In-toilet disinfection of fresh fecal sludge with ammonia naturally present in excreta

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Courtesy of IWA Publishing

A simple treatment method, Safe Sludge disinfection, was developed to disinfect pathogens in fresh fecal sludge using the ammonia naturally present in excreta. In the first step, urea is hydrolyzed to ammonia (NH3/NH4+). In the second step, Ca(OH)2 is added to raise the pH level such that NH3, a known disinfectant, is the dominant form of ammonia; subsequently, the waste is stored until sufficient disinfection is achieved. In a closed system at 23 °C, Safe Sludge disinfection achieved >9.3 log10 and >4.0 log10 decrease of indigenous Escherichia coli and seeded MS2 coliphage, respectively, within 10.6 hours, and 2.0 log10 inactivation of seeded Ascaris suum eggs within 2 weeks. Disinfection of feces at high pH with no urine addition was tested for comparison, and similar inactivation levels were achieved for E. coli and MS2 bacteriophage. However, for Ascaris eggs only 0.38 log10 inactivation was achieved over 2 weeks. For control samples (feces plus urine only), no inactivation of bacteria or virus indicators was observed and inactivation of Ascaris eggs was also low (0.42 log10). To illustrate how the Safe Sludge concept could be incorporated into a waterless household toilet, a conceptual design and prototype was developed, called the pHree Loo.

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