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The present work aimed to evaluate whether the use of an innovative method such as hydrodynamic cavitation (HC) is suitable for the simultaneous removal of surfactants of different chemical natures (non-ionic, anionic and cationic) from actual car wash wastewater at different numbers of passes through the cavitation zone and different inlet pressures. An additional novelty was the use of multi-criteria decision support, which enabled the selection of optimal HC conditions that maximized the removal of each group of surfactants and chemical oxygen demand (COD) with minimal energy input. For the optimal HC variants, Fourier transform infrared spectroscopy (FT-IR/ATR) as well as investigations of surface tension, zeta potential, specific conductivity, system viscosity and particle size were carried out. The highest reduction of non-ionic surfactants was found at 5 bar inlet pressure and reached 35.5% after 120 min. The most favourable inlet pressure for the removal of anionic surfactants was 3 bar and the removal efficiency was 77.2% after 120 min, whereas the most favourable inlet pressure for cationic surfactant removal was 3 bar, with the highest removal of 20% after 120 min. The obtained results clearly demonstrate that HC may constitute an effective, fast and cost-efficient method for removing surfactants from real industrial wastewater. [ABSTRACT FROM AUTHOR]

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]

Spent coffee grounds (SCGs) constitute the main solid residue of the coffee brewing process. SCGs are generated in significant amounts daily, worldwide. The effective management of this waste through biological processes is still an unresolved problem. In this study, the application of hydrodynamic cavitation (HC) as a pre-treatment method for improving the biodegradability of SCGs suspended in municipal wastewater was proposed. An orifice plate with a conical concentric hole having inlet/outlet diameter of 3/10 mm was applied as the cavitation inducer. Three inlet pressures were chosen: 3, 5 and 7 bar. The effects in time intervals of 0, 5, 10, 20, 30 and 45 min were evaluated. The application of HC led to enhanced biodegradability for each case. The results of multi-criteria decision indicated that the most efficient combination in terms of biodegradability and energy usage was obtained at the pressure of 5 bar and duration of 20 or 30 min, depending on the adopted weights. The improvements of DOC/TOC (dissolved organic carbon/total organic carbon) ratio were 57% and 71%, as compared to the untreated samples. The release of caffeine was found at pressures of 5 and 7 bar. However, at 5 bar, this effect was noticed for the longest times, 30 and 45 min, respectively. [ABSTRACT FROM AUTHOR]

Organic materials (mainly composts, bark and shavings, heather twigs) are the substances most often used as packing beds in biofilters. The aim of the study was to evaluate the rate of hydrogen sulfide removal in pine bark. The initial concentration of hydrogen sulfide was up to 58% v/v. The removal rates of this gas, using the pine bark bed, ranged from 0.003 cm³g-1 min-1 (115.64 g m-3h-1) to 0.040 cm³ g-1 min-1 (1541.85 g m-3h-1). The results of a preliminary test suggest that the process is abiotic. In order to eliminate biotic pathways of hydrogen sulfide removal, the samples were sterilized. [ABSTRACT FROM AUTHOR]