Heat Pretreatment Research Articles

Thermal pretreatment of Lantana camara for improved biogas production: Process parameter studies for energy evaluation

The rigid lignocellulosic structure of Lantana camara impedes the hydrolysis phase and reduces the biogas production during anaerobic digestion of Lantana camara. Hence, the current study focuses on the impact of various heating pretreatment techniques, viz., hot air oven (HAO), autoclave (ATC), hot water bath (HWB), and microwave (MCW) on L. camara to speed up hydrolysis and boost up biogas production. ATC pretreatment of L. camara was witnessed to be most efficient compared to HAO, MCW, and HWB pretreatment. ATC pretreatment enhanced the solubilization (45.44%), and an increment in volatile fatty acids (VFA) was observed (56.75%) at 110 °C for 80 min when correlated to the untreated (control). Cumulative methane production following ATC pretreatment had risen to 3656 mL in 5 weeks from 2895 mL in 7 weeks. Thermal pretreatment of Lantana camara broke down the rigid lignocellulosic structure, accelerating the hydrolysis stage and improving biogas production simultaneously. To the best of our knowledge, this is the first thermal pretreatment study conducted on Lantana camara for biogas production.

Assessment of Electrothermal Pretreatment of Rambutan (Nephelium lappaceum L.) Peels for Producing Cellulose Fibers.

Agroindustrial wastes are renewable sources and the most promising sustainable alternative to lignocellulosic biomass for cellulose production. This study assessed the electrothermal pretreatment of rambutan peel (RP) for producing cellulose fibers. The pretreatment was carried out by Ohmic heating at a solid-to-liquid ratio of 1:10 (w/v) in a water/ethanol (1:1, v/v) mixture as the electrical transmission medium at 60 ± 1 °C for different holding times (15, 30, and 60 min). Ohmic heating did not significantly influence the total fiber yield for the various holding times. However, the compositions of the samples in terms of extractives, lignin, hemicellulose, and α-cellulose content were significantly influenced. In addition, the electrothermal pretreatment method reduced the bleaching time of RP by 25%. The pretreated fibers were thermally stable up to 240 °C. Ohmic heating pretreatment times of 15 and 30 min were found most promising, reducing the required bleaching chemicals and increasing the α-cellulose yield. The pretreated bleached cellulose fibers had similar properties to nontreated bleached fibers and could be efficiently processed into stable gels of strong shear-thinning behavior with potential application as rheology modifiers in food products. Our results demonstrate that rambutan peel could serve as a promising sustainable alternative to woody biomass for cellulose production. Ohmic heating meets the requirements for industrial applications as it is eco-friendly, improves the efficiency and energy consumption in fiber processing, and could as well be included in the processing of similar food wastes.

Adhesion and corrosion resistance of polycaprolactone coating on NiTi alloy surface after alkali heat pretreatment

Selective laser melting of nickel-titanium alloy (SLM-NiTi) can precisely control the size of the sample molding structure and has attracted extensive attention due to its special superelasticity and shape memory effect. However, the biological inertness and poor corrosion resistance of SLM-NiTi alloy limit their wide application as biomedical implant materials. In this study, polycaprolactone (PCL) coating was prepared on SLM-NiTi alloy by dipping and pulling method, and the effects of alkali heat pretreatment on the morphology, adhesion, corrosion resistance, long-term stability and biomineralisation of the PCL coatings were investigated. The results showed that PCL coating can substantially improve the performance of SLM-NiTi alloy, and the PCL coating after alkali heat pretreatment has higher adhesion (increased from 1,747 to 2,498 mN) and lower corrosion current density (reduced by about an order of magnitude compared to PCL coating alone). In addition, the necessary stability, biomineralisation and biocompatibility ability of coatings were also further improved. Therefore, the alkali heat pretreated PCL-coated SLM-NiTi alloy has good application prospects in implants due to its superior properties.

Fusion of Vermicompost and Sewage Sludge as Dark Fermentative Biocatalyst for Biohydrogen Production: A Kinetic Study

The present study explores the synergy between vermicompost and the anaerobic sewage sludge as inoculum for biohydrogen production using food waste as a substrate. Experiments were designed and performed in two phases of operation. In the first phase, the vermicompost (VC) was used as inoculum and food waste as substrate at three different organic loading rates of 10 gVS/L (VC1), 20 gVS/L (VC2), and 30 gVS/L (VC3). In the second phase of operation, the inoculums were combined with a proportion of 50% (VC+AS). The study showed an effective biohydrogen production of 20 gVS/L when the mixing ratio of vermicompost and anaerobic sludge was 50:50. The results inferred that effective synergy was observed between the combined consortia of the inoculum, which induces a more effective metabolic pathway for enhanced hydrogen production. H2 production was 33 mL/gVS (VC1), 48 mL/gVS (VC2), 35 mL/gVS (VC3), 46 mL/gVS (AS), and 50 mL/gVS (VC+AS). Heat pretreatment (100–120 °C) of the inoculum suppresses the methane-producing microorganisms and increases the hydrogen-producing microbes. In addition to hydrogen production, different metabolites are formed in the liquid phase, such as acetic acid, butyric acid, and propionic acid of 2.957 g/L, 4.286 g/L, and 2.123 g/L, respectively, with an energy content of 257 J/day with VC+AS. In addition, a kinetic model was studied for the cumulative hydrogen production curves using the modified Gompertz model, and the fit infers that the experimental data fitted well, with high coefficients of determination for VC+AS (R2 (G) > 0.99).

Hythane and methane production in a multistage anaerobic hythane reactor (MAHR): Stage separation, functional microbe selection, thermodynamics, and kinetics

The establishment of a multistage anaerobic hythane reactor (MAHR) that integrates biohythane and biomethane production into a single reactor demonstrates promising potential for simultaneously producing hythane and methane. However, separating hythane and methane production in a single reactor remains a challenge, and stages separation in MAHR system is not well understood. Moreover, the necessity to heating pretreatment of the inoculum for acidogenesis and hythane production is impractical for the full-scale application of MAHR due to the extra economic and energy input. Therefore, heating preselected and not preselected inocula were adopted in this study to reveal the biofuel production performance and the mechanisms of stage separation in MAHRs with different inoculum strategies. Results indicated that stable hythane and methane production of MAHR without inoculum preselection could be achieved and maintained after a longer start-up period compared to the preselected inoculum condition. A comparable hythane and methane production and organics conversion performance were observed in the two MAHRs during stable period, in which hythane with a suitable hydrogen concentration (5%-25%) and methane with a high concentration (57%-75%) were produced. Supported by the more stable microbial correlation networks, MAHR without inoculum preselection suggested a higher methane production rate (13.5 ± 2.8 L/L/d) and was resistant to organic loading shock (80 g COD/L/d). Furthermore, microbial diversity, thermodynamics, and kinetic analysis revealed that the stage separation was highly dependent on microbial dynamics, metabolism characteristics, and reactor configurations. Acetogens (Desulfovibrio and Syntrophobacter) and aceticlastic methanogens (Methanosaeta and Methanosarcina) were more likely to wash out form the hythane production zone (Mh) and be enriched in the methane production zone (Mm) compared to acidogens (Streptococcus, Rikenellaceae_RC9_gut_group, Bacteroides, etc.) and hydrogenotrophic methanogens (Methanobacterium and Methanobrevibacter). The results from this study deepened the understanding of functional microbial community dynamics and stage separation mechanisms, which provided insights into the design, start-up, and full-scale operation of MAHR.

The effect of Joule heating on collapse and water absorption of wood

ABSTRACT The effect of Joule heating on collapse, shrinkage, water absorption and compressive strength of timber was investigated. Results indicate that the tangential and volumetric collapse reduced significantly by ∼53% and ∼48%, respectively, with Joule heating in Eucalyptus nitens. Maximum tangential shrinkage was significantly lower, due to the reduction of collapse in Joule heated samples, as normal shrinkage was not affected by Joule heating. Reduction in collapse was achieved without a statistically significant increase in water absorption capacity or a decrease in compressive strength. Further, the estimated costs for Joule heating pre-treatment were estimated to be competitive compared to conventional steam recovery of collapse.

Enhanced volatile fatty acid production from anaerobic fermentation of waste activated sludge by combined sodium citrate and heat pretreatment

In this study the combination pretreatment of sodium citrate (SC) and heating was investigated to enhance the volatile fatty acid (VFA) production during anaerobic fermentation of waste activated sludge (WAS). The results showed that the combined pretreatment (0.3 g-SC/g-TSS + at 121 ℃ for 30 min) resulted to the maximum VFA yield of 354.5 mg-COD/g-VS, which was 16.4, 6.0 and 2.0-fold of that of control, with sole SC and sole heat pretreatment, respectively. Meanwhile, the combined pretreatment greatly improved the proportion of acetate and butyrate, while the production of propionate significantly decreased. Mechanism analysis indicated that the combined pretreatment effectively promoted WAS disintegration and solubilization. Moreover, the heat pretreatment exhibited superior performances to the SC pretreatment on release of organic matters and enhancement of VFA production in the combined pretreatment. The microbial analysis revealed that with the combined pretreatment the microbial community shifted toward hydrolysis-acidification, such as Enterobacter and Macellibacteroides.

Factors associated with soils suppressive to black scurf of potato caused by Rhizoctonia solani

Soils in which disease fails to develop despite pathogen presence are considered disease-suppressive. They offer sustainable, effective protection to plants against infection by soil-borne pathogens. Naturally disease-suppressive soils have been reported for diseases of a diverse range of agricultural crops worldwide yet the underlying mechanisms of disease suppression are still not completely understood. Two large greenhouse experiments, conducted during 2017/18 (Year 1) and 2018/19 (Year 2), determined that soils naturally suppressive to stem canker and black scurf of potato (caused by Rhizoctonia solani) are present in vegetable-arable cropping soils of the Auckland and Waikato regions of New Zealand. Soil was pre-treated with heat prior to inoculation with R. solani and compared with untreated and uninoculated controls to ascertain if stem canker and black scurf suppression was ‘general’, or ‘specific’ (i.e. transferable; possibly involving specific microorganisms). Rhizoctonia solani inoculation was also combined with transfer of one part test soil to nine parts of a known disease-conducive soil. Abiotic factors such as soil texture and organic matter content influenced black scurf incidence and severity. Soil microorganisms were also involved in disease suppression since black scurf incidence and severity markedly increased when they were eliminated or reduced by soil heat pre-treatment. Microbial profiling of the soils through sequencing revealed that taxa of geographically close soils of the same type had similar fungal and bacterial community structure and diversity even though they differed in their capacity to suppress black scurf. These results suggest that although the soil microbiome as a whole, was mainly responsible for soil disease suppressiveness, certain bacterial genera or species may play a role in black scurf suppression.

Hydrolysis of Mixed Sugarcane Bagasse and Rice Husk Using Cellulase Enzyme for Reducing Sugar Production

Reducing sugar can be produced from lignocellulosic raw materials. The content of polysaccharides such as cellulose, hemicellulose, and starch will be broken down into simpler carbohydrates. This study used a mixture of sugarcane bagasse and rice husks as lignocellulosic raw materials. The lignin content in the raw material must be removed through delignification or pretreatment so that enzymes can access cellulose and hemicellulose. This study used a physics-chemical pretreatment method, in which lignocellulosic material soak in 3% NaOH then heated with microwave and boiling water. The next process is enzymatic hydrolysis with variations of cellulase enzymes activity 0.434, 0.871, 2.61, and 3.49 FPU/g mixture of bagasse and rice husks. The cellulase enzyme used in this study was also derived from the fungus Trichoderma viride. Analysis of the sugar concentration resulting from hydrolysis used the DNS method with the 3.5-dinitrosalicylic acid reagent. The concentration of sugar from hydrolysis using a variety of enzymes with microwave heating pretreatment and boiling water pretreatment obtained the highest results which were the same at the addition of enzyme activity 3.49 FPU/g substrate at 24 hours, namely 4.077 g/L and 15.18 g/L. The optimum time for enzymatic hydrolysis is 12 hours and optimum enzyme activity is the addition of enzyme activity 2.61 FPU/g. The average concentration of sugar hydrolyzed by the addition of Trichoderma viride solution in pretreatment using microwave heating was 0.7611 g/L with a yield of 21.01 mg sugar/g substrate and with pretreatment in boiling water obtained 0.8679 g/L with a yield of 23.95 mg sugar/g substrate.

Enhancement of bioactive compounds and oxidation stability of soybean oil by enrichment with tocols and γ‐oryzanol extracted from rice bran using ultrasound and ohmic heating

Soybean oil is beneficial from a nutritional viewpoint; however, the high concentration of polyunsaturated fatty acid presents a high risk of oxidation. This study incorporated α- and γ-tocopherols and γ-oryzanol as natural antioxidants from rice bran into soybean oil to improve oxidation stability of the oil using ohmic heating-assisted ultrasound extraction. Moisturized bran (30% wet basis) was pretreated using an ohmic heater at 100 and 200 V/cm before ultrasound extraction using soybean oil as a green solvent. Raw and steamed rice bran extracted by ultrasound without ohmic heating were used as controls. Enriched soybean oil obtained from ohmic heating pretreatment gave the highest concentration of α- and γ-tocopherols, γ-oryzanol, and antioxidant activities with low concentrations of free fatty acids, thiobarbituric acid, and peroxide values. Results suggested that ohmic heating-assisted ultrasound extraction showed potential to enrich soybean oil with bioactive compounds. Practical applications Soybean oil can be enriched with tocols and γ-oryzanol from rice bran to increase oil quality and oxidative stability. Ohmic heating was applied to assist ultrasound extraction of tocols and γ-oryzanol from rice bran. Extraction of edible vegetable oils using ohmic heating-assisted ultrasound is an alternative green process to improve oil quality and produce functional vegetable oils enriched with value-added compounds.

Comparative anaerobic digestion of sewage sludge at different temperatures with and without heat pre-treatment

Anaerobic digestion of sewage sludge is generally conducted under mesophilic (around 35 °C) or thermophilic (around 55 °C) conditions, whereas it is conducted at lower temperatures in some wastewater treatment plants without heating. In this study, we compared the anaerobic digestion of sewage sludge at 15, 25, 30, 35, 45, and 55 °C following hyperthermophilic pre-treatment at 80 °C for 24 h. Laboratory-scale reactors were operated continuously for more than 1000 days, and batch experiments were performed to evaluate the reaction kinetics. Biogas production rates at 15 °C with and without pre-treatment divided by that at 35 °C without pre-treatment were 0.73 and 0.78, respectively. The dewaterability of the digested sludge was evaluated by the capillary suction time (CST). The CST was approximately 50 s at 15 °C with and without pre-treatment and was slower than the CST at 35 °C. Compared to the shear rate, viscosity was higher at lower temperatures; however, it decreased with pre-treatment, which reduced the energy required for mixing in the reactors. Pre-treatment eliminated Escherichia coli from the sludge; however, E. coli (approximately 105 colony forming unit/g-total solids) was detected after digestion at temperatures ≤30 °C. Pre-treatment was also useful to replace a part of heat treatment required for digested sludge before it was used as fertilizer. Gene sequencing analyses indicated the effects of pre-treatment and digestion temperature on the microbial community in the digested sludge. Co-generation of biogas is useful to obtain both electricity and heat; however, heat from co-generation is sometimes limited. To maximize electricity recovery, the use of low temperature digesters has the potential to reduce fuel costs. The results indicate that anaerobic digestion at low temperatures with or without heat pre-treatment can be an efficient and cost-effective method of treating sewage sludge.

Drought Stress Pre-Treatment Triggers Thermotolerance Acquisition in Durum Wheat

Durum wheat is strongly affected by climatic constraints such as high temperatures and drought, which frequently lead to yield reduction. Damages due to high temperatures are related to plant thermotolerance, a trait determined by two components: basal and acquired thermotolerance. In this study, the effect of drought and heat stress imposed singularly or sequentially was investigated in ten durum wheat cultivars (cvs) at the physiological and molecular level. The traits analyzed were cell membrane stability, relative water content, proline content, and expression level of several genes for heat shock proteins (HSPs). Our results indicate that drought priming can induce the acquisition of thermotolerance in most cultivars already classified as able to acquire thermotolerance by heat pre-treatment. Proline accumulation was correlated to cell membrane stability, meaning that the most thermotolerant cvs were able to accumulate higher levels of proline. Acquired thermotolerance is also due to the activation of HSP gene expression; similarly, pre-treatment with water stress was able to activate HSPs expression. The results reported indicate that water stress plays an important role in inducing thermotolerance, comparable to mild heat stress pre-treatment. This is the first report on the effect of drought stress on the acquisition of thermotolerance.

Investigation of rice performance characteristics: A comparative study of LR, ANN, and RSM.

Parboiling is a type of heat pretreatment used in rice processing to reach higher head rice yield and improve the nutrition properties of raw rice. In this research, the goals were prediction and determination of optimum conditions for parboiled rice processing using the response surface method (RSM) as well as modeling the output values by linear regression (LR) and artificial neural networks (ANN). The parameters including steaming time (0, 5, 10, and 15 min), dryer type (solar and continuous dryers), and drying air temperature (35, 40, and 45°C) were employed as input values. In addition, the breakage resistance (BR) and head rice yield (HRY) were selected as output values. The ANN‐based nonlinear regression, the multi‐layer perceptron (MLP), and the radial basis function (RBF) have been developed to model the process parameters, as well as the central composite design (CCD) was conducted for optimization of BR and HRY values. The outputs of RBF network have been successfully applied to predict higher coefficient of determination of BR and HRY as 0.989 and 0.986, respectively, indicating the appropriateness of the model equation in predicting head rice yield and breakage resistance when the three processing variables (steaming time, dryer type, and drying air temperature) are mathematically combined. Also, the lower root mean square error (RMSE) was obtained for each one as 0.043 and 0.041. The optimum values of BR and HRY were obtained as 12.80 N and 67.3%, respectively, at 9.62 min and 36.9°C for a solar dryer with a desirability of 0.941. In addition, the same values were obtained as 14.50 N and 72.1%, respectively, at 8.77 min and 37.0°C for a continuous dryer with a desirability of 0.971.

Effect of Surface Charge Characteristics of Ferroelectric LiNbO3 on Wettability of Ionic Liquids

Electrowetting is a widely used and effective method to tune the wettability of ionic liquids at solid-liquid interfaces, but it usually requires an external electric field. Here, we proposed a strategy for conveniently tuning ionic liquid wettability by adopting ferroelectric LiNbO3 single crystals as functional substrates. A heating pretreatment process was applied to modulate the surface charge characteristics of LiNbO3 substrates, leading to an improved wettability of [EMIM][BF4] and [EMIM][NTf2] on the LiNbO3 substrates with both positively poled (+Z) and negatively poled (−Z) surfaces. This work may be of great interest in the field of ferroelectric-based microelectronics.

Impact of Thermal Pretreatment of Saliva on the RT-PCR Detection of SARS-CoV-2.

The use of saliva directly as a specimen to detect viral RNA by RT-PCR has been tested for a long time as its advantages are relevant in terms of convenience and costs. However, as other body fluids, its proven inhibition effect on the amplification reaction can be troublesome and compromise its use in the detection of viral particles. The aim of the present work is to demonstrate that saliva pretreatment may influence the RT-PCR amplification of three gene targets of SARS-CoV-2 significantly. A pool of RNA from confirmed COVID-19 patients was used to test the influence of heat pretreatment of saliva samples at 95°C for 5, 10, 15 and 20 min on the amplification performance of ORF1ab, E, and N SARS-CoV-2 genes. Prolonged heating at 95°C significantly improves the Ct value shift, usually observed in the presence of saliva, increasing the limit of detection of viral genes ORF1ab, E, and N. When tested using a cohort of COVID-19 patients' saliva, the increased time of heat pretreatment resulted in a significant increase in the detection sensitivity.

Influence of Heat Pre-treatment and Oxidative Pre-treatment on the Spray Dried Powder of Lactobacillus rhamnosus

Influence of Heat Pre-treatment and Oxidative Pre-treatment on the Spray Dried Powder of Lactobacillus rhamnosus

Heating Pre-Treatment of Copper Ores and Its Effects on the Bond Work Index

Comminution is the stage with the largest energy consumption in the mining process. Therefore, several pre-treatments have been proposed to reduce the energy requirements of this stage. This work analyzed the effect of a heating pre-treatment on the Bond index. A conventional heating pre-treatment was applied to a Chilean copper ore. The ore was heated to temperatures from 300 to 600 °C using a conventional furnace, resulting in a reduction of 19% in the Bond work index. Due to the pre-treatment, the mineral cracked in several areas. Microfracture and composition analyses of these areas confirmed that crack generation in the ore is due to the thermal stress produced by the pre-treatment. The fracture analysis explains the reduction in the Bond work index, since crack generation started at similar temperatures to those at which the reduction in the Bond work index was observed. In addition, the analysis also shows that micro-cracks occur between and through different phases, which may have an impact on mineral liberation. These results also show that, under a moderate high temperature, an important reduction in energy consumption can be obtained.

Heat-pretreated Lactobacillus rhamnosus GG shows enhanced survival capacity after spray drying

Recently, research in the probiotic field is attracting attention worldwide, also in the pharmaceutical industry. New insights are gained about the functionality of beneficial bacteria, like Lactobacillus rhamnosus GG, and their role in health and disease. It is therefore also important to study the impact of industrial processing techniques on the viability and functionality of probiotics. Different stresses, that hamper bacterial viability, are inherent to different processing techniques. As probiotics need to be alive and active by definition, the manufacturing of successful pharmabiotics remains challenging. Therefore, it is interesting to assess the effect of strategies that improve bacterial viability after spray drying. In this study, heat pretreatment of Lactobacillus rhamnosus GG enhanced bacterial viability with one log-unit after spray drying. Finally, Lactobacillus rhamnosus GG proved to have the capacity to develop resistance to consecutive spray-drying cycles, creating a more robust strain of Lactobacillus rhamnosus GG.

Blanching effects on convective air-drying and sorption properties of papaya

This study investigated the influence of blanching on the drying kinetics of papaya from the perspective of the microstructure of the tissue and the water sorption behavior. Drying kinetics and water effective diffusion coefficients were determined based on Fick’s law considering shrinkage. Intense cellular changes were observed in blanched tissues images obtained by light microscopy and transmission electron microscopy. Heat pretreatment increased the water diffusion coefficients and the drying rates in comparison with fresh fruit. Severe color changes were induced by blanching, resulting in color loss during drying. At intermediate moisture ranges, sorption isotherms of blanched papayas showed lower water sorption capacity than those of fresh fruit, therefore the critical moisture for microbial growth in fresh papayas is higher than in blanched ones. The compensation theory was satisfied for fresh fruit but not for blanched fruit, which presented distinctive sorption behavior attributed to cellular damage caused by heat pretreatment.

Construction of Recombinant Saccharomyces cerevisiae with Ethanol and Aldehydes Tolerance via Overexpression of Aldehyde Reductase.

Furfural and hydroxy-methyl-furfural (HMF) are produced by lignocellulosic biomass during heat or acid pretreatment and are toxic to yeast. Aldehyde reductase is the main enzyme to reduce furfural and HMF. To improve the conversion efficiency of lignocellulosic biomass into ethanol, we constructed Saccharomyces cerevisiae with overexpression of aldehyde reductase (encoded by ari1). The gene of aldehyde reductase (encoded by ari1) was cloned via polymerase chain reaction (PCR) and ligated with the expression vector pGAPZαC. Western blot coupled with anti-His tag confirmed overexpression of the ari1 gene. The growth curves of the wild and ari1-overexpressed strain in the YPD medium were found to be almost identical. Compare to the ari1-overexpressed strain, the wild strain showed a longer doubling time and lag phase in the presence of 20 mM furfural and 60 mM HMF, respectively. The real-time PCR results showed that furfural was much more potent than HMF in stimulating ari1 expression, but the cell growth patterns showed that 60 mM HMF was more toxic to yeast than 20 mM furfural. S. cerevisiae with ari1 overexpression appeared to confer higher tolerance to aldehyde inhibitors, thereby increasing the growth rate and ethanol production capacity of S. cerevisiae in an aldehyde-containing environment.