Graduation Year

2010

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Global Health

Major Professor

Ricardo Izurieta, M.D., Dr.P.H.

Co-Major Professor

Boo Kwa, Ph.D.

Committee Member

Azliyati Azizan, Ph.D.

Committee Member

Jaime Corvin, Ph.D.

Committee Member

Linda Whiteford, Ph.D.

Keywords

Ascaris, inactivation, urea, ammonia, feces, solar toilet

Abstract

Access to sustainable sanitation systems is a determining factor in human health and economic development. However, more than a third of the world’s population lives without access to improved sanitation facilities. To meet the sanitation United Nations Millennium Development target, "halve, by 2015, the proportion of people without sustainable access to safe drinking water and basic sanitation", a wide range of non conventional sanitation technologies have been implemented in developing countries, including waterless systems. These systems function by diverting urine away from feces and collecting, storing, and dehydrating the fecal material in watertight dehydration vaults. From a public health perspective, adequate inactivation of fecal pathogens in a sanitation system is essential before any use or disposal of fecal material. In rural areas of El Salvador, the solar toilet is capable of inactivating fecal pathogens and reducing the prevalence of parasitic infections in its users when compared to other waterless systems. Nevertheless, not all solar toilets are able to inactivate completely Ascaris spp. ova after the recommended storage period. Un-ionized ammonia (NH3) has the potential to inactivate pathogens in solutions and sludge, including Ascaris spp. ova. This study hypothesized that adding ammonia to the solar toilet will improve the technology since pathogen inactivation with ammonia could be potentiated by the alkaline medium and high temperatures achieved inside the toilet vaults.

To evaluate this approach, a series of experiments in solution and biosolid were performed in a laboratory environment using physical and chemical parameters similar to those achieved by the solar toilet. Eggs of the swine Ascaris species, Ascaris suum, were used as model in all experiments. In ammonia solution, the parasite ova were stored for a period of three days and; in biosolid, the parasite ova were stored for two months. Urea was used as the source of ammonia in biosolid. In addition to the experiments with ammonia, normal viability and morphological changes within the parasite ova during incubation in vitro at 28 C° were investigated and described to complement current literature published.

Results from the experiments in ammonia solution indicated that addition of ammonia (1% and 2%) could improve the system since the critical parameters that significantly reduced A. suum ova viability to zero in three days could be achieved by the solar toilet: temperature of 35°C or higher and pH value of 9.3. Results from the experiments in biosolid further showed that inactivation of A. suum ova was faster in samples exposed to urea and to temperatures higher than 28°C. All samples exposed to urea achieved 100% inactivation after 14 days (28°C), 3 days (35°C) and 24 hours (40°C and 45°C). Survival analysis of the data showed that there was a significant difference (p value <.0001) between the inactivation achieved in the samples exposed to urea (1% and 2%) and the samples not exposed to urea. A logistic regression analysis estimated the effect of Urea (Treatment, OR: 25.9), Temperature (OR: 1.8), and Storage (OR: 1.17) on inactivation.

Results from the experiment with A. suum ova in normal incubation solution showed that the ova went through clearly identified morphological changes at different speed of development. Two new additional stages of development were identified (Pre-larva 1 and Pre-larva 2) and no significant statistical difference was observed among the viability reported early in incubation and the one reported after three weeks of in vitro incubation, indicating that early stages of development may be use as an alternative to reduce the time to report viability.

The results of this study suggest that inactivation of Ascaris spp ova by ammonia is possible in fecal material stored in the solar toilet or any other dry toilet, if the following physical and chemical conditions are met: a closed vault with a minimum temperature of 28°C; an initial pH of 8.3, minimum moisture of 27.5%, and addition of 1% urea to the biosolid. At 28°C longer storage time would be required for 100% inactivation while at higher temperatures less time of storage would be necessary. A community intervention is recommended to include field conditions and human behavior as other predictors for Ascaris spp. inactivation by ammonia.

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