Thoughts and Countermeasures for the Treatment of Urban Plastic Waste (I)

Abstract: This article reviews the status quo of urban plastic waste, the main ways of governance, and discusses relevant issues and makes recommendations.

Keywords: plastic waste; recycling; environmental protection

With the development of urban economy, the expansion of city scale, the increase of resident population and floating population, and the continuous improvement of residents' living standards, the number and types of urban waste are showing rapid growth. According to statistics, two-thirds of the more than 600 cities in the country are surrounded by garbage loops. Taking Wuxi as an example, there are 152 garbage transfer stations in the city, and annual garbage removal volume is 800,000. “Statistics also shows that the total amount of garbage generated in China each year reaches 150 million tons, and the annual municipal waste management costs thus invested are nearly 40 billion.Urban domestic waste has become an ecological issue and a social issue that seriously constrains the sustainable development of the city.

1 Plastic Waste Causes Ecological Crisis

As we all know, plastic as a novel material has been rapidly developed due to its excellent performance, convenient processing, and low price. It is not only widely used in various fields of the national economy such as industry, agriculture, and national defense, but also penetrates into people's daily life. Since the reform and opening up, China's plastics industry has developed rapidly. The annual processing volume has increased at a rate of 10%. At present, the output of plastic products exceeds 20 million tons, ranking second in the world. It is undeniable that plastic materials have made tremendous contributions to the advancement of technological advancement, social development, and improvement of living standards. However, with the large-scale application of plastics, the waste generated is also increasing day by day. In particular, plastic packaging materials are closely related to the daily consumption activities of urban residents. A large number of disposable packaging materials, such as shopping bags, fast food boxes, beverage bottles, etc., entered the urban waste system soon after undergoing a short-term consumption process. In developed countries such as Europe and the United States, the proportion of plastic waste in the total urban waste is close to 10% by weight, and up to 30% to 40% by volume, and the number has risen year by year. China is a developing country, but plastic waste accounts for 10% of the world's total. In coastal cities, waste plastics account for 8% to 10% of municipal solid waste, which has reached the level of developed countries. In Wuxi alone, plastic waste accounted for the proportion of municipal solid waste. The highest year was 9.83% in 1996. In the six years from 1996 to 2001, the average number was 6.6%. These facts show that plastic waste has become an important part of urban household waste. Comprehensive treatment of municipal solid waste must be included in the planning and management of urban sanitation.

Plastic waste is different from ordinary household waste. It is a polymer synthetic material with light weight. It is thrown away indiscriminately. It is easy to fly with the wind. Because it is not easy to rot under natural conditions, it is easy to deteriorate soil and water sources by discarding it in the wild and rivers. Random burning of toxic gases can pollute the air. Therefore, how to manage the burden and pollution caused by plastic waste on the environment has attracted the attention of the global environmental protection industry and industry as early as the 1960s. In the long-term governance process, it also accumulated a lot of successful experience.

2 Three Effective Ways of Plastic Waste Disposal

How to manage the environmental pollution caused by plastic waste, the overall goal is to achieve reduction, harmlessness, and resource utilization. At present, there are mainly the following three ways.

2.1 Sanitary landfill

Landfilling is the traditional treatment of municipal solid waste. This method is to use artificially constructed landfills to bury the wastes in the ground one by one, cover the top of the soil and cover the grass to harmonize with the surrounding environment.
The key to landfill technology is anti-seepage and biogas treatment. Anti-seepage is to prevent some of the buried materials from decomposition due to decomposition or rain soaking dissolved toxic substances and take some isolation and isolation measures; biogas treatment is to set biogas power generation and combustion equipment for timely treatment of biogas.

Due to the use of natural terrain to construct landfills, a large amount of manpower, material resources and finances can be saved. Therefore, sanitary landfills still occupy a large proportion in many countries. For example, in the United States, with an annual output of nearly 200 million tons of garbage, more than 6,000 landfills can handle 73% of them. According to a landfill with an annual treatment capacity of nearly 12Kt, the production of biogas can be used to generate electricity for more than 100,000 households. Family use.

Landfill disposal waste mainly has the following problems:

(1) Take up a lot of land. The problem is particularly prominent in large cities where the potential for land resources is limited and where the per capita area is relatively small. For example, in the Yangtze River Delta where the economy is growing in size, with the continuous increase of waste, it is becoming more and more difficult to add landfill sites, and the cost of landfilling is also increasing year by year.

(2) Worries about environmental pollution. Improper handling of landfills, gases from the decomposition of organic matter, dissolved substances from the chemical decomposition of waste, and precipitation of some plastic additives can cause pollution to the atmosphere, surface and groundwater.

(3) Low resource utilization rate. Except that a few landfills can use biogas to generate electricity to recover some of the energy, landfills make most of the wastes become real waste, and waste a lot of valuable energy and raw material resources in waste plastics.

2.2 Incineration

Many municipal wastes can be disposed of by incineration. Incineration can reduce waste volume by 85% to 90%, solve a large amount of waste accumulation problems, and make use of the energy contained in waste. According to data from the United States, incineration of ton of municipal waste can generate 25,000 kWh, equivalent to the price of electricity. % USD/degree. In addition, the flue gas emitted by power generation is used to preheat the air and atomize the fuel or combustion, which can save 10% to 15% of the fuel. The incineration method accounts for about 2% of the waste disposal capacity in China. This is mainly due to the high construction and operating costs of the incineration treatment equipment. In addition, the incineration method requires a higher calorific value of the waste. Generally speaking, the heat value of foreign countries is greater than 3360kJ/kg, but in our country it is required to be more than 5000kJ/kg, which can not meet the requirements of the need to continuously add auxiliary fuel to help burn, thereby increasing the cost.

In urban waste, plastic waste has the highest calorific value, with an average calorific value of 32.5 mJ per kilogram. When incinerators are burned, the calorific value of the plastic can be used to supplement and promote the complete combustion of non-plastic waste. Incineration of waste into the environment is a sensitive issue. Some data from the past suggest that harmful substances such as greenhouse gases, acid gases, dust, and ash discharged during incineration will have more adverse effects on humans and the environment. However, current research shows that incineration is performed on commercial incinerators. The amount of greenhouse gas carbon dioxide emitted by waste is much smaller than that of the oil, steel, cement, and chemical industries. Second, in terms of sulfur and hydroxide that can cause acid rain, waste plastics are a relatively clean fuel compared to carbon-based fuels such as conventional fuels and coal. In addition, the two-to-British emissions that caused the public to worry and panic, further research suggested that previous reports had exaggerated components. In fact, there is no correlation between the amount of emissions from the two to the UK and the content of plastics in the waste. All wastes, except glass and metal, contain chlorine content that can produce two to three inches of chlorine. The test results show that as long as advanced pollution control devices are used to ensure adequate combustion, the two emissions from the flue can be lower than the stringent European emission standards.

Plastic waste has recently been used as a fuel in blast furnace smelting. This technology was developed by researchers in Germany and Japan. It is based on the principle that the plastic component is mainly composed of carbon and hydrogen. Therefore, it can be used as a reducing agent and heat-generating agent for blast furnace smelting, like coke, pulverized coal and heavy oil. Blast furnace fuel. Since this technology was put into operation, it has achieved very significant economic and social benefits.

The advantages of this technology are:

(1) The thermal efficiency of waste plastics in blast furnaces reaches 80%, and waste plastics are simply burned in an incinerator, and the heat utilization rate for heating and power generation is 30% to 40%.

(2) The cost of treatment as a fuel is only 30% to 60% of incineration or recycling, which is economically advantageous.

(3) The amount of harmful gas emissions is only 0.1% to 1% of incineration and has little impact on the environment.

(4) Provides a new energy source for blast furnace ironmaking, and is advantageous to the improvement of economic indicators of blast furnaces compared with the pulverized coal injection technology.

As this technology opens up a new way for the comprehensive utilization of waste plastics, it also provides a new means for the metallurgical industry to save energy and increase profits. Its potential development prospects have attracted the attention of domestic research departments and they have begun research and development.

2.3 Recycling

The recycling of plastic waste is through various ways to recycle the waste plastics that are easy to recycle and have recycling value. The specific methods are as follows:

2.3.1 Recycling

Most of the waste plastics are thermoplastic plastics. Since the molecular structure is not damaged, such processes as sorting, washing, drying, smashing, mixing of ingredients, and granulation can be reprocessed into plastic products.

Waste plastic recycling can save 85%~90% of resin energy compared with new materials, saving processing energy by 6%~17%.

The successful use of waste plastics for recycled products now appears to depend on the following factors: (1) There is a scientific and rational recovery system from collection and disposal to disposal; (2) Advanced technology and equipment support, such as selecting an Austrian production The plastic bottle screening equipment can identify PET bottles, PVC, PE, PP, PS, PA, ABS, PC and other 8 kinds of plastic bottles. Whether or not the plastic bottle is labeled or the bottle is deformed, it can The plastic bottles are sorted at speeds of 5 to 7 per second, which greatly improves the efficiency of the processing; (3) Profitable space. If there is more support in the policy and reduce the cost of recycling, professional manufacturers will have the enthusiasm.

For waste plastics that are heavily contaminated, difficult to separate, and have lost valuable value, recycling is obviously not appropriate.

2.3.2 Pyrolysis Production Ports, Gas Fuels, and Recovery Monomers

In today's energy shortage, waste plastics can be regarded as valuable solid petrochemical raw materials, which are pyrolyzed into various hydrocarbons such as kerosene, gasoline, heavy oil, and gaseous fuels. It is reported that 1kg of waste plastic can produce 1L of oil crystals, of which gasoline accounts for about 50%, and kerosene and light oil account for 25% each. The use of highly efficient catalysts during pyrolysis can increase oil yields, improve oil quality and reduce production costs.

There are still many problems in the promotion of this technology in China, such as simple production equipment, imperfect process equipment, low quality of oil products, and pollution caused by direct discharge of waste materials. When foreign materials evaluate the technology, it is considered that only waste plastic can be collected free of charge. Only economically feasible when the annual processing volume exceeds 5kt. It is generally believed that if the crude oil price is lower than the total cost of collecting and processing waste, then there will be problems with promotion.