Cell Wall Breakage Research Articles

Unlocking hidden potential of rice bran: Enzymatic treatment for enhancing techno-functional properties

Rice bran (RB) is a by-product with limited application due to technological constraints. Enhancing its technological functionality as potential food ingredient will improve the sustainability of rice production. The aim was to study the impact of enzymatic and thermal treatments on defatted rice bran using six distinct commercial enzymes (carbohydrases and proteases) and dry heating by evaluating its technological, nutritional and functional properties. Enzymatic treatment increased up to 208% the soluble dietary fiber content (8.19 g/100 g) of defatted RB. Moreover, the solvent retention capacity, including water, oil, sodium carbonate, and sucrose, exhibited a noteworthy increase across all treatments (p < 0.05). Bran color changed after treatments, increasing its luminosity (L*) and decreasing the value of a* in all cases, but b* decreased when treated with protein-acting enzymes while increased with carbohydrate-acting enzymes. Proteases played a pivotal role in reducing particle size and forming gels requiring minimal force for application. Microscopic analysis revealed that carbohydrases-treated samples exhibited prominent cell wall breakage, while protease-treated ones showed a gel-like surface with less distinct protein bodies and layered walls. These comprehensive study sheds new transformations brought about by these enzymatic interventions, offering valuable insights into the optimization of rice bran functionality.

The viable but non-culturable (VBNC) status of Shewanella putrefaciens (S. putrefaciens) with thermosonication (TS) treatment

Although thermosonication (TS) treatment has been widely used in food sterilization, the viable but non‐culturable (VBNC) of bacteria with TS treatment has still concerned potential food safety and public health. The molecular mechanism of VBNC status of bacteria with TS treatment is not clearly known. Therefore, in this study, we used Shewanella putrefaciens, which was a common putrefactive bacteria in aquatic products, to study the VBNC state of bacteria with TS treatment. Firstly, our results revealed that S. putrefaciens still could enter the VBNC state after TS treatments: 50 kHz, 300 W, 30 min ultrasonic treatment and 70 °C heating; Subsequently, we found the VBNC state of S. putrefaciens can resist the damage of TS treatment, such as cell wall break, DNA degradation, etc; Finally, four-dimensional data-independent acquisition-based proteomics showed that under VBNC state, S. putrefaciens upregulated functional proteins to resist TS treatment, such as: ribosomal proteins to accelerate the synthesis of stress proteins to counteract TS treatments, ornithine decarboxylase SpeF and MraY to repair TS treatment-induced damage, etc. Meanwhile, S. putrefaciens downregulates metabolic and transport functional proteins such as dehydrogenase to reduce the metabolism. Importantly, among those proteins, the ribosomal transcriptional regulatory protein family, such as rpsB, etc, may be the key proteins for S. putrefaciens entering VBNC state. This finding can provide some new strategies for preventing VBNC status of bacteria with TS treatment, such as: inhibition of key proteins, etc.

Synergistic effects of superfine grinding and high hydrostatic pressure on the contents, distribution, digestive behaviors and antioxidant activities of polyphenols in barley leaves

Barley leaves (BLs) naturally contained abundant phenolics, most of which are hardly completely released from food matrix during gastrointestinal digestion. Superfine grinding (SFG) and high hydrostatic pressure (HHP) are generally used to treat the functional plants due to their effectiveness to cell wall-breaking and improvement of nutraceutical bioavailability. Thus, this study investigated the synergistic effects of SFG and HHP (100, 300, 500 MPa/20 min) on the bioaccessbility of typical phenolics in BLs during the simulated in-vitro digestion. The results demonstrated that the highest bioaccessbility (40.98%) was found in the ultrafine sample with HHP at 500 MPa. CLSM and SEM confirmed SFG led to microstructurally rapture of BLs. Moreover, the recovery index of ABTS radical scavenging activity and FRAP of HHP-treated ultrafine and fine BLs samples maximumly increased by 53.62% and 9.61%, respectively. This study is expecting to provide the theoretical basis to improve the consumer acceptance of BLs.

Steam explosion pretreatment: Dramatic reduction in energy consumption for wheat bran grinding

Wheat bran has attracted attention for its high dietary fiber content with unique nutritional value. Grinding wheat bran into flour to produce whole wheat products effectively meets the surging demand for functional foods. Nonetheless, the grinding of high-tenacity wheat bran requires a huge amount of energy, which raises the costs of wheat bran flour. To reduce the energy consumption in wheat bran flour, we proposed a steam explosion pretreatment assisted wheat bran grinding process in this study. Steam explosion (0.5 MPa, 2 min) allows effective destruction of the wheat bran dense structure, reduces the mechanical properties of the wheat bran, and increases the yield and cell wall breakage rate of the wheat bran flour. The steam explosion pretreatment can reduce energy consumption by 57.6% in the wheat bran grinding process, which offers tremendous opportunities for making industrial production a success story. Besides, reconstituted whole wheat flour with the addition of steam-exploded wheat bran exhibited excellent processing properties. Overall, this work demonstrates that steam explosion pretreatment has a significant effect on wheat bran and drastically reduces energy consumption during wheat bran grinding, and steam-exploded wheat bran flour can upgrade the processability of reconstituted whole wheat flour, which holds tremendous application potential.

Sustainable ultrasound-assisted extraction of Polygonatum sibiricum saponins using ionic strength-responsive natural deep eutectic solvents

The sustainable extraction of saponins was investigated using natural deep eutectic solvents (NADESs) combined with ultrasound-assisted extraction. A novel NADES (butyric acid-urea) that was responsive to ionic strength was designed and used as the extractant. Ultrasound treatment and a catalyst ferric chloride with plant cell wall breaking function were applied to improve the extraction efficiency.Since the solubility of the NADES varied significantly with ionic strength, 95% of NADES was readily separated from the water phase after the addition of sodium chloride, while saponins remained in the water phase for easy collection. The reuse capacity of NADES, the eco-friendliness of the extraction method, and the antioxidant activity of the extract were further evaluated.NADES was continuously recovered and used to extract Polygonatum sibiricum powder: the yield of saponins did not decrease after five cycles of recovery and re-extraction. The penalty point on the “Eco-scale” suggested that the extraction method was “green” (i.e. eco-friendly).Compared with ethanol extracts, the NADES extracts showed a higher saponin concentration and antioxidant activity.The study can contribute to the sustainable and green extraction of hydrophilic active substances in the food and pharmaceutical industries.

Optimisation and modelling of ultrasonic-assisted extraction of canthaxanthin from Chromochloris zofingiensis using eutectic solvents

Carotenoids are well-known bioactive compounds and high-value nutritional molecules. Chromochloris zofingiensis, a unicellular green alga, is a promising source of commercial carotenoids owing to its robust growth, easy cultivation, and facile scale-up. However, this microalga has a very rigid three-layered cell wall that hinders extraction. Meanwhile, traditional extraction methods are complicated and cause serious pollution. To address these issues, a eutectic solvent (ES) was identified from 15 candidates for the ultrasonic-assisted extraction of canthaxanthin from C. zofingiensis for the first time. Remarkably, this hydrophobic ES comprising octanoic and decanoic acid displayed novel dual functions of breaking the cell wall and carotenoid extraction. Under the optimised extraction conditions obtained using a response surface methodology (ultrasound at 50 ℃ for 49 min, octanoic acid-to-decanoic acid molar ratio of 2.3:1, and solid-to-solvent ratio of 66.2 mg/mL), the maximum yield of canthaxanthin (60.5 μg/mL) was equal or superior to that using traditional organic extractant after grinding to break the cell wall. Furthermore, only the ES was employed as the extraction solvent, and the canthaxanthin content obtained by pre-grinding under the same condition (70.4 μg/mL) was much higher than that of grinding and extraction with ethanol (62.2 μg/mL). Possible mechanisms of cell wall breakage and component extraction were investigated based on extraction kinetic analysis, molecular dynamics simulation, and scanning electron microscopy observation. This ES is non-volatile and environmentally friendly, making it a simple, sustainable, and effective alternative extractant for carotenoids in microalga. There is considerable potential for its industrial-scale development and applications in various fields such as food, medicine, and cosmetics.

Physiological responses of plants to in vivo X-ray damage from X-ray fluorescence measurements: insights from anatomical, elemental, histochemical, and ultrastructural analyses.

X-ray fluorescence spectroscopy (XRF) is a powerful technique for the in vivo assessment of plant tissues. However, the potential X-ray exposure damages might affect the structure and elemental composition of living plant tissues, leading to artefacts in the recorded data. Herein, we exposed in vivo soybean (Glycine max (L.) Merrill) leaves to several X-ray doses through a polychromatic benchtop microprobe X-ray fluorescence spectrometer, modulating the photon flux density by adjusting either the beam size, current, or exposure time. Changes in the irradiated plant tissues' structure, ultrastructure, and physiology were investigated through light and transmission electron microscopy (TEM). Depending on X-ray exposure dose, decreased K and X-ray scattering intensities and increased Ca, P, and Mn signals on soybean leaves were recorded. Anatomical analysis indicated the necrosis of epidermal and mesophyll cells on the irradiated spots, where TEM images revealed the collapse of cytoplasm and cell wall breaking. Furthermore, the histochemical analysis detected the production of reactive oxygen species and the inhibition of chlorophyll autofluorescence in these areas. Under certain X-ray exposure conditions, e.g. high photon flux density and long exposure time, XRF measurements may affect the soybean leaves structures, elemental composition, and cellular ultrastructure, inducing programmed cell death. Our characterization shed light on the plant's responses to the X-ray-induced radiation damage and might help to establish proper X-ray radiation limits and novel strategies for in vivo benchtop-XRF analysis of vegetal materials.

Ultrasound-assisted extraction and characteristics of maize polysaccharides from different sites

Antitumor, antioxidant, hypoglycemic, and immunomodulatory properties are all exhibited by maize polysaccharides. With the increasing sophistication of maize polysaccharide extraction methods, enzymatic method is no longer limited to a single enzyme to extract polysaccharides, and is more often used in combination with ultrasound or microwave, or combination with different enzymes. Ultrasound has a good cell wall-breaking effect, making it easier to dislodge lignin and hemicellulose from the cellulose surface of the maize husk. The “water extraction and alcohol precipitation” method is the simplest but most resource- and time-consuming process. However, the “ultrasound-assisted extraction” and “microwave-assisted extraction” methods not only compensate for the shortcoming, but also increase the extraction rate. Herein, the preparation, structural analysis, and activities of maize polysaccharides were analyzed and discussed.

Antioxidative Activities of Micronized Solid-State Cultivated Hericium erinaceus Rich in Erinacine A against MPTP-Induced Damages.

The Lion's mane mushroom (Hericium erinaceus, HE) is a traditional medical mushroom with high nutritional and economic value. HE possesses anticancer, antimicrobial, antioxidant, immunomodulating, neurotrophic, and neuroprotective activities. The present study evaluated the protection and antioxidative activities of micronized mycelium of HE (HEM) in mice treated with 1-methyl-4-phenylpyridinium (MPTP). HEM was cultivated via solid-state fermentation and micronized using cell wall-breaking technology to increase its bioavailability when ingested. Erinacine A, the bioactive compound in the HEM, played a pivotal role in antioxidant defense. We found that micronized HEM could recover the dopamine level in the mice striatum in a dose-dependent manner that had been greatly reduced during MPTP treatment. Moreover, the malondialdehyde (MDA) and carbonyl levels were reduced in the livers and brains of the MPTP + HEM-treated groups compared with the MPTP group. Additionally, antioxidant enzyme activities, including catalase, superoxide dismutase (SOD), glucose-6-phosphate dehydrogenase (G6PDH), and glutathione reductase (GRd), were elevated after the administration of HEM in MPTP-treated mice in a dose-dependent manner. Taken together, our data indicate that HEM cultivated via solid-state fermentation and processed with cell wall-breaking technology showed an excellent antioxidant efficacy.

Cell wall breaking of Haematococcus pluvialis biomass facilitated by Baijiu jiuqu fermentation with simultaneously production of beverages

The microalgae Haematococcus pluvialis is a commercial source of natural astaxanthin. However, mature cells develop rigid three-layer wall structures and a repulsive odor. This study applied a liquid static fermentation system to screen hydrolyzing microorganisms for cell wall hydrolysis. Baijiu jiuqu and Gutian hongqu were found to have promising potential for application. The fermentation using 2% baijiu jiuqu and 2% glucose for pre-activation achieved comparable recovery of carotenoids to homogenizer disruption methods and produced stable fragrance which may be attributed to ethyl octanoate, hexyl formate, and phenethyl butyrate, as revealed by gas chromatography-mass spectrometry analysis. The abundance of astaxanthin molecules was slightly affected by fermentation with fold change < 2, while molecules with higher fold change (>10) were mainly carbohydrates, lipids, and steroids proving the safety of the fermentation. This study provides a new scheme for the biorefining of Haematococcus. pluvialis, potentially contributing to the industrial production of natural astaxanthin.

Chemical digestion method to promote activated sludge cell wall breaking and optimize the polyhydroxyalkanoate (PHA) extraction process

A novel protocol for the recovery of PHA from mixed-cultures proposed. In this experiment, activated sludge for PHA synthesis was investigated and a two-stage chemical digestion method was used for activated sludge to improve the yield of PHA. The highest PHA extraction combination that could be obtained in this experiment was sodium hypochlorite(NaClO) plus sodium dodecyl sulfate (SDS), and the optimal concentration of NaClO solution was 25 % (v/v), and the ratio of the dry weight of activated sludge to SDS was 1:2. The recovery and purity of PHA were 72.14 % and 54.47 %, respectively. The reaction time between NaClO and activated sludge affects the recovery of PHA, and the optimal reaction time of NaClO was experimentally obtained as 30 min. The purity of the PHA extract obtained after purification using methanol was improved.

One-Pot, Water-Based Disruption of Cell Walls and Astaxanthin Extraction from Haematococcus pluvialis by Mechanochemistry

In this study, a new method for efficient astaxanthin extraction from Haematococcus pluvialis (H. pluvialis) by mechanochemistry was developed. The method is a water-based and water-reused one-pot procedure, which can simultaneously achieve cell wall breaking and astaxanthin extraction from H. pluvialis. In addition, the optimized process parameters were determined based on studies of different conditions; an elevated recovery of astaxanthin extraction yield (91.6 wt %) was achieved using 1 g of dried H. pluvialis and 4 mL of water at 200 rpm in 30 min with a ball-to-material ratio of 90 (m/m). The underlying mechanism revealed the extraction process by electron microscopy, thermodynamic analysis, spectroscopic determination, and particle size distribution analysis. The results of this study followed the sustainability criteria that include the concept of circular economy and contribute to the achievement of items 3, 6, 12, and 14 of the UN Sustainable Development Goals.1 This method innovates a new way for green and gentle extraction of natural fatty-soluble substances.

Fungal Secondary Metabolites/Dicationic Pyridinium Iodide Combinations in Combat against Multi-Drug Resistant Microorganisms.

The spread of antibiotic-resistant opportunistic microbes is a huge socioeconomic burden and a growing concern for global public health. In the current study, two endophytic fungal strains were isolated from Mangifera Indica roots and identified as Aspergillus niger MT597434.1 and Trichoderma lixii KU324798.1. Secondary metabolites produced by A. niger and T. lixii were extracted and tested for their antimicrobial activity. The highest activity was noticed against Staphylococcus aureus and E. coli treated with A. niger and T. lixii secondary metabolites, respectively. A. niger crude extract was mainly composed of Pentadecanoic acid, 14-methyl-, methyl ester and 9-Octadecenoic acid (Z)-, methyl ester (26.66 and 18.01%, respectively), while T. lixii crude extract's major components were 2,4-Decadienal, (E,E) and 9-Octadecenoic acid (Z)-, and methyl ester (10.69 and 10.32%, respectively). Moreover, a comparative study between the fungal extracts and dicationic pyridinium iodide showed that the combination of A. niger and T. lixii secondary metabolites with dicationic pyridinium iodide compound showed a synergistic effect against Klebsiella pneumoniae. The combined formulae inhibited the bacterial growth after 4 to 6 h through cell wall breakage and cells deformation, with intracellular components leakage and increased ROS production.

GoSAMTs are required for pectin methyl-esterification and mucilage release in seed coat epidermal cells.

GoSAMTs play a role in the methylation of polysaccharides synthesized by the Golgi. Pectin homogalacturonan (HG) methyl-esterification is essential for the proper function of this polysaccharide in cell walls. In order to better understand the role of GoSAMTs in HG biosynthesis, we analyzed mucilage methyl-esterification in gosamt mutants. To determine the function of GoSAMT1 and GoSAMT2 in HG methyl-esterification we utilized epidermal cells of seed coats, as these structures produce mucilage, which is a pectic matrix. We evaluated differences in seed surface morphology and quantified mucilage release. We measured methanol release, and used antibodies and confocal microscopy to analyze HG methyl-esterification in mucilage. We observed morphological differences on the seed surface and delayed, uneven mucilage release in gosamt1-1gosamt2-1 double mutants. We also found changes in the distal wall length indicating abnormal cell wall breakage in this double mutant. Using methanol release and immunolabeling, we confirmed that GoSAMT1 and GoSAMT2 are involved in HG methyl-esterification in mucilage. However, we did not find evidence of decreasing HG in the gosamt mutants. Confocal microscopy analyses detected different patterns in the adherent mucilage and a greater number of low-methyl-esterified domains near the seed coat surface, which correlates with a greater number of "egg-box" structures in this region. We also detected a shift in the partitioning between the Rhamnogalacturonan-I soluble and adherent layers of the double mutant, which correlated with increased amounts of arabinose and arabinogalactan-protein in the adherent mucilage. The results show that the HG synthesized in gosamt mutant plants is less methyl esterified, resulting in more egg-box structures, which stiffen the cell walls in epidermal cells and change the rheological properties of the seed surface. The increased amounts of arabinose and arabinogalactan-protein in adherent mucilage, also suggests that compensation mechanisms were triggered in the gosamt mutants.

Optimization of cell wall breaking process of the microalgae Haematococcus pluvialis.

Haematococcus pluvialis can synthesize and accumulate astaxanthin, and is regarded as the organism with the highest content of astaxanthin in the current nature. However, only when Haematococcus pluvialis cell wall is broken can the astaxanthin be effectively extracted. Therefore, the breaking of the hard cell wall of Haematococcus pluvialis becomes the key difficulty hindering the extraction of astaxanthin. In this study, the cell wall was broken using enzyme digestion and mechanical action and the response surface methodology was used to optimize the cell wall breaking process. Taking the cell wall breaking rate of Haematococcus pluvialis as the index, the single factor experiment was used to calculate the effects of solid-liquid ratio, enzyme type and dosage, digestion temperature, digestion pH and hydrolysis time on the cell wall breaking rate. When the ultrasonic power is 175 W and the ultrasonic time is 2 min, the highest wall breaking rate is 68.8%. The high pass tissue grinder has the best wall breaking efficiency of 70.3% in 6 min and 70 Hz. In combination with single factor analysis and response surface analysis, the optimum enzyme digestion conditions were determined as follows: the ratio of material to liquid was 1:150, the amount of enzyme was 1%, the ratio of Pectinase to cellulase was 1:1, and the optimum hydrolysis conditions were as follows: hydrolysis time 5 h, hydrolysis temperature 55 °C, pH 5.5; and the amount of enzyme was 1%. The theoretical wall breaking rate is 77.2%, the actual extraction rate is 75.4%, and the relative error is 2.2%. In conclusion, the method of using combined enzyme to break the wall of Haematococcus pluvialis is simple, mild, green and efficient. It can be used in the processing of broken wall.

Pesticin-Like Effector VgrG3cp Targeting Peptidoglycan Delivered by the Type VI Secretion System Contributes to Vibrio cholerae Interbacterial Competition.

Vibrio cholerae can utilize a type VI secretion system (T6SS) to increase its intra- and interspecies competition. However, much still remains to be understood about the underlying mechanism of this intraspecies competition. In this study, we isolated an environmental V. cholerae strain E1 that lacked the typical virulence factors toxin-coregulated pilus and cholera toxin and that encoded a functional T6SS. We identified an evolved VgrG3 variant with a predicted C-terminal pesticin-like domain in V. cholerae E1, designated VgrG3cp. Using heterologous expression, protein secretion, and peptidoglycan-degrading assays, we demonstrated that VgrG3cp is a T6SS-dependent effector harboring cell wall muramidase activity and that its toxicity can be neutralized by cognate immunity protein TsiV3cp. Site-directed mutagenesis proved that the aspartic acid residue at position 867 is crucial for VgrG3cp-mediated antibacterial activity. Bioinformatic analysis showed that genes encoding VgrG3cp-like homologs are distributed in Vibrio species, are linked with T6SS structural genes and auxiliary genes, and the vgrG3cp-tsiV3cp gene pair of V. cholerae probably evolved from Vibrio anguillarum and Vibrio fluvialis via homologous recombination. Through a time-lapse microscopy assay, we directly determined that cells accumulating VgrG3cp disrupted bacterial division, while the cells continued to increase in size until the loss of membrane potential and cell wall breakage and finally burst. The results of the competitive killing assay showed that VgrG3cp contributes to V. cholerae interspecies competition. Collectively, our study revealed a novel T6SS E-I pair representing a new T6SS toxin family which allows V. cholerae to gain dominance within polymicrobial communities by T6SS. IMPORTANCE The type VI secretion system used by a broad range of Gram-negative bacteria delivers toxic proteins to target adjacent eukaryotic and prokaryotic cells. Diversification of effector proteins determines the complex bacterium-bacterium interactions and impacts the health of hosts and environmental ecosystems in which bacteria reside. This work uncovered an evolved valine-glycine repeat protein G3, carrying a C-terminal pesticin-like domain (VgrG3cp), which has been suggested to harbor cell wall hydrolase activity and is able to affect cell division and the integrity of cell wall structure. Pesticin-like homologs constitute a family of T6SS-associated effectors targeting bacterial peptidoglycan which are distributed in Vibrio species, and genetic loci of them are linked with T6SS structural genes and auxiliary genes. T6SS-delivered VgrG3cp mediated broad-spectrum antibacterial activity for several microorganisms tested, indicating that VgrG3cp-mediated antimicrobial activity is capable of conferring bacteria a competitive advantage over competitors in the same niches.

Effects of Pre-Heating Between Controlled Temperature Microwave Heating and Hot Air Oven Heating in Protein Extraction Process of Soybeans

Abstract Heating is an important treatment before protein extraction process. Rapid heating of microwave heating (MW) was investigated to compare with hot air oven (HA) heating prior to protein extraction in soybeans. Heating temperature was controlled at 50°C, with the heating time of 15, 30, 45, 60 and 75 min. The control treatment was no heat treatment. The treated samples were analyzed i) the total protein using Kjeldahl method, ii) the protein soluble by Bradford method and iii) cells microscope investigated by scanning electron microscope (SEM). The results were found that the pretreatment of 75 min microwave (MW75) heating provided the highest protein with the amount of absorbance value and total protein of 3.0365 ± 0.004 mg mL-1 and 3.70 ± 0.01% respectively. The lowest protein extraction of 2.7707 ± 0.020 mg mL-1 and 3.38 ± 0.005% total protein value occurred in the condition of 15 mines hot air oven (HA15) heating. The investigation using scanning electron microscope (SEM) revealed that protein extraction correlated with the enlargement and breakage of cell wall and endosperm caused by microwave heating rather than hot air oven heating. The rapid heating of microwave and heating time influenced the amount of extracted protein. Keywords: Soybean, Protein, Microwave, Hot air, Heating

Steam Explosion Pretreatment for Improving Wheat Bran Extrusion Capacity.

Extrusion improves the texture of wheat bran and enhances its product edibility, making it a promising processing method. However, the extrusion performance of wheat bran without any treatment is not satisfactory and limits the utilization of wheat bran in food processing. In this study, steam explosion pretreatment was used to treat wheat bran to investigate its promotion of wheat bran extrusion. The results showed that steam explosion could increase the extrusion ratio of wheat bran extrudate by 36%. Grinding the steam-exploded wheat bran extrudate yields wheat bran flour with smaller particle sizes and higher cell wall breakage. Fourier transform infrared spectroscopy and chemical composition results revealed that steam explosion degraded insoluble dietary fiber and disrupted the dense structure of the cell wall in wheat bran. The water-extracted arabinoxylan and soluble dietary fiber content of steam-exploded wheat bran were 13.95% and 7.47%, respectively, improved by 1567.42% and 241.75% compared to untreated samples. The total phenol and flavonoid contents, water solubility index, and cation exchange capacity of steam-exploded wheat bran extrudate were all superior to raw wheat bran extrudate. In summary, this study demonstrates that steam explosion improves the extrusion capacity of wheat bran and facilitates its utilization.

Cell wall fracture mechanism in ultrasonic-assisted cutting of honeycomb materials

Revealing the ultrasonic cutting mechanism of honeycomb composite is important for determining the acoustic parameters of the ultrasonic system and selecting the parameters of the cutting process. Understanding more details of the stress on the cell wall from ultrasonic vibrating tool and the conditions for cell wall breakage is essential to study the machining mechanism. According to the evolution of contact state between the straight edge cutter and the honeycomb cell wall in a cycle, the cutting force acting on the cell wall is divided into three stages: transverse cutting load action, longitudinal cutting load action, and no cutting load action. The cell wall deflection and stress equations under transverse cutting load were established by applying elastic thin plate small deflection theory. The deformation and fracture characteristics of the honeycomb cell wall were analyzed by combining the analytical and the finite element model. The results showed that the ultrasonic vibration of the cutter greatly improved the stiffening effect of the cell wall and its fracture was caused by the deflection under the transverse cutting load, which exceeded the maximum allowable deformation after local stiffening. In addition, with only longitudinal cutting load, it was difficult to break the critical buckling state that leads to cell wall fracture.

Electrochemical treatment of waste activated sludge: Volume reduction mechanism and improvement possibilities

In this study, a PbO2 plate electrode was synthesized and optimized for the electrochemical treatment application of waste activated sludge from a municipal wastewater treatment. The sludge dewaterability and mass reduction with different electrolysis time and voltage were quantified to evaluate the treatment efficiency. The mechanism of cell breaking was studied by evaluating different electrochemical oxidation pathways. Results showed that the electrochemical treatment at a voltage of 25 V and electrolysis time of 120 min improved the dewaterability of the sludge by 35.9%, and the concentration of mixed liquor suspended solids (MLSS) was reduced by 33.7%. Using Scanning Electron Microscope (SEM) and Cell fluorescence staining experiments, the impact on the integrity of sludge cells was evaluated. Results showed that electrochemical process clearly destroyed the sludge cell structure and lead to the cell death. Further investigation revealed that hydroxyl radicals (·OH) and sulfate radicals (SO4·-) produced during the electrochemical treatment played a major role in the cell wall-breaking, while chloride ions (Cl-) in the electrolyte significantly enhanced the effect due to formation of chloride-related oxidants. The PbO2 electrode was modified by chemically reduced graphene oxide (RGO) to improve the ·OH production capacity. Results showed that the PbO2(0.05 RGO by wt.%) electrode had the highest ·OH production rate (81.7 μmol/(cm2·min)). The electrode improved the removal of MLSS and MLVSS by 11.3% and 11.5%, respectively. And the sludge dewatering and cell destruction were enhanced by 7% and 15.1%, respectively. Adding more NaCl was confirmed as an effective method to improve the electrochemical performance of sludge treatment mainly due to the higher content of active Cl- species formed.