Positive Impacts of the Overall-Process Management Measures on Promoting Municipal Solid Waste Classification: A Case Study of Chongqing, China

Abstract

Municipal solid waste (MSW) classification is a national strategic objective and an important component of successful municipal solid waste management (MSWM). Some failures of pilot programs suggest that safeguarding measures are essential for MSW classification. A questionnaire survey of public awareness and attitudes toward MSW source-separated collection in Chongqing’s main districts was conducted, and the results indicated that the proportions of respondents willing to participate in MSW classification and provide money for it were 67.9% and 86.2%, respectively. The positive impacts of the overall-process management measures on promoting MSW classification in Chongqing’s main districts, including source-separated collection system, transportation system, treatment and disposal system, and environmental sanitation prevention system, were analyzed comprehensively. The analyses revealed that a 98% resident participation rate was obtained for MSW source-separated collection with the application of a cloud-based platform and traceability system. Moreover, the secondary transportation and comprehensive “4 + 1” (four waste incineration plants and one waste landfill) disposal mode showed significant advantages with respect to costs and environmental friendliness. In view of the environmental sanitation risks, the prevention and control of environmental sanitation were developed in Chongqing. The future prospects have also been discussed. The refinement and regionalization of source-separated collection are proposed as the possible solution.

1. Introduction

With the rapid development and urbanization of China, municipal solid waste (MSW) generation is increasing, as is the complexity of its components, thereby posing severe challenges for municipal solid waste management (MSWM) [1,2]. In 2004, China became the largest MSW producer globally [3,4]. Since then, the total amount of MSW in China increased from 155.1 million tons in 2004 to 228.0 million tons in 2018, and the annual growth rate averaged 2.8% [5]. The research of Ye et al. [6] indicated that MSW classification is effective in reducing waste and promoting material recycling, and correct MSW classification can reduce MSW by 30–40% through recycling. For instance, the reuse of 1 million tons of waste paper from MSW classification can avoid the deforestation of 600 square kilometers of forests [7].

The Chinese government attaches great importance to the MSW source-separated collection, which is a main target of MSWM in China’s 13th Five-Year Plan (13th Five) released on 17 March 2016 [1]. MSW source-separated collection begins from the generation of MSW and includes the entire process of collection, transportation, and disposal, aiming to promote waste minimization, resource utilization, and sustainable development [8]. In order to solve the problem of “garbage-surrounded cities” in China, eight cities were selected as pilot cities to carry out MSW classification in 2000 [9,10]. Additionally, the renewed MSW classification was initiated in March 2017 for 46 cities, including Chongqing, Beijing, and Shanghai. The tagline “waste classification, the new fashion” given by the president set off an upsurge in China. The government carried out many pilot programs to promote MSW classification through substantial investments in waste-sorting facilities, publicity, and education [11]. However, the effects of these pilot programs were limited due to poor participation of residents, mixed transportation and disposal after classification, and lack of sound regulations and policies for MSW classification [9]. Therefore, it is important to undertake safeguarding measures for MSW classification, while most Chinese cities still lack the overall-process management measures for promoting MSW classification.

Studies on MSW classification in China have mainly concentrated on the developed coastal cities, but very few have focused on inland cities and less-developed areas. The authors implemented a case study in Chongqing’s main districts. Chongqing is a representative inland city and has a total GDP that ranked fifth place in 2019. In addition, it is one of the four municipalities in China under the direct administration of the Chinese central government, along with Beijing, Shanghai, and Tianjin. As the main districts of Chongqing are situated between the Yangtze River and the Jialing River, and many rivers have suffered from varying degrees of waste pollution, MSWM in Chongqing is becoming increasingly important for the environmental protection of the reservoir area [12,13]. The amount of MSW generated in Chongqing was next only to Beijing and Shanghai in 2015, so the volume reduction, harmless disposal, and energy recovery corresponding to MSW were crucial [14]. In response to national requirements, the Chongqing Municipality implemented the “Administrative Measures for Classification of Municipal Solid Waste” in January 2019, which required MSW to be classified into recyclables, putrescible waste, hazardous waste, and other waste. Several pilot programs were carried out. Chongqing is expected to realize the full coverage of MSW classification by 2022. In order to achieve this target, Chongqing has taken a series of safeguarding measures to promote MSW classification.

To analyze the residents’ awareness and attitudes toward MSW source-separated collection and to evaluate the efforts of the safeguarding measures developed for MSW classification, the questionnaire survey and practical investigation were conducted in Chongqing’s main districts under this study. The MSW classification system in Chongqing’s main districts is divided into four parts: source-separated collection system, transportation system, treatment and disposal system, and environmental sanitation prevention system. Based on a comprehensive analysis of the case study in Chongqing’s main districts, some prospects for future development in MSWM have also been proposed under this study, which aims to provide a reference for the MSW classification of other Chinese cities.

2. Methodology

2.1. Study Area

Chongqing, one of the megacities in southwestern China, has an area of approximately 82,000 km² and a population of approximately 31 million. Its geographic location is longitude 105°11′–110°11′ and latitude 28°10′–32°13′. The central urban area of Chongqing consists of nine main districts: Yuzhong, Jiangbei, Nan’an, Jiulongpo, Shapingba, Dadukou, Beibei, Yubei, and Ba’nan. The locations of the regions where the questionnaire survey and practical investigation were conducted are shown in Figure 1.

2.2. Questionnaire Design

The initial questionnaire was designed by considering the actual situation at the study sites, existing literature, and a series of discussions with subject-matter experts. It was modified based on the results of the preliminary investigation to form the final questionnaire. The final questionnaire consisted of two parts, and the content of the questionnaire is included in Online Resource S1. The first part contained a series of questions about the awareness and attitudes of the respondents towards MSW source-separated collection, including their willingness to participate in MSW classification and provide money for it, if they were familiar with the MSW classification standard, and if they could sort waste accurately [15]. During the survey, if the respondents responded positively towards willingness to pay (WTP), they could continue to answer the question on the charging method. Conversely, if the respondents were unwilling to pay (0WTP), the reasons for the unwillingness were enquired about. The second part collected the respondents’ socio-economic characteristics in terms of age, gender, education level, annual income, household size, and place of residence.

2.3. Data Collection

The questionnaire survey and practical investigation were carried out in January 2020 in Chongqing’s main districts. The questionnaire survey was conducted for the data collection regarding the source-separated collection system. With a method of cluster random sampling, at least three densely populated streets were randomly chosen for investigation in each district, which covered the major residential living areas of Chongqing’s main districts. To ensure the results were representative of the entire region, the authors randomly investigated 210 residents with a confidential questionnaire. After excluding invalid questionnaires that missed important information, a total of 196 valid responses were received, indicating an effective rate of 93.3%. The authors collected and analyzed the data obtained from the valid responses. The authors also conducted several field visits to collect relevant information about the MSW classification system such as the local environmental authority, MSW classification pilot sites, and secondary transfer stations. In addition, some informal discussions were held with local cadres, informal sectors, and sanitation workers to obtain a better understanding of real situations and collect as many public perceptions as possible.

3. Results and Discussion

3.1. MSW Generation and Characteristics

As illustrated in Figure S1, the amount of MSW generated in Chongqing increased from 2.4 million tons in 2004 to 5.5 million tons in 2018, with an average annual growth rate of 6.8%, which was 4.0% higher than the annual growth rate of China [5,16]. With population growth and economic development, the MSW generation in Chongqing grew rapidly, putting pressure on waste transportation and disposal equipment. The composition of MSW in Chongqing’s main districts is shown in

Table 1. Composition of MSW in Chongqing’s main districts in 2015 (%).

Location	Gaofeng Temple Waste Transfer Station, Nan’an District	A Waste Transfer Station, Liangjiang New Area	Baozigou Waste Transfer Station, Dadukou District	Average
Food waste	54.94	42.22	53.99	52.00
Paper	12.08	13.92	16.70	14.18
Rubber and plastics	14.04	13.97	12.68	13.52
Textile	2.62	11.31	4.21	4.98
Glass	5.66	3.91	4.02	4.69
Wood	3.47	2.05	1.37	2.40
Brick, tile, and ceramic	-	3.12	4.21	2.21
Metal	3.41	2.05	0.51	2.05
Ash	0.71	4.54	1.04	1.61
Others	2.53	1.75	-	1.42
Mixture	0.54	1.14	1.29	0.94

Notes: Data from Chongqing Sanitation Monitoring Station and samples from the transfer stations.

. The average proportion of food waste in MSW was the highest at 52.0%, followed by paper, rubber, and plastics. The recyclable components (including paper, rubber and plastics, fiber, glass, and metal) and combustible components (including paper, rubber and plastics, fiber, and wood) accounted for 39.4% and 35.1%, respectively, indicating the utilization value of waste recovery.

Figure 2 shows the comparison of MSW composition between 2011 and 2015. The MSW composition data were obtained from the Chongqing Sanitation Monitoring Station. Food waste content and specific weight decreased significantly. With the strengthening of environmental consciousness, the proportions of recyclables and combustibles have increased [17]. The MSW of Chongqing was characterized by low calorific value and high moisture content due to a high proportion of food waste. The average calorific value was 4466 kJ/kg in 2013, which led to a low level of incineration [18]. Therefore, the MSW source-separated collection is particularly important for handling such problems.

3.2. MSW Source-Separated Collection

3.2.1. Public Opinions towards the MSW Source-Separated Collection

The respondents’ socio-economic characteristics in terms of age, gender, education level, annual income, household size, and place of residence are shown in

Table 2. Socio-economic characteristics of the 196 respondents.

Item	Response	Frequency	Percentage (%)
Gender	Male	97	49.5
	Female	99	50.5
Age	<18	30	15.3
	18–25	50	25.5
	26–35	44	22.5
	36–45	34	17.3
	46–60	23	11.7
	>60	15	7.7
Education	Primary school or lower	17	8.7
	Junior high school	24	12.2
	Senior high school or secondary technical school	30	15.3
	Junior college	39	19.9
	Undergraduate or above	86	43.9
Annual income	CNY < 20,000	24	12.2
	CNY 20,000–40,000	29	14.8
	CNY 40,000–80,000	38	19.4
	CNY 80,000–120,000	40	20.4
	CNY > 120,000	65	33.2
Household size	1	14	7.1
	2	25	12.8
	3	70	35.7
	4	49	25.0
	5 or above	38	19.4
Place of residence	Shapingba	32	16.3
	Yuzhong	18	9.2
	Jiulongpo	18	9.2
	Yubei	39	19.9
	Beibei	11	5.6
	Jiangbei	17	8.7
	Ba’nan	21	10.7
	Nan’an	20	10.2
	Dadukou	20	10.2

. The respondents comprised 49.5% males and 50.5% females. To ensure that the respondents could understand the questionnaire and provide valid answers, the minimum age of the respondents was set at seven years. Up to 84.7% of the respondents were over the age of 18 years. More than half of the respondents had a junior college degree or above, of which the proportion of undergraduate or above was the highest (43.9%). Up to 54.6% of the respondents had annual incomes between CNY 20,000 and CNY 120,000, and only 12.2% of the respondents had annual incomes less than CNY 20,000, which reflected the income level of different groups in Chongqing. Approximately 73.5% of the respondents had 2–4 members in their families, 7.1% were single households, and 19.4% were larger families (more than five members). The residence distribution of the respondents was relatively uniform. These values were generally representative of Chongqing’s main districts.

As shown in Figure 3, 69.9% of the respondents had sufficient waste-sorting facilities in their communities, 65.3% of the respondents expressed their willingness to participate in MSW classification, 26.0% were willing but could not insist on it, and 5.1% said “no”. The main reasons for the unwillingness were lack of classification awareness, complexity and time spent in classification, inadequate waste-sorting facilities, mixed transportation and disposal after classification, and negative herd mentality [19]. More than half of the respondents (67.9%) were unfamiliar with the four categories of waste in Chongqing, and only 25.5% of the respondents could sort waste accurately, indicating that publicity and education programs might have been poorly implemented [20]. This showed that the government should strengthen publicity and education through diverse means to enhance public awareness of MSW source-separated collection, such as using networks and various media sources which have proven to be more efficient [21]. Approximately 41.8% of the respondents hoped that the government could strengthen financial and policy support to improve public awareness about MSW classification, and the remaining tended to suggest stepping up publicity. The proportion of WTP choice was 86.2%, and only 13.8% chose the 0WTP. The reasons for choosing 0WTP were as follows: lack of money to pay (11.1%), the classification effects after payment may not be satisfactory (51.8%), the government should be responsible for the payment (7.4%), refuse to pay but would participate actively in this program (29.6%). In addition, the respondents who chose WTP tended to suggest charging based on waste quantity (35.4%) and on the household (31.2%), and 25.9% of the respondents suggested charging based on the number of permanent residents. This study could provide a reference for future waste charging policies.

3.2.2. Promotion Measures for the MSW Source-Separated Collection

In order to accelerate the progress of MSW classification, Chongqing launched pilot programs for the MSW source-separated collection in different communities. In 2019, the pilot sites in Chongqing’s main districts were further expanded to cover 358 communities in 43 streets and towns. The authors investigated a few MSW classification pilot sites, such as Gangqiu Community in Jiulongpo District and Jinsha Shui’an Community in Jiangbei District, where the cloud-based platform and traceability system were developed for intelligent MSW classification. The smart waste bins integrated with face recognition, quick response (QR)code scanning, and integrated circuit (IC) card were designed. The process of users putting waste is shown in Figure 4a.

As shown in Figure 4b, the smart waste bins were divided into five recyclable waste inlets for fiber, paper, metal, general plastics, and plastic bottles, in order to avoid cross-contamination. The hazardous waste recycling bins were also marked with various inlets, such as slim lights, expired cosmetics, expired drugs, and electronic waste. Moreover, the pilot communities were provided with waste bags with QR codes, which could be used to trace the source of waste. Furthermore, the residents who classified correctly could be rewarded with bonus points as encouragement, and those who classified incorrectly could be explained through one-to-one meetings conducted by volunteers. Multiple options for bonus-point exchange were provided, including cash withdrawal, shopping mall consumption, automatic vending machine exchange, and point of sale (POS) machine consumption. As of June 2019, the mixed waste in the Gangqiu Community had been reduced from 1.8 t/day to 1.3 t/day, of which 0.4 t was perishable waste, 0.1 t consisted of recyclables, and 0.8 t consisted of other waste. Furthermore, the waste classification awareness rate of residents reached 100%, the participation rate was 98%, and the placement accuracy rate was 83%.

3.3. MSW Transportation

The collection and transportation of MSW in Chongqing’s main districts are mainly through secondary transportation supplemented by primary transportation. The secondary transportation mode refers to the waste being transported to the small and medium-sized primary waste transfer stations after the collection of waste bins, then to the large-sized secondary waste transfer stations, and then to the waste disposal plants for treatment and reuse. This mode is usually used when the amount of waste is large and the transportation distance is long (≥30 km). The primary transportation mode means that the waste is only transported to one waste transfer station after collection and then to the waste disposal plants. At present, there are three secondary waste transfer stations in Chongqing (Figure 5), including the southern Jieshi transfer station, western Zouma transfer station, and northern Xiajiaba transfer station, which serve Chongqing’s main districts.

The entire process of waste loading, compression, and unloading in the secondary transfer stations is completely automated, mechanized, and closed, which significantly reduces the secondary pollution caused by leachate and odor during transportation. The secondary transfer stations are equipped with fully automatic gas exhaustion and supply systems, as well as disinfection and deodorization systems that continuously purify the exhaust gases.

Moreover, compared with the primary transportation, adding secondary transfer stations can significantly decrease the total transportation distance from 168,900 km/day to 163,400 km/day in the case of a large amount of waste and long transportation distance, which helps in reducing waste collection and transportation costs [22,23]. This is conducive to reducing pollution sources and controlling environmental sanitation risks during transportation [24]. The establishment of secondary transfer stations greatly decreases the work intensity of waste disposal plants, reducing the total number of transport vehicles traveling to the four waste disposal plants from 73 vehicles/h to 49 vehicles/h. Furthermore, the new waste transfer vehicles can be loaded with various transfer boxes of kitchen waste and other waste, so as to integrate the original single transfer vehicles into one, which can at least double the transportation capacity and decrease the energy consumption by 48.6%. All waste transport vehicles are equipped with GPS monitoring systems to obtain real-time information and improve transfer efficiency.

3.4. MSW Treatment and Disposal

Hazardous waste, recyclables, putrescible waste and other waste are usually collected in red, blue, green and gray waste collection containers, respectively. The treatment and disposal methods vary according to the characteristics of the four classified wastes, as shown in Figure 6.

(i)

Hazardous waste: It includes waste materials resulting from items such as batteries, fluorescent lights, thermometers, medicines and their packaging, pesticides, and disinfectants [25]. Hazardous waste is transported to the hazardous waste temporary storage sites by special vehicles, where it is weighed, inspected, classified, and filed; finally, it is transported to professional and qualified disposal enterprises. At present, there are 18 transportation and storage enterprises and 45 utilization and disposal facilities for hazardous waste in Chongqing.

(ii)

Recyclables: These consist of abandoned paper, plastic, metal, textile, electronic products, glass, and paper–plastic–aluminum composite packaging [26]. Recyclables are often collected at the source by scrap buyers and in the “Recyclable Waste” bins [27]. After collection at recycling stations, these items are transported to various types of resource recycling enterprises. There are 8980 recycling stations, 11 waste-sorting centers, and 1 resource trading center in Chongqing.

(iii)

Putrescible waste: It is also called wet waste, and it mainly consists of kitchen waste and waste from livestock and farmers’ markets [28]. Perishable waste without waste bags is put into the “Perishable Waste” collection containers and then transported to resource utilization plants. Presently, four perishable waste disposal facilities in Chongqing are in operation. As of 2014, the Heishizi kitchen waste disposal plant’s total disposal capacity was 1000 t/day, and the perishable waste disposed of could produce 18 t of biodiesel and 50,000 kW·h of electricity.

(iv)

Other waste: It refers to waste not included in the above categories, which is less hazardous without reuse value, such as ash, brick, tile, and ceramic. After collection, other waste is transported and disposed of safely through incineration and landfill.

At present, the terminal harmless disposal technology of MSW in Chongqing is mainly based on incineration, supplemented by the sanitary landfill. The harmless disposal capacity of MSW in Chongqing has increased with an average annual growth rate of 9.1% [18]. By the end of 2019, the harmless disposal rate of MSW reached 100%, and the disposal capacity of incineration was approximately 8100 t/day, which accounted for 95% of the harmless disposal. The end residues of incineration are ash (bottom ash and fly ash). After the operation of solidification/stabilization, the ash is put into the landfill site for safety landfill. The MSW disposal system in Chongqing’s main districts can be summarized as the “4 + 1” mode, i.e., four waste incineration plants and one landfill, which has continued to increase the proportion of incineration to achieve zero landfill for MSW. At present, the actual disposal capacities of the Tongxing waste incineration plant, Fengsheng waste incineration plant, and Jiangjin waste incineration plant have reached 1500 t/day, 3500 t/day, and 4500 t/day, respectively. The design disposal capacity of the Luoqi waste incineration plant is 3600 t/day, which will serve as a hot backup incineration plant after the completion of the project. The service scope and the amount of waste to be disposed of by the four major MSW incineration plants in Chongqing are shown in Table S1.

3.5. Environmental Sanitation Prevention

Studies have shown that MSW is rich in organic matter and a large number of pathogenic microorganisms can grow and multiply rapidly under proper conditions [29]. The pathogenic microorganism pollution due to the breaking of waste bags and secondary manual sorting during the process of MSW source-separated collection is a serious issue and poses great environmental sanitation risks for sanitation workers and residents. The incidence of respiratory diseases in sanitation workers is higher than that in ordinary people, and sanitation workers are more susceptible to infectious diseases [30]. Under the situation of widespread epidemics (such as COVID-19 and SARS), the prevention and control of environmental sanitation during the overall process of MSW classification is a significant concern, particularly for sanitation workers and residents. Considering these issues, Chongqing has currently put forward an environmental sanitation prevention system.

Sufficient personnel protection equipment, such as masks, gloves, and disinfectants, should be provided to sanitation workers. Residents should maintain a proper distance from others when throwing away waste and then wash their hands quickly. It is necessary to increase the frequency and intensity of disinfection for waste rooms, and the generators of slightly acidic electrolyzed water can be installed in waste rooms for atomization disinfection. The atomized aerosol particles can be evenly distributed on the waste surface, which not only kills the common pathogenic microorganisms effectively but also controls the odor emanating from waste.

Moreover, the MSW transportation should be arranged with fixed vehicles, workers, and routes. The routes should avoid densely populated areas and congested roads, and the vehicles should be kept closed during transportation. The vehicles, ground, and cleaning tools should be disinfected after every round of loading and unloading waste. It is forbidden to mix medical waste into the domestic waste disposal system. Landfill plants should minimize the landfill operation surface, strictly ensure a daily coverage rate of 100%, and spray deodorant and disinfectant on the waste surface periodically. Mobile medical waste emergency incineration treatment equipment can be introduced when unexpected public health emergencies occur.

4. Future Prospects

4.1. Expansion of Investigation Coverage

The number of valid questionnaires was relatively small compared to similar studies. The main reason was that some questions were difficult for elderly respondents to provide valid answers to. Another issue was that we focused the investigation area on Chongqing’s main districts. It is necessary to expand the scope of the investigation to Chongqing city in future studies.

4.2. Refinement of Source-Separated Collection

Although Chongqing has vigorously promoted the MSW source-separated collection and achieved preliminary results, some issues still exist. For instance, the current waste categories are not comprehensive enough when it comes to the reuse and recycling of classified materials. Learning the advanced laws, management, and successful experiences of MSW source-separated collection systems from Japan and Germany as well as increasing the waste categories to eight or more could be useful. Further classifying recyclables, such as paper, plastic, fabric, wood, and metal, can keep the resource attributes, reduce the pollution attributes as much as possible, and improve the utilization value of various recyclables. Deep cleaning of recyclables should be carried out simultaneously to improve the quality of the recycled products.

4.3. Regionalization of Source-Separated Collection

The source-separated collection should be expanded to the rural areas of Chongqing as soon as possible [31]. The rural solid waste (RSW) source-separated collection should be carried out based on the actual situation of rural areas and the characteristics of RSW, instead of using the method adopted for MSW classification. The financial resources and environmental legislative systems of source-separated collection should be strengthened quickly. It is essential to complete infrastructure and implement economic incentives to improve the residents’ willingness to participate in source-separated collection. Additionally, the resource utilization technology for biogas residue and biogas slurry should be developed to realize the complete utilization of food waste [32].

5. Conclusions

This paper focuses on the positive impacts of the overall-process management measures on promoting MSW classification in Chongqing’s main districts. The results and recommendations are as follows: (i) The total amount of MSW in Chongqing showed an increasing trend, reaching 5.5 million tons in 2018. Food waste and recyclables were the main components, accounting for 52.0% and 39.4% of the total waste, respectively. (ii) According to the investigation of awareness and attitudes for MSW source-separated collection, the proportions of those willing to participate in MSW classification and provide money for it were 67.9% and 86.2%, respectively. (iii) The study analyzed the MSW classification system in detail, including source-separated collection, transportation, treatment and disposal, and environmental sanitation prevention. Results showed that a 98% resident participation rate was obtained for MSW source-separated collection with the application of a cloud-based platform and traceability system. Additionally, the secondary transportation and comprehensive “4 + 1” disposal mode showed significant advantages and potential for reducing costs and increasing environmental friendliness. In view of the environmental sanitation risks, the prevention system was developed in the overall process of MSW classification for guaranteeing the health of sanitation workers and residents. (iv) To improve the MSWM in Chongqing’s main districts, the refinement of waste categories and waste classification promotion in the rural areas are urgently required. The related regulations, policies, and infrastructure need to be further improved and implemented.