Influence Of Microwave Pretreatment Research Articles

Influence of Microwave Pretreatment on Biogas Production from Co-‎Digestion of Corn Cobs and ‎ Cow Manure

Influence of Microwave Pretreatment on Biogas Production from Co-‎Digestion of Corn Cobs and ‎ Cow Manure

Effect of Microwave Pretreatment on Grindability of Lead-Zinc Ore

The influence of microwave pretreatment on grindability of lead-zinc ore was studied through comparison analysis on the changes of particle size distribution, percentage of below 0.074 mm, energy consumption, and other indexes of grinding products before and after microwave pretreatment in the ball milling process. The results showed that the grindability of lead-zinc ore was improved obviously by microwave pretreatment. The particle size distribution curve of the grinding products was obviously higher than that of the samples without microwave irradiation. The yield of size fraction below 0.074 mm was also improved in a certain degree. Pulsed microwave irradiation was more effective than continuous microwave irradiation when other microwave parameters were consistent. The comprehensive energy consumption of lead-zinc ore pretreated by different microwave parameters was lower than that without microwave irradiation under the same grinding fineness. The total energy consumption was down by 30.1% when irradiated for 15 s at 7 kW power, and it was lower than that without microwave irradiated. The results showed that pulsed microwave pretreatment was more effective in reducing the comprehensive energy consumption of grinding process for lead-zinc ore. And water quenching after microwave irradiation can improve the grindability and reduce the energy consumption of grinding for lead-zinc ore.

Microwave Pretreatment of Vegetable Materials to Increase the Extraction Yield of Natural Products

It was designed and built a laboratory experimental installation (LEI) for the microwave pretreatment of vegetable materials. To study the influence of microwave pretreatment on the total phenolic content (TPC), a conventional extraction of polyphenols from treated and untreated fresh sea buckthorn leaves was performed. For short extraction times, the amount of phenolic compounds was higher for the extracts obtained from treated leaves, but a long pretreatment time (28 s) led to a decrease in TPC. The qualitative analysis showed that the chemical composition is not affected by the microwave pretreatment.

Influence of microwave pretreatment on the flavor attributes and oxidative stability of cold-pressed rapeseed oil

ABSTRACTThis study investigated the effect of microwave (MW) pretreatment on oil yield and the microstructure of rapeseeds, and examined the variations in oxidative stability, tocopherol content and flavor attributes of rapeseed oils extracted by cold pressing or solvent-based methods. Rapeseed moisture content was adjusted to 15% and the seeds were subjected to MW treatment at 200, 400, and 600 W. Compared to untreated samples with the same moisture content, MW pretreatment significantly (p < 0.05) increased the oil yield (by 9–23%), and total tocopherol contents (by 17–23%). Additionally, the oxidative stability of oils extracted from MW-pretreated rapeseeds was significantly (p < 0.05) improved. The analyses of headspace solid-phase microextraction gas chromatography mass spectrometry showed that the relative amount of of pungent compound 4-isothiocyanato-1-butene reduced by 74–95%, whereas that of the non-pungent compound methallyl cyanide increased by 95% in the oils extracted from MW-pretreated rapeseeds. Heterocyclic compounds such as furans and pyrazines appeared in the oils after MW pretreatment and created a special roasted flavor, suggesting that MW pretreatment had a positive effect on the flavor of rapeseed oils.

The combined effect of ultrasonic and microwave pre-treatment on bio-methane generation from co-digestion of petrochemical wastewater

This work investigates the combined influence of ultrasonic and microwave pre-treatment on bio-methane generation from anaerobic digestion of petrochemical wastewater and waste activated sludge. The results revealed that co-digestion of waste activated sludge with petrochemical wastewater produced approximately 0.22 L CH4/g VSadded. However, the highest bio-methane generations from individual digestion of petrochemical wastewater and un-pretreated waste activated sludge were 0.19 and 0.17 L CH4/g VSadded, respectively. In addition, co-digestion enhanced bio-methane generation by 18%–32% relative to individual digestion of the wastes. Using microwave and ultrasonic pre-treatments on the waste sludges before the co-digestion process resulted in supplementary enhancement of bio-methane generation by 53% and 25%, respectively, relative to co-digestion with un-pretreated waste activated sludges. The maximum biogas and bio-methane productions, 0.47 L/g VSadded and 0.33 L CH4/g VSadded, were attained from the co-digestion of 30-min microwave pre-treated waste activated sludge and petrochemical wastewater, respectively. The scientific contribution of the present work on the influence of microwave pre-treatment may play a role in the development of an energy-efficient strategy for waste management.

Influence of microwave pre-treatment on sludge solubilization and pilot scale semi-continuous anaerobic digestion

Anaerobic digestion is widely applied for the recovery of energy from waste activated sludge. Pre-treatment methods are of high interest to increase the biodegradability of the sludge and to enhance the digestion efficiency. This paper studies the application of a microwave pre-treatment. An experimental set-up of two pilot scale semi-continuous digesters was used. During a long term experiment, one of the reactors was fed with untreated sludge, while microwave pre-treated sludge (336kJ/kg sludge) was introduced in the second one. A solid retention time of 20days was kept during the experiments. (Organic) dry solids, carbohydrates, proteins and volatile fatty acids were monitored during digestion. It was seen that the microwave pre-treatment resulted in an effective solubilization of the organic matter in the sludge. The changes to the sludge composition resulted in an increase in biogas production by 50%, while the methane concentration in both reactors remained stable.

Microwave irradiation to pretreat rosemary (Rosmarinus officinalis L.) for maintaining antioxidant content during storage and to extract essential oil simultaneously

An efficient microwave pretreatment (MP) method was employed to maintain quality of postharvest rosemary leaves. The influence of MP on the contents of carnosic acid (CA) and rosmarinic acid (RA) in rosemary leaves was investigated under four storage conditions (sunlight, shade, −20°C, 55°C). Rosemary leaves after MP (800W, 15min) had much lower degradation rates of CA and RA than those of non-treatment samples during the storage period. Moreover, retentions of CA and RA of pretreated leaves stored in the shade and −20°C were higher than those of 55°C and sunlight. In the pretreatment process, we simultaneously used microwave radiation to extract essential oil. No obvious differences were found in yield or composition between essential oils obtained by MP and hydrodistillation. Thus, MP could be a good method for extracting essential oil and maintaining quality in rosemary and other aromatic herbs.

Improvement of grinding characteristics of Indian coal by microwave pre-treatment

The influence of microwave pretreatment on the grindability of high-ash Indian coal was investigated. Scanning electron microscope analysis characterized the micro fractures in microwave treated coal samples, which may be due to the thermal stress cracking resulting from the microwave pretreatment. X-ray diffraction analysis showed that the microwave treated coal had a higher peak compared to the untreated coal indicates that the crystallinity increased with the microwave exposure time. The calculation of the Hardgrove grindability index indicated an increase in the ease of grinding or an increase in the grindability index of the microwave treated coal. Bond grindability tests showed that the work index decreased 15.4% after a microwave exposure time of 120 s. Grindability tests showed that the microwave treated coal ground much more rapidly initially than the untreated coal, with the specific rate of breakage (S 1) increasing by an average of 15%. The results showed that the rates of breakage of both microwave untreated and treated coal samples were dependent on particle size.

Iron ore grindability improvement by microwave pre-treatment

The influence of microwave pre-treatment on grindability of iron ore (Orissa, India) was investigated by grindability tests. SEM analysis characterized the micro-fractures in microwave treated sample. This may be due to the thermal stress cracking resulted from microwave energy pre-treatment. XRD analysis showed the crystalline content of the sample. It was found that the microwave treated iron ore has peak more than that of untreated ore, i.e. the crystallinity increased with the microwave exposure time. The calculation of HGGI indicated increase in the ease of grinding or decrease in grindability index of the microwave treated ore. Grindability test showed that the microwave treated iron ore grinds much more rapidly initially than the untreated ore. The results showed that the breakage function of both microwave untreated and treated iron ore is dependent of the particle size. The grindability increased significantly as a result of microwave pre-treatment with the specific rate of breakage ( S i ) increasing by an average of 50%. It was concluded that microwave assisted grinding produced good results particularly for grinding characteristics.

Influence of microwave pretreatment on the bioleaching behaviour of low-grade complex sulphide ores

Mineralogical information on the mechanisms by which microwave pretreatment improves the bioleaching behaviour of low-grade complex sulphide ore, and an interpretation of the interrelationship between mineralogy, microwave processing, and bioleaching process are provided in this study. The influence of microwave irradiation on the bioleaching behaviour and mechanisms of a low-grade complex sulphide ore subjected to microwave heating in a kitchen type microwave oven at a power output 1100 W for 5 min was investigated in a mixed mesophilic bacterial culture through bioleaching experiments and electrochemical techniques. Results revealed that microwave treatment improved the bioleaching of behaviour of the ore, with more effect on copper and iron dissolutions than on zinc and lead. Both microwave treated and untreated samples showed similar electrochemical behaviour. However, microwaved samples displayed higher reactivity, dissolution rates, dissolution currents, current densities and a decreased polarization resistance. Increase in dissolution of the microwaved treated samples resulted from phase changes in the ore which promoted galvanic interaction within the system, decrease in the amounts of sulphur contents, and an increase in electrochemical sites resulting from an increase in the number of cracks induced by microwave heating.

An investigation into the influence of microwave treatment on mineral ore comminution

The influence of microwave pre-treatment on mineral ore breakage has been investigated. Samples of lead–zinc ore were microwave pre-treated prior to strength testing and change in strength with microwave exposure time determined. Comparisons of change in strength were made between microwave-treated and -untreated material. Using a multimode microwave cavity, it was found that strength could be significantly reduced in 0.5 s when using 15 kW of microwave power. Lower powers in this type of cavity were found to be less effective. Drop weight tests were used to quantify the change in strength in terms of reduction in required comminution energy. Reductions of up to 40% were achieved for particles of mean size 14.53 mm. Preliminary tests in a single-mode microwave cavity gave strength reductions of 50% at 10 kW of microwave power with a residence time of only 0.1 s, indicating that high electric field strength is important in the failure of ore. A preliminary energy balance indicating the benefits of single-mode heating is presented.