Hydrochar-Amended Recycled Concrete Aggregate for Plant Production and Carbon Retention

Hydrochar produced through hydrothermal carbonization of organic residues serves as a char-organic input strategy aimed at closing nutrient loops, enhancing substrate function, and supporting sustainable plant production. This study investigates the effect of hydrochar feedstock and application rates on the physicochemical properties and early plant performance in recycled concrete aggregate (RCA), a significant component of construction and demolition waste. The research evaluates the potential of hydrochar to transform RCA into a viable substrate for sustainable urban landscaping and geo-environmental infrastructure development. Wood-derived and eggshell-derived hydrochars were compared, applied at rates of 5% and 10% by mass, to cultivate Brassica rapa var. chinensis for 21 days under controlled conditions. The assessment quantifies key material properties, including pH, electrical conductivity, organic matter, and total organic carbon. Additionally, plant production indicators such as germination rates, root and shoot development, biomass, and leaf area are measured, along with post-harvest carbon metrics to explore carbon sequestration potential. The experimental design emphasizes the response to application rates and the trade-offs associated with ionic strength and alkalinity. The goal is to identify hydrochar characteristics and amendment rates that promote growth-favorable chemistry, avoiding salinity or pH stress. This research seeks to establish practical guidelines for integrating hydrochar into low-cost, circular substrates for urban plant production and geo-environmental greening.

The authors would like to acknowledge the financial support provided by the State Key Laboratory of Climate Resilience for Coastal Cities (ITC-SKLCRCC26EG01) and the Research Grants Council of HKSAR (C5033-23G).

Keywords: hydrochar, plant production, recycled concrete aggregate, carbon sequestration