₄ emission from the surface of a landfill in operation, the IPCC default model was applied, based on the IPCC standard method for input parameters of a landfill [32]. As explained above, the CO₂ emissions were not accounted for since the carbon generated was of biogenic origin.

The IPCC method allows one to estimate the annual amount of fugitive CH₄ emission landfill surface to the air through a limited set of parameters, for which the IPCC guidelines provide default values [34]. As explained in [35], the potential production of CH₄ L_O [Gg CH₄/Gg MSW] was calculated (via Equation (11)):

$$L_o=MCF\times DOC\times {DOC}_F\times F\times \frac{16}{12}$$

(11)

where MCF = correction factor (depending on the type of landfill) [-]; DOC = degradable organic carbon content [GgC/Gg MSW]; DOC_F = fraction of carbon that eventually undergoes decomposition [%]; F = CH₄ content by volume in the landfill gas [%]. The default values of 0.6, 0.77, and 0.5 were used for MCF, DOC_F, and F, respectively.

DOC was calculated according to Equation (12), which takes into account the composition in percentage content by mass of the incoming waste to be landfilled [35]:

$$DOC=\left(0.4\times A\right)+\left(0.17\times B\right)+\left(0.15\times C\right)+\left(0.3\times D\right)$$

(12)

where A = paper, cardboard, and textile fractions of the incoming waste; B = waste from parks, gardens, and other organic waste of the incoming waste; C = food waste fraction of the incoming waste; D = wood fraction of the incoming waste.

The potential volume of CH₄ emission from the landfill surface was calculated as shown in Equation (13):

$$E_{CH4}=\left[\left({MSW}_{in}\times L_O\right)-R\right]\times \left(1-OX\right)$$

(13)

where MSW_in = amount of MSW input to the landfill [t]; R = volume of CH₄ from the landfill, recovered and neutralized in the landfill [Gg]; OX = oxidation index in soil or in the material covering the waste [-]. The default value of 0 was used for both R and OX.

Finally, the carbon footprint of MSW landfilling (CF_Lan) was obtained converting the methane generated to equivalent CO₂, as explained in Equation (14):

$${CF}_{Lan}=E_{CH4}\times 28\times 1000$$

(14)

where 28 = CH₄ to CO₂ warming conversion factor [t-CO₂/t-CH₄] [30].

2.3.4. Separate Collection and Mechanical Recycling Setting

Recycling is associated with the environmental credit resulting from the recovery of materials obtained from separate collection. It was assumed that the MSW fractions involved in separate collection and further recycling were food waste and yard waste such as organic waste, paper, plastic (flexible and rigid), and metals and glass as dry waste. A specific diversion factor was assumed for each separate collected waste fraction in order to estimate the amount of waste properly collected and diverted from a mixed to a separate collection. In particular, the diversion factors were 85% for organic waste (both food and yard waste), 75% for paper, 95% for both metals and glass, and 3.5% and 24% for flexible and rigid plastic, respectively (values adapted from [36]). It is important to note that the diversion factors of plastic waste are much lower than the other ones since they account for only the polymers and items which are actually recyclable (PET, HDPE, PP, and LDPE) [37,38]. The carbon footprint of the separate collection scheme was neglected.

Organic waste was recycled according to the model explained in Section 2.3.5, while the carbon footprint of separate collected dry MSW recycling (CF_Rec,D) was obtained through Equation (15):

$${CF}_{Rec,D}=\sum _{i=1}^n{SCDMSW}_i\times F_{Rec,i}$$

(15)

where SCDMSW_i = amount of separate collected dry MSW of the i MSW fraction [t]; F_Rec,i = emission factor of the i MSW dry fraction separate collected [t-CO₂/t-MSW]; n = number of MSW dry fraction separate collected = 5 (paper, flexible plastic, rigid plastic, metals and glass). F_Rec,i values were assumed to be −0.550 t-CO₂/t-MSW, −0.972 t-CO₂/t-MSW, −1.782 t-CO₂/t-MSW, −4.367 t-CO₂/t-MSW and −1.067 t-CO₂/t-MSW for paper, flexible plastic, rigid plastic, metals and glass, respectively (values adapted from [39,40]). Since material recovery represents emissions savings, these factors include a minus sign. In particular, the value for flexible plastic was assumed to be that of LDPE while that of rigid plastic was a combination of PET, HDPE, and PP according to the proportion presented in [37].

2.3.5. Organic Recycling Setting (Anaerobic Digestion and Composting)

Organic waste collected separately was treated through anaerobic digestion (AD) and/or composting. In S4, the whole amount of organic waste was treated through composting only, producing compost for agricultural use. In S5, only food waste was treated through AD, while yard waste (mixed with the digestate in output from AD) was treated through composting. The AD plant converted organic waste into a CH₄-rich biogas, which was then converted in electric and thermal energy through a CHP system. The final degradation of the food waste input to the AD system was assumed equal to 95%. An example of the environmental performance for S5 is provided in Appendix A.

The carbon footprint of AD (CF_AD) was obtained using Equation (5), considering only the factors of B₂ and C₁. B₂ was calculated as shown in Equation (7), assuming the energy consumption of the AD plant was 60 kWh/t (primary data). In this case, C₁ was calculated by Equation (16):

$$C_1=\frac{{SCFW}_{in}\times B_Y\times {LHV}_B\times \eta \times F_e}{1000}$$

(16)

where SCFW_in = amount of separate collected food waste in input to the AD plant [t]; B_Y = biogas yield from food waste digestion (primary data) [Nm³/t-FW]; LHV_B = lower heating value of the biogas produced (primary data) [kWh/Nm³]; η =electric energy efficiency of the CHP system = 35 [%] [41]. An important assumption of this study was that the amount of thermal energy produced from AD was used as self-thermal consumption of the AD process itself. For this reason, CF_AD did not consider the C₂ factor.

The carbon footprint of composting (CF_C) can be obtained using Equation (5), considering only the factors of B₂ and B₃, plus a credit from the compost use, C₃. B₂ was calculated as shown in Equation (7), assuming the energy consumption of the composting plant was 24 kWh/t (primary data). B₃ was calculated via Equation (17):

$$B_3={OW}_{in}\times F_{C,N2O}\times F_{N2O}$$

(17)

where OW_in = amount of organic waste input to the composting plant [t]; F_C,N2O = composting N₂O emission factor = 5 × 10⁻⁵ [t-N₂O/t-OW] [42]. The CO₂-Eq. emissions obtained from the decomposition of organic material derived from biomass sources (e.g., food waste, wood, etc.) were not included in the calculation because the carbon was of biogenic origin [32].

C₃ was calculated through Equation (18):

$$C_3={OW}_{in}\times F_C\times C_{out}$$

(18)

where F_C = emission factor for the use of compost in agriculture = −0.050 [t-CO₂/t-compost] [39]; C_out = specific compost production of the composting plant = 0.46 [t-compost/t-OW] (primary data).

3. Results

The technical and environmental results of each country for each scenario proposed are summarized in

Table 3. Environmental results in terms of carbon footprint [t-CO₂-Eq./FU].

Country	Category	S0	S1	S2	S3	S4	S5
Cambodia	Burden	1.360	0.661	0.956	1.010	0.622	0.634
	Landfill	1.360		0.941	0.576	0.218	0.218
	MBT			0.015	0.015	0.007	0.007
	Incineration (burden)		0.661		0.419	0.386	0.386
	MSW combustion		0.589		0.399	0.369	0.369
	Process		0.072		0.020	0.017	0.017
	N2O		0.001		0.000	0.000	0.000
	AD (burden)						0.012
	Composting					0.011	0.010
	Process					0.005	0.005
	N2O					0.006	0.005
	Credit	0.000	−0.746	0.000	−0.442	−0.521	−0.562
	Recycling (dry)					−0.115	−0.115
	Paper					−0.029	−0.029
	Plastic					−0.033	−0.033
	Metal					−0.042	−0.042
	Glass					−0.010	−0.010
	Recycling (compost)					−0.010	−0.009
	AD (credit)						−0.041
	Incineration (credit)		−0.746		−0.442	−0.397	−0.397
	Power supply		−0.336		−0.199	−0.179	−0.179
	Heat supply		−0.411		−0.243	−0.218	−0.218
	Total	1.360	−0.085	0.956	0.568	0.101	0.072
Thailand	Burden	1.141	0.775	0.722	0.980	0.615	0.625
	Landfill	1.141		0.707	0.453	0.126	0.126
	MBT			0.015	0.015	0.007	0.007
	Incineration (burden)		0.775		0.511	0.472	0.472
	MSW combustion		0.703		0.488	0.455	0.455
	Process		0.072		0.023	0.018	0.018
	N2O		0.001		0.000	0.000	0.000
	AD (burden)						0.010
	Composting					0.009	0.009
	Process					0.004	0.004
	N2O					0.005	0.005
	Credit	0.000	−0.855	0.000	−0.461	−0.735	−0.770
	Recycling (dry)					−0.279	−0.279
	Paper					−0.050	−0.050
	Plastic					−0.035	−0.035
	Metal					−0.146	−0.146
	Glass					−0.048	−0.048
	Recycling (compost)					−0.008	−0.008
	AD (credit)						−0.035
	Incineration (credit)		−0.855		−0.461	−0.448	−0.448
	Power supply		−0.385		−0.207	−0.201	−0.201
	Heat supply		−0.470		−0.254	−0.246	−0.246
	Total	1.141	−0.080	0.722	0.519	−0.120	−0.145
Vietnam	Burden	1.620	0.418	1.149	1.037	0.418	0.430
	Landfill	1.620		1.134	0.771	0.177	0.177
	MBT			0.015	0.015	0.005	0.005
	Incineration (burden)		0.418		0.250	0.224	0.224
	MSW combustion		0.345		0.235	0.214	0.214
	Process		0.072		0.015	0.010	0.010
	N2O		0.001		0.000	0.000	0.000
	AD (burden)						0.012
	Composting					0.012	0.012
	Process					0.006	0.006
	N2O					0.006	0.006
	Credit	0.000	−0.586	0.000	−0.376	−0.574	−0.616
	Recycling (dry)					−0.173	−0.173
	Paper					−0.081	−0.081
	Plastic					−0.024	−0.024
	Metal					−0.049	−0.049
	Glass					−0.019	−0.019
	Recycling (compost)					−0.011	−0.011
	AD (credit)						−0.042
	Incineration (credit)		−0.586		−0.376	−0.390	−0.390
	Power supply		−0.264		−0.169	−0.176	−0.176
	Heat supply		−0.322		−0.207	−0.215	−0.215
	Total	1.620	−0.169	1.149	0.660	−0.156	−0.186

and

Table 4. Technical results expanded for the different categories for each scenario for Cambodia, Thailand, and Vietnam.

Country	Category	S0	S1	S2	S3	S4	S5
Cambodia	Total energy generated (El) [kW]		0.098		0.058	0.052	0.066
	Total energy generated (Th) [kW]		0.415		0.246	0.221	0.221
	Specific energy generated inc. (El) [kW/t]		0.098		0.207	0.222	0.273
	Specific energy generated AD (El) [kW/t]						0.035
	Specific energy generated (Th) [kW/t]		0.415		0.881	0.943	0.943
	Ashes disposed of [t]		0.133		0.036	0.026	0.026
	MSW disposed of [t]	1		0.741	0.462	0.199	0.199
	Materials recycled [t]					0.288	0.279
Thailand	Total energy generated (El) [kW]		0.112		0.060	0.059	0.070
	Total energy generated (Th) [kW]		0.475		0.256	0.249	0.249
	Specific energy generated inc. (El) [kW/t]		0.112		0.188	0.238	0.280
	Specific energy generated AD (El) [kW/t]						0.035
	Specific energy generated (Th) [kW/t]		0.475		0.800	1.013	1.013
	Ashes disposed of [t]		0.157		0.050	0.023	0.023
	MSW disposed of [t]	1		0.741	0.420	0.159	0.159
	Materials recycled [t]					0.359	0.351
Vietnam	Total energy generated (El) [kW]		0.077		0.058	0.051	0.065
	Total energy generated (Th) [kW]		0.326		0.246	0.217	0.217
	Specific energy generated Inc. (El) [kW/t]		0.077		0.207	0.375	0.465
	Specific energy generated AD (El) [kW/t]						0.035
	Specific energy generated (Th) [kW/t]		0.326		0.881	1.593	1.593
	Ashes disposed of [t]		0.111		0.036	0.013	0.013
	MSW disposed of [t]	1		0.741	0.462	0.135	0.135
	Materials recycled [t]					0.412	0.403

, and Figure 2, Figure 3 and Figure 4. The description of each scenario is detailed in the following sections.

3.1. Current Scenario: Landfill (S0)

The current scenario S0 achieved the worst environmental performance for each country. S0 resulted in an environmental burden of 1.360, 1.141, and 1.620 t-CO₂-Eq./FU for Cambodia, Thailand, and Vietnam, respectively (Table 3). Thailand showed the best performance while Vietnam had the worst one (Figure 3). The technical performance was the same for each country: the entire amount of MSW was disposed of and no energy could be recovered in this scenario (Figure 4 and Table 4).

3.2. MSW Incineration (S1)

The use of incineration (S1) revealed a carbon footprint of −0.085, −0.080, and −0.169 t-CO₂-Eq./FU, for Cambodia, Thailand, and Vietnam, respectively. In this case, the negative values obtained meant that the system generated an environmental credit for all the countries assessed (Figure 3). In contrast to S0, the best result was achieved in S1 by Vietnam, whose carbon footprint value was double that obtained by Thailand and Cambodia. Indeed, for each country, the great burden obtained from the MSW combustion was exceeded by the electric and thermal energy recovered (Table 3). The burden obtained from the combustion was almost ten times greater than that obtained by the incineration process itself while that from N₂O emission was near to zero and negligible.

For S1, the technical assessment evaluated the amount of waste disposed of and the amount of energy recovered. Regarding the first aspect, 0.13 (Cambodia), 0.16 (Thailand) and 0.11 (Vietnam) tons of ashes were disposed of, for which the carbon footprint of landfill was null. These values were almost comparable between the assessed countries. From an energetic point of view, the total amounts of electric and thermal energy generated were 0.10 kW and 0.41 kW for Cambodia, 0.11 kW and 0.48 kW for Thailand, and 0.08 kW and 0.33 kW for Vietnam. If Cambodia and Thailand achieved comparable results, Vietnam had a slightly lower performance. The MSW composition (higher in combustible and organic fractions for Thailand and Vietnam, respectively) was the effect of these differences.

3.3. MSW Mechanical–Biological Treatment (MBT) (S2)

The use of MBT, which characterized S2, resulted in an environmental burden of 0.956, 0.722, and 1.149 t-CO₂-Eq./FU for Cambodia, Thailand, and Vietnam, respectively. Similarly to S0, Thailand achieved the best environmental performance in S2 while Vietnam had the worst. Despite the MBT process being characterized by an impact of 0.015 t-CO₂-Eq./FU (much lower than the one generated by incineration process in S1), the main impact was generated by the landfilling of the processed MSW (about 98% of the total impact of S2). However, the introduction of MBT pretreatment before landfilling reduced the environmental burden obtained in S0 from a maximum of 38.1% (Thailand) to a minimum of 29.7% (Cambodia). In any case, S1 resulted in the second most impacting scenario.

From a technical point of view, S2 was the scenario with the second highest amount of MSW landfilled (0.74 ton for every country) (Table 4). Even in this case, no energy could be recovered. Thus, the technical performance was equal for all the countries assessed.

3.4. Integrated MBT Incineration (S3)

The adoption of incineration after MBT (S3) resulted in an environmental burden as well, emitting 0.568, 0.519, and 0.660 t-CO₂-Eq./FU for Cambodia, Thailand, and Vietnam, respectively. The best and worst performances were achieved by Thailand and Vietnam but in S3 the deviation of the results was the lowest. As summarized in Table 3, for every country the carbon footprint of landfill was almost half of the one registered in S2. This result was possible thanks to the screening process at the end of MBT, as will be further explained in the next paragraph. In addition, it is interesting to note that landfilling was the major contribution to the impact for Cambodia and Vietnam while for Thailand incineration was the most impacting activity, having even more impact than landfilling.

In general, despite the adoption of an integrated MBT–incineration system resulting in an environmental burden, it reduced the impact registered in S0 and S1. Indeed, the impacts in S3 were 58.2% (Cambodia), 54.5% (Thailand), and 59.3% (Vietnam) lower than the ones achieved in S0. Furthermore, they were 40.6% (Cambodia), 28.1% (Thailand), and 42.6% (Vietnam) less impactful than the ones in S1.

The benefit of S3 is visible also under a technical light. Indeed, in S3, about 0.47 ton of processed MSW was disposed of at the end of MBT and about 0.04 ton of ashes post-incineration. These values were significantly lower than the ones of S1 and S2, respectively. This was possibly due to the screening at the end of MBT, which diverted the combustible fractions to incineration (resulting in lower ashes) and then stabilized the MSW sent to landfill (resulting in a lower carbon footprint, as shown in Table 3). From an energetic point of view, the average total amount of energy generated in S3 was 0.06 kW of electric and 0.24 kW of thermal energy, respectively (Table 4). The greater amount of energy generated in S1 than in S3 was due to the greater input of incineration (1 ton and 0.46 for S1 and S3, respectively). On the other hand, considering the energy generated per ton of input waste it is worth noting that S3 resulted in a greater energy generation than S1 (112%, 69%, and 201% more for Cambodia, Thailand, and Vietnam, respectively). The higher performance of S3 was possible thanks to the implementation of MBT and its screening process, as explained before. The removal of the organic fraction during incineration resulted in the higher performance of the process. Overall, technical performances were similar between the countries, revealing slight lower values for Vietnam.

3.5. Separate Collection-Based Scenario: Composting (S4)

The adoption of a separate collection for materials for recycling resulted in a total carbon footprint of 0.101, −0.120, and −0.156 t-CO₂-Eq./FU for Cambodia, Thailand, and Vietnam, respectively. In this case, only two countries achieved an environmental credit, while Cambodia obtained a slight environmental burden. Obviously, the effect was mainly due to the recycling of dry materials, especially of metals, glass, and paper (Table 3). The recycling of organic waste resulted in a balance between the burden from the composting process and the benefit from compost use. Concerning burdens, every category remained almost unchanged if compared to the one of S3, apart from the one of landfill, which was reduced by 62%, 72%, and 77% for Cambodia, Thailand, and Vietnam, respectively. Additionally, the credits were similar to that of S3 and actually, in some cases (Cambodia and Thailand) they were lower than that of S3. However, the credits achieved from incineration (and then energy recovery) were still a significant part of the credits achieved.

The technical results show the reason for these values. Indeed, the total energy amounts produced in S3 and S4 were similar, revealing why the credits achieved in these scenario were unchanged. However, the specific energy yields from the incineration were significantly improved, with the values of S4 being almost two times higher than those of S3 (except for Cambodia). This confirms the diversion of some waste (especially organic) from the mixed stream has a benefit not only for further recycling but for the treatment of the mixed waste as well. The amount of MSW disposed of decreased 57%, 62%, and 71% compared to the values of S3 for Cambodia, Thailand, and Vietnam. The total amounts of materials recycled were 0.288, 0.359, and 0.412 tons for Cambodia, Thailand, and Vietnam, respectively.

3.6. Separate Collection-Based Scenario: Combined AD-Composting (S5)

The addition of AD to the organic waste treatment scheme did not have a significant effect on the environmental performance of the system: the total carbon footprints were 0.072, −0.145, and −0.186 t-CO₂-Eq./FU for Cambodia, Thailand, and Vietnam, respectively. Only Cambodia was shown to have an environmental burden while Thailand and Vietnam increased the environmental credit already obtained in S4. The difference between S4 and S5 was due to the credit obtained via AD of about −0.04 t-CO₂-Eq./FU. Indeed, there is evidence that anaerobic digestion of food waste has a specific energy yield lower than that obtained from MSW incineration [43,44].

Additionally, from a technical point of view, the difference was visible only in the electric energy recovered, since the adoption of AD contributed only to the production of this energy form.

4. Discussion

In the previous section, the results of each scenario were described and compared between the countries assessed. The results showed clear differences not only between the countries assessed but in their performance according to the scenario proposed. These differences are mainly attributed to the composition of MSW that each country produced.

Indeed, in the contexts where the organic fraction was higher (Vietnam and Cambodia), the impacts achieved from the scenarios based on biological processes without any recovery (landfilling S0 and MBT S2) were the highest. The more organic waste was produced, the more methane was generated in landfill (and then the greater the impact that resulted). As a consequence, Thailand (which had a lower amount of organic waste) obtained the lowest environmental burden (and then the highest environmental performance) in S0 and S2.

On the other hand, when the incineration technology was considered (S1), the presence of organic waste did not generate impacts since it was composed of biogenic carbon (even if it reduced the MSW heating value and the energy production). This had a consequent impact on the environmental credits, showing Cambodia and Vietnam (characterized by the highest organic waste production) had the best performance in S1. In particular, Vietnam had not only the highest amount of organic waste but also the lowest amounts of textiles and plastic (which are the fractions that most affect the incineration burdens) compared to Cambodia and Thailand.

When incineration and biological processes without recovery were matched (S3), the credits achieved by the presence of organic waste in incineration were balanced by the burdens resulting from the presence of the same waste in landfilling or MBT. For this reason, the deviation of the results was lower.

In S4 and S5, we introduced the scheme of a separate collection aiming at material recovery (S4 and S5), mainly focused on the collection of organic waste. With this system, the more organic waste was collected, the greater the environmental benefit achieved. Indeed, in these scenarios, Vietnam (having the highest amount of organic waste) had the smallest carbon footprint of the three countries. Thailand (which had the lowest amount of organic waste), had a smaller (but still negative) carbon footprint than that of Vietnam. On the other hand, Cambodia, producing a similar amount of organic waste to Vietnam, did not achieve an environmental credit. This was due to the lower presence of glass and metals (whose recycling has the two highest emission factors) and the lower environmental credit obtained from the recycling of dry waste, which was not enough to balance the high impact of landfilling (due to the high value of organic waste).

From a technical point of view, it is well recognized that recycling should be the best option not only because it generates new raw materials (avoiding the necessity to use virgin materials) but also because it avoids to dispose in landfill waste or ashes from incineration. Particularly, the disposal of ashes does not affect the environmental performance of the system proposed in this work, but contributes to reduce the volume of landfilling sites and associated costs.

This study could help MSW managers, providing simple and effective tools to evaluate the effectiveness of different MSW treatment schemes in a specific context. Our next works will focus on the economic analysis of these systems, which were not evaluated at this level due to the lack of such information at present. One possible limitation of this study relates to the sources of MSW composition, which were obtained mainly based on the scientific literature. Specific surveys should be developed by government authorities in order to have clear and reliable data.

5. Conclusions

The present work has shown the environmental and technical assessment of different MSW treatment schemes for Cambodia, Thailand, and Vietnam, revealing the following results:

• The current scenario achieved the worse environmental and technical results in every country;
• Incineration of non-pretreated MSW resulted in an environmental credit for all the countries assessed. The benefit was lower in the context characterized by a lower content of organic waste (Thailand);
• Scenarios based on direct landfilling of MSW, MBT, or a combined MBT incineration system resulted in an environmental burden. In these cases, the higher amount of organic waste negatively affected the performance of the systems;
• Separate collection-based systems obtained an environmental credit as well, except in the case of Cambodia, since the lack of valuable materials for recycling (metals and glass) could not compensate for the burdens of the landfilling;
• From a technical point of view, the combination of MBT followed by incineration provided the highest energy recovery yield, especially if a separate collection scheme was adopted;
• Separate collection-based scenarios produced the lowest amount of waste landfilled and the highest amount of recycled materials;
• The implementation of a suitable MSW treatment scheme has to deal with several factors, such as MSW composition, which could result in the identification of different, more suitable systems for different countries;
• The Asian MSW management system could be improved through treatment technologies, whose performances are not usually similar to the ones referred to in the European context.