Pretreatment of herbal waste using sonication.

[Display omitted] • A novel method for increasing the biodegradability of herbal waste. • The biodegradability index was enhanced via cavitation by more than 70%. • An effective destruction of complex organic compounds was observed. • Solubilization of carbohydrates occurred with a related monosaccharides release. • Spectroscopy analysis did not reveal formation of new compounds via cavitation. The effect of hydrodynamic cavitation (HC) and the manner it affects the biodegradability of herbal waste suspended on municipal wastewater subjected to mechanical pre-treatment was examined in this paper. The HC was performed at an optimal inlet pressure equal to 3.5 bar and with the cavitation number of 0.11; the number of recirculation passes through the cavitation zone amounted to 30.5. The BOD 5 /COD ratio was enhanced by more than 70% between the 5th and 10th minute of the process, indicating the enhanced biodegradability of herbal waste shortly. Fiber component analysis, FT-IR/ATR, TGA and SEM analysis were conducted to check the findings and to demonstrate changes in the chemical and morphological structure of herbal waste. It confirmed that hydrodynamic cavitation visibly influenced the herbal composition and their structural morphology, decreased hemicellulose, cellulose and lignin content, but did not form the by-products affecting the subsequent biological treatment of herbal waste. [ABSTRACT FROM AUTHOR]