Effects of Biochar on Vegetation and Material Fertility of Construction Waste and Completely Decomposed Granite

Department of Civil and Environmental Engineering, the Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China

^* Corresponding author: tldelacruz@connect.ust.hk

Abstract

Construction and demolition waste (CDW) represents a promising sustainable alternative for various geo-environmental applications. While CDW shares some properties with natural soil, its high alkalinity and poor water retention pose challenges for effective utilization, requiring amendments to enhance its suitability for plant growth. This study explores the potential of biochar, a carbon-rich material produced through pyrolysis of peanut shells at 500°C, as an amendment to improve the chemical, physical, and biological properties of CDW. Its chemical and morphological properties were analysed to evaluate the effectiveness of biochar in enhancing CDW as a planting medium. Similar assessments were conducted on biochar-amended CDW, with additional physical tests focusing on unsaturated properties. Completely Decomposed Granite (CDG), a widely occurring soil type in Hong Kong, was included as a natural benchmark for comparison. The findings indicate that, despite the widespread use of biochar in improving soil fertility and water retention in agricultural applications, it was ineffective as an amendment for CDG or CDW. The high alkalinity and chemical composition may have interacted unfavorably with biochar, leading to limited improvements in plant growth and soil properties. This suggests that while biochar has proven beneficial in other soil types, it may not be suitable for CDW-based substrates in its current form. These results highlight the need for further research to identify alternative amendments better suited to CDG and CDW. Future studies should explore different organic or mineral-based additives, optimize biochar pre- treatment methods, or investigate biochar blends to enhance their effectiveness.