Hydrodynamic Cavitation Pretreatment Research Articles

The flow pattern effects of hydrodynamic cavitation on waste activated sludge digestibility

The disintegration of raw sludge is of importance for enhancing biogas production and facilitates the degradation of substrates for microorganisms so that the efficiency of digestion can be increased. In this study, the effect of hydrodynamic cavitation (HC) as a pretreatment approach for waste activated sludge (WAS) was investigated at two upstream pressures (0.83 and 1.72 MPa) by using a milli-scale apparatus which makes sludge pass through an orifice with a restriction at the cross section of the flow. The HC probe made of polyether ether ketone (PEEK) material was tested using potassium iodide solution and it was made sure that cavitation occurred at the selected pressures. The analysis on chemical effects of HC bubbles collapse suggested that not only cavitation occurred at low upstream pressure, i.e., 0.83 MPa, but it also had high intensity at this pressure. The pretreatment results of HC implementation on WAS were also in agreement with the chemical characterization of HC collapse. Release of soluble organics and ammonium was observed in the treated samples, which proved the efficiency of the HC pretreatment. The methane production was improved during the digestion of the treated samples compared to the control one. The digestion of treated WAS sample at lower upstream pressure (0.83 MPa) resulted in higher methane production (128.4 mL CH4/g VS) compared to the treated sample at higher upstream pressure (119.1 mL CH4/g VS) and control sample (98.3 mL CH4/g VS). Thus, these results showed that the HC pretreatment for WAS led to a significant increase in methane production (up to 30.6%), which reveals the potential of HC in full-scale applications.

Numerical Study of Hydrodynamic Cavitation Pretreatment of Food Waste: Effect of Pressure Drop on the Cavitation Behavior

Hydrodynamic cavitation (HC) has a wide range of application scenarios. However, there are few studies on the HC treatment of food waste (FW). A Venturi device is designed and operated and plays a clear role in changing the characteristics of FW. The medium viscosity is often neglected when studying cavitation behavior by numerical simulations. We use the Herschel–Bulkley model to describe the viscosity curves of artificial FW samples obtained experimentally. RANS numerical simulation is carried out with a simplified 2D axisymmetric CFD-based model considering the non-Newtonian fluid properties. A numerical simulation study is carried out for FW (TS = 10.0 wt%) at pressure drop (ΔP = 0.05–0.4 MPa). The numerical simulation results show the variation of flow characteristics, viscosity, vapor volume, turbulent viscosity ratio, cavitation number, and pressure loss coefficient. With the increase in ΔP, the flow rate in the Venturi throat increases, and the average viscosity decreases. It reduces the inhibition effect of viscosity on cavitation. The position of incipient vacuoles at the moment of cavitation is constant and unrelated to the variation of ΔP. Under the effect of increasing ΔP, the average vapor volume fraction is increased, and the cavitation effect is enhanced; the cavitation number (σ) is decreased, and the cavitation potential is improved. A larger ΔP should be selected to increase the cavitation efficiency E of the device.

Monitoring effects of hydrodynamic cavitation pretreatment of sodium oleate on the aggregation of fine diaspore particles through small-angle laser scattering

Hydrodynamic cavitation (HC) enhanced fine particle aggregation could be largely due to the generation of tiny bubbles and their role in bridging particles. However, the lack of adequate characterizations of aggregates severally limits our further understanding of the associated aggregation behaviors. In this study, the aggregation of fine diaspore particles was comparatively investigated in sodium oleate (NaOl) solutions with and without HC pretreatment through the small-angle laser scattering (SALS) technique in a shear-induced aggregation (SIA) system. Results showed that HC pretreatment caused the formation of bulk nanobubbles (BNBs), which significantly modified the particle interactions and thereby modified the size and mass fractal dimension (Df) of aggregates under different SIA conditions. Although HC pretreatment did not noticeably alter the gradual change trend of aggregate size and structure characteristics under specific variables, BNBs bridging facilitated the aggregation process towards the diffusion-limited cluster aggregation model, resulting in the formation of larger but looser aggregates. This effect was more pronounced under relatively high NaOl concentrations. Apart from BNBs, the aggregation was also affected by cavitation bubbles formed during shear cavitation, which was more significant under high stirring intensity conditions (i.e., 1800 rpm) than the low stirring intensity conditions (i.e., 600 rpm).

Hydrodynamic cavitation as a promising pretreatment technology to enhance the efficiency of cellulose nanocrystal production via enzymatic hydrolysis

Enzymatic hydrolysis to produce cellulose nanocrystals (CNCs) offers economical and sustainability advantages. However, since this is still an emerging technology, further improvements are needed to make the process feasible for scale-up. In our study, we propose a novel approach using hydrodynamic cavitation (HC) as a pretreatment technology to enhance the efficiency and yield of CNC production. HC treatments conducted under various scenarios induced structural modifications of the cellulose fibers that facilitated their defibrillation and subsequent enzymatic hydrolysis. Isolation through hydrolysis involved the synergistic action of specific enzymes, including xylanase and endoglucanase. Xylanase acted on the hemicellulosic fraction, breaking down the xylan structure and exposing the cellulose fibers. Subsequently, endoglucanase targeted the amorphous regions of cellulose, releasing CNCs. By integrating the HC pretreatment with enzymatic hydrolysis, we achieved remarkable results. High-yield CNCs, reaching approximately 60%, were obtained with a crystallinity index ranging from 81% to 85%. Moreover, this process demonstrated a significant reduction in total energy consumption of approximately 56%, contributing to its economic viability. Furthermore, CNCs with diverse morphologies, aspect ratios, and viscosity profiles were produced, enabling the tailoring of their properties for specific and new applications.

Microbial Community of the Acidogenic Fermentation of Urban Waste: Effect of the Hydrodynamic Cavitation Pre-treatment

Microbial Community of the Acidogenic Fermentation of Urban Waste: Effect of the Hydrodynamic Cavitation Pre-treatment

Printing Ink Wastewater Treatment Using Hydrodynamic Cavitation and Coagulants/Flocculants

Raw printing ink wastewater (PIW) was treated with various inorganic coagulants and organic flocculants (anionic and cationic polyacrylamides). These processes were also examined as post treatment step following hydrodynamic cavitation. Treatment effectiveness was assessed through color, chemical oxygen demand (COD) and total suspended solids (TSS) removal. The addition of 4500 mg L−1 polyaluminum chloride coagulant in undiluted PIW (COD: 17000 mg L−1) resulted in 99% color removal, 96% COD and TSS removal, after settling for 2 h. The addition of 10 mg L−1 of anionic polyacrylamides in the sample reduced settling time to only 5 min, with concomitant 96–98% removal efficiency. The addition of a 4 min hydrodynamic cavitation pretreatment step reduced coagulant addition by 33%, for the treatment of undiluted PIW (with 10 mg L−1 anionic polyacrylamide), while removals were ranged between 96 and 98%. Economic analysis for the undiluted PIW showed that costs were reduced by ca. 20% with the hydrodynamic cavitation pretreatment step. Moreover, sludge characterization showed the presence of maghemite, aluminum chloride and potassium aluminum silicate. Finally, toxicity tests revealed a significant attenuation of the toxic potential of undiluted PIW, thus indicating the enhanced efficiency of the proposed combined process (hydrodynamic cavitation and coagulation/flocculation).

Hydrodynamic cavitation pre-treatment of urban waste: Integration with acidogenic fermentation, PHAs synthesis and anaerobic digestion processes

Urban waste can be valorized within a biorefinery approach, producing platform chemicals, biopolymers and energy. In this framework, hydrodynamic cavitation (HC) is a promising pre-treatment for improving biodegradability due to its high effectiveness and low cost. This paper deals with the effect of HC pre-treatment on the acidogenic co-fermentation process of thickened sewage sludge from a WWTP and seasonal vegetable waste from a wholesale market. Specifically, HC was assessed by testing two sets of parameters (i.e., treatment time of 30 and 50 min; vacuum pressure 1.4 and 2.0 bar; applied power 8 and 17 kW) to determine its effectiveness as a pre-treatment of the mixture. The highest increase in sCOD (+83%) and VFAs (from 1.93 to 17.29 gCODVFA L−1) was gained after 50 min of cavitation. Fermentations were conducted with not cavitated and cavitated mixtures at 37 °C on 4 L reactors in batch mode, then switched to semi-continuous with OLR of 8 kgTVS m-3 d−1 and HRT of 5–6.6 d. Good VFAs concentrations (12.94–18.27 gCODVFA L−1) and yields (0.44–0.53 gCODVFA gVS(0)−1) were obtained, which could be enhanced by pre-treatment optimization and pH control. The organic acid rich broth obtained was then assessed as a substrate for PHAs storage by C. necator. It yielded 0.37 g g−1 of polyhydroxybutyrate, such biopolymer resulted to have analogous physicochemical characteristics of commercial equivalent. The only generated side-stream would be the solid-rich fraction of the fermented effluent, which valorization was assessed through BMP tests, showing a higher SGP of 0.42 Nm3 kgTVS−1 for the cavitated.

Effects of Hydrodynamic Cavitation-Assisted NaOH Pretreatment on Biofuel Production from Cyanobacteria: Promising Approach

Eukaryotic microalgae and prokaryotic cyanobacteria can grow in various water and wastewater types, and both can grow biomass by taking nutrients and converting atmospheric CO2 into useful products. Biofuels obtained by processing this landless grown biomass are defined as “third-generation biofuels”. In this study, the effects of hydrodynamic cavitation (HC)-assisted NaOH pretreatment on methane production from cyanobacteria were investigated. Cyanobacterial biomass was isolated from thermal springs located in the southwest of Turkey (Denizli-Turkey) and identified as Desertifilum tharense. Desertifilum tharense biomass was grown on a laboratory scale, and along with its compositional characteristics, culture-specific parameters were determined. HC-assisted NaOH pretreatment was applied to evaluate optimum process conditions for enhancing methane production from D. tharense. In the experimental design, process parameters of cavitation number (Cv: 0.3-0.7), NaOH concentration (0–4%), solid content (1.5%), reaction time (4h), and reaction temperature (30°C) were combined to reveal the parameter-specific impact of HC pretreatment. The effect of the HC-assisted NaOH pretreatment was further investigated with molecular-bond and surface structure characterization. Along with the energy equivalent of obtained biofuel, energy requirements for cultivation, harvesting, pretreatment, and anaerobic digestion (AD) were calculated to determine the process’s overall energy efficiency. Kinetic parameters of raw and pretreated D. tharense were determined by first-order, cone, modified Gompertz, and reaction curve models. The results revealed that by the application of pretreatment, a 2-35.3% soluble COD increase was achieved, whereas methane production was increased from 241.5 to 290.6 mLCH4 gVS−1. Application of HC with a low Cv of 0.3 boosted methane production up to 20.3% compared to the raw D. tharense.

Lignin – Derived antioxidants as value-added products obtained under cavitation treatments of the wheat straw processing for sugar production

Most of biorefinery technologies are focused on the utilization of plant polysaccharides into chemicals, whereas lignin, the second most abundant natural polymer, is commonly used as a resource to generate power. This is the first report on flavones-bound lignin obtained by wheat straw (WS) pretreatment under low-frequency ultrasound (US) and hydrodynamic cavitation (HC) in sugar production processing. US and HC procedures carried out in aqueous 0.2–0.4% NaOH solutions and various liquid/biomass ratios strongly decreased the lignin content in the solid fraction by 30–45% and 25%, respectively, compared to non-treated WS. Moreover, НС pretreatment increased (approximately tenfold) the portion of ordered cellulose in residual biomass that could hinder the further enzymatic hydrolysis of WS. By means of sequential HC and US pretreatment the ordered cellulose content in solid fraction significantly decreased, compared to the HC alone. Furthermore, it was demonstrated that, after US pretreatment, hemicelluloses and oligomeric fragments of lignin and ligno-carbohydrate complexes were transferred into the liquid phase. In particular, tricin derivatives were detected in liquid fractions with a concentration of 30–35% on o.v.d. ash free sample, and more than 50 compounds associated with low-molecular-weight lignin fragments. These compounds were tentatively identified using high-resolution mass spectrometry (HR-MS) based fragmentation (sequencing) and a self-made database, showing that 16 out of 50 identified compounds belonged to the fragments of model lignin structural units. Tricin and low molecular weight lignin derivatives may find applications as strong antioxidants (i.e. lipidic systems). These findings proved that waste lignin streams obtained after cavitational processes could be a source of value-added products from WS conversion.

Influence of hydrodynamic cavitation pretreatment on coal flotation

The flotation of fine coal particles has been a long-standing challenge in coal processing industry. In this study, the influence of hydrodynamic cavitation pretreatment (HCP) on coal flotation was investigated. A special HCP experiment system was designed for the conditioning of pulp based on the cavitation phenomenon through a venturi tube. Flotation results indicate that, compared with the conventional flotation method, HCP increases combustible recovery of concentrate by about 5%, besides, 50% collector dosage or 25% frother dosage can be saved with HCP under the same combustible recovery of concentrate. Meanwhile, HCP enhances the flotation rate constant by 9.41%. The sieving analysis of flotation products reveals that HCP flotation has a better response for fine coal particles relative to that of coarse coal particles. The bubble observation tests confirm the existence of micro-nano bubbles generated by HCP and the selective generation of micro-nano bubbles on the surface of coal. In addition, HCP leads to an obvious improvement of dispersion of collector. The aggregation of fine coal particles caused by HCP is another important contribution for the coal flotation. [Received: May 18, 2019; Accepted: March 28, 2020]

Biomass Pretreatment via Hydrodynamic Cavitation Process.

There are three essential steps involved in bioethanol production from lignocellulosic biomass feedstocks. They are pretreatment, hydrolysis, and fermentation process. Among them, biomass pretreatment is an expensive and energy-intensive process used to remove the lignin and make the feedstock amenable for bioethanol production. The hydrodynamic cavitation can also be used for biomass pretreatment process. In order to improve the effectiveness of biomass pretreatment, a combination of any two methods of physical, chemical, and biological pretreatment can be used. A combination of the hydrodynamic cavitation pretreatment of biomass with the chemical or biochemical catalyst can be performed better than the individual pretreatment method. In this chapter, a protocol is describes the biomass pretreatment via a combined hydrodynamic cavitation with biocatalyst process.

Influence of hydrodynamic cavitation pretreatment on coal flotation

Influence of hydrodynamic cavitation pretreatment on coal flotation

Assessment of multiple pretreatment strategies for 2G L-lactic acid production from sugarcane bagasse

The bioprospecting of sugarcane bagasse (SCB) through alkali, acid, and hydrodynamic cavitation pretreatment methods and their combinations were evaluated based on bagasse composition, enzymatic hydrolysis, and lactic acid productivity using Bacillus coagulans NCIM 5648. From 100.0 g of SCB, L-lactic acid production of 26.16 g, 8.78 g, 14.15 g, 14.33 g, and 24.61 g in alkali, acid, sequential acid-alkali, sequential alkali-acid, and cavitation with alkali pretreatment was obtained, respectively. Considering the holistic approach from SCB to L-lactic acid, alkali pretreatment is found to be the best method with L-lactic acid titer of 68.7 g/L, the productivity of 2.86 g/L/h, and yield of 0.92 g/g which has resulted in 82.5% higher product yield from SCB as compared to alkali-acid pretreatment. Cavitation in presence of alkali evolved as the next better route with L-lactic acid titer of 62.5 g/L, the productivity of 2.60 g/L/h, and yield of 0.92 g/g. Though the highest glucose release of 89.3 g/L was achieved during enzymatic hydrolysis with sequential alkali-acid-pretreated SCB that resulted in the highest L-lactic acid titer of 71.8 g/L, the productivity of 2.99 g/L/h and fermentation yield of 0.90 g/g.

Pre-treatment of distillery spent wash (vinasse) with vortex based cavitation and its influence on biogas generation

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 pre-treated at varying number of passes (between 1 and 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.

Modeling & simulation studies on batch anaerobic digestion of hydrodynamically cavitated tannery waste effluent for higher biogas yield.

This study describes the efficacy of the pretreatment method of tannery waste effluent (TWE) by hydrodynamic cavitation (HC) prior to anaerobic digestion (AD) using a slit venturi cavitating device operated at 5 bar pressure for 2 h. The HC effect caused faster disintegration and solubilization of larger organic molecules into smaller ones, so that it could be easily digested by the microbial cells resulting in higher degradation rates, lower acclimatization time, higher COD reduction of the TWE and higher biogas generation. The biogas yield and % COD reduction was almost twice higher in HC treated TWE compared to raw TWE. Biogas yield of 68.57 mL/g volatile solids with 43.17% COD reduction was obtained during AD of HC treated TWE in 2 L bioreactor with 10% seed dosage. 'AD' Simulator developed in MATLAB represented the AD performance for both raw and HC treated TWE feed and predicted for concentrations of organic polymers, monomers, VFA and biogas produced, in which model parameter optimization was done by validations using methane production data from bioreactors. The AD simulator estimated higher hydrolysis rate constants for HC treated TWE than for raw TWE as observed in the experiments. Biogas production increased up to 7.8 and 11.8 folds for raw and HC treated TWE samples respectively by adding food waste to TWE feed with organic loading rate of 48 h. Cost estimations proved that cost of excess biogas produced by anaerobic digestion of HC treated TWE mixed with food waste, recovers the extra cost of HC pretreatment when compared to raw TWE alone, establishing HC as an effective pre-treatment tool prior to AD.

Cavitation-based pretreatment strategies to enhance biogas production in a small-scale agricultural biogas plant

Biogas production from lignocellulosic biomass e.g. animal manures and agricultural residues may play a fundamental role as renewable energy sources. Many pretreatment methods can be used to prepare these substrates for biogas production. In this study, hydrodynamic cavitation and ultrasound were used for agricultural residues pretreatment to enhance its biomethanization. A small-scale study allowed to assess biogas productivity and energy efficiency for agricultural biogas plant (ABP) with/without cavitation-based pretreatment of cattle manure and wheat straw. Hydrodynamic cavitation pretreatment (HCP) and ultrasonic pretreatment (UP) significantly enhanced biogas production to 430 and 460 L methane/kg volatile solids (VS), respectively. The final net energy output of ABP/ABP-UP/ABP-HCP was respectively 56/52/61 kWh/d (p < 0.05). Our study showed, that hydrodynamic cavitation could be an efficient technique for agricultural residues pretreatment.

Electricity Generation from Rice Bran by a Microbial Fuel Cell and the Influence of Hydrodynamic Cavitation Pretreatment.

Single-chamber microbial fuel cells (MFCs) were constructed using rice bran (carbon source) and pond bottom mud (microbial source). The total electric charge obtained in the MFC combining rice bran with pond bottom mud was four times higher than that in MFC using only rice bran. Phylogenetic analyses revealed dominant growth of fermentative bacteria such as Bacteroides and Clostridium species, and exoelectrogenic Geobacter species in the anode biofilms, suggesting that mutualism of these bacteria is a key factor for effective electricity generation in the MFC. Furthermore, rice bran, consisting of persistent polysaccharide, was pretreated by the hydrodynamic cavitation system to improve the digestibility and enhance the efficiency in MFC, resulting in 26% increase in the total production of electricity.

An advanced pretreatment strategy involving hydrodynamic and acoustic cavitation along with alum coagulation for the mineralization and biodegradability enhancement of tannery waste effluent

In the present study, coagulation followed by cavitation was studied as a pretreatment tool for tannery waste effluent (TWE) with the aim of reducing its COD, TOC, TSS etc. and enhancing its biodegradability to make it suitable for anaerobic digestion. Initially, coagulation was applied to TWE using alum as a coagulant. The residual pH of treated effluent was found to be around pH of 4.5 where maximum COD and TSS reduction was achieved. In order to enhance the efficiency of pretreatment process, coagulated tannery waste effluent (CTWE) was further subjected to hydrodynamic cavitation (HC) and ultrasonication (US). In case of HC, effect of process parameters such as inlet pressure and dilution on the treatment of CTWE was initially investigated. Lower operating pressure (5 bar) was more favorable for the treatment of CTWE using HC in order to enhance the biodegradability index (BI) from 0.14 to 0.57 in 120 min. The CTWE samples when subjected to 50% dilution, HC pretreatment exhibited higher percentage and quantum reduction in TOC and COD. On the other hand, pretreatment of TWE using coagulation followed by US demonstrated that BI of effluent was enhanced from 0.10 to 0.41 in 150 min. Energy efficiency evaluation for all processes at their optimized conditions was done based on the actual amount of COD reduced per unit energy delivered to the system. Coagulation followed by HC for the pretreatment of TWE was found to be six times more energy efficient as compared to coagulation followed by US.

Anaerobic Digestion of Cattle Manure Influenced by Swirling Jet Induced Hydrodynamic Cavitation.

In this work, a modified swirling jet-induced cavitation has been employed for increasing anaerobic digestion efficiency of cattle manure. The hydrodynamic cavitation (HC) treatment improved the organic matter solubilization and the anaerobic biodegradability of cattle manure. The degree of disintegration increased by 5.8, 8.9, and 15.8% after the HC treatment at 6.0, 7.0, and 8.0 bars, respectively. However, the HC treatment at 7.0 bars had better results in terms of methane production. This result may be attributed to the possible formation of toxic and refractory compounds at higher inlet pressures, which could inhibit the methanization process. Further, total Kjeldahl nitrogen content was found to decrease with increasing inlet pressures, as the pH and the turbulent mixing favored the ammonia stripping processes. HC treatment decreased the viscosity of the treated cattle manure, favoring the manure pumping and mixing. Considerations on the energy input due to the HC pre-treatment and the energy output due to the enhanced methane yield have been presented. A positive energy balance can be obtained looking at the improved operational practices in the anaerobic digesters after the implementation of the HC pre-treatment.

Monitoring of full-scale hydrodynamic cavitation pretreatment in agricultural biogas plant

The implementation of hydrodynamic cavitation (HC) pretreatment for enhancing the methane potential from agricultural biomasses was evaluated in a full scale agricultural biogas plant, with molasses and corn meal as a supplementary energy source. HC batch tests were run to investigate the influence on methane production, particle size and viscosity of specific energy input. 470kJ/kgTS was chosen for the full-scale implementation.Nearly 6-months of operational data showed that the HC pretreatment maximized the specific methane production of about 10%, allowing the biogas plant to get out of the fluctuating markets of supplementary energy sources and to reduce the methane emissions. HC influenced viscosity and particle size of digestate, contributing to reduce the energy demand for mixing, heating and pumping. In the light of the obtained results the HC process appears to be an attractive and energetically promising alternative to other pretreatments for the degradation of biomasses in biogas plant.