Abstract
Human faeces (HF) are treated as wastes in many parts of the world, a resource that can be converted to energy and fuels. To enhance the understanding of fuel conversion processes and decomposition characteristics, this study investigated the pyrolysis behaviour and evolved gas profiles of HF using thermogravimetry with gas chromatography–mass spectrometry methods. Kinetic parameters were deduced using model-free kinetic models. Results are compared with simulant faeces (SF), wood biomass (WB) and HF–WB blends. The pyrolysis of HF involved two decomposition peaks — a fronting peak with weight loss of ∼51 wt% and a tailing shoulder peak with weight loss of ∼15 wt%. The apparent activation energy for HF varied from 122–382 kJ/mol at conversion rates of 10%–90% using Kissinger–Akahira–Sunose model. Some of the key pyrolysis products for HF at 370 °C were 4-methoxy-phenol, n-hexadecanoic acid, phenol, 4-methyl- and indole isomer (pyrrolo[1,2-a]pyridine). At 530 °C, evolved gases were largely fragmented with high proportions of alkanes and alkenes including 3-dodecane, 2-undecane, 6-tridecene, 2-propenylidene-cyclobutene. These products differed to WB that are largely hydroxyphenyls and methoxyphenols with guaiacyl or syringil structures. Blending with WB improved pyrolysis of HF, irrespective of the proportions of blend.
Highlights
The need to transit to a sustainable future is changing the way we manage natural resources and waste
This study cannot ascertain the factors promoting suggested synergistic interactions; the results show that blending Human faeces (HF) with wood biomass (WB) improved weight loss rate by 91%, as such HF can be blended with other biomass materials for energy generation
These results have been compared to wood biomass (WB) and simulant faeces (SF) to highlight key differences and similarities
Summary
The need to transit to a sustainable future is changing the way we manage natural resources and waste. Organic materials (e.g. food wastes, crop residues and manure) that are usually treated as waste, are nowadays considered valuable feedstocks for chemicals, fuels and energy (Lens et al, 2004; He et al, 2008) This includes human excreta (urine and faeces), resources that would otherwise be sent to the wastewater treatment plant and in many parts of the world, inappropriately disposed into the environment (Strande and Brdjanovic, 2014; Diener et al, 2014). The use of human faeces for energy generation is gaining reputation because faeces are a rich biomass source: consisting of undigested fats, protein, polysaccharide, bacterial biomass, unabsorbed nutrients, gut secretions, digestive juices and cell shedding (Rose et al, 2015) They can be subjected to heat, like any biomass material, with or without the presence of oxygen to generate valuable energy products including faecal char and solid fuel. Efficient conversion requires a good understanding of the decomposition characteristics, devolatilization processes
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