Peepoo contains five grams of urea – a non-hazardous chemical that is the most common artificial fertiliser in the world. When the urea in Peepoo comes into contact with faeces or urine, a breakdown into ammonia and carbonate takes place, driven by enzymes that naturally occur in faeces. As the urea is broken down, ammonia starts to inactivate infectious organisms and sanitisation process begins.
Disease causing pathogens, which may be found in faeces, can be rendered inactive within four weeks. When Peepoo disintegrates in the soil, the ammonia is taken up by plants along with nutrients from the human excreta.
Pathogens in Human Excreta
The management of faeces is an issue of hygiene since the main excretion of food borne pathogens is with the faeces and thus contributes to the spread of diseases. The presence of organisms in urine that cause diseases is at a considerably lower level than in faeces. With conventional urine processing, urine sorting diversion, the primary source of microbial contamination is derived from faeces.
Human excreta can contain infectious microorganisms as bacteria, viruses and parasites. They mostly infect the gastrointestinal system and are thereby mostly shed with the faeces where they can be excreted in high amounts; for example, a billion viruses per gram of faeces. Because some types of organisms survive for a long time or even multiply in the environment, diseases can spread via contaminated water, food or hands for a long time as well. In some cases, the illness can be diagnosed to a specific microorganism, but in many cases the source of infection remains unknown or a person might even be infected with several types of microorganism at the same time.
Where sanitation is poor, bacterial infections such as thypoid fever, cholera and shigellosis are common. Cholera can be life threatening if the infected person does not receive health care. Viruses are assumed to be responsible for many undiagnosed cases and rotaviruses are by far the largest cause of diarrhoea in children. This contributes significantly to child mortality in developing countries.
Enteric parasitic infection with helmints and protozoa are of greater concern in developing countries than in industrialised countries. On a worldwide basis, Ascaris lumbricoides, the human roundworm is the most common helminth infection, with more than 25% of all humans being infected. Ascaris infection, even though in many cases may not be life-threatening, disables nutrient uptake and hampers child development. Protozoa as amoeba, cryptosporidia and giardia are responsible for a majority of enteric infections, causing both illness and death.
The self-sanitisation in Peepoo is based on urea, the most common nitrogen fertiliser in the world and a non-hazardous chemical. When the urea comes into contact with faeces and urine a breakdown into ammonia and carbonate takes place, driven by enzymes naturally occurring in faeces. The treatment of the faeces thus begins at the moment of defecation. Peepoo is designed to optimize the contact between faeces and urea so that the urea dissolves and decomposes rapidly. As the urea breaks down, ammonia starts to inactivate infectious organisms. The carbonates that are produced when urea decomposes help to control the pH at a level that supports the ammonia sanitisation. The Peepoo polymer is developed to contain the ammonia within Peepoo during the time sanitisation occurs.
Disease-causing microorganisms, bacteria, viruses and parasites which may be found in high concentrations in faeces, are inactivated within four weeks in Peepoo. Both urine and faeces can be sanitised in Peepoo, however few pathogens are excreted with the urine.
Untreated faeces cannot be regarded as sanitised until after one to two years of storage has passed. The urea treatment is the most efficient of the simple low-tech treatments available. In the end, when the Peepoo polymer degrades in the soil, the ammonia is taken up by plants along with nutrients from the human excreta.
The microcidal effect from ammonia in the form of NH3 on gastrointestinal pathogens has been documented by several independent research teams during the last three decades. The established practise to sanitise source separated urine by storage is based on ammonia evolving from urea excreted in the urine. Urea, CO(NH2)2, was the first organic compound to be artificially synthesized from inorganic starting materials and today more than 90% of world urea production is used as a nitrogen fertiliser. Urea has been used to sanitise different biomaterial and is used in Peepoo. Urea as a chemical disinfectant is user friendly as it has latency before it decomposes into ammonia and because the pH is only slightly alkaline. The urea sanitised material will have an increased plant nutrient content due to the high nitrogen content of the urea, 46.7%.
The microbial inactivation is mainly dependent on the concentrations of ammonia, and a combination of 20 ̊C and 50 mM NH3 have been detected as a threshold for persistent parasites such as Ascaris. Bacterial pathogens are inactivated at lower concentrations and temperatures. Even though it’s functional at ambient temperatures, an increase in temperature speeds up the inactivation.
As a single use toilet, Peepoo has to account for a great variation in the faeces. High pathogen concentrations are expected when a person with infection uses Peepoo, whereas when a non-infected person uses Peepoo, the material is not contagious. Approximating that faeces from a sick person can contain 1,000,000,000 pathogenic bacteria and viruses and 10,000 Ascaris eggs per gram of faeces, a decrease in pathogen concentration of respectively 0.64 and 0.29 log10 per day is needed to sanitise Peepoo within two weeks and 0.32 and 0.14 log10 per day within four weeks. This puts higher requirements on the sanitation efficiency of Peepoo compared to sanitisation systems where faeces from infected and non-infected persons are mixed.
How much ammonia that will be present in sanitising form, NH3, is dependent on pH and temperature. Peepoo is designed to, upon urea decomposition, give a pH 9, a pH at which between 35% and 51% of the ammonia will be in the form of NH3 at 24ºC and 34ºC, respectively. The application of urea in Peepoo is based on base line weight investigations in slum settings so that the amount of urea is enough to reach targeted NH3 concentrations even when faecal loads are high.
The focus for the sanitisation process in Peepoo has been on parasites because they are known to be resistant to chemical sanitisation. Previous studies in the laboratory have proven in line with recent investigations of Peepoo in the field examining naturally excreted pathogens. The studies indicate that at tropical temperatures inactivation will be faster than previously assumed. During the time of sanitisation, Peepoos will not degrade to such an extent that there will be a risk of diseases spreading to the environment and the single use aspect with enclosed faeces makes further handling clean.