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(si apre in una nuova finestra)). 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(si apre in una nuova finestra)).
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/(si apre in una nuova finestra)) 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.
