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This paper analyzes the effect of inlet pressure on the index of biodegradability of cavitated herbal waste (HW) following its suspension in mechanically treated wastewater (MTW) for further biological processes. Hydrodynamic cavitation (HC) was carried out at inlet pressures of 3.5, 5.0, and 7.0 bar. The BOD5/COD ratio increased by 30% between the 5th and 10th minutes of the process, with the inlet pressure amounting to 3.5 bar, which indicated increased biodegradability of HW. For the higher inlet pressures used, the value of the biodegradability index (BI) increased by 23% and 13% for 5.0 and 7.0 bar, respectively, after 60 min of the process. The value of COD as well as the VS, TS, TC and TOC concentrations dropped for each analyzed inlet pressure, which indicated that complex organic compounds were effectively destroyed. The highest disintegration degree (DDCOD) was achieved with an inlet pressure of 3.5 bar. SEM analysis was performed to analyze the changing morphological structure of the HW. It was proven that the structural morphology of the herbal waste was significantly influenced by hydrodynamic cavitation, which could affect subsequent biological processing. [ABSTRACT FROM AUTHOR]

[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]

In this study, we evaluate the usefulness of mature landfill leachate (MLL) as a carrier allowing hydrodynamic cavitation (HD) of brewery spent grain (BSG). The HD experiments were conducted using an orifice plate with a conical concentric hole of 3/10 mm (inlet/outlet diameter) as a constriction in the cavitation device. The initial pressure was 7 bar and the number of recirculation passes through the cavitation zone reached 30. The results showed that complex organic matter was degraded and solubilized when cavitating the MLL and BSG mixture. The biochemical oxygen demand (BOD5) increased by 45% and the BOD5/total chemical oxygen demand (COD) ratio increased by 69%, whereas the COD, total solids, and nutrient concentration dropped noticeably. However, Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) revealed the generation of possibly toxic HD byproducts such as aromatic compounds. This seems to indicate that MLL could not be regarded as a suitable carrier for BSG cavitation. [ABSTRACT FROM AUTHOR]