Toward a safe and circular thermochemical process to sanitize human feces in resource-poor environments

• Autor(a) principal: Bittencourt, Flavio Lopes Francisco
• Data de Publicação: 2023
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/16973
• topic: Engenharia Mecânica; Combustão; Saneamento; Termoquímica; Sustentabilidade; Fezes humanas; subject.br-rjbn

Defecating in precarious facilities or even in the open environment is an undeniable reality in low-income countries. Despite the efforts made in recent years, unimproved facilities and the practice of open defecation are still generating around 70 wt% of the worldwide fecal matter. Smoldering combustion can be a fast, viable, and efficient mechanism to mitigate the impacts of fecal matter on the surrounding environment, using the energy potential of feces to transform them into solid and gaseous products without pathogens. Nevertheless, using human waste as a feedstock brings many challenges, especially regarding its hazardous aspect, rheologic properties, naturally moist state, and very-low permeability. In this thesis, a latrine-like device is conceptualized, constructed, and operated. The end products are safe for reuse from the perspective of circular economy and sustainability. A novel smoldering configuration driven by vacuum-induced airflow is studied to understand a series of thermal events that changes the aspects of propagating a combustion front in a smoldering reactor: the combination of a reactive porous bed shrinking with time and an open inlet increases the effects of free convection. Negligible free convection effects are observed when the shrinkage is meager; however, from the moment the thermal plume starts to grow, the boundary layer is squeezed into the reactor wall, gradually quenching the combustion front. A Nusselt number correlation expresses the energy available at the fluid-porous interface that can be recovered for secondary processes. After understanding and dominating the combustion process using the novel smoldering configuration, we present and launch the FeD-Latrine, reproducing in a laboratory-scale, real defecation scenarios to destroy fresh feces with an average dropping rate of 120 g/h. For the first time, fresh feces are destroyed in a smoldering reactor without decreasing their moisture content. To accomplish it, the arrangement of the FeD-Latrine uses out-of-bed heat to transform fecal matter into fecal chars and ashes. Even though the FeDLatrine emits pollutants at a controlled rate, reducing the global CO2-eq can make it even more sustainable. In such context, we present an integrated process for CO2 reduction and capture, using a gas looping to oxidize combustible gases and create favorable conditions to capture CO2 in bed. CaO used as a sorbent captures up to 8 mmol of CO2 per gram. Compared to kinetic-dominant processes for CO2 capture, we obtain an efficiency of around 52 %. Our findings show that using the FeD-Latrine to replace typical pit latrines reduces 60% of the CO2-eq emissions. Finally, a field trip to an Amazon community reveals that thermochemical processes are already part of the community member's routine, providing evidence of the potential application of thermochemical units for sanitation in resource-poor environments.