Non-isothermal thermogravimetric kinetic analysis of the thermochemical conversion of human faeces

Abstract

The “Reinvent the Toilet Challenge” set by the Bill & Melinda Gates Foundation aims to bring access to adequate sanitary systems to billions of people. In response to this challenge, on-site sanitation systems are proposed and being developed globally. These systems require in-situ thermal treatment, processes that are not well understood for human faeces (HF). Thermogravimetric analysis has been used to investigate the pyrolysis, gasification and combustion of HF. The results are compared to the thermal behaviour of simulant faeces (SF) and woody biomass (WB), along with the blends of HF and WB. Kinetic analysis was conducted using non-isothermal kinetics model-free methods, and the thermogravimetric data obtained for the combustion of HF, SS and WB. The results show that the devolatilisation of HF requires higher temperatures and rates are slower those of WB. Minimum temperatures of 475 K are required for fuel ignition. HF and SF showed similar thermal behaviour under pyrolysis, but not under combustion conditions. The activation energy for HF is 157.4 kJ/mol, relatively higher than SS and WB. Reaction order for HF is lower (n = 0.4) to WB (n = 0.6). In-situ treatment of HF in on-site sanitary systems can be designed for slow progressive burn.

Thermogravimetric analysis of the combustion of marine microalgae Spirulina platensis and its blend with synthetic waste

“…The frequency factor and reaction order values are a guide for estimating the reaction rate [ 50 ]. In addition, a non-integer order of reaction was found at every investigated zone, which demonstrated that the thermochemical conversion process of the samples took place in a complex reaction mechanism [ 68 ].…”

Planning and communicating prototype tests for the Nano Membrane Toilet: A critical review and proposed visual tool

“…This mechanical flush -a rotating bowl and rubber swipe activated by moving the toilet lid -separates the user from a tank underneath the toilet pan (Tierney, 2014;Tierney, 2017). Solids are separated through settling and displacement, transported by an screw conveyor (Mercer et al, 2016) and subsequently dried and combusted (Fidalgo et al, 2019;Onabanjo et al, 2016), while the liquid fraction is extracted through a weir and purified through membrane processes (Kamranvand et al, 2018;Wang et al, 2017), driven by the heat of the combustion, which is transferred via a heat exchanger (Hanak et al, 2016). The toilet pedestal, including the mechanical flush, the screw conveyor, and the liquid weir are considered the NMT's front end.…”

Isothermal drying characteristics and kinetics of human faecal sludges

“…Thermogravimetric analysis (TGA) enables material characterisation because it measures the change in mass of a material with respect to time or temperature, as the material is subjected to controlled temperature and heating changes 11 , 12 . Based on TGA techniques, drying rates are shown to vary from one sludge to another, depending on sample composition, origin, treatment method and retention time 13 , 14 .…”