Composting Toilets And Humanure

The flush toilet is, in the narrow frame of hygiene and convenience, a genuine achievement. It removes human waste from the immediate human environment efficiently and reliably. In the wider frame of resource cycling and ecological function, it is a system designed to destroy nutrient cycles while consuming potable water.

In the United States, toilets account for roughly 30% of indoor water use — the single largest category. At 6-13 liters per flush and an average of 5 flushes per person per day, a household of four people consumes 120-260 liters of drinking-quality water daily simply to convey feces to a sewer.

That sewer carries the material to a treatment plant (in cities) or a septic system (in rural areas). In both cases, the biological treatment process decomposes organic matter and removes pathogens — but the nutrients do not return to soil. They are either destroyed (nitrogen is converted to nitrogen gas and released to the atmosphere, eliminating the energy embedded in synthetic nitrogen fertilizer production), discharged to waterways (where phosphorus causes eutrophication), or — in some advanced treatment systems — partially recovered in biosolids that may or may not be applied to land, often on industrial agricultural sites, not household gardens.

The ecological cost is systemic: nitrogen must be re-fixed from the atmosphere using natural gas through the Haber-Bosch process (consuming roughly 1-2% of global energy output annually) and phosphate must be mined from finite rock deposits. The flush toilet is a one-way valve in a nutrient cycle that, from an ecological standpoint, must be closed.

Composting toilets are the closing of this valve.

The visceral resistance to humanure is understandable. Feces have been associated with disease transmission since humans first made the connection between contaminated water and cholera, typhoid, and dysentery. The diseases are real. The question is: what conditions convert feces from a disease vector to a safe soil amendment?

The pathogens of concern in human feces:

- Escherichia coli O157:H7 and other enteric bacteria: die at 55°C within minutes. Highly sensitive to temperature. - Salmonella spp.: die at 55°C for 30 minutes, or at 70°C almost instantly. - Campylobacter: sensitive to heat, desiccation, and oxidation. Dies rapidly in well-aerated compost. - Cryptosporidium parvum: heat-sensitive. Dies at 64°C for 2 minutes, or 55°C for extended exposure. - Giardia lamblia: cysts die at 55°C for 5 minutes. - Ascaris lumbricoides (roundworm): the most thermally resistant pathogen. Eggs are killed at 50°C for 1 hour, or 55°C for 15 minutes. Ascaris is the benchmark — if you kill Ascaris, everything else is dead. - Hepatitis A virus: killed at 70°C for 4 minutes or 60°C for sustained exposure.

The EPA's standard for treating sewage sludge (biosolids) to "exceptional quality" (safe for all land applications including home gardens) requires 55°C for 3 consecutive days in a turned windrow, or 55°C for 15 days in a static pile. This is achievable in a properly managed hot compost pile.

Fecal-oral transmission routes that composting eliminates:

Direct contact with human feces is the primary vector for enteric disease in places without sanitation. Composting properly breaks this route: the material is containerized, processed at lethal temperatures, and stored as finished compost that poses no greater pathogen risk than any other compost. Flies — which transfer pathogens from feces to food — are excluded from covered compost piles. Runoff and water table contamination are eliminated when material is contained.

The risk profile of well-managed humanure compost is essentially equivalent to food compost or garden soil. The cultural risk perception is orders of magnitude higher than the actual risk. This gap is where tradition, sanitation history (much of it justified), and squeamishness converge to prevent a rational resource decision.

Commercial units range from simple containers with fans to sophisticated continuous-process composting chambers. The key design decisions:

Self-contained vs. remote composting:

Self-contained units (BioLet Composting Toilet, Nature's Head, Air Head) have the composting chamber directly below the toilet seat. Urine and feces enter the same chamber and must be composted in place. The main challenge: balancing moisture. Urine is 95% water; adding urine to the composting chamber constantly raises moisture levels, which creates anaerobic conditions (odor, slowed decomposition). Solutions include: an electric heating element that evaporates moisture continuously, a separator that routes urine to a separate container, or a thermostatically controlled fan that provides drying airflow. Self-contained units work well for low-use situations (vacation cabins, off-grid tiny homes, boats) where the daily load is modest.

Remote composting units (Clivus Multrum, Phoenix, Envirolet) have the toilet installed conventionally in the bathroom, but waste drops through a large-diameter (200-300 mm) chute into a composting chamber in a basement, crawl space, or below-grade vault. The composting chamber is much larger, allows better moisture management, and handles higher throughput. These are more suitable for permanent residences.

Continuous-process vs. batch:

Continuous-process systems receive fresh input at one end while finished compost is removed at the other. The material moves through the composting zone over time, spending sufficient time at high temperature to be rendered safe. Clivus Multrum pioneered this design in the 1960s.

Batch systems fill one chamber, close it off, and allow it to fully compost before use. Meanwhile, a second chamber receives fresh input. When the first chamber is fully composted (typically 1-2 years), it is emptied and put back into service while the second chamber finishes. This "double-vault" design is used widely in developing-world sanitation programs and works reliably with simple materials.

Key operational requirements for commercial units:

- Bulking material addition after each use (sawdust, wood chips, peat moss — amounts specified by manufacturer) - Periodic mixing or turning (some units have integrated turning mechanisms) - Moisture management (fan operation, liquid overflow monitoring) - Temperature monitoring in hot-composting designs - Removal of finished compost on the manufacturer's schedule (typically every 6-18 months)

Common failure modes:

- Insufficient carbon bulking material: the system becomes wet and anaerobic, producing hydrogen sulfide (rotten egg odor). Solution: add more bulking material, increase aeration. - Overloading: more waste than the composting volume can process. The composting process is outrun by inputs. Solution: reduce load, or add a second unit. - Cold conditions: composting slows significantly below 10°C and stops below 5°C. Units in cold climates need insulation and potentially supplemental heating to maintain function. - Fly intrusion: houseflies and drain flies can access the composting chamber if not properly sealed. They do not prevent composting but create nuisance. Solution: seal all access points, ensure the vent stack draws air away from the toilet seat.

Joseph Jenkins' Humanure Handbook (now in its fourth edition, freely available online) presents a simple, low-cost, high-reliability composting system that requires no commercial equipment.

The core apparatus:

- A standard toilet seat mounted on a wooden box frame - A 5-gallon (20 L) bucket as the catch container, with a bucket-within-a-bucket design (inner bucket is lifted for emptying, outer bucket catches any drips) - A lidded container of dry sawdust (untreated) beside the toilet - A ladle or scoop for the sawdust

The process:

After each use, add sufficient sawdust to fully cover the deposit and eliminate visual evidence. This performs multiple functions: absorbs moisture (critical for preventing odors), adjusts the carbon-to-nitrogen ratio of the material, covers the material so flies cannot access it, and prevents ammonia volatilization (which would waste nitrogen and cause odor).

When the bucket is full (typically every 3-7 days for one person), it is carried to the outdoor compost pile.

The outdoor pile:

Jenkins specifies a dedicated "humanure pile" — not commingled with kitchen or garden compost. This is because of the extended composting period and the different regulatory and safety considerations.

The pile is built in a dedicated area with good drainage. The base is wood chips or straw. Each bucket of material is emptied and covered with a thick layer of straw or wood chips (the cover material absorbs moisture, maintains the carbon balance, and prevents odor and fly access). After one year of additions, the pile is closed to new input and allowed to compost for a second year before use.

The temperature question:

A well-managed pile with the right carbon addition will heat. The center of an active pile should reach 55-70°C. Jenkins documents temperature data from his own pile over multiple years. The standard criticism of the humanure system is that not all home compost piles reliably achieve and sustain the temperatures required for pathogen kill. This is true — a cool, inactive pile does not sterilize the material. The counter-argument: the two-year minimum retention time provides extensive die-off opportunity through mechanisms beyond heat alone (desiccation, UV exposure when the pile surface dries, competition from other soil organisms, predation by actinomycetes and other decomposers). Studies of pathogen survival in cold-composted material show significant die-off even without sustained high temperatures, though the science is less settled here than for hot composting.

The practical guarantee: If you're concerned about temperature, ensure your pile heats. A pile of the right moisture and C:N ratio in a climate with warm summers will heat spontaneously. If it doesn't, investigate: it's either too wet, too dry, too small, or missing some element. A garden thermometer inserted in the pile confirms the temperature.

Urine deserves separate treatment because it is categorically different from feces in its contamination profile.

Healthy human urine is produced from blood filtrate by the kidneys and is essentially sterile at the point of production. (Urinary tract infections, which can introduce bacteria into urine, are the exception — and affected individuals should divert urine to the sewer during illness.) The pathogens associated with wastewater are fecal-oral pathogens. Urine is not fecal.

Urine composition (approximate): - Water: 95% - Urea: 2% (the primary nitrogen compound, rapidly converted to ammonium in soil) - Creatinine: 0.1% - Sodium chloride: 0.1% - Various salts, hormones, metabolites

Nitrogen and phosphorus in urine are in highly plant-available forms. One person's urine production represents roughly: - Nitrogen: 4-10 g/day (comparable to 1-2 g of synthetic urea fertilizer, or 5-10 mL of fish emulsion) - Phosphorus: 0.5-1.5 g/day - Potassium: 1-3 g/day

A household of four produces 50-80 g of nitrogen in urine per day — enough to significantly fertilize a substantial garden area if captured and applied.

Application methods:

Direct soil application (diluted): Dilute 1:10 with water. Apply to the root zone of established non-edible plants, fruit trees, or crops where edible portions are not in contact with the soil. Do not apply to leafy greens, strawberries, or other crops where edible surfaces are close to soil level. In practice: apply around the drip line of trees, not near stems.

Compost pile activator: Undiluted urine applied to the center of a compost pile provides rapid nitrogen, which accelerates decomposition. This is traditional — the compost pile has been "fed" urine in folk agriculture globally.

Straw bale gardening: Urine is an excellent preconditioning agent for straw bale gardening, where high nitrogen is needed to initiate decomposition of the bale.

Separated systems: Urine-separating toilet seats (available commercially) route urine to a separate collection vessel while feces go to the composting chamber. This dramatically reduces moisture in the composting chamber (preventing anaerobic conditions) and produces a valuable liquid fertilizer that can be stored and used in a controlled way.

Concerns with urine application: - Pharmaceuticals: pharmaceuticals excreted in urine (hormones, antibiotics, chemotherapy agents) are present at trace levels. For household garden use, the concentrations are generally negligible. In intensive agricultural applications this is a more studied concern. - Salt: urine contains sodium chloride. In salt-sensitive soils or with very high application rates, sodium accumulation can be a concern. Standard dilution and application rates pose no practical risk. - Odor: fresh urine is largely odorless. As urea hydrolyzes to ammonia, odor develops. Apply to soil quickly, where soil bacteria process the ammonia. Do not store undiluted urine for extended periods.

The regulatory picture for composting toilets is complex and jurisdiction-specific.

Where composting toilets are explicitly permitted: - Most US states allow NSF Standard 41-certified composting toilet units. NSF 41 establishes performance standards for non-liquid waste composting toilets. Systems meeting this standard are generally permitted as alternatives to flush toilets in appropriate contexts. - Florida, Arizona, New Mexico, Colorado, and many other western states have explicit composting toilet regulations. - Australia: all states and territories have provisions for composting toilets, typically requiring approval of the specific unit model and an ongoing maintenance agreement. - New Zealand: permitted under the Building Act with appropriate design documentation. - Scandinavia: widespread acceptance; several municipalities actively promote composting toilet adoption.

Where the picture is murky: - Many jurisdictions have composting toilet regulations but require a backup flush toilet connection as well — defeating much of the purpose. - The use of composted humanure output is frequently restricted even where the composting process itself is permitted. Regulations may require burial, landfill disposal, or application only to non-food-crop areas. - Building codes in many jurisdictions require a "conventional sanitary system" as a minimum standard, with composting toilets as an addition, not a replacement.

The practical path:

For rural properties: many rural jurisdictions require only a septic system of some type. A composting toilet with a small, properly designed graywater system (for sink/shower water) often satisfies rural sanitation requirements with minimal friction.

For urban and suburban properties: the regulatory environment is more restrictive. The most practical approach is often to install a composting toilet alongside an existing flush toilet, use the composting toilet for the majority of household waste, and keep the flush toilet available for guests and regulatory compliance.

For owner-builders in permissive jurisdictions: the double-vault batch composting toilet is the simplest, lowest-cost, and most maintainable design — widely accepted in developing-world sanitation programs (UDDT — Urine Diverting Dry Toilet) and increasingly recognized in developed-world alternative building codes.

To close the loop: the global food system depends on nitrogen and phosphorus. Nitrogen fertilizer is energy-intensive to produce; phosphate rock is a finite mined resource with no viable substitute in agriculture. Current estimates suggest economically accessible phosphate rock reserves will be significantly depleted within 50-100 years at current consumption rates.

Human excreta globally represent: - Nitrogen: approximately 22 million tonnes per year (roughly 14% of global synthetic nitrogen fertilizer use) - Phosphorus: approximately 3 million tonnes per year (roughly 22% of mined phosphate fertilizer use)

This is not a marginal resource. It is a significant fraction of the nutrient inputs that global agriculture depends on, currently being systematically destroyed and discharged.

At personal scale, one household composting toilet captures and returns 100% of the household's excretory nutrients to soil. This is not a gesture — it is a complete break with a destructive nutrient cycle and the establishment of a closed loop.

The composting toilet does not solve the global sanitation infrastructure problem. But for anyone with the land to use the output and the autonomy to choose their sanitation system, it is the most ecologically rational choice available. The technology is simple, reliable when properly managed, and proven across millennia of agriculture in East Asian traditions and decades of modern practice.

The barrier is not technical. It is cultural. And cultural barriers are the only kind that reason, example, and a few years of thriving compost can overcome.