When we throw a garbage bag into the collection point, it doesn't just "disappear"; it enters an industrial cycle system composed of precision machinery, chemical processes, and strict environmental standards.
To realize a "Sound Material-Cycle Society," Kyoto City employs a series of high-tech means to treat waste. Here is a hardcore breakdown of the treatment processes for various types of garbage.
Kyoto Waste Treatment Process Flowchart
Burnable Garbage: From Incineration to "Melting Resource Recovery"
Kyoto City's Clean Centers (such as the Southern and Northeastern Clean Centers) do not just "burn" garbage; they are actually thermal power plants and mineral manufacturing plants.
Step 1: Negative Pressure and Deodorization
Garbage trucks unload waste into a huge Waste Pit. To prevent odors from escaping, the inside of the waste pit is kept under negative pressure, and the extracted odorous air is sent directly into the incinerator to be completely decomposed at high temperatures.
Step 2: 850°C+ High-Temperature Complete Combustion
Huge cranes grab the garbage and feed it into the Stoker-type Incinerator.
- Temperature Control: The temperature inside the furnace is strictly controlled between 850°C ~ 950°C.
- Purpose: This temperature range maximizes the suppression of the generation of the highly toxic substance dioxin.
- Waste Heat Utilization: The heat energy generated by combustion heats water into high-pressure steam, which drives a steam turbine to generate electricity. The annual power generation of Kyoto City's Clean Centers can supply tens of thousands of households.
Step 3: Exhaust Gas Purification (Gas Cleaning)
The flue gas after combustion is extremely turbid and must undergo multiple filtrations:
- Bag Filter: Adsorbs fine dust like a giant vacuum cleaner.
- Gas Cleaning Tower: Sprays lime slurry and activated carbon to neutralize acidic gases and adsorb residual heavy metals.
Step 4: Ash into "Gems" (Melting Furnace)
This is the most critical step. The bottom ash remaining after combustion and the fly ash filtered out are sent to the Melting Furnace.
- 1200°C Ultra-High Temperature: At extremely high temperatures, the ash is melted into a magma-like liquid.
- Water Cooling Solidification: The liquid flows into water and cools instantly, turning into granules like black glass sand, called Molten Slag.
- Usage: The volume of this molten slag is only 1/2 of the ash, and it is very strong and non-toxic. It is widely used for paving materials, asphalt mixtures, and concrete aggregates.
Bottles, Cans, PET Bottles: The Ultimate Application of Physical Laws
The Resource Waste Treatment Center is like a giant "physics laboratory," using magnetic force, wind force, and optics for automatic sorting.
Step 1: Bag Breaking and Impurity Removal
First, machine blades cut open the garbage bags, and a Wind Sorter blows away mixed plastic bags and light paper scraps. A manual assembly line removes non-recyclable foreign objects (such as lithium batteries and lighters).
Step 2: Magnetic Separator
Using powerful magnets, steel cans are instantly sucked up and separated from other items on the conveyor belt.
Step 3: Aluminum Separator (Eddy Current Separator)
This is a black technology utilizing the Eddy Current principle.
- The machine generates a high-frequency changing magnetic field.
- When aluminum cans pass through, eddy currents are generated on the aluminum surface, which in turn produces a repulsive magnetic field.
- The aluminum cans are "flicked away" from the conveyor belt into a dedicated recycling bin.
Step 4: Optical Sorting (For PET Bottles)
- Near-Infrared Sensors scan the material of the bottles on the conveyor belt.
- Once PET material is identified, a high-pressure air nozzle at the end of the machine precisely sprays a jet of air to blow the PET bottle into the recycling channel, while other plastic bottles fall naturally.
Plastics: Moving Towards "Chemical Recycling"
Plastic containers and packaging collected in Kyoto City, after being compressed and baled, are mainly treated through Chemical Recycling technology, which is a relatively advanced treatment method in Japan.
Core Technology: Coke Oven Chemical Feedstock Recycling
Many plastics are sent to steelworks (such as Nippon Steel & Sumitomo Metal, etc.).
- Raw Material Input: Waste plastics are shredded and fed into Coke Ovens used for steelmaking.
- Anaerobic Pyrolysis: Heated in an oxygen-free environment.
- Products:
- Coke (40%): Used as a reducing agent for steelmaking.
- Oil (40%): Becomes chemical raw material oil.
- Coke Oven Gas (20%): Used as fuel for power generation.
- Significance: This method replaces the coal resources originally needed with waste plastics, achieving carbon emission reduction.
Final Disposal Site (Landfill): Not the End, But a "Capsule"
All residues that cannot be recycled or burned, as well as some incineration ash, eventually come to Kyoto City's Eco-Land Otowa (located in Fushimi Ward).
This is not simply digging a hole and burying it, but a huge environmental isolation capsule.
- Sandwich Structure: Uses a "garbage layer + soil cover layer" alternating burial method to prevent garbage scattering and bad odors.
- Impermeable Layer: The bottom is lined with multiple layers of high-strength waterproof sheets to prevent dirty water from seeping into groundwater and soil.
- Leachate Treatment: Sewage (leachate) generated in the landfill is collected through pipes and sent to a dedicated water treatment plant. After biological treatment and chemical precipitation, it is purified to meet discharge standards before being discharged into rivers.
Why Separate So Finely?
After seeing these processes, you might understand:
- If moisture is not drained: To maintain 850°C, the incinerator needs to spray more auxiliary fuel, increasing costs and carbon emissions.
- If batteries are mixed in: Squeezing in a crusher or garbage truck can cause a fire, destroying expensive processing equipment.
- If bottles are not washed: Dirty residues will corrode recycling equipment and reduce the purity of recycled materials, leading to downgraded processing (turning into low-end products).
Every sorting trash can in Kyoto is the starting point connecting your home to this high-tech environmental protection factory.