Rotten garbage refers to landfills that fail to meet sanitary landfill requirements in terms of construction standards, environmental protection, and other aspects. Due to the lack of anti-seepage and covering measures, the garbage gradually ages and decomposes under biological and physical effects. The leachate and leached substances produced in this process can pollute the surrounding groundwater, soil, and air, and pose a potential serious threat to human health. Given the potential hazards of stale garbage, relevant national departments have formulated remediation plans and supported cities with surplus incineration capacity in thermal power plants to excavate, screen, and incinerate stale garbage from landfills.

The screening process for aged garbage adopts a process flow of "manual sorting particle size screening density sorting double magnetic separation", with a designed processing capacity of 500t/d. Manual sorting mainly involves separating large debris such as stones and wooden boards; Particle size screening is mainly used to separate humus soil with a particle size of less than 35mm using a drum screen. The humus soil is subjected to magnetic separation to remove iron metals and then reused as a resource; The screened material with a particle size greater than 35mm enters the density sorting system to separate light waste and heavy waste. Light waste mainly consists of plastics and textiles, which are compressed and packaged before being sent to the incineration power plant for disposal. Heavy materials mainly consist of inert materials such as bricks and tiles, which are selected by the magnetic separation system and backfilled with iron metals; The iron metals sorted out from the project are recycled and reused by downstream recycling enterprises.

The proportion of humus soil in aged garbage is the highest, reaching 46.4%~58.9%, followed by light materials (plastics and textiles), accounting for 29.8%~45.3%, iron metal content is only 0.0%~0.1%, and other garbage (stones, plastics, wood, and other inert garbage) accounts for 8.3%~11.2%. Research has shown that the proportion of humus soil (particle size ≤ 50mm) in garbage with a landfill age of 4-9 years is 30.8% to 56.3%. The particle size of humus soil is smaller, but the proportion of humus soil mass after screening is higher, mainly because: firstly, the composition of household waste in different regions is different, and the particle size and proportion of humus soil formed after landfilling vary; 2、 Non formal landfills, where garbage is not compacted or covered, allow rainwater to seep into the garbage heap in large quantities, while air seeps through the gaps between the garbage, resulting in the heap being in a state of high water and oxygen content, accelerating the oxidation of organic matter in the heap, promoting the degradation rate of organic waste, and forming humus soil; 3、 After excavation and stacking before screening, stale garbage has a lower moisture content, which is conducive to separating humus soil from other garbage.

The process flow of "manual sorting coarse screening wind separation magnetic separation" can effectively achieve the separation of aged garbage materials, which has high reference value for the selection of screening technology for aged garbage in informal landfills. The high content of heavy metals in humus soil in aged garbage will limit its reuse. When it exceeds the risk control value of soil pollution in agricultural land, it is necessary to strengthen supervision to avoid its reuse in agricultural planting. The light substances in stale garbage are mainly treated by incineration. Although it can quickly reduce the amount, it will not create economic benefits for the project. In the future, by solving the technical problem of cleaning and improving the quality of light substances, we can expand the ways of reusing light substances.