Thesis
Phytotoxicity and Ecotoxicology of Hydrothermal carbonisation-treated wastes
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2023
DOI:
https://doi.org/10.25918/thesis.374
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Abstract
Hydrothermal carbonisation (HTC) has recently attracted attention as an energy efficient thermochemical method for converting wet wastes to carbonised material (hydrochar). Hydrochar can be used as a soil amendment to recycle carbon (C) and nutrients for improving soil productivity. However, hydrochar effect on plant growth is inconsistent, and also impact on soil organisms and microbial functions is not well known.
To ascertain the effect of hydrochar on plant growth and factors influencing the responses, a systematic review and meta-analysis was conducted. Overall, hydrochar reduced seed germination (-38 %) and shoot biomass (-10 %). Hydrochar application dose was the most influential factor, with increasing negative impact occurring above >16 t/ha.
To further elucidate the mechanism leading to overall plant reduction with hydrochar, the role of hydrochar feedstock and HTC temperature on phytotoxicity was investigated using plant bioassays, spectroscopy and wet chemistry. Hydrochar produced at 260 °C reduced (20 to 30 %) wheat growth due to toxicity, whilst hydrochar produced at lower HTC temperatures (170 - 200 °C) had no significant effect under sufficient soil nutrition. Under low soil nutrition, hydrochar (170 - 200 °C) reduced wheat growth up to 50 % (apparent-phytotoxicity) due to nutrient deficiency exacerbated by microbial nutrient immobilisation.
To elucidate the impact of hydrochar on soil biota, the effect of hydrochar on earthworms (Eisenia fetida) and soil microbial functions were investigated. Hydrochar produced at 260 °C caused more earthworm avoidance than hydrochar produced at 200 °C. Hydrochar toxins were revealed to be polar/non-polar or elevated salt concentration. Soil respiration, total PLFA, qCO2, enzyme activities and N mineralisation essentially increased following soil amendment with hydrochar.
Since hydrochar produced at high temperature (260 °C) was toxic to plants and soil fauna (earthworms); 1) aging of hydrochar in soil for 30 d, and 2) post-pyrolysis (400 °C) were investigated for toxicity mitigation. Toxicity was mitigated by both aging and post-pyrolysis, with post-pyrolysis being more effective with feedstocks presumed to produce more toxic organic compounds (i.e. lignocellulosic biomass) during HTC.
The findings provide a new understanding of hydrochar toxicity and provide strategies to effectively utilise hydrochar in agroecosystems. Fundamentally, hydrochars (170 to 200 °C) are potential soil amendments, though nutritional supplementation to soil may be required to offset possible nutrient drawdown. In case hydrochar (260 °C) is to be used, sustainable post-treatment like aging hydrochar in soil for 30 d must be conducted.
Details
- Title
- Phytotoxicity and Ecotoxicology of Hydrothermal carbonisation-treated wastes
- Creators
- Henry Luutu
- Contributors
- Terry J Rose (Supervisor) - Southern Cross UniversityShane Reid McIntosh (Supervisor) - Southern Cross UniversityMick Rose (Supervisor) - Southern Cross UniversityLukas Van Zwieten (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xi, 215
- Identifiers
- 991013200113702368
- Copyright
- © H Luutu 2023
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis