Hyogo’s Hardest Recycling Problem Is a Wet Diaper

A disposable diaper leaves a factory almost weightless. It reaches the waste system carrying much more than the paper pulp, plastic and absorbent polymer from which it was made. Japan consumes an estimated 510,000 to 570,000 metric tons of diapers a year by dry product weight. Once used, the annual discarded mass rises to 2.04 million to 2.28 million tons. Municipalities are not simply feeding paper and resin into incinerators. They are paying to move and heat a large quantity of absorbed liquid.

Hyogo Prefecture has decided that this stream deserves its own map. On August 24, its Environmental Improvement Division announced the first exchange meeting for a study formally called the “Construction of a Recycling Model for Used Disposable Diapers.” Scheduled for August 31 in Kobe, the session is intended to connect diaper producers and users with cities, towns, waste authorities, vehicle makers, processors, retailers, financial institutions, researchers and citizens.

The breadth of that invitation reveals the real problem. Recycling is often narrated from the center of a factory: material enters, clean commodity leaves. A diaper system begins somewhere less photogenic—with a caregiver tying a bag, a parent carrying it to a collection point, a worker preventing that bag from bursting in a compactor truck and a buyer deciding whether the recovered pulp has reliable specifications. Miss any link and an elegant treatment technology becomes an expensive way to make unwanted inventory.

The first machine in the system is a household decision

In June, the Environment Ministry selected Hyogo as one of eight fiscal 2026 projects in its municipal support program for the reuse of used disposable diapers. The official project sheet gives the prefecture a specific first assignment: work with Shisō City, a municipality stretching into the mountains of western Hyogo, to study household diaper waste. The research is to identify willingness to separate it and practical problems including odor.

That is a more consequential starting point than it sounds. Institutional sources such as nursing homes and childcare centers produce comparatively predictable volumes. Managers can train a workforce and set a single storage rule. Household waste is scattered among thousands of kitchens, bathrooms and care routines. Summer heat, housing type, distance to a collection point, bag price, disability, access to a car and the privacy of the bin can all determine whether a policy survives contact with daily life.

Hyogo’s proposed model is prefectural because the geography crosses municipal systems. Kobe and the Hanshin corridor offer population density and short collection routes but scarce storage space and neighborhood sensitivities. Harima’s industrial zone offers possible processors and material users. Mountain communities have lower volumes, greater travel distance and roads vulnerable to severe weather. A system optimized for one can fail in another.

The August 31 meeting is due to run from 2 to 4 p.m. at Lasse Hall. A public first part includes a presentation from the Environment Ministry’s Resource Circulation Division; a workshop follows behind closed doors. The Japan Environmental Sanitation Center is serving as secretariat. The declared range of participants extends from eldercare and childcare providers to municipalities, intermunicipal authorities, haulers, special-purpose vehicle manufacturers, diaper companies, retailers, finance, researchers, students and civic groups.

Convening them is only a beginning. The model will need to say who distributes bags, who inspects contamination, which government owns operational data, who pays when fuel costs rise, who carries liability for leakage and what happens if a processor closes. A stakeholder list is not yet a chain of custody.

A waste stream shaped by aging—and by every stage of life

Japan’s diaper market has crossed over. Of the approximately 17.6 billion units produced in 2024, about 9.6 billion were adult products and 8.0 billion were children’s products. Production for children had fallen to roughly two-thirds of its 2014 level; adult-diaper production was about 1.4 times the level a decade earlier.

The Environment Ministry estimates that discarded adult diapers will rise from about 1.53 million tons in 2023 to 2.14 million in 2050. Children’s diaper waste is projected to fall from about 630,000 to 500,000 tons. The combined stream still grows by roughly 480,000 tons. Meanwhile other municipal waste shrinks with population and source separation. Diapers represented 5.5 percent of municipal waste in 2023; the official projection rises to 6.6–7.1 percent in 2030 and 7.7–12.7 percent in 2050.

Those ratios matter for the next generation of incinerators. Removing even about 6 percent of the incoming stream might allow a smaller replacement plant, according to the ministry’s guidance. But the implication depends on timing. A city still paying the fixed cost of an existing furnace may save little by diverting material. A regional authority designing a new one could avoid decades of excess capacity.

Japan counted 36.19 million people aged 65 or older in September 2025, or 29.4 percent of the population. Yet calling diapers merely “aging waste” distorts the human story. Babies, disabled people, patients, family caregivers, nurses, care workers and nursery staff all rely on absorbent products. A recycling program built around shame will suppress participation. One built around dignity treats continence care and the material afterward as ordinary public-health infrastructure.

A used diaper is not an embarrassing exception to the waste system. It is evidence that the system follows bodies through childhood, disability, illness, work and old age.

Incineration has a water problem, but the physics are local

High moisture lowers the calorific value of waste. In some incinerators, a wet diaper stream can increase the need for auxiliary fuel. Salts in urine, including sodium, can contribute to corrosion of refractory material and equipment. In places with high aging rates, the national guideline reports scenarios in which diapers account for as much as half the sodium in the overall waste stream and 23 percent of fossil carbon dioxide from treatment.

These are conditional findings, not a universal indictment of every furnace. The same guideline says the effect on overall waste quality and chlorine concentration may be limited. Results depend on furnace design, the mixture of other waste, moisture and operations. Plants that efficiently recover electricity or heat have a different baseline from those that incinerate without energy recovery.

Separate collection creates its own burden: bags and containers, more truck movements, protected storage, washing, sterilization, wastewater treatment and residual disposal. Moving a load whose mass is mostly absorbed liquid across the prefecture can erase both financial and climate benefits. A decision cannot be made from the processor’s gate fee alone.

The life-cycle comparisons in the 2026 national guideline are useful but easy to misuse. The main baseline assumes total incineration without electricity generation. Outcomes change with water content, diaper composition, child-to-adult product mix, grid emissions, travel distance and the virgin product displaced by recovered material. Recycling may lower emissions in a given route; the document does not establish that every recycling route is always lower-carbon.

Hyogo therefore needs more than a prefecture-wide average. It should publish route-specific mileage and load factors, actual moisture and contamination, power and water use, wastewater performance, recovered-material yields and the real incinerator baseline. A mountain route and a dense urban route are different environmental products even if they end at the same plant.

“Diaper recycling” is at least four different industries

A disposable diaper is a composite. Fluff pulp spreads liquid. Plastic films and nonwoven material contain it. Super absorbent polymer—known as SAP—locks much of it in place. Recovering one component may contaminate or degrade another. Japan’s 2026 guideline organizes established processes into four broad routes. The official umbrella term, saisei riyō-tō, covers both material recovery and qualifying forms of heat recovery such as solid-fuel production, distinct from ordinary waste-to-energy incineration. Each route therefore makes a different claim on the word recycling.

Other work includes carbonized or semi-carbonized products, feedstock for sustainable aviation fuel and chemical recovery of SAP. Pulp has been directed to toilet paper, cardboard, construction products, business cards and diapers. Plastics can become bags, boxes, flooring, playground equipment, imitation lumber or pallets. Recovered SAP is being explored for new diapers, cat litter and absorbent material for emergency toilets.

The destination determines the quality of the loop. Drying mixed material into fuel can avoid some fossil combustion, but the material is burned at the next step. Returning pulp to a new absorbent product is “horizontal recycling,” but it demands higher and more consistent specifications. Neither label alone reveals how much material was recovered, how much residue was incinerated or whether the output actually sold.

Hyogo has not selected among these routes. Its model may ultimately need more than one. High-volume institutional material could justify one type of recovery near an industrial user, while a remote area might find shorter-distance fuel production more credible. The comparison should be made with a common accounting boundary so an option does not look cleaner merely because its wastewater, residue or final combustion falls outside the spreadsheet.

Sanitation lives in the details: tied bags, intact loads, tested pulp

National guidance starts the collection protocol at the toilet. Where feasible, fecal matter is removed there; the diaper is placed in a bag, and the mouth is tied against leakage and odor. A compactor truck can rupture a bag and expose workers or equipment, so vehicle choice, container design, loading practice and cleaning plans matter. Summer storage intervals cannot simply be copied from a winter pilot.

The waste-law boundary also changes by source. Ordinary household diapers are municipal waste. Products discarded by care facilities may be business-related municipal waste. Items used for patients with specified infections must be screened out of the general recovery stream and managed under applicable infectious-waste rules. A safe protocol should not require households to display a diagnosis; medical providers and collectors need a clear, confidential decision path.

Privacy is operational, not ornamental. An opaque bag, a screened drop point and a collection charge that does not punish high-need households can determine whether families participate. The program must also measure labor shifted upstream. An extra separation routine may sound trivial in a proposal but accumulate into hours for already pressed nursery and care staff.

At the factory end, “washed” is not a quality standard. Japan adopted JIS S 0261:2024 for recycled pulp used in urine-absorbent products. The standard addresses appearance and odor, pH, arsenic and heavy metals, total bacteria and the absence of E. coli, among other qualities. Eco Mark criteria created in May 2025 require selection, washing, sterilization and disclosure of recycled content for qualifying products. Test results, rejected lots and corrective actions should be traceable to source and process conditions.

The need for care is not an argument against recovery. It is an argument against pretending that a sealed industrial machine begins the story. Public confidence will be won or lost at collection points and in published quality results long before a shopper encounters a product containing recycled pulp.

Reverse logistics will decide whether Hyogo is one market or three

New diapers move outward through concentrated warehouses. Used ones must move backward from thousands of small sources. They are time-sensitive, heavy, odorous if mishandled and unsuitable for indefinite storage. The reverse network must create industrial scale without making water travel farther than the recovered material is worth.

There are at least three architectures to test. A centralized model sends dense urban and institutional volumes directly to a large processor. A hub model consolidates multiple municipalities and perhaps reduces water or volume before long-distance transport. A distributed model treats smaller streams closer to mountain communities, possibly making fuel or a semi-processed input for another plant.

Each architecture changes government responsibilities. Municipalities control ordinary-waste collection. Intermunicipal authorities may operate incinerators. The prefecture can coordinate markets and routes across borders but cannot make hauling costs disappear. Private haulers and specialized vehicles add flexibility; contracts must preserve service if a single supplier exits.

The last mile of this reverse network runs forward again—to a customer for pulp, plastic, SAP or fuel. An impressive recovery rate means little if output accumulates in a warehouse. Long-term offtake agreements need product specifications, prices or adjustment rules, minimum volumes and a destination for off-spec material. Public procurement may create initial demand, but it should not conceal a product that cannot compete on verified performance.

Japan has moved from local invention to national specifications

Used-diaper recovery in Japan has a history longer than the current policy cycle. Municipalities including Ōmuta in Fukuoka developed material-recovery systems. Hōki Town in Tottori introduced a diaper-to-fuel process in 2011. Their experience gave the Environment Ministry enough evidence to publish its first municipal guideline in March 2020.

By fiscal 2023, national policy had settled into three tracks: collect and organize information, support municipal planning, and assist businesses. Hyogo adopted its Resource Circulation Promotion Plan in January 2024. The pulp standard arrived that year, Eco Mark criteria followed in 2025 and the ministry issued its substantially expanded technical and life-cycle guideline in April 2026. In June, it chose eight local support projects, with a stated national goal of 150 municipalities implementing or considering reuse by fiscal 2030.

Private investment is also moving from whole-diaper treatment toward individual materials. Unicharm markets ozone-processed recovered pulp under the name RefF. Its description of the underlying process as a world first is a company claim based on its own survey, not an independent public designation. In June 2026, Sumitomo Seika announced a pilot facility at its Himeji Works to chemically recycle SAP recovered from used diapers. The company project is geographically relevant, but no official source says Hyogo has selected it for the prefectural model.

Kao has separately demonstrated carbonization in Kamikatsu, Tokushima. These projects show a widening technology field, not a single national winner. The policy achievement may ultimately be less glamorous: consistent definitions, sampling, sanitation tests, mass-balance reporting and contracts that let municipalities and manufacturers compare one route with another.

Seven ledgers Hyogo should open before calling the model circular

The national target counts municipalities that are implementing recovery or merely considering it. That encourages study, but it is not a tonnage target. Hyogo should resist measuring progress by meetings held, partners enlisted or households invited. The useful evidence begins after material moves.

Prevention belongs in the same ledger. The national guideline gives one care scenario in which shifting from five tape-style diapers a day to one tape-style diaper and five pads reduces waste by more than 40 percent. That is an illustration, not universal care advice. Skin condition, continence, mobility and staffing determine what is safe. Waste reduction must never mean fewer necessary changes. Still, lighter products, appropriate combinations and access to reusable options can avoid material before a recycler consumes water and power.

The most useful Hyogo model may not be one machine imposed across the prefecture. It may be a common set of sanitary rules, data, contracts and decision tests that allows three geographies to choose different processes without hiding costs. Dense cities can reveal collection efficiency. Industrial Harima can test material markets. Mountain communities can expose the point at which aggregation becomes counterproductive.

A diaper is intimate while it is used and anonymous once it enters a furnace. Recycling makes the middle visible: someone must separate it, someone must handle it and someone must stand behind the material returned to commerce. If Hyogo can make those responsibilities visible too, its contribution will be more durable than a ribbon-cutting.