Pathogens and Composting Toilet Systems

Properly designed and maintained, composting toilet systems should contain, immobilize and/or destroy pathogens -- organisms that cause human disease -- especially in a healthy population.

Still, when planning systems, pathogens and vectors need to be considered. This is particularly a concern in areas with endemic diseases, such as warm regions, where pathogens flourish.

When discussing human excrement systems, the diseases we are concerned about include amebiasis, cholera, cryptosporidiosis, gastroenteritis, infectious hepatitis, parasite-related disease, salmonelliosis, shigellosis, typhoid fever, and other diarrheal disease.

How Pathogens are Attenuated, Immobilized or Destroyed in a Composting Toilet System
Whereas conventional wastewater treatment technologies depend on chemical or thermal disinfection to reduce pathogens, in a composting toilet it is accomplished by the following:

1. Containment

Pathogens cannot survive for long once they have left the human host. They have co-evolved over thousands of years with the human race and thrive only within the narrow chemical and environmental parameters of the human body. Like all organisms, human pathogens have specific lifetimes. An organism's lifetime is shortened in the hostile environment of an aerobic composter. Human pathogens in a composter are like fish out of water: They don't live for long. Containing the excreta for an extended period of time brings about the death of pathogens and reduces the risk of infecting new hosts through ingestion, the primary pathway for enteric pathogen transmission.

2. Competition

The competition among composting organisms for available carbon and other nutrients is intense. Human pathogens become food for the well-adapted aerobic soil organisms that thrive in the composter. When the available nutrients are consumed, the microorganisms begin to consume their own protoplasm to obtain energy for cell maintenance. When this occurs, the microorganisms are said to be in the "endogenous phase." When these organisms die, their protoplasm and cellular matter is digested by other organisms. Eventually, if no new food sources are presented, all of the energy will be released and the matter fully oxidized. The end of this phase results in an end-product that is very stable and safe.

3. Antagonism

Some composting organisms produce toxic substances which harm, inhibit or kill other organisms. For example, the actinomycete Streptomyces griseus produces streptomycin, well-know antibiotic. The soil bacteria Bdllovibrio bacteriovorus parasitizes the infamous Echerichia coli (E. coli), and multiplies within the host cell, eventually killing it.

4. Adverse Environmental Factors

Factors such as pH, temperature, moisture and ammonia content and retention time also play roles. Note: temperatures above 131°F (55°C) do kill pathogens in a short time, but composting toilet systems do not attain these temperatures unless they are highly heated.

Other: Pasteurization

An even faster and controlled way of killing or reducing pathogens is pasteurization. This method is derived from the work of Louis Pasteur (1822-1895), a French researcher who discovered that pathogens were destroyed by heating the matter in question for one hour at 62°C (143.6°F), then cooling it rapidly to prevent re-inoculation. Pasteurization can be accomplished by a variety of means, but the most common is by applying sufficient heat from external sources such as electric or propane heaters. In some cases, the use of microwave or solar energy is used.

What are Pathogens?
Pathogens, or pathogenic organisms, are responsible for the transmission of communicable diseases. They are generally bacteria, viruses and parasites, such as worms, amoebae or protozoa, that invade the body and cause illness by a variety of means that overwhelm the immune system and damage or destroy living tissue.

Excreta, primarily the feces of human and domestic animals, can contain pathogens. Each pathogen has its own life cycle. For some, that includes a "saprophytic" or non-host period, when it is viable after exiting its human host and transmission from one host to another can occur. This is the same stage in which these pathogens can be killed or immobilized. Long-term survival of pathogens outside a host is rare, because they are outside their best environment. They usually need to be put into an aqueous environment to live longer.

Fortunately for general public health, only a few of the hundreds of pathogens have high enough survival rates in an aerobic environment (like the composter) that they can play a significant role.

Typical Pathogen Survival Rates at 20° to 30°C in Various Environments*
Pathogen	Freshwater and Wastewater	Survival Time in Days**
		Crops	Soil
Bacteria
Fecal coliforms***	<60 but usually <30	<30 but usually <15	<120 but usually <50
Salmonella (spp.)***	<60 but usually <30	<30 but usually <15	<120 but usually <50
Shigella***	<30 but usually <10	<10 but usually <5	<120 but usually <50
Vibrio cholerae****	<30 but usually <10	<5 but usually <2	<120 but usually <50
Protozoa
E. histolytica cysts	<120 but usually <15	<10 but usually <2	<20 but usually <10
Helminths
A. lumbricoides eggs	Many months	<60 but usually <30	<Many months
Viruses
Enteroviruses***	<120 but usually <50	<60 but usually <15	<100 but usually <20

(Ron Crites and George Tchobanoglous, Small and Decentralized Wastewater Management Systems (United States: McGraw-Hill, 1998).

How are they transmitted?
Pathogens are carried to new hosts from infected persons' excrement by:

• Direct contact with raw feces or, in rare cases, urine
• Vectors (insects, rats, birds, etc.) that pick up contaminated matter on their feet and deposit it on human food or in washing or drinking water
• Washwater from bathing and laundry of infected individuals
• Indirect contact with floor drains and pipes that are collecting and breeding grounds for bacteria
• Ingesting contaminated meats and vegetables
• Drinking or bathing in contaminated water

Pathogens and Inadequate Sanitation
Pathogens that are transmitted in human excrement are of particular concern in parts of the world that have inadequate or no sanitation. The consequences of failing to provide adequate sanitary conditions -- particularly a means of containing and treating human excreta -- range from simple diarrhea and stomach cramps to death, especially for children and the elderly.

In the developing world -- particularly warmer climates, where pathogens flourish -- inadequate sanitation means excreta in water sources. Containing excreta through the use of pit latrines can be a step in the right direction, but these latrines can still contaminate groundwater.

A better sanitation measure is the containment and composting of excrement and washing one's hands with soap and water after defecating. Simple hand washing is now re-emerging as the most important measure in preventing disease transmission. Hand washing breaks the primary connection between surfaces contaminated with fecal organisms and the introduction of these pathogens into the human body. The use of basic soap and water, not exotic disinfectants, when practiced before eating and after defecating, may save more lives than all modern methodologies and technologies combined.

Measuring the Risk of Infection
The likelihood of infection by the various pathogens (called "man severity" in the public health field) is important for risk assessment. For example, in northern climates where the temperature drops below freezing, Ascaris lumbricoides (roundworm) is virtually nonexistent. However, in warm climates it is a common pathogen excreted by humans, dogs, cats and other animals. The risk, therefore, is lower in the North than in the South.

Most pathogens we should be concerned about are found in the feces of infected people and are transmitted by contact, directly or indirectly, through open wounds on the skin or ingestion of contaminated food and water. Water contaminated with the feces of an infected person is the most common carrier of pathogens. Poor personal hygiene is another significant pathway. If the hands are not thoroughly washed after defecation, transmission of fecal pathogens on the hand to one's mouth or foods is inevitable.

What dose does it take to get sick?
The infectious dose is the number of pathogens required to infect a host. It varies from pathogen to pathogen. Ingestion of only one or more cysts or eggs of parasitic worms may cause disease. In contrast, most bacterial or viral illnesses require the consumption of hundreds to thousands of organisms to produce illness.

(See the Appendix for an explanation and listing of wastewater-borne pathogens of concern.)

Ascaris lumbricoides (Roundworm)
Roundworm may be the most ubiquitous parasite of humans, with an estimated one billion people infected worldwide. In some communities, infection rates reach 100 percent. It deserves special attention here, because of its reputation for long-term survival in dry or anoxic environments. However, moist composting is a hostile environment for parasites out of their hosts; in a composter, the nutritional, physical, chemical and thermal conditions fall out of the narrow range needed for their long-term survival. Also, antagonism with other, better adapted organisms will kill foreign organisms.

Not that it should be downplayed: Ascaris is tenacious. One report documented the discovery of eggs that were viable years after being painted into the floor of a slaughter house. Ascaris can be the "old man" of pathogens when excreted into a composting toilet. But if you have ascaris in your composter, you probably have it in you, as well as in your pets, yard, animal pens and garden, too! What is key then is to keep this material out of water and the food cycle. The composter is usually part of the solution (containing and processing it), and properly maintained, not likely to contribute to its transmission.

Some research has been conducted in this realm in recent years. In a paper titled "Composting Toilets and Intestinal Parasites," medial scientist Sandie Safton reported on studies of end-product/humus from 16 site-built models -- in southeast Australia. She found organisms such as Blastocystis hominis, Dietnamoeba fragilis, Entamoeba coli and Enterobius vermicularis (pinworm) in the excrement deposited in the systems. A total of 118 humus/end-product samples from all of the systems tested negative for parasites and commensal organisms. "The complete absence of these organisms in the final product indicates that the systems are in fact working with respect to the destruction of pathogenic parasites and commensals," she wrote. "It may not necessarily be the high temperatures that are associated with composting that are responsible for pathogen destruction, but it may simply be time and adverse environmental conditions. The fact that parasites and commensals that have resistant ex-host (out-of-human) stages are unable to survive in these conditions suggest that bacterial pathogens would also be destroyed. the humus/end-product could therefore, with the exception of viruses, be considered pathogen free."

Zentrum fur Angewandte Okologie Schattweid, a Swiss research center that studies ecological growing and lifestyle practices, found pathogens were destroyed after exposing end-product from composting toilets to temperatures of about 160°F at least twice over two days.

Jordforsk Centre for Soil and Environmental Research, in Norway, found polio virus was killed in composting toilets. In a 1994 study Jordforsk tested human waste inoculated with polio virus and composted in thermophilic conditions (temperatures reaching 60°C) and mesophilic conditions (reaching 38°C). Coliform and polio were almost totally destroyed with thermophilic composting. In mesophilic conditions, coliform was reduced by 90 percent, and polio by 99.2 percent. This underlines the need for long-term containment or further processing.

Composting versus Drying Drying toilets are increasingly popular in the developing world where arid climates can dry excrement fast and where water is scarce. Many of these systems rely solely on dehydration to desiccate the feces. This matter is then put out on fields. Urines is diverted and drained into the nearby soil. (Urine can make an excellent fertilizer, but it is rarely collected from these systems.) Often caustic lime or wood ash is added to control odors, but these additives are a double-edged sword: They do aid in odor control, but they can also inhibit or stop the natural biological decomposition process. The result is dried, unstable feces and toilet paper. While drying toilets can be a less expensive form of excrement management (these systems may require no vent pipes), we are reluctant to encourage dehydration here, as there is the possibility that it would ultimately result in large masses of rehydratable waste and the attendant problems of attracting flies and other vectors. Further, dehydrating pathogenic bacteria can prompt pathogens to become endospores, essentially a form that can survive for decades until rehydrated, when they would return to their full potency. The eggs of the parasite Ascaris lumbricoides have been viable for years in a dry environment. Also, the nutrients in the dried, unoxidized matter are not available to plants. Dried organic matter will require biological processing before plants can use its nutrients safely, so processing might as well occur in the beginning.

References

Sandie Safton, "Composting Toilets and Intestinal Parasites," presented at the Innovative Approaches t the On-Site Management of Waste and Water conference, Southern Cross University, Lismore, N.S.W., 1996

Enferadi, Cooper, et al, "Field Investigation of Biological Toilet Systems and Gray water Systems" (USEPA, 1980).

T. Roher and C. Jaeber "Versuchezur Hygienisierung von Fakalkomposten aus Komposttoiletten in Einzelhaushalten" (Zentrum Fur Angewandte Okologie Schattweid, Switzerland, 1997) Jordforsk, Shellinga 1432 As, Norway

J. Martin and D. Focht "Soils for the Management of Organic Wastes and Wastewater" (Soil Science of American, Wisconsin 1977)