Microwave Pretreatment Research Articles

Iron Removal from Low-Grade Pyrophyllite Ore by Microwave Irradiation and Dry Magnetic Separation

Owing to its unique properties, pyrophyllite is an economical alternative to many minerals in different applications. The presence of iron-bearing minerals in Saudi pyrophyllite hampers its industrial uses. The aim of this study was to examine the removal of iron from Saudi low-grade pyrophyllite ore using two approaches. The first approach involves dry high-intensity magnetic separation, whereas the second approach involves microwave pretreatment of the ore before dry magnetic separation. For the first approach, the studied operating parameters were roll speed; feed rate, field intensity, and feed particle size. For the alternative approach, microwave treatment followed by dry magnetic separation, the microwave irradiation time and the magnetic field intensity were studied. The results show that the combined microwave treatment and dry separation method could provide high-purity pyrophyllite for filler industries. Microwave irradiation for 30 min was optimal to change impurity phases (i.e., pyrite, hematite) into ferromagnetic phases in microwave-treated pyrophyllite samples. At a magnetic field intensity of 2000 Gauss, the 30 min microwave-irradiated pyrophyllite sample achieved an iron recovery of 11.2% in non-magnetic fractions, with a removal efficiency of 89% with an alumina recovery of 91.31%.

Effects of different pretreatment methods on the degree of substitution, structure, and physicochemical properties of synthesized malic acid sweet potato starch ester.

The preparation of malic acid starch ester (MSE) is mostly carried out using a high temperature method, but there are problems such as high energy consumption, long preparation time, and uneven heating. Microwave technology can be used to overcome these limitations. The semi-crystalline structure of starch granules hinders the modifier's access to the matrix, thus limiting the esterification reaction. Physical techniques can act on the interior of the starch to create a number of active sites, thereby facilitating the reaction of the starch with esterification reagents. Therefore, this study investigated the effect of starch pretreatment by microwave, heat-moisture, and ultrasonic techniques on the degree of substitution (DS), structure, and physicochemical properties of MSE synthesized by the microwave method. The DS of MSE was increased after pretreatments. The modified starch obtained by different pretreatment methods did not show new characteristic peaks, while the MSE synthesized showed new absorption peaks near 1735 cm-1. The granular structure and morphology of the modified starch obtained by microwave and heat-moisture pretreatment were gelatinized and aggregated, while some of the starch particles of the modified starch obtained by ultrasonic pretreatment appeared pore-sized. The relative crystallinity and gelatinization enthalpy of the MSE were reduced, but the crystallization pattern remained as A-type. Overall, the results suggest that various pretreatment methods can enhance the DS of MSE by disrupting the structure of starch. The findings of this study provide theoretical support for improving the DS of esterified starch. © 2024 Society of Chemical Industry.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ РАЗЛИЧНЫХ ВИДОВ ПРЕДВАРИТЕЛЬНОЙ ОБРАБОТКИ КАБАЧКОВ ПЕРЕД СУШКОЙ НА ОРГАНОЛЕПТИЧЕСКИЕ ПОКАЗАТЕЛИ ГОТОВОГО ПРОДУКТА

The aim of the study was to investigate the effect of various types of preliminary processing of zucchini before drying on the organoleptic properties of the finished product. The object of the study was fresh zucchini of the Kalazina F1 variety. The study was conducted at the Krasnodar Research Institute for Storage and Processing of Agricultural Products – a branch of the Federal State Budgetary Scientific Institution SKFNTSSVV. The organoleptic properties of the finished product were determined depending on the method of preliminary processing. During the organoleptic evaluation, it was found that the sample treated with a 1 % citric acid solution received the maximum overall score – 4.7 points. The lowest score was received by samples № 1 and № 2 (microwave 480 W for 120 s and 640 W for 60 s). Microwave pre-treatment in various parameters has a significant effect on the taste and the presence of an unpleasant aftertaste compared to other samples. Samples treated with a solution of citric acid in various dosages have a sour taste and prevent darkening of the product during drying. It has been established that various types of pre-treatment affect the quality of the dried product. It is worth noting the advantages of pre-treatment of zucchini with a 1 % solution of citric acid, which affects not only the extension of shelf life by reducing the moisture content of the product, but also the organoleptic properties. In addition, treatment with a 1 % solution of citric acid makes it possible to preserve the organoleptic properties of dried zucchini (prevents surface darkening), as well as reduce the moisture content of the product compared to the control sample.

Synergic effect of thermo-chemical pretreatment of waste-activated sludge on bio-methane enhancement

Sustainable and environmentally friendly energy production is feasible via anaerobic digestion (AD) of organic wastes, such as waste-activated sludge (WAS). However, due to its limited degradation, a pretreatment strategy is applied to WAS to enhance its bio-degradation and, thus, biogas yield. Alkaline (0.5%–9% g NaOH/gTS, 30 min), microwave (MW) (90°C–175°C), and hybrid (0.5% g NaOH/gTS +125°C) pretreatments were applied to WAS. The characterization of untreated and pretreated WAS revealed that with higher alkaline and MW pretreatment, the soluble chemical oxygen demand (sCOD), carbohydrate, and protein increased; however, the readily biodegradable COD (rbCOD) rate was unlike the sCOD. The sCOD was 7%–18%, 8%–23%, and 37% for alkaline, MW, and hybrid pretreatments, respectively. Stronger alkaline and MW pretreatment induced higher turbidity, capillary suction time, and lower average particle size. AD of alkaline-, MW-, and hybrid-pretreated WAS produced 94% (0.5% NaOH), 125% (MW at 125°C), and 199% (0.5% NaOH and MW at 125°C) increased biogas, respectively, compared to the AD of untreated sludge. The AD data on the alkaline-, MW-, and hybrid-pretreated BMP assays fitted well with the modified Gompertz model with a coefficient of determination above 0.95. The PCA analysis showed that biogas production is closely correlated with pretreatment temperature, VFA production, rbCOD, sCOD, and soluble carbohydrates and protein. Microbial genome sequencing analysis showed an improvement in microbial abundance and diversity. Acetoclastic methanogen (Methanothrix) growth was improved by 37% (MW pretreatment). Abundances of Methanosarcina, using all three metabolic pathways for methanogenesis, were 17, 21, 11, and 48% in the control, alkaline-, MW-, and hybrid-pretreated digestate, respectively, corresponding to 186% improvement in hybrid pretreatment when compared to the control.

Effect of various aging conditions and treatment methods on thermal degradation of coffee waste/epoxy composites

In composites containing lignocellulosic fillers, the chemical composition of the filler mostly determines the heat resistance. Based on the rules of green chemistry, new bio-based composites were developed from the waste of industrial crop product coffee (CW), and their thermal stability in different aging environments was examined by thermogravimetric analysis (TGA). Alkali (NaOH), microwave (MW), ultrasound (US), and alkali pretreatment followed by microwave (NaOH+MW) were applied to modify the CW. The effect of various applied treatment methods and environmental conditions such as UV radiation, water sorption, seawater, and hydrothermally agings on the thermal properties of the composites was investigated. Fourier-transform infrared spectroscopy (FTIR) and Field emission scanning electron microscopy (FE-SEM) were used in the characterization of composites. Among the environmental factors tested, seawater and hydrothermal aging affected the thermal resistance of the composites the most, while NaOH+MW affected it most among the processing methods. Although the thermal stability of unaged and UV-exposed MW-CW composites was found to be the highest, it was more affected by aging in seawater, pure water, and hydrothermal environments. As a result, MW was found to be more effective among the treatment methods in terms of thermal properties under UV conditions, confirming that the adoption of environmentally friendly methods and surface modification of the filler can provide superior composites.

A chemometric approach to assess the oil composition and content of microwave-treated mustard (Brassica juncea) seeds using Vis–NIR–SWIR hyperspectral imaging

The wide gap between the demand and supply of edible mustard oil can be overcome to a certain extent by enhancing the oil-recovery during mechanical oil expression. It has been reported that microwave (MW) pre-treatment of mustard seeds can have a positive effect on the availability of mechanically expressible oil. Hyperspectral imaging (HSI) was used to understand the change in spatial spread of oil in the microwave (MW) treated seeds with bed thickness and time of exposure as variables, using visible near-infrared (Vis–NIR, 400–1000 nm) and short-wave infrared (SWIR, 1000–1700 nm) systems. The spectral data was analysed using chemometric techniques such as partial least square discriminant analysis (PLS-DA) and regression (PLSR) to develop prediction models. The PLS-DA model demonstrated a strong capability to classify the mustard seeds subjected to different MW pre-treatments from control samples with a high accuracy level of 96.6 and 99.5% for Vis–NIR and SWIR-HSI, respectively. PLSR model developed with SWIR-HSI spectral data predicted (R2 > 0.90) the oil content and fatty acid components such as oleic acid, erucic acid, saturated fatty acids, and PUFAs closest to the results obtained by analytical techniques. However, these predictions (R2 > 0.70) were less accurate while using the Vis–NIR spectral data.

Investigation of the influence of the processing method before drying on the organoleptic characteristics, the amount of weight loss and microbiological parameters of zucchini chips

Drying is one of the most popular ways to preserve plant materials by reducing humidity and preventing microbiological contamination and it is a promising direction in the food industry. The article presents the results of the research in the development of effective technologies for preparing zucchini for drying, ensuring acceleration of the drying process, as well as maintaining or improving organoleptic characteristics (for example, to prevent excessive darkening). The article describes the results of the influence of pre-treatment of zucchini before drying on quality indicators – organoleptic indicators (appearance, consistency, taste, smell, color, shape, size) and physicochemical indicators (weight of fresh raw materials and dried product, moisture content of the finished product) and microbiological safety (MAFAnM, coliform bacteria, mold, yeast). The types of pre-treatment of zucchini before drying were microwave treatment, C6 H8 O7 solution (citric acid), NaCl solution (saline solution), microwave treatment + C6 H8 O7 solution, microwave treatment + NaCl solution. During the organoleptic assessment, it was found that the best organoleptic indicators are provided by treatment with 5% NaCl solution (4.8 points) and 1% C6 H8 O7 solution (4.7 points). Microwave pre-treatment in various parameters led to the appearance of characteristic bitterness and an unpleasant aftertaste. Treatment with a solution of citric acid in various dosages imparts a sour taste and prevented darkening during drying. It was found that various types of pre-treatment do not affect the duration of drying of zucchini, which was, on average, 7 hours. Microwave treatment reduced humidity to 3.4%, citric acid – to 3.6%, saline solution – to 4.6%, while complex treatment did not affect the reduction in moisture content of the dry product and, in general, the duration of drying. As a result of the microbiological assessment, it was noted that the amount of MaFAnM and mold fungi were within acceptable imits, and the growth of coliform bacteria was absent, which corresponded to the indicators of regulatory documents.

Effect of microwave combined with ultrasonic pretreatment on the flavor of composite stewed soup‐stock

AbstractIn order to increase the content of flavoring components and nutrients in the stock, effects of microwave (MW) combined with ultrasonic pretreatment on water‐soluble proteins, flavor nucleotides, volatile gas constituents and sensory evaluation in the stewed stock were explored. The results showed that, compared with the control group (CK), MW, and ultrasonic (US) pretreatment could significantly promote the degradation of nucleotides and form a large number of 5′‐flavor nucleotides. The combined treatment of MW and US promoted protein hydrolysis and increased the content of water‐soluble protein. The microwave combined ultrasonication pretreated stew stock had the brightest color and the overall sensory score was better than that of the CK. In addition, GC–MS analysis showed that a total of 49 volatile substances were detected in the stock samples. After microwave combined ultrasonication pretreatment, the relative contents of aldehydes and alcohols in the stock increased significantly. The sensor response value of the electronic nose was the highest, indicating that the intensity of flavor characteristics increased. Therefore, MW combined with ultrasonic pretreatment can effectively promote the formation and dissolution of nutrients, and increase the content of flavorful nucleotides and volatile gases.Practical applicationThis study provides a novel processing method for traditional stewed stock. Ultrasonic combined with MW treatment can quickly degrade the protein in the raw material and dissolve it into the stock. At the same time, it promotes the formation of flavor nucleotides and accelerates the Maillard reaction to produce more flavor substances. The technology has the advantages of short processing time, environmental protection and safety. It can be used as a potential pretreatment technology to regulate the flavor of stock‐soup.

Microwave facilitated bacterial liquefaction of sago biomass for efficient biomethane production: Energy and cost assessment

Sago has been considered to be a major staple food throughout the world for centuries. Thus, the sago processing industry also contributes to economic growth. However, waste disposal from this industry is an environmental concern and is addressed in this study. The generated solid waste sago is a starchy-rich substrate that is underutilized and can be exploited for bioenergy production. The present study focused on improving the hydrolytic potential of sago biomass during anaerobic digestion by implementing the combined microwave and bacterial pretreatment techniques. The microwave liquefaction yields the maximum solubilization of 11 % at the microwave power of 720 watts and the time of 11 min. Incorporation of bacterial pretreatment significantly enhances COD solubilization from 11 % to 31.6 %. This combined pretreatment of sago biomass shows the biomethane generation of 0.223 L/gCOD compared to the microwave (0.106 L/gCOD) and control sample (0.044 L/gCOD). Energy and cost analysis of combinative pretreatment shows a positive net energy of 0.97 kWh/kg and a net cost of -1.63 USD/ton. Thus, this combined pretreatment can be effectively adapted on an industrial scale with further improvements.

Effects of microwave irradiation at various temperatures on biosludge disintegration

ABSTRACT The waste biological sludge disintegration by using microwave irradiation was investigated at a ramping rate of 2°C/min and 5 min holding time at various target temperatures. Significant disintegration of biosludge was observed and the highest disintegration degree was determined about 82% at the temperature of 110°C. Increase of target temperature elevated the energy needs to 98, 123 and 148 kWh/kg TS at the temperatures of 75°C, 90°C and 110°C, respectively. The gradual increase of sugar and protein in the sludge slurry with increasing temperatures indicates successful degradation. The microwave pretreatment increased the specific surface area of the sludge by particle size reduction. The specific surface area of raw sludge was 70 m2/kg and rose to approximately 253.7 m2/kg at 110°C with an increment ratio of 260%. Although a significant NH4–N release was not observed, PO4–P concentrations increased from 11.0 mg/L to 16.3, 20.7 and 29.2 mg/L at the temperatures of 75°C, 90°C, 110°C, respectively. While the specific filter resistance of waste biological sludge was about 1.0 × 1013, increasing the microwave target temperature, the ability of dewatering decreased and the highest SFR value of 5.1 × 1014 was observed at the temperature of 110°C.

Stripping of aggregate from mortar in waste concrete heated by microwave: Mechanisms of differential-temperature stress and vapor expansion pressure

Microwave heating, which is used for pre-treatment of concrete before it is comminuted, stands as a strong candidate for selective liberation of multiphase materials like concrete. This paper is concerned with the selective liberation of concrete's raw constituents (particularly aggregate) for recycling by considering the water content of concrete as a parameter of microwave heating for the first time. The deterioration law of the concrete's performance was characterized by the variation in the splitting tensile strength and relative dynamic modulus after heating by microwave at different water contents. Besides, tests were conducted to evaluate the performance of the interface transition zone (ITZ) between aggregate and mortar as well as to investigate the reasons for the stripping behavior of aggregate-mortar, which included the interface tensile strength test, temperature measurement, and porosity test. The deterioration law of splitting tensile strength and relative dynamic modulus revealed that the performance of concrete was subject to different degrees of damage depending on the water content. Furthermore, experimental results showed that interface bonding strength between aggregate and mortar was dramatically impaired, and a large temperature difference was generated between the aggregate and mortar during microwave heating. Meanwhile, the permeable pores increased considerably even when the specimens were dried. In the presence of water, the intactness of ITZ between aggregate and mortar was destroyed by microwave heating, and its performance was significantly lowered, which led to the occurrence of stripping behavior between aggregate and mortar. This was reaffirmed by the microstructure presented by scanning electron microscopy. Thus, the newly developed microwave pre-treatment improved by providing appropriate water contents for concrete corresponding to different strength grades is a promising method for recycling aggregate from waste concrete.

An efficient and eco-friendly method for removing sericin using microwave-assisted steam degumming

Silk is a promising textile resource, but its degumming treatment still lacks efficient and non-polluting methods. In this paper, an innovative silk degumming process combining microwave pre-treatment and steam degumming is introduced. When the technical parameters of microwave-steam synergistic degumming were 10 min of microwave, 120 ℃ of steam temperature, and 30 min of steam time, the degumming efficiency of the specimen was three times of the traditional Na2CO3 degumming method, and the energy consumption was only one-half of the traditional method. In terms of time efficiency, the traditional Na2CO3 degumming took 2.75 h, while this novel method took only 0.75 h. Among the samples, the mechanical properties of the specimens treated with microwave for 10 min were the best, with the warp breaking strength of 542.20 N and the weft breaking strength of 356.19 N. Meanwhile, the hygroscopicity and air permeability were also the best compared to the traditional treating samples. This indicates that microwave-steam synergistic degumming technology is a clean technology with the advantages of high sericin degumming rate, short degumming time, low energy consumption, and no use of any chemicals. This method is conducive to achieving better and faster sustainable development.

Magnetic iron oxide nanoparticle enhanced microwave pretreatment for anaerobic digestion of meat industry sludge

Our study investigates the effects of iron oxide (Fe3O4) nanoparticles combined microwave pretreatment on the anaerobic digestibility and soluble chemical oxygen demand (SCOD) of meat industry sludge. One of our main objectives was to see whether the different microwave-based pretreatment procedures can enhance biogas production by improving the biological availability of organic compounds. Results demonstrated that combining microwave irradiation with magnetic iron oxide nanoparticles considerably increased SCOD (enhancement ratio was above 1.5), the rate of specific biogas production, and the total cumulative specific biogas volume (more than a threefold increment), while having no negative effect on the biomethane content. Furthermore, the assessment of the sludge samples’ dielectric properties (dielectric constant and loss factor measured at the frequency of 500 MHz) showed a strong correlation with SCOD changes (r = 0.9942, R2 = 0.99), offering a novel method to evaluate pretreatment efficiency.

Enhanced anaerobic co-digestion of cattle manure with food waste and pig manure: Statistical optimization of pretreatment condition and substrate mixture ratio

This study investigated the optimal pretreatment condition and mixture ratio of cattle manure (CM) for its efficient anaerobic co-digestion (AcoD) with food waste (FW) and pig manure (PM). The pretreatment performances of thermal (TM), microwave (MW), and ultrasound (US) technologies and the AcoD performance were statistically and experimentally evaluated at various mixture ratios of CM, FW, and PM. The results revealed that the most effective pretreatment condition with the TM, MW, and US pretreatments was 129.3 °C for 49.6 min, 824.2 W for 7.3 min, and 418.0 W for 36.3 min, respectively. The best AcoD performance of optimally pretreated CM (PCM) was achieved when 30.5 % PCM was mixed with 42.5 % FW and 27.0 % PM. A long-term evaluation showed that the start-up rate for the anaerobic mono-digestion of PCM was 2.3 times faster than that of CM and the amount of methane produced was 4.7 times higher; process stability was thus preferentially maintained under a higher organic loading rate (OLR) (2.0 kg-VS/m3∙d). The start-up rate for the AcoD of PCM with FW and PM was 1.2 times higher than that of the AcoD of CM with FW and PM. Although the performance gap between the AcoD reactors after steady state was not significantly different, the PCM AcoD reactor provided a more stable operation under a higher OLR (5.0 kg-VS/m3∙d). This study demonstrates that the pretreatment and co-digestion of CM could significantly enhance the production of biogas and improve process stability.

Energy efficient biohydrogen production from waste activated sludge through a novel phase separated pretreatment

Disintegration of sludge by microwave irradiation is considered an energy-intensive pretreatment as it demands more significant energy input to achieve the desirable solubilization. Extracellular polymeric substance (EPS) present in the floc matrix of sludge limits the extent of sludge solubilization. Hence, this study attempted to disrupt the EPS with potassium peroxymonosulphate (PPMS) before microwave (MW) pretreatment to attain maximal solubilization in an energy-efficient way. A maximal EPS disruption was achieved at 0.009 g/g TS of PPMS dosage and treatment time of 36 min. The outcome of the phase-separated pretreatment shows that PPMS induced MW pretreatment (PPMS-MW) obtained a maximum chemical oxygen demand (COD) solubilization of 35.67 % at a specific energy input of 8795 kJ/kg TS. In contrast, the MW pretreatment achieved only 22.41 % at a specific energy input of 21973 kJ/kg TS. When comparing both PPMS-MW and MW pretreatments, an ample amount of energy was saved by PPMS-MW than MW. The biohydrogen production potential assay showed that PPMS-MW obtained an increased biohydrogen production of 79.76 mL/g VS compared to MW (50.10 mL/g VS). Thus, this phase-separated PPMS-MW pretreatment was considered efficient compared to MW pretreatment.

Synergistic microwave and acidic deep eutectic solvent-based pretreatment of Theobroma cacao pod husk biomass for xylooligosaccharides production

The bioconversion of lignocellulosic biomass into novel bioproducts is crucial for sustainable biorefineries, providing an integrated solution for circular economy objectives. The current study investigated a novel microwave-assisted acidic deep eutectic solvent (DES) pretreatment of waste cocoa pod husk (CPH) biomass to extract xylooligosaccharides (XOS). The sequential DES (choline chloride/citric acid, molar ratio 1:1) and microwave (450W) pretreatment of CPH biomass was effective in 67.3% xylan removal with a 52% XOS yield from total xylan. Among different XOS of varying degrees of polymerization, a higher xylobiose content corresponding to 69.3% of the total XOS (68.22 mg/g CPH) from liquid fraction was observed. Enzymatic hydrolysis of residual xylan from pretreated CPH biomass with low commercial xylanase (10 IU/g) concentration yielded 24.2% XOS. The MW-ChCl/citric acid synergistic pretreatment approach holds great promise for developing a cost-effective and environmentally friendly method contributing to the sustainable production of XOS from agricultural waste streams.

Microwave pretreatment effects on the aroma precursors, sensory characteristics and flavor profiles of fragrant rapeseed oil

Microwave technology offers a rapid and uniform heating method. This study investigated how microwave pretreatment affects the aroma precursors and flavor of fragrant rapeseed oils (FROs). Microwave pretreatment led to decreased levels of polyunsaturated fatty acids, sugars, protein-bound amino acids, and glucosinolates. Using gas chromatography–mass spectrometry, we identified 66 volatile compounds in the oil samples. Among these, based on odor activity values (OAV ≥ 1), we found 9 aldehydes, 1 ketone, 6 pyrazines, 1 isothiocyanate, and 7 nitriles as the key aroma-active compounds, contributing fatty-like, nutty-like, and pungent-like odors, respectively. The electronic nose results highlighted W5S and W1W as primary sensors for determining the flavor profiles of FROs. Notably, aroma-active pyrazines exhibited strong negative correlations with sucrose, cysteine, lysine, and isoleucine. This research provides essential insights for enhancing the aroma of FROs.

Effect of Microwave Pretreatment on the Properties and Microstructure of Low-Concentration Carbon Dioxide Early Cured Cement-Based Materials

The utilization of microwave drying technology has expanded across various sectors due to its rapid processing speed, reduced operation time, lower sample temperatures, and consistent heating. In this research, microwave pretreatment was implemented prior to carbonation curing with low concentrations, and an array of tests including moisture content, compressive strength, carbonation depth, CO2 absorptivity, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were utilized to investigate the effect of microwave pretreatment on the properties and microstructure of cementitious materials under early carbonation curing with low CO2 concentrations. The findings reveal that microwave pretreatment significantly decreases the moisture content within the test specimens, expediting the ingress of CO2 and improving the compressive strength of the specimens. At the same time, the effectiveness of microwave pretreatment in reducing moisture content diminishes as the pretreatment time increases. The absorption of CO2 is relatively rapid in the early stage of carbonation curing, with over 50% of the CO2 absorption occurring within the 0–6 h period of carbonation curing. The hydration products and microstructure of the uncarbonated part inside the specimens are generally consistent with the normal curing state. The formation of CaCO3 contributed to the densification of the specimen by infilling its internal voids, thereby enhancing its compressive strength. Although carbonation curing enlarges the average pore size of the samples, it also serves a filling function, making the samples more compact and reducing the porosity.

Effect of low microwave temperature on the physical and chemical properties of waste activated sludge

In this study, the effect of microwave (MW) irradiation at a target temperature of 80 °C with a heating rate of two °C/min and a holding time of five minutes on the physicochemical properties of activated sludge was studied. The results showed that subjecting biosludge to MW pretreatment resulted in a reduction in particle size to 14.5, 44.6, and 72.8 for d10, d50, and d90, respectively and an increase in the specific surface area of the biosludge to 235.9 m<sup>2</sup>/kg. Pretreatment resulted in an increase in soluble oxygen demand, sugar, and protein concentrations to 2,380.0 mg/L, 66.5 mg/L, and 1.81 g/L, respectively. A slight increase in the release of inorganic compounds, especially NH<sub>4</sub>-N and PO<sub>4</sub>-P, was observed in the disintegrated biosludge. While there was an increase in release of K and Zn, a decrease in concentrations of Na, Ca, Mg, and Al in the liquid was observed after MW irradiation. It was determined that the dewatering property deteriorated after biosludge disintegration, as it increased from raw sludge to disintegrated sludge by 21-fold.

Enhanced biomethane production from Scenedesmus sp. using polymer harvesting and expired COVID-19 disinfectant for pretreatment

This study evaluates the repurposing of expired isopropanol (IPA) COVID-19 disinfectant (64% w/w) to pretreat algal biomass for enhancing methane (CH4) yield. The impact of harvesting methods (centrifugation and polymer flocculation) and microwave pretreatment on CH4 production from Scenedesmus sp. microalgal biomass were also investigated. Results show minimal impact of harvesting methods on the CH4 yield, with wet centrifuged and polymer-harvested biomass exhibiting comparable and low CH4 production at 66 and 74 L/kgvolatile solid, respectively. However, microalgae drying significantly increased CH4 yield compared to wet biomass, attributed to cell shrinkage and enhanced digestibility. Consequently, microwave and IPA pretreatment significantly enhanced CH4 production when applied to dried microalgae, yielding a 135% and 212% increase, respectively, compared to non-pretreated wet biomass. These findings underscore the advantage of using dried Scenedesmus sp. over wet biomass and highlight the synergistic effect of combining oven drying with IPA treatment to boost CH4 production whilst reducing COVID-19 waste.