Towards circular sanitation systems: Resource recovery via pyrolysis of human excreta
Author(s)
Koulouri, Maria Eleni
Type
Thesis
Abstract
More people are now using on-site sanitation technologies than sewered connections. Human excreta management remains challenging and requires an understanding of all sanitation service chain components and their interactions: from source conditions (i.e. toilets) to treatment and resource recovery. This research used pyrolysis to recover resources from human excreta, focusing on the effect of two key source interventions (1. urine diversion; 2. biomass addition) aiming to improve the circularity of sanitation systems.
Firstly, the effects of source separation of human excreta on resource recovery were investigated for different pyrolysis temperatures. Source separation maximised nitrogen recovery (70% of N losses avoided) and improved biochar properties relevant to agricultural applications. It also improved the quality of produced solid fuels, including a 50% increase in the biochar’s calorific value.
Subsequently, faecal biochars were enriched with nutrients from fully hydrolysed human urine via adsorption and precipitation, creating a combined fertiliser and soil amendment. The main NH4–N adsorption mechanism was ion exchange (K+↔NH4+), while precipitation was the primary mechanism for P recovery (>98% P recovered with MgO addition). The combination of MgO (Mg:P=1.5) with the lower biochar dose tested (25 g/L) yielded the most NP-rich fertiliser.
Carbon sequestration potential was investigated for the co-pyrolysis of human faeces with wood biomass. The systematic assessment of biochar stability and the quantification of carbon flows among pyrolysis products were carried out for the first time in the context of human excreta. Synergistic effects took place during co-pyrolysis, and 50% wood content (~30g/toilet user/day) was sufficient to enhance carbon stability and storage.
The laboratory-based findings were applied to assess the resource recovery potential of an operating faecal sludge treatment plant located in Kampala, Uganda. Overall, this research established quantifiable links between sanitation source conditions and resource recovery objectives, contributing towards the design of circular sanitation systems.
Firstly, the effects of source separation of human excreta on resource recovery were investigated for different pyrolysis temperatures. Source separation maximised nitrogen recovery (70% of N losses avoided) and improved biochar properties relevant to agricultural applications. It also improved the quality of produced solid fuels, including a 50% increase in the biochar’s calorific value.
Subsequently, faecal biochars were enriched with nutrients from fully hydrolysed human urine via adsorption and precipitation, creating a combined fertiliser and soil amendment. The main NH4–N adsorption mechanism was ion exchange (K+↔NH4+), while precipitation was the primary mechanism for P recovery (>98% P recovered with MgO addition). The combination of MgO (Mg:P=1.5) with the lower biochar dose tested (25 g/L) yielded the most NP-rich fertiliser.
Carbon sequestration potential was investigated for the co-pyrolysis of human faeces with wood biomass. The systematic assessment of biochar stability and the quantification of carbon flows among pyrolysis products were carried out for the first time in the context of human excreta. Synergistic effects took place during co-pyrolysis, and 50% wood content (~30g/toilet user/day) was sufficient to enhance carbon stability and storage.
The laboratory-based findings were applied to assess the resource recovery potential of an operating faecal sludge treatment plant located in Kampala, Uganda. Overall, this research established quantifiable links between sanitation source conditions and resource recovery objectives, contributing towards the design of circular sanitation systems.
Version
Open Access
Date Issued
2024-10-27
Date Awarded
01/03/2025
License URL
Advisor
Templeton, Michael
Fowler, Geoffrey
Sponsor
Imperial College London
Society of Chemical Industry
Royal Academy of Engineering
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)