Hydrodynamic Cavitation Treatment Research Articles

Continuous Cultivation of Microalgae in Cattle Slaughterhouse Wastewater Treated with Hydrodynamic Cavitation

Cattle slaughtering produce large amounts of wastewater containing high concentrations of organic matter and nutrients and requires significant treatment before disposal or reutilization. However, the nutrients contained can be valued as a medium for microalgal biomass generation. In this work, hydrodynamic cavitation (HC) followed by membrane filtration or biological (microalgae cultivation) treatment in continuous mode were performed. From cattle slaughterhouse wastewater (CSW), by the effect of HC treatment with air injection in batch mode, more than 20% of the chemical oxygen demand (COD) was removed. In a continuous HC process, the COD content in output was 324 mg O2/L, which is 68% lower than the supplied CSW. After that, 76% of residual COD was removed by filtration through a tubular alumina membrane (600 nm). Finally, 85% of residual COD after HC treatment in 24 h in a batch mode was removed by microalgae. On the other hand, the COD concentration in the output was around 59 mg O2/L in continuous mode, which represents 85–93% COD removal. The process involving HC and microalgae growing looks promising since in addition to water treatment, the microalgae produced could be valued in a biorefinery concept.

Hydrodynamic cavitation-enhanced heterogeneous activation of persulfate for tetracycline degradation: Synergistic effects, degradation mechanism and pathways

• Mass transfer and oxidant utilization are two key issues in SO 4 •− oxidation. • Hydrodynamic cavitation (HC) is a green, effective solution to solve these issues. • Mass transfer was enhanced by HC-induced turbulence via Fe 0 → Fe 2+ →Fe 3+ →Fe 2+ . • HC promotes persulfate (PS) utilization in HC-Fe 0 /PS system. • Mass spectra and theoretical calculations reveal tetracycline degradation pathways. Mass transfer and oxidant utilization are perhaps two of the most critical issues in sulfate radical (SO 4 •− ) based advanced oxidation technologies (AOTs) and their scaled-up implementation. In this study, we propose using hydrodynamic cavitation (HC), considered a green, effective method, to promote both mass transfer and oxidant utilization in zero-valent iron (Fe 0 ) activated persulfate (PS) system. Whilst the BET surface area of Fe 0 was increased by 8 times after HC treatment, concentration of Fe 2+ derived from Fe 0 oxidation is greatly increased for effective PS activation. The reappearance of Fe 0 and Fe 2+ after cavitation ensured a good reusability of the catalyst. Likewise, the impact of pH revealed that TC adsorption on catalyst at acidic pH favored its degradation compared with that at higher pH. With respect to oxidant utilization, it is observed that PS even at a high dosage (2.8 mM) was completed converted within 30 min in the HC-Fe 0 /PS system. According to SEM, TEM, and BET analysis, we conclude that the microjets induced by cavitation bubbles or direct abrasion by HC agitation have contributed to the removal of hydroxide/oxide layers on the Fe 0 surface, thus reactivating its catalytic activity. Given these reasons, we observed up to 97.80% removal of Tetracycline (TC), the model pollutant, with a synergistic coefficient as high as 2.62. After confirming SO 4 •− as the most dominant reactive species, five degradation pathways of TC were proposed given the intermediate evidence from LC-MS/MS analysis and density functional theory (DFT) calculations. Results from this study could provide new insights into the role of HC on PS activation and shed light on the potential implementation of the SO 4 •− -based AOTs for scaled-up wastewater treatments.

Efficiency Evaluation of Cavitation Heat Generator Used for Desalination of Saline Solutions

Nowadays, the issue of efficient desalination and treatment of seawater for its further use in various domains of human activity is of much interest worldwide. There are plenty of known treatment techniques. This research paper discusses the method of hydrodynamic cavitation treatment in a heat generator in various modes and proves the performance efficiency of this method. The process of treating saline solutions of different concentrations and registration of electric conductivity of solutions are studied. The possibility of changing the concentration of salt in the solution by treating it in a vortex cavitation heat generator is undertaken. The efficiency of the cavitation process depends on the temperature of the working environment: with the temperature increase, the desalination intensity decreases. Two possible scenarios of the process are revealed, i.e., the decrease in the concentration of salt in the solution or its increase in the presence of a salt source. When working on depleted solutions with a salinity of 1÷5 ‰ at high temperatures, the reverse diffusion of previously adsorbed salts from the internal surfaces into the solution takes place. When working on solutions of elevated concentrations in the same high-temperature range, the reverse diffusion decreases and at a salinity of 67 ‰, its effect ceases, since the concentration of salts on the inner surfaces becomes comparable to the concentration of the solution. The hypothesis of centrifugal separation of salts from water is experimentally proved.

Non-thermal hydrodynamic cavitation processing of tomato juice for physicochemical, bioactive, and enzyme stability: Effect of process conditions, kinetics, and shelf-life extension

Fresh tomato juice was processed by hydrodynamic cavitation (HC) at 5 to 15 psi pressures for 5–30 min. A full factorial design was applied to optimize the HC treatment of tomato juice quality. Optimal conditions were recorded at 10 psi for 10 min, which showed no significant (p < 0.05) change in lycopene content to that of freshly obtained unprocessed tomato juice (control). After processing, the retention of 93% ascorbic acid and 96.6% of total phenolic compounds (TPC) was observed. Similarly, sedimentation and viscosity were mildly affected by HC processing (89.2 and 94.4% of values in the treated sample, respectively). While pH, total soluble solids (TSS), titratable acidity (TA) of HC treated sample remained unchanged (p < 0.05). The results were also compared with the conventional thermally processed tomato juice (90 °C for 90 s). Although thermal treatment resulted in the inactivation of 92.2% of pectin methylesterase and a 5 log reduction in total plate counts, it also showed significant reductions in ascorbic acid (61.4%), TPC (72.3%), and physical properties (37.7% of SI and 83.2% viscosity). However, HC processing could achieve a maximum of 4.9% inactivation of PME and 1 log reduction at high treatment conditions, respectively (15 psi for 30 min). The shelf-life study showed more retention of bioactives and better physicochemical properties in tomato juice samples stored at 4 °C for 15 days than the control. Sensory evaluation revealed that the overall acceptability of the optimized HC treated (0.714) sample was better than the thermally treated sample (0.591). The observed results concluded that HC-treated tomato juice was comparatively better than thermally-treated tomato juice in retaining bioactive compounds. Consequently, HC constitutes a promising approach in food processing to improve and retain the beneficial properties of tomato juice.

Hydrodynamic cavitation efficiently inactivates potato virus Y in water

Waterborne plant viruses can destroy entire crops, leading not only to high financial losses but also to food shortages. Potato virus Y (PVY) is the most important potato viral pathogen that can also affect other valuable crops. Recently, it has been confirmed that this virus is capable of infecting host plants via water, emphasizing the relevance of using proper strategies to treat recycled water in order to prevent the spread of the infectious agents. Emerging environmentally friendly methods such as hydrodynamic cavitation (HC) provide a great alternative for treating recycled water used for irrigation. In the experiments conducted in this study, laboratory HC based on Venturi constriction with a sample volume of 1 L was used to treat water samples spiked with purified PVY virions. The ability of the virus to infect plants was abolished after 500 HC passes, corresponding to 50 min of treatment under pressure difference of 7 bar. In some cases, shorter treatments of 125 or 250 passes were also sufficient for virus inactivation. The HC treatment disrupted the integrity of viral particles, which also led to a minor damage of viral RNA. Reactive species, including singlet oxygen, hydroxyl radicals, and hydrogen peroxide, were not primarily responsible for PVY inactivation during HC treatment, suggesting that mechanical effects are likely the driving force of virus inactivation. This pioneering study, the first to investigate eukaryotic virus inactivation by HC, will inspire additional research in this field enabling further improvement of HC as a water decontamination technology.

Bovine milk processing impacts characteristics of extracellular vesicle isolates obtained by size-exclusion chromatography

Extracellular vesicles facilitate intercellular communication by transferring bioactive molecules with the potential to elicit host responses. Raw bovine milk contains functional extracellular vesicles that are taken up by humans. By comparing with extracellular vesicles from unprocessed bovine milk, the impact of pasteurisation, hydrodynamic cavitation treatment, or homogenisation on purity of milk extracellular vesicles isolated by a series of centrifugation steps followed by size-exclusion chromatography was assessed. Extracellular vesicles could be isolated from all four source materials, though to varying extents as evident from Western blots. In particular, homogenisation resulted in co-isolation of non-extracellular vesicle material such as β-casein, β-lactoglobulin, and triacylglycerol. RNA concentrations were highest in extracellular vesicles derived from the three processed source materials, thus indicating co-isolation of other RNA-containing detergent-labile particles in addition to native milk extracellular vesicles. Overall, this study shows that the history of milk processing impacts the purity of milk extracellular vesicles.

Orifice based hydrodynamic cavitation of sugarcane juice: Changes in Physico-chemical parameters and Microbiological load

An orifice based hydrodynamic cavitation system was developed for treating fresh sugarcane juice, non-thermally. The effect of hydrodynamic cavitation treatment parameters such as pressure (2.5, 3, and 3.5 bar), processing time (10, 20, 30, 40 min), and type of orifice plate geometry on the physicochemical attributes such as temperature rise, pH, titratable acidity (TA), total soluble solids (TSS), viscosity, change in colour and microbial load of the sugarcane juice were investigated. The maximum rise in temperature during the treatment was 22 °C at 3.5 bars with the 17 number of orifices. The pH decreased from 4.94 to 4.64 and TSS significantly reduced (p < 0.01) from 20 to 13 °Brix depending on the severity of the treatment. The reduction in viscosity was in the range of 3–48%. The maximum colour change in the juice could be observed when treated at an inlet pressure of 3.5 bar for a processing time of 40 min with a plate having 17 numbers of orifices. The maximum microbial load inactivation from 5.53 log10 CFU/mL to 3.3 log10 CFU/mL was observed at the highest pressure, processing time, and orifices.

Effect of hydrodynamic cavitation water treatment on Pseudomonas aeruginosa quorum-sensing molecules

Hydrodynamic cavitation treatment was used for the functional inactivation of quorum-sensing lactone molecules of Pseudomonas aeruginosa. Hydroxyl radicals formed as well as the shear effects during the cavitation process induced the inactivation of the signal molecules through hydrolysis reaction coupled with bacterial destruction. Concentration of two different types of homoserine lactones(HSL) molecules was tested after the treatment at various rotational speeds. It was found that the strongest effects can be achieved at speeds > 2000 rpm. This value is considered as an onset speed of dominant cavitation, and it is in agreement with literature data. The experimental trends were in agreement with the calculations based on the finite element modelling, which show a significant increase in average shear stress at higher rotational speeds. Overall, the work has demonstrated the possible effects of hydrodynamic cavitation on the quorum-sensing molecules of Pseudomonas aeruginosa for the first time.

Effect of hydrodynamic cavitation on flocs structure in sewage sludge to increase stabilization for efficient and safe reuse in agriculture

Sewage sludge is the by-product of wastewater treatment processes. Its reuse is central to a circular economy approach and offers a sustainable alternative to its disposal. Treated sludge contains a wide range of nutrients (mainly nitrogen, phosphorus, and potassium), which favor its sustainable employment for agricultural purposes (land-spreading, compost production) and environmental requalification interventions (forestry, silviculture, land reclamation and revegetation). However, if not properly treated, sewage sludge can contain various contaminants such as heavy metals, organic pollutants, pathogens, and other emerging contaminants, which pose a threat for crops production and human health. Hydrodynamic cavitation (HC) is an eco-friendly and cost-efficient pretreatment that can enhance sewage sludge stabilization in both anaerobic and aerobic digestion units, thereby making safe its management and disposal. In this study, HC was used for the gradual disintegration of activated sludge (reaching a maximum disintegration degree (DDPCOD) of 19.2% after 8 h of treatment), and the solubilization of the dissolved organic matter (increasing the Soluble Chemical Oxygen Demand (SCOD) from 244 to 4,578 mg L−1 after 8 h of treatment). Then, both dynamic light scattering analysis and stereoscopic microscope observations proved that HC can also lead to a size reduction of sludge suspended particles. In addition to evaluate the HC treatment efficiency, in this work was also provided a brief discussion on the possible procedures to be followed for the safe and efficient sewage sludge disposal on land after it has been HC-treated.

Comparative assessment of HTST, hydrodynamic cavitation and ultrasonication on physico-chemical properties, microstructure, microbial and enzyme inactivation of raw milk

The effects of high-temperature short time (HTST), ultrasonication (US) and hydrodynamic cavitation (HC) on physicochemical properties, alkaline phosphatase (ALP) activity, microorganism, degree of protein hydrolysis (DPH), color, microstructure and overall particle size of raw milk were studied. The separation index (SI) was also measured during storage of treated milk at 4 ± 2 °C for 12 days. US was carried out at different intensities (200, 300, and 400 W) and time (4, 6, and 8 min) and HC at 4, 6, 8, and 10 psi for 5, 10 and 15 min. It was observed that HC showed 21% energy efficiency (η) with higher cavitational yield than US which had η <10%. Microbial log reduction of 2.30 ± 0.17 TPC and 2.26 ± 0.17 (YM) was obtained by HTST treatment. And about 0.9 and 0.7 microbial log reduction were observed in HC and US treatment respectively. Initially in non-thermal treatment, ALP activity increases slightly by 1–2% at 4 psi (HC) and 200 W (US), but with further increase in time and intensity, ALP activity decreases. In addition to that, there was an increase in the DPH from 0.716 ± 0.09% to about 3.608 ± 0.52 and 3.77 ± 0.15% in US and HC treated samples respectively. Also, with an increase in time and intensity, number of fat globules increased with a decreased diameter and overall particle size. In non-thermal treatment, except for samples treated at 200 W (US) and 4 psi (HC), no separation was observed during the storage which could be due to reduced size of fat globules (from 6.3 μm to 3–2.2 μm).

Assessment of the papermaking potential of processed Miscanthus × giganteus stalks using alkaline pre-treatment and hydrodynamic cavitation for delignification

One way of satisfying increased market demand and simultaneously achieving a reduced environmental load in the industrial paper production is the use of fibrous agricultural residues. The aims of this study were i) to investigate the effect of alkaline – hydrodynamic cavitation (HC) pre-treatments on the delignification of Miscanthus × giganteus stalks (MGS) and ii) establishing the suitability of MGS as feedstock and their exploitation in pulp and paper manufacturing. It was demonstrated that the proposed treatment is an efficient delignification method for the non-wood fiber sources, such as miscanthus. A significant outcome of this work was the observation that HC treatment preserved the fibres lengths and surface quality of raw MGS, but at the same time increased the amount of kinked and curled fibers present in cavitated miscanthus fibers. The average miscanthus fiber length was found to be relatively short at 0.45 (±0.28) mm, while the slenderness ratio, the flexibility coefficient and Runkel ratio values were calculated to be 28.13, 38.16 and 1.62, respectively. The estimated physical properties of MGS pulp hand-sheets were 24.88 (±3.09) N m g−1 as the tensile index, 0.92 (±0.06) kPa m2 g−1 as the burst index and 4.0 (±0.37) mN m2 g−1 as the tear index. Overall the current work demonstrated effective use of hydrodynamic cavitation for improving the processing in pulp and paper manufacturing.

Hydrodynamic Cavitation Efficiently Inactivates Potato Virus Y in Water

In the midst of the global water crisis, irrigation is still the largest contributor to global water consumption. One of the contingency measures to cope with this burden is the reuse of wastewater or the implementation of closed irrigation systems that recycle water. These solutions have a positive effect on water use, but can also facilitate the spread of various plant pathogens, including viruses. Plant viruses can destroy entire crops, leading not only to high financial losses but also to food shortages. Potato virus Y (PVY) is the most important potato viral pathogen that can also affect other valuable crops. Recently, it has been confirmed that this virus is capable of infecting host plants via water, emphasizing the relevance of using proper strategies to treat recycled water in order to prevent the spread of the infectious agents. Emerging environmentally friendly methods such as hydrodynamic cavitation (HC) provide a great alternative for treating recycled water used for irrigation. In the experiments conducted in this study, HC inactivated PVY in water samples after 500 HC passes or less. The HC treatment disrupted the integrity of viral particles, which also led to a minor damage of viral RNA. Reactive species, including singlet oxygen, hydroxyl radicals, and hydrogen peroxide, were not primarily responsible for PVY inactivation during HC treatment, suggesting that mechanical effects are likely the driving force of virus inactivation. This pioneering study, the first to investigate eukaryotic virus inactivation by HC, will inspire additional research in this field enabling further improvement of HC as a water decontamination technology.

Production of biologically active peptides by hydrolysis of whey protein isolates using hydrodynamic cavitation

Whey protein isolate (WPI) hydrolysates have higher solubility in aqueous phase and enhanced biological properties. Hydrolysis of WPI was optimized using operating pressure (ΔP, bar), number of passes (N), and WPI concentration (C, %) as deciding parameters in hydrodynamic cavitation treatment. The optimum conditions for generation of WPI hydrolysate with full factorial design were 8 bar, 28 passes, and 4.5% WPI concentration yielding 32.69 ± 1.22 mg/mL soluble proteins. WPI hydrolysate showed alterations in binding capacity over WPI. SDS-PAGE and particle size analysis confirmed the hydrolysis of WPI. Spectroscopic, thermal and crystallinity analyses showed typical properties of proteins with slight variations after hydrodynamic cavitation treatment. ABTS, DPPH and FRAP assays of WPI hydrolysate showed 7–66, 9–149, and 0.038–0.272 µmol/mL GAE at 1–10, 0.25–4, and 3–30 mg/mL concentration, respectively. Further, a considerable enhancement in fresh weight, chlorophyll, carotenoids, reducing sugars, total soluble sugars, soluble proteins content and total phenolics content was noticed during in vitro growth of sugarcane in WPI hydrolysate supplemented medium at 50–200 mg/L concentration over the control. The process cost (INR/kg) to hydrolyze WPI was also calculated.

Acoustic and hydrodynamic cavitation assisted hydrolysis and valorisation of waste human hair for the enrichment of amino acids

Hair waste in large amount is produced in India from temples and saloons, India alone exported approximately 1 million kg of hair in 2010. Incineration and degradation of waste human hair leads to environmental concerns. The hydrothermal process is a conventional method for the production of hair hydrolysate. The hydrothermal process is carried out at a very high temperature and pressure, which causes the degradation of heat-sensitive essential amino acids, thereby depleting the nutritional value. This work deals with alkaline hydrolysis of human hair using acoustic and hydrodynamic cavitation, and comparison with the conventional method. The optimal operating conditions for highest efficiency was observed, for the hydrolysis of 1 g of sample hairs in 100 mL of solution, at 4:1 (KOH: hair) ratio, soaking time of 24 h, the ultrasonic power density of 600 W dm−3 (20 KHz frequency and input power 200 W) or hydrodynamic cavitation inlet pressure of 4 or 7 bars. Cavitation results in rupture of disulfide linkages in proteins and mechanical effects lead to cleavage of several hydrogen bonds breaking the keratin sheet structure in hair. Breakdown of bonds leads to a decrease in viscosity of the solution. 10% and 6% reduction in viscosity is obtained at optimal conditions for ultrasonic and hydrodynamic cavitation treatment, respectively. FTIR analysis of produced hair hydrolysate confirmed that the disulfide bonds in hair proteins are broken down during cavitation. The amino acid of hair hydrolysate, prepared using cavitation, has a relatively higher digestibility and nutritional value due to the enhancement of amino-acid content, confirmed using amino acid analysis. Cavitation assisted hair hydrolysate has a potential application in agricultural engineering as a fertilizer for improvement of the quality of the soil and land. Cavitation based hair hydrolysate can also be used as an environmentally friendly and economical source of essential amino acids and digestibles for animal or poultry feed.

Investigation of sludge solubilization and phosphorous release in anaerobic side-stream reactor with a low pressure swirling jet hydrodynamic cavitation treatment

In this study, the feasibility of a novel hydrodynamic cavitation (HC) system was evaluated to speed up the biological sludge reduction mechanisms of the anaerobic side-stream reactor (ASSR) process. In the first part of the research, HC was performed on ASSR sludge by using a low pressure swirling jet cavitation system, named Ecowirl – EW 25. The effects of the Ecowirl – EW 25 system, in terms of sludge solubilisation, disintegration degree and microbial activity, were investigated considering two different injection plates, respectively, with two and four injection slots and four different treatment times, from 10 to 80 minutes. The best results were achieved after 80 min of HC treatment, using the plate with two injection slots and with a specific supplied energy (SE) equal to 12670 kJ kg TSS-1. Respirometric tests showed an increase in the readily biodegradable COD through the HC treatment of sludge. Moreover, low endogenous decay rates (bH) were measured on the ASSR sludge for SE lower than 6340 kJ kg TSS-1 revealing that the sludge solubilization was due to a modification in the floc structure rather than a decrease in the biomass viability. In the second part of the research, the solubilized sludge, after HC treatment, was used as carbon substrate for the biological activity of bacteria into the ASSR, such as total phosphate accumulating organisms (TPAOs). Results revealed that the phosphorous releasing and uptake rate, obtained using the HC treated sludge as carbon source, were comparable with those obtained with the addition of a ready biodegradable carbon source such as acetate.

Oxidative treatment of crude pharmaceutical industry effluent by hydrodynamic cavitation

Abstract The present study investigates the oxidative technique of hydrodynamic cavitation (HC) for the treatment of a highly refractive, bulk drug industry effluent with an initial total organic carbon (TOC) content of 69960 mg/l. A qualitative insight into the pharmaceutical industry, drug production, and effluent characteristics is presented. Experiments on the undiluted effluent were conducted in accordance with central composite design (CCD). For the venturi-based HC studies, variation of pH (3.63-10.36), inlet pressure (2.95-13.04 bar), and treatment time (26.36-93.63 min.) were studied, besides investigating their effects on treatment efficiency. HC treatment yielded a maximum 25% reduction in TOC with a cavitational yield of 65.69 × 10-3 mg/J for an optimum combination of pH 7, inlet pressure 8 bar, cavitation number of 0.242, and treatment time 60 minutes (17 recirculations). Furthermore, synergetic effects of increasing inlet pressure and effluent temperature were quantified, and found to effectuate a maximum increase of 1781% in vapour pressure, and decrease of 77% in cavitation number. Lastly, effects of operating factors on treatment efficacy and the success of HC system were summarized.

Hydrodynamic cavitation of raw milk: Effects on microbial inactivation, physical and functional properties

The effects of hydrodynamic cavitation treatment of raw milk at different temperatures (outlet temperatures of 40, 50, 60 or 72 °C) were evaluated in relation to corresponding reference heat treatments. Physical and functional changes were studied and microbial inactivation was evaluated by the total bacterial count. Hydrodynamic cavitation reduced the mean milk fat globule size to 3.29–1.40 μm, depending on the treatment temperature. Treatment did not result in a significant increase in whey protein denaturation and did not affect acid gel formation. A reduction of >1 log unit in the total bacterial count was obtained, which was primarily ascribed to the temperature increase during treatment. Thus, this study illustrates that HC treatment can provide a heating unit allowing for simultaneous pasteurisation and reduction in MFG size, with minimal changes to the physical and functional properties of the milk.

Surfactant degradation using hydrodynamic cavitation based hybrid advanced oxidation technology: A techno economic feasibility study

Surfactant degradation is a challenging problem related to wastewater treatment. The source of such wastewater can be industrial or domestic, with concentrations varying in between 1 to 300 mg/L. Due to the sheer volume of such streams, both kinetics of degradation as well as scale of operation become the governing criteria for the success of a technology. In this work, the authors have reported for the first time, the possibility of treating surfactant (sodium dodecyl sulphate, SDS) laden wastewater using hydrodynamic cavitation (HC) technology. A systematic approach has been adopted whereby the following modus operandi were taken: (i) selection of orifice diameter for HC treatment, (ii) studying the effect of pH and inlet pressure for SDS degradation using HC, (iii) effect of varying SDS concentration (2, 5, 10 and 15 mg/L) and subsequent degradation studies, (iv) addition of H2O2 along with HC and optimization and (v) addition of Fenton at various ratio in the optimized HC systems. It was observed that (i) 1.6 mm was the optimum orifice diameter for carrying out HC process, (ii) pH = 2 and pressure = 5 bar were the optimized operating conditions for HC process, (iii) 5 g/L H2O2 was the optimized concentration for HC + H2O2 system, (iv) By coupling HC process with Fenton:H2O2 = 1:3 ratio, 99.46% SDS degradation was obtained within 60 min. This result is encouraging at laboratory scale and further investigation and understanding of such a technology can definitely help in providing scaled up solutions both for domestic and industrial applications.

High-pressure jet-induced hydrodynamic cavitation as a pre-treatment step for avoiding cyanobacterial contamination during water purification

Due to specific physical properties, hydrodynamic cavitation (HC) is assigned to the powerful technologies for treating the biotic contamination in water including cyanobacteria. Contaminated water stream (CWS) can be cavitated directly by passing through some HC device, or indirectly when high-pressure jet stream (HPJS) is directed against its flow. Relatively small HPJS stream can thus treat a big volume of CWS in a short time or even work in continuous mode. Cyanobacteria floating in the CWS are forced to flow through the mixing cavitation zone. Within 2 h after single HC treatment, cyanobacterial cell suspensions showed disintegration of larger colonies and enhanced biomass sedimentation. Additional pre-treatment of CWS with low amounts of hydrogen peroxide (H2O2; 33, 66 and 99 μmol/L) enhanced the effect of HC and led to further inhibition of cyanobacterial photosynthesis (maximum quantum yield of photosystem II decreased by up to 60%). The number of cyanobacterial cells in the treated CWS decreased continuously over 48 and 72 h, though some cells remained alive and were able to recover photosynthetic activity. The technique proposed (direction of a HPJS against a CWS and pre-treatment with low H2O2 concentrations) provides (i) effective removal of cells from the water column, and (ii) reduced contamination by organic compounds released from the cells (especially cyanotoxins) as the cell membranes are not destroyed and the cells remain alive. This process shows potential as an effective pre-treatment step in water purification processes related to cyanobacterial contamination.

Synergistic advance Fenton oxidation and hydrodynamic cavitation treatment of persistent organic dyes in textile wastewater

This is an investigation into the treatment of simulated Orange II sodium salt (OR2) contaminant in wastewater using jet-loop hydrodynamic cavitation in hybrid combination with hydrogen peroxide (H2O2) and nano zero valent iron (nZVI). A 69.8 % degradation of OR2 (10 mg/L) was achieved per hour in the jet-loop hydrodynamic cavitation system by itself (inlet pressure = 400 kPa, pH = 2, volume = 10 L). The combination of H2O2 and iron (II) sulfate in the jet loop hydrodynamic cavitation was not very effective. This is due to the possible scavenging effect of the iron (II) sulfate and H2O2 on the hydroxyl radical. However, the combinational treatment using an optimum amount of H2O2 and nZVI in the jet loop hydrodynamic cavitation resulted in 99 % decolouration of the OR2 solution within an hour treatment. 74 % mineralisation was also achieved as a function of % TOC reduction (400 kPa, pH 2, 1 mg/L H2O2, 1 mg/L nZVI, 1 h). The enhancement of the degradation with hydrogen peroxide, iron sulfate or nano zero valent iron led to the generation of nitrate ions and sulfate ion as evident by the UV spectrometer, TOC, FT-IR and GC–MS analysis. This result shows the synergistic enhancement in the mineralization of azo dye containing industrial wastewater during the combinational treatment with advanced Fenton oxidation (H2O2 and nZVI) in the jet loop hydrodynamic cavitation system.