||The fate of intestinal parasites and pathogenic bacteria in the composting toilet
SOSSOU, Seyram Kossi
On-site sanitation systems have gained much interest in recent years. One such system is the urine diverting composting toilet, which are promoted to sanitize human excreta for recycling them into fertilizer. A composting toilet using waste material as bulking agent has the potential to trap pathogens that might be contained in human feces. Unfortunately, in some marginal area, composting toilet could not get specific conditions for destroy all pathogens. Several studies have reported the inactivation of pathogenic bacteria and viruses in composting toilet. However, the removal of intestinal parasites has not been so far studied since parasites tend to have stronger resistance than pathogenic bacteria and viruses. Therefore, this study aimed to investigate the fate of intestinal parasites and pathogenic bacteria in the composting toilet for sanitizing compost from composting toilet.Chapter 1 describes the background and the objectives of this research. The literature review has summarized the state of the art regarding to the removal of pathogens in composting toilet, the inactivation mechanisms of the pathogen organism cells during the composting process and the different adequate post-treatments for sanitizing compost.Chapter 2 deals with the removal of intestinal parasites (helminthes eggs and protozoan cysts) and that of pathogenic bacteria during the composting process in a composting toilet. Batch experiments were conducted by composting human feces in an aerobic composting reactor during 60 days. The results showed that among parasites, protozoan cysts (Entamoeba hystolitica) were present in humans feces collected at high concentration (854/g mean) than helminthes eggs (Ascaris lumbricoides) (204/g mean). A mesophilic temperature, desiccation and alkaline pH were obtained during the composting process. Compared to pathogenic bacteria (Salmonella sp), which were eliminated totally after 30 composting days, helminthes eggs were reduced after 35 days; while protozoan cysts were still present after 60 days. In high concentration, protozoan cysts have survived stronger than helminthes eggs in the composting toilet and may constitute a sanitary risk when used as fertilizer. Because of the persistence of intestinal parasites in composting toilet, both helminthes eggs and protozoan cysts are good indicator for the removal of intestinal parasites.Chapter 3 elucidates the inactivation mechanisms of pathogenic bacteria cells in composting toilet during the composting process. The inactivation mechanisms were evaluated by culture E. coli strain as pathogenic bacteria in 3 types of media namely Tryptic Soy Agar, Desoxycholate Agar and Compact Dry EC. By comparing, the inactivation rate constant of E. coli, the damaged components and/or functions of bacteria cell were estimated in three different composting matrixes (sawdust, rice husk and charcoal). The results showed that composting process and composting matrixes did not significantly affect inactivation rate of pathogenic bacteria; however, these differences affected damaging component or function of the bacteria cells. The composting process damaged the bacteria cell from membrane and enzyme to metabolisms while the composting matrix damaged from membrane to enzymes and metabolisms. However, the composting process, when accompanied with alkaline pH, changed the damage part of bacteria more lethally with nucleic acid damage.iiiChapter 4 evaluates the post-treatment of compost by storage treatment for a short time. Fresh composts produced in composting toilet with continuous feces supply, were stored for 2 months, in uncontrolled conditions. The microbiology analysis of fresh and stored composts, showed that, both composts contained indicator bacteria (fecal coliforms, enterococci, spores of sulphite-reducing clostridia), pathogenic bacteria (Salmonella) and intestinal parasites (helminthes eggs and protozoan cysts), at levels above suggested limits for compost quality. There was no significant difference of the microbial level in fresh and stored composts exanimated, thus the storage period tested resulted in slow reduction of microorganisms for compost quick sanitizing. However the microbial level in fresh and stored composts from a composting toilet was known and their health implications suggested further sanitizing treatments.Chapter 5 evaluates the post-treatment of compost by solar heating as thermal treatment. Fresh composts from composting toilet were inoculated with indicator microorganisms and subjected to solar heating (direct sunlight and solar box). The inactivation rate constant and the decimal decay of microorganisms in compost were estimated by using the inactivation kinetics. The result showed that the temperature regime produced by direct sunlight and solar box were categorized in mesophilic (>30°C) and pasteurization (>70°C), respectively. The log reduction of microorganisms in compost by solar box was significantly higher than that of direct sunlight. The inactivation of microorganisms was slower in compost heated by direct sunlight but fast in compost heated by solar box, thus the decimal decay occurred rapidly with solar box heating while it was prolonged with direct sunlight heating. The high and uniform temperature distribution obtained with solar box during heating proved to be an efficient option for sanitizing compost.Chapter 6 evaluates the post-treatment of compost by urea addition as alkaline treatment. Fresh composts from composting toilet were inoculated with indicator microorganisms and subjected to different urea concentrations (0.5-2% w/w) and temperatures (22, 32 and 42°C). The inactivation kinetics parameters were determined in relation to pH, ammonia content and temperature during treatment time. The results showed that urea addition to compost enhanced inactivation of microorganisms. The inactivation rate constants of all microorganisms tested were positively correlated to the increase of NH3 (aq) concentration and temperature. The relationship between inactivation rate of microorganisms and ammonia through urea concentration and temperature were established. Therefore, the best decimal decay of E. coli, enterococci and A. eggs occurred with 2% w/w urea concentration at 42°C within 0.9, 1.1 and 1.4 days, respectively. Urea treatment has proved to be an efficient option for safe use of compost from composting toilet.Chapter 7 summarizes the most important findings as conclusions of this research and future studies are listed.
Hokkaido University（北海道大学）. 博士(工学)