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Hydrodynamic cavitation is being increasingly pursued for the development of an intensified and compact wastewater-treatment process. Experimental data on the degradation of water contaminated with three commonly used solvents (acetone; ethyl acetate, EA; and isopropyl alcohol, IPA) using vortex-based cavitation devices are presented. The influence of operating flow or pressure drop across cavitation devices (150 to 300 kPa), operating temperatures (20 to 45 °C), concentrations of pollutant (1000 to 50 000 ppm), and scales of the cavitation reactor (with a scaling-up factor of 4, maintaining the geometric similarity) has been reported. A new reaction-engineering model based on the number of passes through the cavitation device was developed to interpret degradation behavior. The model provides a convenient way to estimate the per-pass degradation factor from batch experiments and allows its extension to continuous processes and to more-sophisticated models for estimating the generation of hydroxyl radicals. The model showed excellent agreement with experimental data. The per-pass degradation factor exhibited a maxima with respect to pressure drop (200–250 kPa) across cavitation devices. Aeration was found to improve degradation performance up to 1 vvm ([L/min]gas/L liquid]). The initial concentrations of acetone (1000 to 50 000 ppm) and IPA (1000 to 22 000 ppm) were found to have a negligible effect on degradation performance. The per-pass degradation factor for EA was 1.5 and 4 times that of acetone and IPA, respectively. The effect of two scales (nominal capacities of the small- and large-scale devices used were 0.3 and 1.2 m3/h, respectively) was investigated for the first time, and it was found that the per-pass degradation factor decreased with scale. The presented model and experimental data provide new insights into the application of hydrodynamic cavitation for wastewater treatment and provide a basis for further work on the scaling-up of hydrodynamic cavitation devices. The results will be useful to researchers as well as practicing engineers interested in harnessing hydrodynamic cavitation for water treatment.

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Lignocellulosic biomass (LCB) is an abundant renewable resource to produce fuels and chemicals.Valorisation of LCB, is however a challenge due to its recalcitrant nature posed by the strongly interlinked cellulose-lignin-hemicellulose structures. A range of physico-chemical and biological LCB pre-treatment methods have been reported in literature for enhancing its bio-utilisation. In this work, we used hydrodynamic cavitation (HC) based on vortex devices as a chemical free, environment friendly LCB pre-treatment method to enhance biomethane production. A bench scale pre-treatment set-up using a vortex based cavitation device was established for the pre-treatment of two common LCB's -grass silage (GS) and sugar cane bagasse (SCB). Dried and powdered feedstocks were used in all the experiments. HC was carried out by operating the cavitation device at a flow rate of ~1.5 m 3 /hr.The feedstocks before and after pre-treatment were characterised for morphological and compositional differences using a range of analytical techniques. Liquid phase products produced upon cavitation were also analysed using a HPLC-RI. Biomethane potential (BMP) was measured for GS and SCB with and without pre-treatment, and a first order model was used to describe the kinetics.Up to 40 % enhancement was observed in BMP after cavitation pre-treatment using vortex based devices. A brief discussion on preliminary cost considerations based on the experimentally observed enhancement in BMP is included. The results indicate significant promise of harnessing hydrodynamic cavitation based pre-treatment using vortex based devices for enhancing biomethane production from LCB.

Alternative renewable energy must emerge to sustainably meet the energy demands of the present and future. Current alternatives to fossil fuels are electricity from solar, wind and tidal energies and biofuels. Biofuels, especially bioethanol could be produced from lignocellulosic feedstock via pre-treatment and fermentation. The cellulose I content of most lignocellulosic feedstock is significant, yet its highly crystalline amphiphilic structure interlinked with the lignin network makes it difficult to process for bioethanol production. Processing lignocellulosic biomass via a range of physico-chemical, mechanical and biological pre-treatment methods have been well established, however a relatively new area on the use of cellulose II (a polymorph of native cellulose obtained via mercerisation or regeneration) for the production of bioethanol is still in its early stages. Hence, this review discusses in detail the advantages of using cellulose II over cellulose I as feedstock for bioethanol production. Furthermore, current green and sustainable methods for cellulose II production and the advantages and disadvantages of each method are discussed. In addition, examples from literature reporting higher fermentable sugar and bioethanol yields using cellulose II as feedstock are reviewed, thereby highlighting its importance in the field of bioethanol production. The conclusion from this review suggests that, in all the cases studied, fermentable sugar and/or bioethanol production was found to be higher when cellulose II was used as feedstock instead of native cellulose/lignocellulosic biomass. This higher yield could be attributed to the modified structural and lattice arrangement of cellulose II, its porous volume and degree of polymerisation.

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Distilleries generate high COD (chemical oxygen demand) wastewater streams that are anaerobically digested to produce biogas with sub-optimal yields. In this work, for the first time, novel vortex-based hydrodynamic cavitation (HC) pre-treatment of these waste streams was investigated for significantly enhancing biogas yields. Molasses spent wash (120,000 ppm COD, India) and vinasse (27,000 ppm COD, Brazil) were pretreated at varying number of passes (between 1 -20) through the HC device at constant inflow, biochemical methanation potential (BMP) was measured and described using a first order model. Vortex-based HC pre-treatment led to 14% enhancement (2 passes) in BMP from spent wash (difficult to digest compared to vinasse) with a net energy gain of 1 GJ/ton COD. 10-22% increase in biogas yields from large-scale industrial spent wash digesters confirmed the laboratory findings. The work presented is useful and can be translated to recalcitrant feedstock for enhancing valorization using vortex-based HC pre-treatment.