Blanket deployment of conventional sewer systems is no longer regarded as a realistic or even desirable development goal, particularly to meet the needs of growing urban populations in low- and middle-income countries. Where onsite sanitation is the norm, the treatment of faecal sludge (FS) within a FS management system (FSM) is a pressing concern. This research investigated pyrolysis as a novel approach for FS treatment, demonstrating its applicability at laboratory- and full-scale.

The comprehensive quantification of organic and inorganic constituents revealed significant influences of the sanitation technology (urine-diverting dry toilets (UDDT), ventilated improved pit latrines (VIP), septic tanks (ST)), introducing an unprecedented understanding of FS composition. Nevertheless, the application of pyrolysis was constrained by the high inorganic content reducing the calorific value, with FS from VIPs, UDDTs and STs measuring median ash fractions of 51.2, 37.8 and 33.2 %dwb respectively, leading to ash fractions >60% in FS-derived chars.

This research shed light on the relationships between organic FS composition and its pyrolytic decomposition, formerly regarded as a black box, which can now be classified as follows: 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); continued carbonisation (>500°C). Thus, a minimum pyrolysis temperature of 500°C was recommended to ensure completion of the main pyrolysis reactions.

For the first time, operational data from full-scale FS pyrolysis is presented. The findings show that continuous pyrolysis combined with mechanical dewatering offers considerable space savings in comparison to established treatment technologies. If pyrolysis is utilised in end-of-pipe scenarios, co-pyrolysis with auxiliary materials such as biomass was deemed indispensable. As novel FSM approaches such as container-based sanitation become more widely applied, a higher degree of source control will favourably influence FS properties, improving the suitability of pyrolysis for use in FSM.