Agricultural film recycling turns white pollution into green development
Editor's note: After the autumn harvest ends and before the next production cycle begins, in addition to the straw that needs to be handled, the agricultural film used in the previous crop also needs to be cleaned up and recycled in time. Agricultural film recycling can not only effectively solve the "white pollution" problem, but its resource-based utilization can also turn waste into treasure, which is of great significance for promoting the sustainable development of agriculture.
1 Present situation: Heavy use, light recycling, agricultural film residue causes "white pollution"
In the late 1970s, China introduced its first piece of agricultural plastic film. Since then, through the unremitting efforts of agricultural science and technology workers across the country, agricultural plastic film began to be applied on a large scale in China and gradually became the fourth major agricultural production material after seeds, pesticides and chemical fertilizers. After more than 30 years of development and application, plastic film mulching has become one of the most important agronomic technologies in China. Especially in the northwest region, film mulching plays a crucial and irreplaceable role in boosting the expansion and quality improvement of dryland farming and in stabilizing grain output and increasing yields. In Gansu, a typical dryland farming area in China, with the application of agricultural plastic film, agricultural science and technology personnel successively successfully developed and promoted autumn film mulching, early-spring film mulching and full film with soil covering and hole sowing dryland farming technologies. Thanks to the adjustment of the province's grain structure and the large-scale promotion of dryland farming technologies, Gansu's grain production not only bid a complete farewell to the history of grain shortage, but also achieved grain self-sufficiency with a surplus.
How can a piece of plastic film enable originally arid and barren land to unleash such enormous grain production potential? In this regard, Yan Changrong, a researcher at the Institute of Environment and Sustainable Development in Agriculture of the Chinese Academy of Agricultural Sciences, who has long been engaged in agricultural plastic film research, believes that plastic film mulching has the effects of increasing temperature, preserving water and fertilizer, improving soil physical and chemical properties, increasing soil fertility, inhibiting weed growth and reducing diseases, and can help promote crop growth and development and increase yields.
"Plastic film mulching can increase the average daily soil temperature by 3 to 5 degrees, and it also changes the water circulation process and reduces the evaporation of ineffective water. These are crucial for ensuring the growth of some crops in China, especially in dry areas," Yan Changrong said. But at the same time, our research found that after decades of application, the areas polluted by residual agricultural plastic film completely overlap with the areas where plastic film is used.
What kind of pollution does residual agricultural film cause? In this regard, the reporter learned during interviews that if plastic film remains in the soil, it will first destroy the soil structure and cause soil compaction; second, it will affect seed growth and development and even affect the quality and use of some crops. For example, although peanuts are excellent feed, residual agricultural film in the soil can cause continuous evaporation of water, affecting the growth and utilization of peanuts.
In response to current misunderstandings about the problem of residual agricultural plastic film pollution, Yan Changrong believes that qualified PE plastic film does not contain plasticizers, and the problem of plasticizers in soil has nothing to do with plastic film; at the same time, there is also no evidence showing that certain components in farmland plastic film will enter our food chain.
2 Way out: Eliminate ultra-thin plastic film and improve the recycling rate
At the national on-site meeting on promoting the comprehensive utilization of agricultural plastic film recently held in Lanzhou, representatives from key provinces and regions applying plastic film generally believed that doing a good job in recycling waste plastic film is an arduous task, and a prevention and control strategy of "walking on two legs" must be adopted: source control and efficient recycling.
"First, when producing plastic film, corresponding standards must be strictly formulated, such as eliminating ultra-thin plastic film. Only when the thickness and tensile strength of the film are sufficient can it be picked up. Preparations for recycling must be made from the very beginning," said Yuan Yamei, a senior agronomist at the Agricultural Technology Extension Station of the Xinjiang Production and Construction Corps.
Xinjiang is the province and region with the largest area of agricultural plastic film use in China. Plastic film is widely used in the production of crops such as cotton, processing tomatoes, corn and vegetables. At the same time, it is also one of the areas in China with serious plastic film residue pollution. In recent years, on the basis of the state's continuously increasing support, Xinjiang has also continuously increased funding input for the recycling and utilization of waste agricultural film in farmland, implementing pilot demonstration construction for pollution control in 40 counties and cities across the region, especially publicizing and guiding enterprises to produce plastic film with a thickness of 0.01 mm or more, encouraging farmers to use thickened plastic film, actively promoting mulching methods conducive to recycling, and promoting residual film recycling and utilization from the source. In 2014, Xinjiang also issued the mandatory local standard "Polyethylene Blown Agricultural Ground Cover Film."
In fact, improving plastic film quality standards through legislation, increasing the recycling rate, and strengthening supervision and management of the entire process of plastic film application have become a realistic choice for the application and promotion of agricultural plastic film in many provinces and regions. Establish and improve systems for plastic film recycling and processing, and take the path of resource-based reuse. In response to problems such as farmers' weak environmental awareness, Hebei, on the basis of carrying out publicity and training in multiple forms, seeks funding through multiple channels to support the application of standard-thickness agricultural film and the recycling of waste agricultural film. Heilongjiang, through active efforts, established 15 agricultural cleaner production demonstration projects for residual plastic film. In the two major plains areas, with one county as the focus, it renovated, expanded or built waste plastic processing plants to radiate and drive surrounding areas; in several central townships in each county and district, enterprises established waste agricultural film recycling stations to pay for the recycling of waste plastic film and uniformly package and transport it to processing plants for renewable resource utilization.
"The comprehensive utilization of plastic film and pollution control is a systematic project with many influencing factors, wide involvement and great difficulty in governance," said Wang Yanliang, deputy director of the Department of Science, Technology and Education of the Ministry of Agriculture. In order to do a good job in agricultural plastic film pollution control, agricultural departments at all levels across the country should fully summarize and promote good experiences and good practices from various places, continuously increase work efforts, and strive to achieve a recycling and comprehensive utilization rate of agricultural film of more than 80% in the current season by 2020.
3 Future: Actively carry out applied research on degradable film
In addition to doing a good job in supervision and management, recycling and regeneration, developing degradable plastic film to replace PE film is the best way to explore solving residual film pollution in farmland, and this can solve the problem of plastic film residue from the source. However, the application of degradable plastic film still faces a series of problems and challenges.
"Although it has been tested locally for more than four years, because there are too many influencing factors, further comparative tests may still be needed," said Liu Hongjin, an agronomist at the Rural Ecological Energy and Environmental Protection Station of the Inner Mongolia Autonomous Region. Degradable plastic film causes little environmental pollution, but its cost is high, resulting in a product price higher than ordinary plastic film, which brings certain difficulties to popularization and promotion. Tang Jirong, director of the Agricultural Ecological Environmental Protection Management Station of Gansu Province, believes that "because climate and environments differ from place to place and agricultural production conditions vary, the required degradation time of plastic film also differs from place to place. For example, Gansu vigorously promotes autumn film mulching technology. After mulching in autumn, sowing does not take place until March or April of the following spring. Some degradable plastic films degrade automatically before the sowing season, so they simply cannot be used."
The reporter also learned during interviews that at present, domestic degradable plastic film still has problems such as insufficient product stability and relatively poor active degradation.
"Due to the complexity of the degradation and application of degradable plastic film, the same formulation of degradable film has different degradation performances in different places and for different crops. It must be promoted for use through applied research," Yan Changrong believes. Research and development of degradable plastic film should make breakthroughs in raw materials, formulations and touch processes. In addition, the use of biodegradable plastic film should be organically combined with regions and agricultural production conditions, research on the adaptability of plastic film mulching technology should be strengthened, and new ways to solve "white pollution" should be actively explored.
Agricultural film recycling must pass three hurdles
◇Thickness and toughness meet standards◇Financial subsidies are given◇Waste agricultural film has somewhere to go
For the current state of agricultural production in China, apart from some areas with the conditions to try promoting degradable agricultural film, most still focus on agricultural film recycling. So, what conditions are needed to recycle agricultural film?
First, agricultural film must meet certain requirements in thickness and toughness. Agricultural film that is too thin has poor strength and is easily broken. After one production cycle, it appears in a broken state on the soil surface, and recycling is basically impossible. According to the production standard "Polyethylene Blown Agricultural Ground Cover Film" formulated by China in 1992 (GB13735-92), the minimum standard for agricultural plastic film thickness is 0.008 mm, and the allowable limit deviation floats up and down by 0.003 mm. At present, some provinces and cities in China encourage the promotion of plastic film with a thickness of 0.01 mm, which can be used for many years and is suitable for various film-removal technologies, and also meets the conditions for agricultural film recycling and reuse.
Second, at present China encourages farmers to recycle plastic film themselves. Most provinces that use agricultural film have agricultural film recycling stations in each township, and farmers collect the agricultural film and send it to recycling points. Compared with the past when agricultural film was scattered in fields, recycling agricultural film requires a certain amount of labor, so financial subsidies to encourage the recycling of old film are very important. Yuzhong County in Lanzhou City adopts a trade-in approach. Since 2013, the provincial, municipal and county governments have subsidized the use of plastic film at three levels. On dry land, an average of 6 kg of plastic film is used per mu, about 70 yuan, with financial subsidies covering nearly two-thirds and individuals paying 25 yuan. This kind of financially subsidized plastic film is called "quota film," that is, new film purchase quotas must be exchanged for recycled old film at a ratio of 2:1. Taking 6 kg of new film as an example, farmers need to exchange 12 kg of old film and 25 yuan to complete the purchase. This measure has to a certain extent increased farmers' enthusiasm for recycling agricultural film, and at the same time reduced the cost burden of using thick agricultural film. "Since the implementation of the trade-in policy, agricultural film with a thickness below 0.008 mm has basically disappeared from our province's market," said Zhang Guangquan, director of the Agricultural Ecological Environmental Protection Management Station of Yuzhong County.
Third, the recycled waste agricultural film must have somewhere to go and must not cause secondary pollution. It is understood that there are mainly two ways to comprehensively utilize waste plastic film: first, after crushing and cleaning the recycled waste plastic film, produce recycled plastic pellets through hot melting and extrusion, and use the recycled pellets for deep processing to produce PE pipes, plastic containers, drip irrigation tapes, etc.; second, directly crush the recycled waste plastic film and mix it with a certain proportion of slag to process and produce recycled products such as sewer well rings, manhole covers and tree grates for urban greening. Waste plastic film is stored at recycling points in each township and collected and taken away by recycling enterprises for a certain fee, while the enterprises bear the transportation costs.
From picking up plastic film to recycling to resource-based reuse, this is a production chain for agricultural film recycling. If the market-oriented operation mechanism can be gradually improved, the "white pollution" caused by agricultural film will also be solved.