Sustainable valorization of traditional Chinese medicine residues via semi-permeable membrane composting: the impacts of nitrogen sources

Abstract

Driven by global disease challenges, the traditional Chinese medicine (TCM) industry has flourished, however, the massive surge in TCM residues has emerged as a major bottleneck to its sustainable development. Semi-permeable membrane aerobic composting provides a key technology for TCM residue valorization, which typically relies on exogenous nitrogen supplementation to optimize the carbon-to-nitrogen (C/N) balance. Nevertheless, a systematic understanding of how differentiated nitrogen sources impact this composting process remains lacking. Herein, this study introduced distinct nitrogen sources as co-substrates for semi-permeable membrane aerobic composting to elucidate their modulation of key physicochemical parameters and microecological succession. The results demonstrated that peanut meal exhibited the optimal composting performance compared to alfalfa meal, soybean meal, and urea. Specifically, its thermophilic phase (> 55°C) persisted for over 7 days, and the organic matter content degraded most rapidly and stably, achieving a reduction rate of 49.8%. At maturity, the ammonium nitrogen (NH₄⁺-N) content and electrical conductivity (EC) dropped to as low as 81 mg/kg and 2606μS/cm, respectively, while the peak total nutrient content reached 5.8%. Meanwhile, the dynamic trend of the ratio of the absorbance at 465 nm to that at 665 nm (E4/E6) aligned with typical aerobic composting patterns, indicating a high degree of humification. Community analysis revealed that Bacillus, Bifidobacterium, and Pseudomonas were the dominant bacterial taxa in the efficient treatments, whereas fungi dominated by Thermomyces, Mycothermus, and Aspergillus were consistently associated with NH₄⁺-N turnover and lignocellulose degradation, these compositional associations suggest a potential contribution of these taxa to compost maturation, which warrants direct functional verification in future studies. Overall, this study provides critical microecological insights and a practical nitrogen optimization strategy for efficient and sustainable TCM residue composting.