Biochar as a Substrate Amendment in Green Roofs A Comparative Analysis of Nutrient Retention, Water Management and Application Techniques
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Författare
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Modellbyggare
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Sammanfattning
Incorporating green roofs offers sustainable solutions to various urban problems, but
they also present challenges such as nutrient leaching, which can impact the
environment and cause eutrophication. Biochar, a carbon-rich by-product of pyrolyzed
biomass, emerges as a potential solution to this problem. This carbon-negative
technology can enhance soil fertility, water retention, and mitigate nutrient loss.
However, the properties and subsequent performance of biochar are heavily influenced
by its feedstock and pyrolysis temperature, resulting in significant variability.
This thesis compared the effectiveness of two types of biochar, conventional wood-chip
biochar and granulated crop-based biochar, in improving the performance of green
roofs. Initial investigations suggested superior adsorption properties in wood-chip
biochar, owing to its high surface area and porosity. However, considering the
application rate based on volume, revealed the granulated biochar to be more beneficial
for adsorption. Granulated biochar, characterized by higher oxygen, nutrients, and ash
content, demonstrated better chemical affinity which was pivotal for adsorption,
outweighing surface area and porosity. No significant differences in water retention
between the two biochars or the unamended substrate were observed, contradicting the
expected behavior of biochar. The long-term effects of different biochars, considering
aging and the impacts of microbial activity, were not analyzed in this study. For
shortterm adsorption efficiency, the optimal technique was to apply biochar as a layer at the
bottom of the substrate. Scientific literature, however, indicated that plants benefited
the most when biochar could interact with the roots. Combining both options was thus
suggested as a solution for maximizing plant benefits, nutrient retention, and carbon
sequestration. The literature review suggested that more studies on biochar addition to
green roofs in the 10-15% (v/v) range are needed, and both plant health and nutrient
retention should be addressed. The thesis concluded with the proposition that better
understanding of biochar could enhance green roofs, offering an environmentally
beneficial solution to the issue of nutrient leaching.
Beskrivning
Ämne/nyckelord
Adsorption, nutrient retention, water retention, carbon sequestration, pyrolysis temperature, feedstock.