These new toilets could solve a global problem

More than half the world’s population lacks safe sanitation. Toilets that operate without running water might help.

This story appears in the July 2019 issue of National Geographic magazine.

A toilet is like a “super vaccine,” says Doulaye Kone of the Bill & Melinda Gates Foundation. “It kills disease where it is produced.” Traditional sanitation systems are costly to build and maintain, so the foundation’s Reinvented Toilet initiative is helping to develop alternatives such as the toilets seen here. Safe and inexpensive to operate, these commodes can function without running water and, in some cases, electricity. They’re also sustainable, eliminating pathogens while recovering nutrients and energy.

A GLOBAL PROBLEM

More than half the world’s people lack safe sanitation. Almost a billion defecate outdoors. Some 361,000 children under age five die each year from sanitation​-related diseases. It’s an urgent issue in cities, where two-thirds of us may live by 2050.

7.6 bil

4.5 bil

892 mil

Total

population

Lack safely managed sanitation services

Practice open defecation

MECHANICAL DRY BIO-COMBUSTION

The Nano Membrane Toilet is a portable, self-contained unit that doesn’t require external power. Waste is mechanically separated. A combustor dries and burns the solids, while liquids are heated and purified. The resulting sanitized ash and water can then be removed for safe disposal.

10

10

users per day

years’ life span

The process takes less than 24 hours to complete.

Untreated water

Treated water

Solids

1

2

3

1

Lowering the lid rotates the bowl and activates a blade that scrapes waste into a tank.

2

An Archimedes’ screw moves solids

into a drying chamber. Liquids are heated into vapor that is filtered through membranes.

Dried solids fall into the combustion cham­ber, where a self-sustaining burning cycle turns them to ash.

3

Dried solids fall into the combustion cham­ber, where a self-sustaining burning cycle turns them to ash.

HIGH PRESSURE AND HEAT

HTClean’s vacuum flush uses water reclaimed from the toilet’s high-temperature and pressure-separation process. The result is purified water and disposable solid-waste cakes. The sewer-free commode currently relies on electricity, but scientists are working to make it completely off-grid.

10

20

years’ life span

users per day

electricity requireD

The process takes about 3-4 hours to complete.

Untreated water

Treated water

Solids

2

3

1

1

A low-water flush is activated by touch screen. Vacuum suction moves the waste and water into a collection tank.

2

The waste is preheated and moved to a reactor where pressure and more heat turn it into liquid and carbonic material.

3

A mechanical press squeezes liquid out of the material, leaving cakes of waste that can be safely discarded and water that is then sent through filters.

PATRICIA HEALY. ART: BRUCE MORSER. SOURCES: BILL & MELINDA GATES FOUNDATION; ALISON PARKER, CRANFIELD UNIVERSITY; CHRISTIAN SEILER, HELBLING; WHO/UNICEF JMP; UNESCO WWAP

A GLOBAL PROBLEM

More than half the world’s people lack safe sanitation. Almost a billion defecate outdoors. Some 361,000 children under age five die each year from sanitation​-related diseases. It’s an urgent issue in cities, where two-thirds of us may live by 2050.

892 mil

4.5 bil

Lack safely managed sanitation services

Practice open defecation

7.6 bil

Total

population

MECHANICAL DRY BIO-COMBUSTION

The Nano Membrane Toilet is a portable, self-contained unit that doesn’t require external power. Waste is mechanically separated. A combustor dries and burns the solids, while liquids are heated and purified. The resulting sanitized ash and water can then be removed for safe disposal.

Untreated water

10

10

Treated water

users per day

years’ life span

Solids

The process takes less than 24 hours to complete.

1

Lowering the lid rotates the bowl and activates a blade that scrapes waste into a tank.

2

An Archimedes’ screw moves solids

into a drying chamber. Liquids are heated into vapor that is filtered through membranes.

Drying chamber

Rotating flush bowl

Liquids warming coil

Holding chamber

Holding chamber

The ash—as much as 100 grams a day for 10 users—is emptied daily.

Membranes

Clean water

Membranes

Dried solids fall into the combustion cham­ber, where a self-sustaining burning cycle turns them to ash.

The purified vapor condenses into water, which flows into a tank that also serves as a footrest.

3

The purified vapor condenses into water, which flows into a tank that also serves as a footrest.

Dried solids fall into the combustion cham­ber, where a self-sustaining burning cycle turns them to ash.

HIGH PRESSURE AND HEAT

HTClean’s vacuum flush uses water reclaimed from the toilet’s high-temperature and pressure-separation process. The result is purified water and disposable solid-waste cakes. The sewer-free commode currently relies on electricity, but scientists are working to make it completely off-grid.

10

20

Untreated water

Treated water

years’ life span

users per day

electricity requireD

Solids

The process takes about 3-4 hours to complete.

2

The waste is preheated and moved to a reactor where pressure and more heat turn it into liquid and carbonic material.

Clean-water tank

Reactor chamber

Multistage filters purify the liquid into water that is used to flush the toilet.

Vent

Output tank for solids

3

A mechanical press squeezes liquid out of the material, leaving cakes of waste that can be safely discarded and water that is then sent through filters.

Normal use yields about 30 10-gram waste cakes a day.

Collection tank

Collection tank

Output tanks for liquid

Output tanks for liquid

1

Excess liquid is moved to a tank for disposal or another use.

A low-water flush is activated by touch screen. Vacuum suction moves the waste and water into a collection tank.

PATRICIA HEALY. ART: BRUCE MORSER. SOURCES: BILL & MELINDA GATES FOUNDATION; ALISON PARKER, CRANFIELD UNIVERSITY; CHRISTIAN SEILER, HELBLING; WHO/UNICEF JMP; UNESCO WWAP