Green products from herbal medicine wastes by subcritical water treatment

Herbal medicine wastes (HMWs) are byproducts of medicine factories, which are mainly landfilled for their environmental problems. Only bearing in mind the contamination and concerns caused by the COVID-19 pandemic and environmental emissions, the worth of herbal medicine wastes management and conversion to green products can be understood. In this work, subcritical water treatment was carried out batch-wise in a stainless tube reactor in the pressure range of 0.792-30.0 MPa, varying the temperature (127-327 degrees C) and time (1-60 min) of extraction. This resulted in new and green material sources, including organic acids, amino acids, and sugars. Amazingly, at very low extraction times (below 5 min) and high temperatures (above 277 degrees C), about 99% of HMWs were efficaciously converted to clean products by subcritical hydrothermal treatment. The results of hydrothermal extraction after 5 min indicated that at low temperatures (127-227 degrees C), the total organic carbon in the aqueous phase increased as the residual solid phase decreased, reaching a peak around 220 degrees C. Acetone soluble extracts or fat phase appeared above 227 degrees C and reached a maximum yield of 21% at 357 degrees C. Aspartic acid, threonine, and glycine were the primary amino acids; glycolic acid, formic acid, lactic acid, and acetic acid were obtained as the main organic acids, glucose, fructose, and cellobiose were substantial sugars produced from the aqueous phase after 5 min of hydrothermal subcritical hydrolysis extraction.

Automated summary

Herbal medicine wastes (HMWs) are mainly landfilled for environmental problems, but their conversion to green products through subcritical water treatment proves to be effective, with about 99% of HMWs efficiently converted to clean products at low extraction times and high temperatures. Substances such as organic acids, amino acids, and sugars are produced, showing potential as new material sources.