Biochar-enhanced two-stage rotary drum-aided vermicomposting of Parthenium hysterophorus: process performance, system optimization, and stabilization mechanisms

Abstract

Efficient stabilization of heterogeneous lignocellulosic biomass remains a critical challenge in engineered biological waste treatment systems. This study presents a quantitatively evaluated two-stage biosystem integrating rotary drum composting (RDC) and vermicomposting for the valorization of Parthenium hysterophorus, with biochar applied as a process-level modifier. Unlike conventional composting studies, this work explicitly links thermophysical behaviour, degradation kinetics, and biological performance within a unified system framework. During the thermophilic RDC phase, biochar enhanced heat retention and moisture buffering, resulting in a higher peak temperature (60.8 °C) compared to the control (56.4 °C) and prolonged thermophilic conditions. Volatile solids (VS) reduction reached 54.6% within 15 days, indicating accelerated degradation kinetics. Subsequent vermicomposting further improved stabilization, with cumulative degradation of 42.01% and reduced respiration rates (1.6 mg g⁻1 VS d⁻1), confirming advanced maturity. Biochar significantly improved nutrient retention, increasing potassium (44.38 g kg⁻1), calcium (10.22 g kg⁻1), and phosphorus (13.05 mg kg⁻1), while enhancing immobilization of trace metals such as Ag and Cr. Earthworm growth kinetics were also enhanced, with a maximum specific growth rate (SGR) of 0.063 day⁻1. The findings demonstrate that biochar modifies system-level heat and mass transfer, microbial accessibility, and stabilization pathways, thereby improving process efficiency and product quality. This integrated biosystem provides a scalable engineering solution for converting invasive biomass into safe, nutrient-rich soil amendments, offering actionable insights for the design and optimization of sustainable waste-to-resource technologies under real-world operating conditions. © The Author(s), under exclusive licence to Springer Nature B.V. 2026.