1. Garbage Trucks Take Trash to Cleaning Factories to Be Burned
The trash bags you put out for collection are taken by garbage trucks to cleaning factories, where most of it is burned. According to Ministry of Environment documents, waste is generally reduced and stabilized by incineration. [2] In fiscal year 2020, out of approximately 40.09 million tons of processed waste nationwide, about 31.87 million tons were directly incinerated. This accounts for roughly 79.5% of the total (calculated from the figures in the report). [2]
The effect of burning is visible in volume. The Edogawa Ward in Tokyo explains for children that when trash is burned and becomes ash, its size shrinks to about 1/20th of the original. [3] A 10-liter trash bag can shrink to the size of a 500-milliliter PET bottle. This is a rough estimate that varies depending on the type of trash. [3]
If the size decreases, the space needed for storage later also becomes smaller. But does the heat from burning just escape into the air? [3]
2. How the Heat from Burning Trash Is Used for Electricity and Other Purposes
Burning trash produces a large amount of heat. In the Ministry of Environment’s statistics for fiscal year 2023, there were 1,004 waste incineration facilities nationwide. Of these, 724 facilities (72.1%) utilize residual heat, and 411 facilities (40.9%) have power generation equipment. [1]
The total electricity generated by all facilities across the country is 10,254 GWh per year. [1] Since 1 GWh is 1 million kWh, this equals approximately 10.2 billion kWh (calculated from multiplication). Although this is a byproduct of waste processing, more than 40% of factories are equipped to generate electricity. [1]
Residual heat is not used only for power generation. When including facilities that do not generate electricity, more than 70% of facilities use the heat for something. [1]
So, waste is burned to reduce it, and the heat is used. However, the ash left after burning does not disappear. Where is this ash placed? [1]
3. Where Incineration Ash from Tokyo's 23 Wards Is Buried in Tokyo Bay
Trash from the 23 special wards of Tokyo has historically been buried in landfills within Tokyo Port after being burned. Currently, the 23 wards use the Outer Central Breakwater Landfill and the New Sea Surface Landfill. The Inner Central Breakwater Landfill has already completed its filling. [4]
Nationwide, the amount finally disposed of in fiscal year 2023 was 3.16 million tons, which is about 8% of the total waste generated (38.97 million tons). [1] The "direct landfill rate," which refers to burying waste without incineration or crushing, was 0.8%. The "reduction rate" for intermediate processing was 99.2%. [1]
It is important to distinguish between the 8% figure for total final disposal and the 0.8% direct landfill rate. The former includes ash and unburned residue after incineration, among other things. The latter is the percentage of waste buried without being burned first. [1]
Per person, out of about 311 kilograms generated annually, final disposal amounts to about 25 kilograms (calculated from national averages, not specific household data). So, how long can these landfills last? [1]
4. How Many Years of Space Are Left in Japan's Landfills?
The Ministry of Environment reports that the remaining capacity of general waste landfills nationwide was 95.75 million cubic meters at the end of fiscal year 2023. This is a 0.9% decrease from the previous year’s 96.66 million cubic meters. [1]
The "remaining years" (the number of years the remaining capacity of landfills will last) indicates how long landfills will last if filled at the current pace. At the end of fiscal year 2023, this figure was 24.8 years, up from 23.4 years the previous year. [1] This is not a prediction that landfills will vanish in 24.8 years. It is an estimate assuming current disposal rates remain constant. If waste is reduced, the time extends; if waste increases, it shortens. [1]
For Tokyo’s 23 wards, the New Sea Surface Landfill is described on the Minato Ward page as the "final landfill" available to the 23 wards. The page states that they aim to use this limited, precious disposal site for as long as possible. [4]
One method to achieve this is a technique applied to ash before burial. The next section looks at technology that turns ash into something like sand. [4]
5. How Melting Incineration Ash into Slag Helps Landfills Last Longer
In some cleaning factories in Tokyo’s 23 wards, incineration ash is melted at temperatures above 1,200 degrees Celsius, then cooled and solidified into "slag," which resembles sand. [3] Making slag reduces the volume of waste buried compared to burying ash directly. [3]
The Minato Ward page lists two methods the 23 wards use to reduce landfill volume: thermal recycling of waste plastics (burning them to use heat) and slagging of incineration ash. It explains that promoting these methods allows the landfill to be used for longer. [4]
The same page mentions a figure of "approximately 50 years or more," but this is an estimate assuming plans proceed as scheduled. Since the page content is older, it is safer not to treat this as a current value. The key point is that factories do not just "burn and finish"; they implement measures at the ash stage to extend the life of the final landfill. [4]
By the way, not all trash is burned. Items separated for recycling take a different path. [4]
6. Why PET Bottles Are Recycled Instead of Burned with Burnable Trash
The path for trash is not a single road of burning. According to Ministry of Environment statistics, the recycling rate in fiscal year 2023 was 19.5%, with 7.63 million tons of resources recovered. [1]
A page from Fukushima Prefecture cites data from the PET Bottle Recycling Promotion Council for 2024, stating that the recycling rate for PET bottles is about 85%. It says that about 58% of recycled products become new PET bottles, while the remaining about 42% become fibers, food trays, and other items. [5]
Note that the 58% figure is a proportion "within the recycled amount," not 58% of all collected PET bottles. Also, since these are figures introduced on a local government page, it is safer to read them as rough estimates. [5]
There are paths for burning to reduce waste, using heat, burying, and reusing as resources. Even trash from the same home goes to different places depending on how it is separated and the local processing methods. [5]
7. How to Find Out Which Path Your Family's Trash Takes
If you have a list of waste separation rules distributed by your local government at home, look at it. You can see the separation category for each item: burnable trash, resource trash, or non-burnable trash. [1]
You can also verify the numbers yourself. If you multiply 851 grams per person per day by 365 days, you get about 311 kilograms. Multiplying that by the final disposal rate of about 8.1% gives about 25 kilograms. With a calculator, you can calculate this for the number of people in your family. [1]
Another step is to find your town’s cleaning factory. Municipal websites often list the factory’s location and whether tours are available. Information on whether they use heat to generate power or where they transport ash may also be included. [1]
The Ministry of Environment’s "Status of Generation and Treatment of General Waste" is a statistic updated every fiscal year. Comparing your town’s numbers with national averages might lead you to new questions. [1]