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Faecal sludge pyrolysis: understanding the relationships between organic composition and thermal decomposition

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Title: Faecal sludge pyrolysis: understanding the relationships between organic composition and thermal decomposition
Authors: Krueger, BC
Fowler, GD
Templeton, MR
Septien, S
Item Type: Journal Article
Abstract: Sludge treatment is an integral part of faecal sludge management in non-sewered sanitation settings. Development of pyrolysis as a suitable sludge treatment method requires thorough knowledge about the properties and thermal decomposition mechanisms of the feedstock. This study aimed to improve the current lack of understanding concerning relevant sludge properties and their influence on the thermal decomposition characteristics. Major organic compounds (hemicellulose, cellulose, lignin, protein, oil and grease, other carbohydrates) were quantified in 30 faecal sludge samples taken from different sanitation technologies, providing the most comprehensive organic faecal sludge data set to date. This information was used to predict the sludge properties crucial to pyrolysis (calorific value, fixed carbon, volatile matter, carbon, hydrogen). Samples were then subjected to thermogravimetric analysis to delineate the influence of organic composition on thermal decomposition. Septic tanks showed lower median fractions of lignin (9.4%dwb) but higher oil and grease (10.7%dwb), compared with ventilated improved pit latrines (17.4%dwb and 4.6%dwb respectively) and urine diverting dry toilets (17.9%dwb and 4.7%dwb respectively). High fixed carbon fractions in lignin (45.1%dwb) and protein (18.8%dwb) suggested their importance for char formation, while oil and grease fully volatilised. For the first time, this study provided mechanistic insights into faecal sludge pyrolysis as a function of temperature and feedstock composition. Classification into the following three phases was proposed: decomposition of hemicellulose, cellulose, other carbohydrates, proteins and, partially, lignin (200–380 °C), continued decomposition of lignin and thermal cracking of oil and grease (380–500 °C) and continued carbonisation (>500 °C). The findings will facilitate the development and optimisation of faecal sludge pyrolysis, emphasising the importance of considering the organic composition of the feedstock.
Issue Date: 15-Nov-2021
Date of Acceptance: 30-Jul-2021
URI: http://hdl.handle.net/10044/1/90952
DOI: 10.1016/j.jenvman.2021.113456
ISSN: 0301-4797
Publisher: Elsevier
Start Page: 1
End Page: 13
Journal / Book Title: Journal of Environmental Management
Volume: 298
Copyright Statement: © 2021 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor/Funder: Engineering & Physical Science Research Council (E
Funder's Grant Number: 144356 (EP/N010124/1)
Keywords: Environmental Sciences
Publication Status: Published
Online Publication Date: 2021-08-05
Appears in Collections:Civil and Environmental Engineering

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