Periodic Reporting for period 1 - FEET (FEET (From Excreta to Energy, Transformation) / Hydrothermal carbonization as a sustainable solution for faecal waste treatment in less developed communities)
Berichtszeitraum: 2020-09-01 bis 2022-08-31
Enormous efforts have been made to overcome global sanitation challenges. However, around half of the global population currently lives without safely managed sanitation services. The Least Developed Countries (LDCs) situation needs particular attention, given that safe sanitation services cover only 26 % of the population. In those conditions, onsite technologies (e.g. latrines and septic tanks) provide more viable options. Without proper treatment, the faecal sludge generated from these onsite systems will most likely be disposed of in the local environment, resulting in pervasive environmental and public health risks. As a result of poor sanitation, diarrhoeal disease prevails and stands as the second leading cause of child mortality in less developed places. It causes more than 0.5 M deaths annually.
Hydrothermal carbonization (HTC) has been suggested as an alternative technology for faecal waste treatment. HTC technology can provide useful carbonaceous materials from various biomasses at high yields. The outcome of HTC is a disease-free thick slurry consisting of solid particles (hydrochar) and liquid (process water). Without intensive post-treatment, these products can be utilized as fertilizer, energy source, soil amendment, adsorbent, etc.
Despite its potential, the gap between the laboratory and the place in need seems still too large. Technical skills for establishing the reactor and treatment system may not be available or affordable in those places in need. To answer this challenge, this research project aims to develop a tailor-made HTC faecal waste treatment technology for LDCs. The main objectives can be presented in two themes.
i) Development of a bench-scale low-cost HTC reactor (BLR).
We aim to develop a tailor-made reactor and operational system for LDC conditions. A test reactor will be developed based on widely available materials and techniques. It will be tested for the selected operational condition for human waste treatment.
ii) Resource recovery from the end-product of hydrothermal treatment of human waste
The solid part (hydrochar) and liquid part (process water) from the end product have a wide range of potential applications. We will investigate their potential as energy and nutrient sources and adsorbents for pathogenic microorganism removal from drinking water.
Hydrothermal carbonization (HTC) has been suggested as an alternative technology for faecal waste treatment. HTC technology can provide useful carbonaceous materials from various biomasses at high yields. The outcome of HTC is a disease-free thick slurry consisting of solid particles (hydrochar) and liquid (process water). Without intensive post-treatment, these products can be utilized as fertilizer, energy source, soil amendment, adsorbent, etc.
Despite its potential, the gap between the laboratory and the place in need seems still too large. Technical skills for establishing the reactor and treatment system may not be available or affordable in those places in need. To answer this challenge, this research project aims to develop a tailor-made HTC faecal waste treatment technology for LDCs. The main objectives can be presented in two themes.
i) Development of a bench-scale low-cost HTC reactor (BLR).
We aim to develop a tailor-made reactor and operational system for LDC conditions. A test reactor will be developed based on widely available materials and techniques. It will be tested for the selected operational condition for human waste treatment.
ii) Resource recovery from the end-product of hydrothermal treatment of human waste
The solid part (hydrochar) and liquid part (process water) from the end product have a wide range of potential applications. We will investigate their potential as energy and nutrient sources and adsorbents for pathogenic microorganism removal from drinking water.
The summary of the results from this project is provided below.
i) Process optimization of HTC-human waste treatment
The property of the end-product from faecal waste treatment is mainly determined by the composition of feedstock and process conditions such as temperature and reaction time. We tested seven experimental conditions to find an optimum temperature duration for the best resource recovery.
ii) Development of Bench-scale low-cost reactor (BLR)
We developed a bench-scale low-cost HTC reactor (BLR) of 2 L capacity using easily accessible resources: stainless-steel pipe materials and welding techniques. It is designed to be operated without any electric devices. The reactor successfully treated human waste for the selected test conditions selected in optimization experiments.
iii) Investigation of energy recovery from the end-product
The hydrochar (the solid part of the end-product) showed comparable calorific values around 24 kJ/g. It is in the range of low-quality coal, charcoal briquette and pellets produced by dry pyrolysis of human faeces. The total energy potential of hydrochar accounts for 49 to 106 % of energy invested for treatment. In contrast, the biogas produced from process water had a limited energy potential of less than 6 % of the energy consumption.
iv) Phosphorus recovery from the hydrochar ash through struvite precipitation
Phosphorus in the raw faeces remained well in the system throughout the experimental procedures. Around 80 % phosphorus was found in the hydrochar and resulting ash from its combustion, and 15 % remained in the process water. We recovered approximately 3 / 4 of the initial phosphorus in faeces as a form of struvite with a direct market potential as a slow-releasing fertilizer.
v) Evaluation of hydrochar for its adsorption removal capacity on Escherichia coli from drinking water
This part of the research is still going on. We produced four types of hydrochar by supplementing the faecal wastes with widely accessible biowastes (garden waste, food waste, and spent coffee grounds). Hydrochar materials produced are being tested for Escherichia coli removal from Zurich Lake water using small sand filtration set-ups.
vi) Hydrothermal humification of faecal waste
We can facilitate humic acid generation during hydrothermal treatment of faecal waste by applying strong alkali substances in the feedstock (high pH). Currently, we are performing the initial laboratory experiments. Humic acid can drastically improve the quality of HTC-faeces products as a soil amendment. Also, adding biochar rich in humic substances has high potential as a supplement facilitating the composting process of faecal sludge.
Sections i), ii), iii), and iv) were incorporated and published in a peer-reviewed open-access academic journal (https://open-research-europe.ec.europa.eu/articles/1-139). In addition to the full paper, communication with the reviewers would help readers better understand more background and reasoning behind the research work. Technical details of the low-cost reactor are available in a data repository (https://doi.org/10.5281/zenodo.5094908).
The output of this project can serve as proof of concept for the HTC-sanitation concept. It was presented in several online and offline meetings with researchers and stakeholders in the relevant fields. Also, it will be presented at an international conference on hydrothermal technologies in 2023 (https://2021htc.weebly.com/) which has been suspended from 2021 due to the pandemic.
Following the presented research, we are applying for several international and Swiss national research grants for testing the HTC-sanitation strategy in field conditions.
i) Process optimization of HTC-human waste treatment
The property of the end-product from faecal waste treatment is mainly determined by the composition of feedstock and process conditions such as temperature and reaction time. We tested seven experimental conditions to find an optimum temperature duration for the best resource recovery.
ii) Development of Bench-scale low-cost reactor (BLR)
We developed a bench-scale low-cost HTC reactor (BLR) of 2 L capacity using easily accessible resources: stainless-steel pipe materials and welding techniques. It is designed to be operated without any electric devices. The reactor successfully treated human waste for the selected test conditions selected in optimization experiments.
iii) Investigation of energy recovery from the end-product
The hydrochar (the solid part of the end-product) showed comparable calorific values around 24 kJ/g. It is in the range of low-quality coal, charcoal briquette and pellets produced by dry pyrolysis of human faeces. The total energy potential of hydrochar accounts for 49 to 106 % of energy invested for treatment. In contrast, the biogas produced from process water had a limited energy potential of less than 6 % of the energy consumption.
iv) Phosphorus recovery from the hydrochar ash through struvite precipitation
Phosphorus in the raw faeces remained well in the system throughout the experimental procedures. Around 80 % phosphorus was found in the hydrochar and resulting ash from its combustion, and 15 % remained in the process water. We recovered approximately 3 / 4 of the initial phosphorus in faeces as a form of struvite with a direct market potential as a slow-releasing fertilizer.
v) Evaluation of hydrochar for its adsorption removal capacity on Escherichia coli from drinking water
This part of the research is still going on. We produced four types of hydrochar by supplementing the faecal wastes with widely accessible biowastes (garden waste, food waste, and spent coffee grounds). Hydrochar materials produced are being tested for Escherichia coli removal from Zurich Lake water using small sand filtration set-ups.
vi) Hydrothermal humification of faecal waste
We can facilitate humic acid generation during hydrothermal treatment of faecal waste by applying strong alkali substances in the feedstock (high pH). Currently, we are performing the initial laboratory experiments. Humic acid can drastically improve the quality of HTC-faeces products as a soil amendment. Also, adding biochar rich in humic substances has high potential as a supplement facilitating the composting process of faecal sludge.
Sections i), ii), iii), and iv) were incorporated and published in a peer-reviewed open-access academic journal (https://open-research-europe.ec.europa.eu/articles/1-139). In addition to the full paper, communication with the reviewers would help readers better understand more background and reasoning behind the research work. Technical details of the low-cost reactor are available in a data repository (https://doi.org/10.5281/zenodo.5094908).
The output of this project can serve as proof of concept for the HTC-sanitation concept. It was presented in several online and offline meetings with researchers and stakeholders in the relevant fields. Also, it will be presented at an international conference on hydrothermal technologies in 2023 (https://2021htc.weebly.com/) which has been suspended from 2021 due to the pandemic.
Following the presented research, we are applying for several international and Swiss national research grants for testing the HTC-sanitation strategy in field conditions.
This project is the first study that employed a non-electric heating method and non-automated operation of the HTC reactor. The results open the possibility of using biomass fuels and manual operation, thus, allowing independence from electricity and electric devices, which are frequently unstable or unavailable resources in LDCs. Also, this project investigated the potential utilisation of faecal waste-HTC products as a nutrient and energy source. These results serve as proof of concept for the low-tech implementation of HTC sanitation in terms of technical feasibility and resource recovery.
The development of low-cost HTC reactor systems can also open new possibilities for decentralised (point-of-use) and small-scale implementation of HTC technology in developed countries (e.g. off-grid animal manure treatment and resource recovery in rural farms). Cutting down the cost of relevant reactor set-up and establishing a safe operational regime will be the main driving force for further development of the low-cost HTC concept. The strong potential of the resource recovery from biowaste and subsequent climate change mitigation effect will be highly valued under the current trends pursuing a more environment-friendly system in the circular economy concept.
The development of low-cost HTC reactor systems can also open new possibilities for decentralised (point-of-use) and small-scale implementation of HTC technology in developed countries (e.g. off-grid animal manure treatment and resource recovery in rural farms). Cutting down the cost of relevant reactor set-up and establishing a safe operational regime will be the main driving force for further development of the low-cost HTC concept. The strong potential of the resource recovery from biowaste and subsequent climate change mitigation effect will be highly valued under the current trends pursuing a more environment-friendly system in the circular economy concept.