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Updated: Sep 15, 2025
08:43
Transformation of Organic Household Leftovers into a Peat Substitute
Published on: July 9, 2019
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Biochar-Compost blends modulate trace element and nutrient dynamics in rooftop farming systems under Mediterranean
Medina Veliu1, Hugo López-Romano2, Giuseppe Picca3
1Univ Gustave Eiffel, GERS-LEE, Bouguenais F-44344, France; Instituto de Ciencias Agrarias (ICA-CSIC), Calle Serrano 115dpdo, Madrid 28006, Spain; Institut de la Recherce en Science et Techniques de la Ville - CNRS FR2488, Centrale Nantes, France.
Ecotoxicology and Environmental Safety
|July 17, 2025
Summary
Biochar-amended composts made from organic waste offer a safe, sustainable alternative to peat for rooftop agriculture (RA). This study shows they reduce plant uptake and leaching of trace elements and improve nutrient retention.
Area of Science:
- Agricultural Science
- Environmental Science
- Soil Science
Background:
- Rooftop agriculture (RA) requires sustainable, lightweight growing media as alternatives to peat.
- Co-composting organic waste with biochar presents a potential solution with reduced environmental impact.
- Knowledge gaps exist regarding the food safety and environmental performance of these compost-biochar substrates.
Purpose of the Study:
- To examine trace element and nutrient dynamics in composts derived from spent coffee grounds, coffee silverskin, and seaweeds, with and without biochar.
- To assess the impact of these substrates on plant uptake and leaching of elements over three years of rooftop cultivation.
- To evaluate the food safety and environmental performance of biochar-amended composts as peat alternatives for RA.
Main Methods:
- Six substrates were created by co-composting spent coffee grounds, coffee silverskin, and seaweeds with and without biochar.
- Tomato, lettuce, and Swiss chard were cultivated on a rooftop in Madrid for three years using these substrates.
- Trace element and nutrient dynamics were analyzed, with specific indices calculated for risk-based element categories to assess plant uptake and leaching.
Main Results:
- Feedstock type significantly influenced trace element and nutrient dynamics; biochar consistently reduced plant uptake and leaching.
- Seaweed-based composts had higher arsenic levels, but biochar reduced plant uptake by up to 40%. Cadmium and lead remained within EU safety limits.
- Biochar enhanced nutrient retention, decreasing phosphorus and nitrogen losses by 40% and 25% respectively over three years.
Conclusions:
- Biochar-amended composts are viable, safe, and sustainable alternatives to peat for rooftop agriculture.
- These substrates support crop production while effectively mitigating environmental risks associated with nutrient leaching and trace element contamination.
- The study provides crucial data on the long-term performance and safety of biochar-based growing media in urban farming contexts.
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