MW Pretreatment Research Articles

Thermo-Chemical Conversion of Microwave Selectively Pre-Treated Biomass Blends

Possibilities of more efficient use of regional lignocellulosic resources (wood, wheat straw, peat) of different origin for an environmentally friendly energy production using selectively MW pre-treated blends of commercial wood or wheat straw pellets with raw peat pellets are studied. A hypothesis is proposed and tested that selective MW pre-treatment of wood or wheat straw pellets at the frequency 2.45 GHz and blending of MW pre-treated pellets with raw peat pellets can be used to enhance and control the thermo-chemical conversion of biomass blends. To test this hypothesis, a combined experimental study and mathematical modelling of the processes were performed. The thermo-chemical conversion of selectively activated blends was experimentally studied using a batch-size pilot device, which consists of a biomass gasifier and a combustor. To evaluate the effect of selective MW pre-treatment of biomass pellets on the thermo-chemical conversion of pre-treated blends, measurements of the kinetics of weight loss, yield of combustible volatiles, flame temperature, heat output of the device, and composition of emissions were made at different MW pre-treatment regimes of wheat straw and wood pellets and different mass fractions of pre-treated pellets in biomass blends. The developed novel 2D numerical model of thermo-chemical conversion of MW pre-treated straw confirmed that the pre-treatment of wheat straw pellets increases the generated heat and significantly affects the temperature distribution in the flame/bed zones. It was confirmed that MW pre-treatment leads to a faster thermal decomposition of biomass pellets, synergistically activating the non-treated parts of blends. The overall improved yield of combustible volatiles and their complete combustion provide a surplus of heat production by limiting the formation of GHG emissions, which allows promoting MW pre-treated biomass of different origin as efficient regional bioenergy resources for energy production.

Thermal Decomposition of Microwave Pre-treated Biomass Pellets

Studies were carried out to evaluate the influence of microwave pre-treatment on the thermal decomposition of different lignocellulosic biomass pellets and on the yield of volatile compounds. Microwave pre-treatment of biomass pellets was performed using a 700 W heat capacity microwave oven by varying the mw irradiation time of biomass pellets along with estimation of the effect of mw pre-treatment on the mass density and elemental composition of pellets responsible for changes of the thermal decomposition and yield of volatiles during the gasification of pre-treated pellets. Experimental studies of the thermal decomposition of pre-treated biomass pellets and formation of volatile compounds (CO, H2, CxHy) were conducted using a laboratory-scale setup with the heat capacity 5 kW which combines a biomass gasifier and a combustor. The results of the complex study allow to conclude that the microwave pre-treatment of biomass pellets promotes an increase of the weight loss rate by decreasing the mass density, but increasing the surface area and reactivity of the pre-treated pellets thus activating the thermal decomposition during the gasification of the pre-treated pellets with a faster and enhanced yield of combustible volatiles. The results of the experimental study suggest that mw pre-treatment of lignocellulosic pellets can be used as a tool to control the thermal decomposition of lignocellulosic pellets and the yield of combustible volatiles.

Polar solvents enhance the efficiency of microwave pre-treatment of woody biomass

Microwave pre-treatment of woody biomass may be the key to unlocking an energy efficient process for the production of renewable chemicals and fuels. Here we investigated the dipolar polarisation mechanism of polar solvents, ranging from dilute aqueous solutions of ethylene glycol, isopropyl alcohol, formaldehyde and water-only, to improve the efficiency of MW pre-treatment of woody biomass. The optimal conditions were 3.7 wt% FA solution for 10 min at 180 °C, where heating rate was accelerated by 50%, saccharification of biomass increased by 56% and stabilised lignin monomers were produced compared to water-only. Autoclave pre-treatment of woody biomass released 3 to 6 times less sugar yield in the presence of water-only and 3.7 wt% FA compared to MW irradiation. Our efficient method can potentially produce three streams of building blocks – cellulose fibres, solvated hemicellulose and stabilised lignin – for transformation into renewable products.

Thermal Decomposition and Combustion of Microwave Pre-Treated Biomass Pellets

The objective of the study was to investigate a more effective use of commercially available biomass pellets (wheat straw, wood, peat) using microwave pretreatment to improve heat production. Pellets were pretreated using the originally designed microwave torrefaction device. The effects of microwave (mw) pretreatment were quantified, providing measurements of the weight loss and elemental composition of pellets and estimating the effect of mw pretreatment on their porosity, surface area and calorific values at pretreatment temperatures of T = 448–553 K. Obtained results show that the highest structural variations and elemental composition during mw pretreatment were obtained for wheat straw pellets, with an increase in reactivity, a decreasing in the duration of the thermal decomposition by about 40% and an increase in the yield of combustible volatiles. Increased reactivity of pretreated pellets enhanced the ignition and burnout of volatiles, decreasing the duration of the burnout of pretreated wheat straw, wood and peat pellets by 40%, 24% and 9%, respectively, and increasing the peak and average values of the flame temperature, heat output, and produced heat energy by 40–50%, with a correlating increase of combustion efficiency and the mass fraction of carbon-neutral CO2 emission. Thus, the applicability of microwave pretreatment for the control and improvement of heat production was confirmed.

Molecular weight distribution of pretreated thickened waste activated sludge and fat, oil, and grease.

Co-digestion samples containing thickened waste activated sludge and fat, oil and grease were subjected to three different pretreatment methods, i.e., microwave at 175°C, hyper-thermophilic stage at 70°C, and conventional heat at 70°C. The soluble matter extracted from the un-pretreated and pretreated samples were subjected to an ultrafiltration (UF) process using four different membrane sizes (300, 100, 10, and 1kDa) for molecular weight distribution analysis. Every pretreatment method had a different effect on the solubilization and redistribution of the soluble matter (SCOD and TVFA). For example while MW pretreatment resulted in a significant increase in the SCOD at the lowest molecular weight (< 1kDa) and at the highest molecular weight (> 300kDa), Hyper pretreatment caused the majority of the SCOD ( ̴62.7% of total SCOD) to be concentrated at the smaller molecular weight range (< 10kDa). The MW and hyper-thermophilic pretreatments were much more effective in increasing samples solubilization and biogas production compared to the conventional heat pretreatment. The hyper-thermophilic samples had the maximum improvement in cumulative biogas production from all the molecular weights compared to MW- and Heat-pretreated samples; Hyper-pretreated samples achieved 86.5% higher cumulative biogas production compared to the control.

Combined MgO nanoparticle and microwave pre-treatment on biogas increase from Enteromorpha during anaerobic digestion

This study evaluated the anaerobic digestion of MgO metal-oxide nanoparticles combined with microwave pretreatment to increase biogas production from microalgae. The result shows the maximum total biogas yield of 342ml and 320ml were achieved by the MW pretreatment of 800W, 4min +15mg/L MgO NPs group and 600W, 6min +5mg/L MgO NPs group, which are 1.38 and 1.30 times compared to control, respectively. The influence of metallic oxide (MgO) NPs and MW pretreatment on anaerobic digestion of Enteromorpha resulted in significant increase in cumulative biogas production. The modified Gompertz equation and Logistic function model were used to simulate the nanoparticle-enhanced anaerobic digestion process, which demonstrate that the modified Gompertz equation can better simulate the fermentation process of microalgae.

Microwave pretreatment promotes the annealing modification of rice starch

Early indica rice starch can only be modified to a small extent by annealing treatment (ANN), which limits its application. Microwave pretreatment (MW) with different intensity was used to enhance the effectiveness of ANN, and single ANN or MW treatments were used as controls. MW pretreatments per se exhibited insignificant or minor effect on the starch. However, MW pretreatment with appropriate intensity could significantly promote the structural and physicochemical modification of the starch in subsequent ANN, including the enhancement of long- and short-range crystalline structures, the increases in gelatinization enthalpy, particle size, peak viscosity, breakdown and G' value, and the decreases in tan δ value. The MW pretreatment could untangle the entanglements between starch chains by inducing violent movement of the chains, which facilitated the molecular rearrangement and interaction during subsequent ANN, thereby promoting the structural and physicochemical changes. This study provided new insights into the annealing mechanism of starch.

Microwave assisted pretreatment of eucalyptus sawdust enhances enzymatic saccharification and maximizes fermentable sugar yield

Abstract There is an urgent need of sustainable and efficient methods for the production of biofuels and chemicals from lignocellulosic feedstock. The purpose of this study was to develop a mild, cost-effective and environmentally benign pretreatment for woody lignocellulose to maximize sugar yield via enzymatic saccharification. Microwave irradiation (MW) of Eucalyptus regnans sawdust in water was investigated and compared directly against conventional liquid hot water (LHW) pretreatment. Following 30 min microwave irradiation at 180 °C, the sugar yield was 3.5 times higher using MW than LHW pretreatment under the same conditions. Complete release of C5 and C6 sugars was achieved after the two-step method of MW pretreatment followed by enzymatic hydrolysis, compared with only 4% without pretreatment and 31% after LHW. Removal of ‘lignin droplets’ formed on the surface of the pretreated fibers via flowing hot water showed only minor improvement in the yield of enzymatic saccharification. Our results support the hypothesis that lignin prevents access of enzymes rather than inhibits their activity. MW accelerated depolymerization of hemicellulose, opening the structure more than LHW pretreatment.

Evaluation of the anaerobic digestion of kitchen waste by thermal pretreatment in a batch leach bed reactor with down flow and the kinetics of methane yields

ABSTRACTThe aim of this study was to evaluate the effects of autoclave and microwave irradiation (MW) pretreatments on the solubilization, biogas and methane yields of kitchen waste (KW). Autoclave (for 30 min @ 120, 1 bar) and MW (for 400 s @ 80, 700 W) pretreatments were used to enhance anaerobic digestion of KW. The anaerobic digestion of KW in autoclave and MW pretreatments were compared with a control in a batch leach bed reactor with down flow (LBR DF). During autoclave and MW pretreatments, the biogas yields were respectively 25.41 and 41.43% higher than the control test and for methane were respectively 22.73 and 38.91% higher than the control test. The highest solubilization efficiency was obtained after MW pretreatment (89.21%), followed by after autoclave pretreatment (85.73%), and the lowest value was obtained with control (61.37%). Mathematical models fitted experimental data with R2>0.9798. The present study shows that autoclave and MW pretreatments can be used to improve biogas and methane yields and solubilization efficiency. Schnute and modified Gompertz models gave a good fit of the first stage of fermentation as well as the asymptotic phase.

Combustion Characteristics of Modified Plant Biomass Pellets

The main objective of this experimental study is to investigate the thermo-chemical conversion of modified biomass pellets of different origin (spruce, aspen and wheat straw). The modification of biomass pellets includes the microwave (mw) pre-treatment of these biomass samples and spraying of waste cooking and mineral oils on the surface of the mw pre-treated pellets. The initial and modified pellets were characterized in terms of the elemental composition, heating values, energy density (bulk), moisture, and ash contents. The results show that for all biomass types mw pre-treatment as well as spraying of waste oils on the surface of pre-treated pellets results in an increase of the carbon content and heating values of the samples relative to the original biomass pellets with direct impact on the gasification and combustion characteristics of these pellets. The experimental study of the effect of biomass pellets modification on their gasification/combustion characteristics includes complex time-dependent measurements of the biomass weight loss rate, temperature, heat production rate, combustion efficiency and products composition. Due to the variations of the elemental composition and heating values of the produced biomass pellets, a correlating increase of the volume fraction of CO2 and produced heat energy at thermo-chemical conversion of biomass was observed. The results of the complex experimental measurements allow to conclude that the proposed modification of plant biomass pellets including their mw pre-treatment with further spraying of waste oils is an effective tool to convert biomass into a fuel with improved combustion characteristics.

A novel microwave assisted surfactant pretreatment of chili post -harvest residue for the production of bioethanol and biopolyme

A novel microwave assisted surfactant pretreatment strategy was evaluated for the production of bioethanol and biopolymer from chili post-harvest residue. Among the various surfactants screened microwave assisted Tween - 20 pretreatment was found to be more effective. Various process parameters affecting pretreatment were optimized by adopting a Taguchi design. The optimum conditions of pretreatment were surfactant concentration of 4% w/w, MW pretreatment time for 1 min, MW power of 550W, biomass loading of 5% w/w and pretreatment time for 45 min. Under optimized conditions 0. 316g/g of reducing sugar per g of dry biomass (g/g) was observed. The hydrolyzate is devoid of major fermentation inhibitors like furfural, 5-hydroxymethylfurfural and organic acids like citric acid, propionic acid, succinic acid and formic acid. Fermentation of the non-detoxified hydrolyzate yielded 1.66% of ethanol and 67.85% of PHB.

Assessment of microbial viability in municipal sludge following ultrasound and microwave pretreatments and resulting impacts on the efficiency of anaerobic sludge digestion.

A range of ultrasonication (US) and microwave irradiation (MW) sludge pretreatments were compared to determine the extent of cellular destruction in micro-organisms within secondary sludge and how this cellular destruction translated to anaerobic digestion (AD). Cellular lysis/inactivation was measured using two microbial viability assays, (1) Syto 16® Green and Sytox® Orange counter-assay to discern the integrity of cellular membranes and (2) a fluorescein diacetate assay to understand relative enzymatic activity. A range of MW intensities (2.17-6.48 kJ/g total solids or TS, coinciding temperatures of 60-160 °C) were selected for comparison via viability assays; a range of corresponding US intensities (2.37-27.71 kJ/g TS, coinciding sonication times of 10-60 min at different amplitudes) were also compared to this MW range. The MW pretreatment of thickened waste activated sludge (tWAS) caused fourfold to fivefold greater cell death than non-pretreated and US-pretreated tWAS. The greatest microbial destruction occurred at MW intensities greater than 2.62 kJ/g TS of sludge, after which increased energy input via MW did not appear to cause greater microbial death. In addition, the optimal MW pretreatment (80 °C, 2.62 kJ/g TS) and corresponding US pretreatment (10 min, 60 % amplitude, 2.37 kJ/g TS) were administered to the tWAS of a mixed sludge and fed to anaerobic digesters over sludge retention times (SRTs) of 20, 14, and 7 days to compare effects of feed pretreatment on AD efficiency. The digester utilizing MW-pretreated tWAS (80 °C, 2.62 kJ/g TS) had the greatest fecal coliform removal (73.4 and 69.8 % reduction, respectively), greatest solids removal (44.2 % TS reduction), and highest overall methane production (248.2 L CH4/kg volatile solids) at 14- and 7-day SRTs. However, despite the fourfold to fivefold increases in cell death upon pretreatment, improvements from the digester fed MW-pretreated sludge were marginal (i.e., increases in efficiency of less than 3-10 %) and likely due to a smaller proportion of cells (10-20 %) in the polymeric network and mixed sludge fed to digesters.

Pretreatment of macroalgal biomass for biogas production

The objective of this study was to evaluate the effect of beating (BT), ball milling (BM) and microwave pretreatment (MW) on the conversion of the macroalgae Laminaria spp. into biogas by anaerobic digestion (AD). The AD was carried out in batch at 38±1°C, over an incubation time of 25days. After 3days of digestion the BT pretreated samples yielded the best result by achieving a methane increase of up to 37% with respect to the raw seaweed. At 25days, both BM and MW pretreatment lowered the methane yield with respect to the raw seaweed. Since BT produced higher methane yields with respect to the untreated sample, it was considered for energy balance analysis. After 3days of digestion, the BT resulted in an energy gain of 28%, while at the end of digestion the break-even point was reached.

Microwave pretreatment of Moringa oleifera seed: Effect on oil obtained by pilot-scale supercritical carbon dioxide extraction and Soxhlet apparatus

The effect of microwave radiation (MW) at three levels of power (100, 200 and 400W) and for three radiation time (30, 60 and 90s) on Moringa oleifera seeds was studied as a pretreatment process prior to oil extraction by pilot-scale supercritical carbon dioxide (SC-CO2) extraction and Soxhlet apparatus. Extraction oil yield by Soxhlet increased with MW pretreatments at 100W for 30, 60 and 90s with respect to untreated seeds. Therefore, these MW conditions were selected for SC-CO2 extraction of oil, carried out at 40°C and 300bar. Combining MW pretreatment at 100W for 30s with SC-CO2 extraction, the maximum oil yield of 35.28% w/w was obtained. The chemical quality of oil extracted by SC-CO2 was higher than Soxhlet oil.

Chemically coupled microwave and ultrasonic pre-hydrolysis of pulp and paper mill waste-activated sludge: effect on sludge solubilisation and anaerobic digestion

The effects of alkali-enhanced microwave (MW; 50-175°C) and ultrasonic (US) (0.75W/mL, 15-60min) pretreatments, on solubilisation and subsequent anaerobic digestion efficiency of pulp and paper mill waste-activated sludge, were investigated. Improvements in total chemical oxygen demand and volatile suspended solids (VSS) solubilisation were limited to 33 and 39% in MW pretreatment only (175°C). It reached 78 and 66% in combined MW-alkali pretreatment (pH 12 + 175°C), respectively. Similarly, chemical oxygen demand and VSS solubilisation were 58 and 37% in US pretreatment alone (60min) and it improved by 66 and 49% after US-alkali pretreatment (pH 12 + 60min), respectively. The biogas yield for US 60min-alkali (pH 12)-pretreated sludge was significantly improved by 47 and 20% over the control and US 60 reactors, respectively. The biogas generation for MW (150°C)-alkali (pH 12)-pretreated sludge was only 6.3% higher than control; however, it was 8.3% lower than the MW (150°C) reactor, which was due to the inhibition of anaerobic activity under harsh thermal-alkali treatment condition.

Effect of microwave pretreatment on the kinetics of ascorbic acid degradation and peroxidase inactivation in different parts of green asparagus (Asparagus officinalis L.) during water blanching

In this study, the effects of two blanching conditions on ascorbic acid (AA) and peroxidase (POD) in different segments of asparagus (bud, upper, middle, and butt) were investigated. The blanching treatments were: blanching in water at 70, 80 and 90°C (WB); microwave heating (900W, 30s) followed by water blanching (MW+WB). AA degradation and POD inactivation in all segments of asparagus for both treatments are well described by first-order models. The degradation rate of AA and POD is gradually increased from butt to bud segment of asparagus. In addition, MW pre-treatment could increase the Ea of AA degradation and decrease the Ea of POD inactivation during water blanching of asparagus. Therefore, it is recommended that the different segments of asparagus should be subjected to different blanching times, and MW pre-treatment could be applied for alleviating AA degradation and accelerating POD inactivation during blanching, cooking and pasteurisation in water.

Effects of microwave pretreatments on the anaerobic digestion of food industrial sewage sludge

AbstractMicrowave irradiation is a novel and very promising technology for sludge conditioning. As pretreatment, it has a verified beneficial effect on the microbial degradation and anaerobic digestion of sewage sludge, but in present work we dealt with the applicability of microwave pretreatments for food industrial sludge. However, studies cannot be found that specialize on the effects of the MW treatments with different intensities on the anaerobic digestion of sludge. In our work we focused on the examination of the effect of MW pretreatment for 0.5, 2.5, and 5 W/g on the carbonaceous biochemical oxygen demand (CBOD5), solubilization of organic matters (sCOD/tCOD), and the mesophilic anaerobic digestion of dairy sewage sludge. It can be concluded that the MW pretreatments were appropriate to enhance the efficiency of anaerobic digestion. With MW pretreatments the specific biogas product could be increased from 220 mL g−1 to more than 600 mL g−1 because of the increased solubility (from 9.7% to more than 40%), and the enhanced accessibility of organic compounds for decomposing bacteria. © 2010 American Institute of Chemical Engineers Environ Prog, 2011

Evaluation of continuous mesophilic anaerobic sludge digestion after high temperature microwave pretreatment

Effect of microwave pretreatment (MW) high temperature (175 °C) and MW intensity to waste activated sludge digested with acclimatized inoculum in single- and dual-stage semi-continuous mesophilic anaerobic digesters at different sludge retention times (SRTs) (20, 10 and 5 days) were investigated. MW pretreatment led to similar sludge stabilization at low SRTs (5 and 10 days). Although lowering MW intensity slightly improved sludge solubilization, it had a negative effect on digestion at low SRTs. Single-stage digesters with MW pretreatment surpass dual-stage digesters performances.

Effect of blanching on the quality of Brussels sprouts ( Brassica oleracea L. gemmifera DC) after frozen storage

Three blanching conditions previous to freezing and frozen storage of Brussels sprouts were compared in terms of their combined effects on texture, surface colour, total chlorophyll, radical scavenging activity (RSA), ascorbic acid and total flavonoids content. The blanching alternatives were: immersion in water (50 °C; 5 min) followed by blanching in water (100 °C; 3 min) (PB); microwave heating (700 W, 5 min) followed by blanching in water (100 °C; 2 min) (MW); and direct blanching in water (100 °C; 4 min) (DB). Fresh controls and treated samples were frozen then stored at −18 °C for 8 months. Texture of sprouts was significantly affected by blanching although all treatments had a similar effect. Freezing and frozen storage caused an additional loss of firmness, but the magnitude was lower than that induced by blanching. With respect to surface colour, the PB method gave the highest − a ∗ values as well as a better Chroma retention than the controls. All treatments increased RSA, ascorbic acid and total flavonoids contents. The only significant differences between treatments was the slightly higher value for − a ∗ and Chroma for the PB method and an increase in final RSA levels for the MW pre-treatment.

Immunohistochemical detection of p53 protein in archival tissues from squamous cell carcinomas of the oral cavity using wet autoclave antigen retrieval

Using a panel of four anti-p53 antibodies (CM-1, PAb 1801, DO7, and PAb 240), the phenotypic characteristics of p53 protein overexpression were investigated in 22 routinely formalin-fixed and paraffin-embedded squamous cell carcinomas of the oral cavity. Conventional immunohistochemical staining without pretreatment for antigen retrieval was compared with wet autoclaving (AC) and microwave irradiation (MW). Applying AC or MW, p53 immunoreactivity was demonstrated in 9/22 cases with PAb 1801 and DO7 antibodies and in 8/22 cases with the CM-1 antibody. Immunostaining with the PAb 240 antibody after AC pretreatment showed p53 positivity in 8/22 tumours, but in only 4/22 following MW pretreatment. Immunostaining without pretreatment revealed only 2/22 p53-positive cases using CM-1, 4/22 with PAb 1801, and 3/22 with DO7. Without pretreatment, the PAb 240 antibody was consistently negative. Wet autoclave pretreatment was significantly superior for all the antibodies used in this study when compared with conventional immunohistochemistry without pretreatment (P < 0.005). It yielded better results than microwave irradiation for antigen unmasking in relation to the PAB 240 antibody (P < 0.05). Wet autoclave pretreatment is recommended as a reliable and highly reproducible method for p53 antigen retrieval in routinely processed archival material. The advantages over microwave pretreatment include simple handling and good preservation of morphology.