Many studies have considered the location of rural waste transfer stations, but most have omitted the impact of transportation network conditions. Traffic accessibility must be considered in optimizing the location of rural waste transfer stations, which is an important difference from the location of rural waste transfer stations. On the basis of previous studies, this study will consider the impact of traffic network on the optimization locations of waste transfer station in the rural areas. The objective of this study was to ensure the minimum Euclidean distance between the waste transfer station and the population center is the maximum, minimize the garbage transportation cost of each population center, construction costs for waste transfer stations, construction and upgrade costs for roads on a traffic network. A multi-objective facility location-network design model and an improved multi-objective simulated annealing algorithm was used to solve the problem. A detailed practical case study was used to illustrate the application of the proposed mathematical model. The results show that transportation network plays an important role in facility location optimization, and the improvement of traffic network conditions can greatly reduce waste transportation costs.
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The phrase 'Not In My Back Yard' (NIMBY) refers to the well-known social phenomena in which residents oppose the construction or location of undesirable facilities near their home. Examples of such facilities include landfills, waste transfer stations and thermoelectri power plants. NIMBY facilities not only provide convenience or services for residents, but also have a strong negative impact on nearby residents (Saameño Rodríguez, ) [1]. The convenience provided by these facilities is shared by the whole society, but the negative impacts may be only borne by some residents closer to them. That's why NIMBY facilities have been resisted by people. When the distribution of benefits and risks is unfair, there will be dissatisfaction (Xiao, ) [2]. Garbage treatment facilities are one of the public facilities with a high degree of evasion.
A good living environment is an indispensable part of realizing the strategy of rural revitalization. In recent years, with the development of rural economy and the continuous improvement of people's living standards, the amount of domestic waste in rural areas has also increased significantly. The garbage problem in rural areas of China has received far less attention than in urban areas. Garbage treatment in rural areas is also the weak link of the whole environmental governance. In addition, different from urban areas, the location of garbage collection and transfer facilities in rural areas is usually unscientific, and the number of facilities is insufficient. Especially, in rural areas of mountainous environment, low traffic accessibility leads to high cost and low efficiency of waste transportation. This has seriously affected the quality of life of residents in rural areas and brought a serious financial burden to rural development.
In recent years, Chinese government departments began to pay more and more attention to the problem of rural garbage disposal. In November , the Ministry of Housing and Urban-Rural Development and other ten departments jointly issued the "Guiding Opinions on Comprehensively Promoting the Management of Rural Garbage", which proposed that more than 90% of China's domestic waste will be effectively controlled by . The waste transfer is the key link of garbage disposal. Waste transfer station is the core of the transfer system and plays the role of scheduling link in the system. In addition, garbage collection and transportation costs account for 70% -80% of the entire garbage disposal system (Nie, ) [3]. Therefore, how to optimize the location of waste transfer station in rural areas, and plan the garbage collection and transportation route, so as to maximize the efficiency of garbage transfer and reduce the cost of garbage transfer. These are the problems that need to be solved to realize the strategy of Rural Revitalization. Some scholars have studied the location of waste transfer stations.
Several researchers emphasized that the location of waste transfer station should be aimed at minimizing the cost. Anderson () [4] first proposed that the construction of waste transfer stations should follow the concept of 'cost optimization'. He stressed that the construction of waste transfer station should ensure the minimum operating cost of the whole waste treatment system. On this basis, Yurteri and Siber () [5] explored the optimal layout of waste transfer stations by constructing a linear programming model, which also laid a theoretical foundation for the location of waste transfer stations. Chang and Lin () [6] optimized the location of waste transfer stations to ensure the minimum total cost of garbage disposal (garbage transportation and facility construction costs, etc.). Chang et al. () [7] studied the optimal locations of waste transfer stations by comprehensively considering economic and environmental benefits. Jia et al. () [8] introduced the concept of reverse logistics system site selection into the location of rural waste transfer stations. First, the set coverage model was used to determine the candidate points of the waste transfer station, and then an integer programming model was built to minimize the operation of the city's garbage collection and transportation system. Gorsevski et al. () [9] proposed a GIS-based multicriteria analysis for siting a landfill in the Polog region of Macedonia.
Some scholars have explored the optimization of waste transportation routes. Greenberg () [10] conducted an optimization analysis of New York City's waste transportation routes. Based on Greenberg () [10], Kirca and Erkip () [11] further used an optimized linear model to analyze and discuss the optimal layout of solid waste transfer stations in a certain region of Turkey. Lv et al. () [12] constructed a site selection-path planning problem model and used a two-stage Tabu search heuristic algorithm to solve the problem to obtain the final location and number of waste transfer stations.
Mathematical optimization approaches have been employed for various situations. Du and Guo () [13] constructed a mathematical model for the layout of urban waste transfer stations and proposed a central transfer algorithm for solving the optimal layout of waste transfer stations, and gave the best transfer schemes for garbage in various settlements. Yu and Solvang () [14] proposed an improved mathematical formula to help decision makers choose the location of different facilities, including treatment plants, recycling plants and disposal sites, providing appropriate technologies for hazardous waste treatment. Gu et al. () [15] fully considered the impact of external effects on the location of waste power plants, and established a bi-level planning model to optimize the location of waste power plants in Wuhan. Gallo () [16] proposes a discrete optimization model and a heuristic algorithm to solve the landfill siting problem over large areas. Zhao and Huang () [17] explored the multi-period network design problem is to determine the location of waste facilities in each period during the planning horizon.
The classical facility location problems include p-median and p-center problems, the maximum covering location problems and the set covering location problems. In general, classical facility location problems consist of some number of facilities to be located within a given network to satisfy a set of customers in respect of some constrains (Rahmaniani and Ghaderi, ) [18].
Travel network design problems address decisions about selecting a number of candidate links between network's nodes to minimize the sum of construction and travel costs (Cocking, ) [19]. Essentially, the facility location-network design problem (FLNDP) is a combination of the facility location and network design problems. Daskin et al. () [20] introduced the first model of FLNDP. Compared with the classical facility location problem, two assumptions are added to the FLNDP. First, the network is not given, and the model determines the configuration of the underlying network. Second, each client is not directly served from facilities and may pass from multiple nodes in the network to get service (Ghaderi and Jabalameli, ) [21]. Melkote () [22] identified three types of FLNDPs: the uncapacitated ULNDP (UFLNDP), the capacitated facility location-network design problem (CFLNDP), and the maximum cover facility location-network design problem (MCLNDP). The results of Melkote's () [22] research were published by Melkote and Daskin (a, b) [23, 24].
On the basis of the above research, many scholars have conducted in-depth study on the FLNDP. Cocking () [19] introduced a greedy algorithm, local search, simulated annealing, variable neighborhood search and a branch-and-cut algorithm to solve static budget-constrained facility location network design problems. Bigotte et al. () [25] proposed an optimization model for integrated urban hierarchy and transportation network planning. This model simultaneously determines which urban centers and which network links should be promoted to a new level of hierarchy so as to maximize accessibility to all classes of facilities. Contreras et al. () [26] proposed a combined FLNDP which simultaneously considered the location of facilities and the design of the underlying network so as to minimize the maximum customer-facility travel time; two mixed-integer programming formulations were presented and compared. Contreras and Fernández () [27] also presented a unified framework for solving the general network design problem that combined design decisions to locate facilities and to select links on an underlying network, with operational allocation and routing decisions to satisfy the users demands. Rahmaniani and Ghaderi () [18] presented a mixed-integer model to optimize the location of facilities and the underlying transportation network to minimize the total costs of transportation and operation. The researchers assumed that several types of transfer links existed (each with a different transport capacity, transportation cost and construction cost) and that the links between two nodes could be divided into various types. Ghaderi and Jabalameli () [21] proposed a model for the budget-constrained dynamic (multi-period) uncapacitated FLNDP. They used a greedy heuristic and a fix-and optimize heuristic based on simulated annealing together with 'branch and bound' and cutting methods to solve the model. Sadat Asl et al. () [28] dealt with fuzzy capacitated facility location-network design model which aims to select the facilities and candidate links in a way that yield to minimize the total costs, containing: costs of opening facilities, link construction and transportation costs.
Through the literature review, it is not difficult to find that most of the previous studies have focused on the location of waste transfer stations in cities, which can not effectively solve the layout problem of waste transfer stations in rural areas. Different from urban areas, the level of traffic accessibility in rural areas is usually low, and the roads are rugged. This directly leads to higher garbage transportation costs, which adds additional financial burden to local government departments that had limited financial expenditure. Therefore, in rural areas, the reasonable layout of waste transfer stations and the construction or upgrading of roads can be considered to improve the accessibility of roads, so as to achieve the goal of improving the efficiency of waste transportation, reducing transportation costs and improving the quality of life of rural residents. The facility location network design method not only considers the location of facilities, but also considers the optimization of road network. This method can be used to solve the problem of optimal layout of rural NIMBY facilities.
China started small-scale trials of waste sorting in , but landfill sites and unmanaged waste continued to encircle cities and local people protested plans to build more incinerators. Gradually, environmental organisations and some local governments came to realise the only way out was sorting and recycling to reduce the need for burning.
In , President Xi Jinping said on a visit to Shanghai that 'waste handling requires everyone's participation.' In July the following year, the city became China's first to make sorting household waste compulsory. A number of other cities have followed in Shanghai's footsteps in the three years since, imposing mandatory sorting, and almost 300 now implement some form of sorting.
The necessity of sorting has been confirmed time and again, but the idea still encounters public resistance when imposed by the state. Some question whether it is fair or economic to make people take on responsibilities that 'the state should bear' or whether top-down imposition regardless of circumstances will work in the long-term. Others complain of a lack of transparency and dialogue from the Shanghai government. They compare that unfavourably with the handling of protests over five incinerators in Panyu, Guangzhou, which exhibited transparent decision-making and openness to dialogue. They complain of a collapse in relations between the people and government over the past decade.
Some objections are not without merit. Local governments are keen to declare success in changing behaviour while there is a notable lack of information on whether that waste, dutifully sorted into coloured containers, is actually handled differently.
The government says the aims of waste sorting are to reduce waste quantities, recover resources and remove harms. Sorting is clearly just one link in the chain. Reduction needs to happen at source, before packaging and other future waste reaches the home, while proper handling and processing of materials for re-use can only be done after sorting. Unfortunately, publicity and debate has focused on the duty of local people to sort their waste. There is little discussion on whether or not those three government aims are being met, or on the government's responsibilities.
The Covid-19 pandemic has presented an extra challenge for waste sorting, especially when lockdowns tightened up in the latter half of . All the talk of waste sorting seemed to fade away.
So, what has happened over these three years? And what still needs to be done to achieve the original aims?
Shanghai was in a Covid-19 lockdown for more than two months from late March to early June . Residents were stuck inside, communities sealed off, most public services ground to a halt. With the collapse in public services, and the loss of a 'sense of control over life' causing reluctance or even refusal to fulfil personal responsibilities, local media asked how waste sorting could ever start up again. But it happened, and faster than might have been expected.
Hao Liqiong is joint founder of Aifen Environmental Protection, a non-profit which since has been working to promote waste sorting. She says 7,000 tonnes of food waste were being separated by citizens daily only three weeks after the lockdown ended, compared to 9,600 tonnes before it started. 'The authorities were surprised,' she said. 'They didn't expect sorting to pick up so quickly.'
A garbage-sorting station outside a residential complex in Shanghai where a modular bio-digester is installed (Image'Jiang Yifan / China Dialogue)
By August, waste sorting was back at the same levels of August the previous year, according to the city's landscaping and urban appearance bureau, which has responsibility for waste handling. The exception was waste from restaurant kitchens, which was still being affected by the lockdown.
Hao says it was no easy task for Shanghai, a city of almost 30 million people, to get to this point, and it is doing better than any other in China.
We thought changing behaviour would be most difficult' What's difficult is changing public servicesHao Liqiong, joint founder of Aifen Environmental Protection
In August, Aifen Environmental Protection published a report on evaluation systems for local waste-sorting efforts across the country, finding that there is more focus on high scores than actual implementation. The outcomes of those evaluations are rarely published in full, making public oversight hard. In some cities, communities invest significant labour and funds in careful checking of waste in order to ensure high scores. If locals are uncooperative, staff may be employed for a 'second sort'. The scoring system itself focuses on process rather than outcomes: how many bin stores are built and how much publicity is carried out, for example, rather than rates of sorting and recycling.
According to Hao, there are wide gaps in implementation between different cities. Some are working hard, while others drag their feet. One worrying phenomena, she says, is that cities that have made more progress, such as Shanghai and Xiamen, are making increasing investments for decreasing returns to get better scores and rankings. Despite this, recycling is failing and sorted food waste and recyclables are not being properly utilised. Many cities struggle with both collection and disposal.
'We thought changing people's behaviour would be the most difficult bit,' said Hao. 'But that turned out to be easy. What's difficult is changing the government's public services.'
Li Yanming is an associate professor at China Agricultural University's College of Resources and Environmental Sciences. This year, his team studied the use of food waste in more than ten Chinese cities, trying to find out why so many contaminants are found in 'sorted' food waste.
They looked at the sorting, collection and handling of that waste. At the sorting stage, they found that while over 90% of respondents said they were willing to sort waste, only 18'21% reported actually doing it. When it came to collection, they found waste was less likely to get mixed up with other waste in cities like Shanghai and Beijing which can afford dedicated food waste trucks. Elsewhere, it was common for waste to become mixed.
They also found that scoring systems work on administrative boundaries. Communities, neighbourhoods and districts get scored, while the waste transporters working across districts don't. The mixing of waste is therefore harder to identify.
An electric tuktuk transporting household food waste zips past houses on Shanghai's Jiaozhou Road (Image: Mark Andrews / Alamy )
Then comes waste disposal and re-use. Li's team looked at data from the Ministry of Housing and Urban-Rural Development and found that less than 17% of cities of prefecture level or higher have the facilities to handle food waste. 'So what if they mix the types of waste?' he says. 'It won't make any difference.'
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Where those facilities do exist, capacity is being outstripped by the growth in demand. Li offers Beijing's Haidian district as an example. Prior to making waste-sorting mandatory, the district could handle 200 tonnes of food waste a day, mostly from catering. Now there are 400 or 500 tonnes of food waste to deal with every day. Even running at full capacity, only 300 tonnes can be processed.
Li says facilities for handling food waste are still being built, a process which will take two or three years to complete. Until the needed capacity is in place, food waste will be incinerated, sent to landfill, or fed into sewage-treatment plants.
Some incinerators were built with food waste in mind. The water content reduces temperatures and so avoids damage to equipment. Incinerator managers often add in food waste for that reason. This helps get rid of some of the food waste that the dedicated facilities can't handle.
Li thinks that having adequate capacity for all the food waste isn't enough. It is also important to make good use of the outputs from the processing.
Digestate smells too bad to use on urban greenery and is not yet certified for agricultural use
Li explains that 80% of food-waste handling in China uses anaerobic digestion to break down organic matter. This creates a mix of digestate and biogas consisting mainly of methane. The methane can be burned to generate power and ideally the digestate will be used as fertiliser. But, Li warns, there is currently nowhere for the digestate to go. It smells too bad to use on urban greenery and is not yet certified by the Ministry of Agriculture for agricultural use. The solid portion of the digestate often ends at the incinerator, while the liquid portion goes through reverse osmosis to clean it. This means extra cost and energy usage. Also, the incinerator slag produced from food waste or solid digestate is rich in calcium, magnesium and phosphorous. If buried in landfill, the slag can cause eutrophication of nearby bodies of water, and if burned the toxic fumes can affect nearby residents.
Li thinks the only way to avoid harm is to ensure all waste is turned into resources. Returning food waste ' and the organic material and nutrients it contains ' to the soil will prevent it becoming sludge and water and air pollution. He and his team have proposed a 'community organic cycle' method. Communities, businesses and government can compost the food and garden waste they produce, and then use that compost on site. This low-tech method could save the costs of removing waste and buying in fertiliser (as well as the pollution arising from fertiliser use). The load on waste transportation would be reduced, along with the risk of types of waste becoming mixed, and the above-mentioned harms would be avoided.
He thinks a full roll-out of this approach in China's cities would cut in half the need to transport food waste. But his calculations show there is only so much demand for compost in urban areas. Further expanding the model will require agricultural use of the compost.
Despite the advent of waste sorting, China still incinerates most of its waste. Growth of incineration capacity is outstripping demand, even though sorting is meant to reduce that demand and so avoid local objections to incineration plants.
According to data presented at an online seminar in June by Li Jiacheng, a researcher with the Wuhu Ecological Centre, incineration capacity in Chinese cities and county seats reached 160 million tonnes a year in . By the end of , national capacity had reached 280 million tonnes a year. At least ten province-level jurisdictions can now incinerate more waste than they can collect and transport, and five had mid- to long-term plans which will see them able to incinerate 100% of their waste. Li points out that this could lead to facilities lying idle, and 'lock in' disincentives to sort and reduce waste.
Two factors are driving the expansion in incineration.
First, China classes these waste-to-power plants as renewable 'biopower' and that means a roughly 0.25 yuan subsidy per kilowatt hour of electricity generated. Li points out that while plastics, rubber and fabrics make up little of the dry weight of what is burned, they contribute the bulk of the heat value and also release fossil-source carbon. Therefore, he says, waste-to-power plants should not be classed as 'biopower'.
The classification runs contrary to attempts to sort biological material ' food waste ' and remove it from incineration. This may hamper waste-sorting efforts. Many Chinese environmental organisations argue incineration of household waste to generate power should not attract renewable subsidies.
A waste-to-energy incinerator in Nanjing, Jiangsu province (Image: Alamy)
Second, in China, waste-to-power plants are seen as a double win on emissions reduction: power is generated without burning fossil fuels, and food waste is burned instead of being sent to landfill where it could create methane ' a greenhouse gas ' as it rots.
But research from No Incinerators, an environmental organisation, shows that in ' net carbon emissions per kilowatt hour for major waste-to-power firms were, at 2.032'3.622 kilograms, far higher than the average for the grid (0.583 kgs) or even for coal power (0.853 kgs). So, while waste-to-power projects may replace fossil fuel generation, they actually emit more carbon. According to research by Wuhu Ecological Centre, energy efficiency at China's waste-to-power firms is commonly lower than 65%, and by EU standards that is classed as 'disposal' rather than 'energy recovery'.
Other research by No Incinerators has found that claims incineration avoids the production of methane rely on assuming very high levels of production in landfill sites. A review of 29 Chinese Certified Emission Reduction (CCER) incineration projects approved in and found that all used landfill sites without gas capture systems as a baseline for comparison. They also all dismissed other practical solutions which would have produced less emissions, such as recovery of landfill gas or only sending food waste to landfill after some recycling. Those selective comparisons allowed the projects to pass as 'reducing emissions'.
What are CCERs?
China Certified Emissions Reductions (CCER) are China's official carbon offsets. They refer to activities by companies to reduce emissions on a voluntary basis, such as renewable power generation, forestry projects and waste-to-energy projects.
With CCER approvals, suspended in , being set to restart, environmental organisations hope to see this loophole plugged to avoid waste-to-power projects squeezing out other approaches that would have greater impact on emissions.
Qu Ruijing, an expert on green and low-carbon strategy, told China Dialogue that incineration is currently seen as harm-free. But he thinks that label shouldn't be applied to techniques or equipment; it is a goal, an aim to reduce environmental impact. 'You can't just build an incinerator and say that's harm-free. That will lead to facilities being built regardless of profitability and the availability of fuel. That will lead to plant owners turning to the government for subsidies. It also ignores the 'producer pays' mechanism,' he said.
Hao Liqiong says the reason why all the publicity and data is currently focused on community waste sorting, transportation and incineration, is because these all fall under the remit of the Ministry of Housing and Urban-Rural Development. She applauds the progress made in big cities like Shanghai, but points out that maintaining separation of waste during disposal and resource recovery needs cooperation with other ministries. In particular, cooperation is needed with the commerce authorities, which manage the circular economy, and the agricultural authorities, which could complete the chain by providing use cases for processed food waste.
In a speech given last year, Zhou Chuanbin, a researcher at the China Academy of Sciences' Research Centre for Eco-Environmental Sciences, said that China was taking too narrow an approach to resource recovery for recyclables such as plastics. This means low-value recyclables are not being recovered, the number of distribution centres is falling, and transportation costs are rising. He recommended linking up the waste disposal and resources recycling networks to reduce the costs of collection, and using subsidies and tax breaks to encourage the recycling of low-value materials, thereby reducing the externalities arising from their incineration or landfill burial.
Liu Jianguo, a professor at Tsinghua University's School of Environment, told China Dialogue that the two systems have not been combined as hoped and continue to operate independently. But he added that the waste-sorting systems have made data available on the quantities and destination of recyclables. Previously, these were not monitored.
If we treat waste sorting like the pandemic, just spending as much as it takes, then we can't claim to be doing a world-class jobLiu Jianguo, a professor at Tsinghua University's School of Environment
Li Yanming was promoting the use of urban food waste to make agricultural fertiliser even before the sorting systems were introduced. For years, he's seen how cross-departmental cooperation is a problem. He says the agricultural authorities are wary of city governments trying to offload their waste problems. This, he warns, means departmental barriers are preventing the circular economy from taking shape.
Liu Jianguo has seen similar problems: 'Each department has its own set roles and positions, its division of interests, and its way of looking at things.' He says that local governments have, in the short term, set up command centres or joint committees, with higher-level leaders pushing progress through. That only works as a 'war-time mechanism', he said. In the long-term, reforms will be needed to normalise the new systems. 'Some kind of cross-departmental coordination mechanism would make things easier,' he added.
When asked what China still needs to do to create a world-class system for dealing with waste, Liu Jianguo said: 'The easy things have already been done.' Next come: an extended producer responsibility system; charging for waste disposal ' with the immediate producer of waste paying by quantity produced; and regional and urban'rural integration ' with an ecological compensation system, so areas with adequate capacity can dispose of waste for areas without, and cities can dispose of rural waste.
'China has the advantage of being able to push through significant investment in short periods of time, with impressive results. But the more advanced cities have already done the easy parts. Long-term effectiveness will require taking advantage of how the market and society works. If we treat waste sorting like we treated the pandemic, just spending as much money and administrative resources as it takes, then we can't claim to be doing a world-class job,' Liu said.
Can the government alone bring about these changes? How can we ensure the changes actually reduce waste quantities, realise resource recovery, and remove harms?
If waste sorting is a job for the people as a whole, that means the people have a right to participate in decision making and oversight. Many industry observers say that public participation has been missing these three years. Some of the organisations mentioned above are providing examples of how to participate ' but more is needed.
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