Chemical Pretreatment Research Articles

Investigation of Different Pre-Treatment Techniques and 3D Printed Turbulence Promoter to Mitigate Membrane Fouling in Dairy Wastewater Module.

This study investigates the enhancement of dairy wastewater treatment using chemical and physical pre-treatments coupled with membrane separation techniques to reduce membrane fouling. Two mathematical models, namely the Hermia and resistance-in-series module, were utilized to comprehend the mechanisms of ultrafiltration (UF) membrane fouling. The predominant fouling mechanism was identified by fitting experimental data into four models. The study calculated and compared permeate flux, membrane rejection, and membrane reversible and irreversible resistance values. The gas formation was also evaluated as a post-treatment. The results showed that the pre-treatments improved UF efficiency for flux, retention, and resistance values compared to the control. Chemical pre-treatment was identified as the most effective approach to improve filtration efficiency. Physical treatments after microfiltration (MF) and UF showed better fluxes, retention, and resistance results than ultrasonic pre-treatment followed by UF. The efficacy of a three-dimensionally printed (3DP) turbulence promoter was also examined to mitigate membrane fouling. The integration of the 3DP turbulence promoter enhanced hydrodynamic conditions and increased the shear rate on the membrane surface, shortening filtration time and increasing permeate flux values. This study provides valuable insights into optimizing dairy wastewater treatment and membrane separation techniques, which can have significant implications for sustainable water resource management. The present outcomes clearly recommend the application of hybrid pre-, main- and post-treatments coupled with module-integrated turbulence promoters in dairy wastewater ultrafiltration membrane modules to increase membrane separation efficiencies.

Nanotechnology Applied to Cellulosic Materials.

In recent years, nanocellulosic materials have attracted special attention because of their performance in different advanced applications, biodegradability, availability, and biocompatibility. Nanocellulosic materials can assume three distinct morphologies, including cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and bacterial cellulose (BC). This review consists of two main parts related to obtaining and applying nanocelluloses in advanced materials. In the first part, the mechanical, chemical, and enzymatic treatments necessary for the production of nanocelluloses are discussed. Among chemical pretreatments, the most common approaches are described, such as acid- and alkali-catalyzed organosolvation, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, ammonium persulfate (APS) and sodium persulfate (SPS) oxidative treatments, ozone, extraction with ionic liquids, and acid hydrolysis. As for mechanical/physical treatments, methods reviewed include refining, high-pressure homogenization, microfluidization, grinding, cryogenic crushing, steam blasting, ultrasound, extrusion, aqueous counter collision, and electrospinning. The application of nanocellulose focused, in particular, on triboelectric nanogenerators (TENGs) with CNC, CNF, and BC. With the development of TENGs, an unparalleled revolution is expected; there will be self-powered sensors, wearable and implantable electronic components, and a series of other innovative applications. In the future new era of TENGs, nanocellulose will certainly be a promising material in their constitution.

Study of Water Filtration Without Chemical Pre-Treatment

This research work focused on studying water purification without chemical pre-treatment. In the studies, alternative approaches were carried out to develop a filter bed suitable for filtering water without the use of chemical treatments that is also cost effective. Polyvinyl Chloride (PVC) pipes (100 × 1700) mm were used as filter boxes. The experiment carried out during the study was divided into two major parts; that is slow sand and rapid sand filter parameters. The slow sand filter consisted of two filter pipes, one consisting of a stratified layer of sand of size range of 0.20 – 0.60 mm with a depth of 700 mm as filter medium. The turbidity, filtration rate and head loss of the effluent across the filter were monitored for 15 days. It was found that slow sand filter plus granular activated carbon (GAC) and rapid sand filter plus GAC were more effective in the removal of turbidity. Turbidity reduced with the increase in time. Rapid sand filter was found to be the least effective in the removal of bacteria while slow sand filter plus GAC was the most effective. The slow sand filter unit gave a very high coliform count compared to other filter units. It was found that the filtration rate plays a vital role in the mechanism of filtration.

Effect of treated clinoptilolite zeolite on alkali-silica reaction

The reactive aggregates can cause a volumetric expansion in the concrete leading to cracking and spalling due to alkali-silica reaction (ASR). The use of natural zeolite as the supplementary cementitious material can reduce the expansion due to ASR by providing physical space for the ASR gel along with the adsorption of alkalis through the cation exchange. However, the rate of reduction in expansion may sometimes not be satisfactory due to the slow rate of cation exchange along with other factors. Therefore, the present study investigates three different treatment techniques (calcination, milling, and chemical pre-treatment) on clinoptilolite zeolite to obtain an optimal method for reducing the expansion due to ASR. Calcination was done at 400 °C for 3 h to increase the amorphous contents, while milling was done for 3 h to increase the specific surface area of zeolite particles leading to increasing pozzolanic activities. The chemical pre-treatment was accomplished with a 1 M Ca(OH)2 solution to largely remove any existing sodium or potassium ions via cation exchange. To observe the physical expansion due to ASR, mortar bars were prepared with highly reactive cherty sand and up to 20% of both untreated and treated zeolite with the replacement of the portland cement. Results revealed that calcination slightly increased the amorphous contents while milling substantially increased the specific surface area of zeolite particles. The chemical pre-treatment successfully transformed the zeolite into calcium-based clinoptilolite zeolite. Results also revealed that the application of up to 20% untreated, calcined, milled, and chemically treated zeolite reduced the ASR expansion by up to 60%, 40%, 70%, and 42%, respectively, compared to the control sample at 28 days. Overall, among the three different treatment methods, milling was the most effective method to reduce the ASR expansion, while calcined and chemically treated zeolite was less effective than untreated zeolite.

Morphological and thermal stability characteristics of oil palm frond and trunk by ultrasound-low alkali-based pretreatment

Oil palm fronds and trunks leave a lot of lignocellulosic residues in the agricultural field. Due to its highly complex chemical composition, the lignocellulosic matrix is difficult to break down. This study aims to investigate the effects of chemo-physical pretreatment of oil palm fronds and trunks with ultrasound in a low alkali concentration solution. The microstructure and thermal stability of the oil palm frond and trunk were investigated using scanning electron microscopy (SEM) and a thermogravimetric (TG) method. SEM analysis proved the deterioration of the lignocellulose matrix of the ultrasound-assisted alkali pretreatment compared to raw. According to the TG results, the decomposition temperature curve of treated oil palm shifted to the right side after 50 percent mass degradation, indicating more excellent thermal stability than untreated oil palm biomass. On the other hand, at a temperature above 350 °C, the pretreated biomass has less thermal stability. It has been demonstrated that a combination of low chemical concentration and physical pretreatments can disrupt the oil palm lignocellulose microstructure and potentially shorten the time required to achieve maximum hydrolysis efficiency. Furthermore, ultrasonication power of 300 W, frequency of 40 kHz, temperature of 80 °C, and time of 30 min in combination with low alkali-based pretreatment in oil palm residue will be helpful in applications requiring greater thermal stability.

Chemical Pretreatments and Anaerobic Digestion Shape the Virome and Functional Microbiome in Fecal Sludge.

The decomposition and pathogen inactivation of fecal sludge (FS) are vitally important for safely managing onsite sanitation and protecting public and environmental health. However, the microbiome and virome assemblages in FS after chemical and biological treatments remain unclear. Here, we reported the differences in the solid reduction and microbiomes of FS subjected to potassium ferrate (PF), alkali (ALK), and sodium hypochlorite (NaClO) pretreatments and anaerobic digestion (AD). The PF and NaClO pretreatments enhanced FS hydrolysis and pathogen suppression, respectively; AD suppressed Gram-positive bacteria. Most of the viromes were those of bacteriophages, which were also shaped by chemical pretreatments and AD. Metatranscriptome analysis revealed distinct gene expression patterns between the PF- and ALK-pretreated FS and the subsequent AD. Differentially expressed gene profiles indicated that genes related to biological processes, molecular functions, and transcriptional regulators were upregulated in ALK-AD and PF-AD samples. These findings suggested that the effect of different treatment technologies on the viral diversity, pathogen abundance, and metabolic function of the core microbiome extends beyond FS decomposition and that the use of combined processes would provide possible alternatives for FS management in pandemic emergencies.

Adsorption Characterization of Lactobacillus sp. for Di-(2-ethylhexyl) phthalate.

Di-(2-ethylhexyl) phthalate (DEHP) is the widely detected plasticizer in foods whose exposure is associated with a myriad of human disorders. The present study focused on identifying Lactobacillus strains with high adsorption potential towards DEHP and further elucidating the mechanism of binding using HPLC, FTIR and SEM. Two strains, Lactobacillus rhamnosus GG and Lactobacillus plantarum MTCC 25,433, were found to rapidly adsorb more than 85% of DEHP in 2h. Binding potential remained unaffected by heat treatment. Moreover, acid pre-treatment enhanced the DEHP adsorption. Chemical pre-treatments, such as NaIO4, pronase E or lipase, caused reduction in DEHP adsorption to 46% (LGG), 49% (MTCC 25,433) and 62% (MTCC 25,433), respectively, attributing it to cell wall polysaccharides, proteins and lipids. This was also corroborated by stretching vibrations of C = O, N-H, C-N and C-O functional groups. Furthermore, SDS and urea pre-treatment, demonstrated the crucial role of hydrophobic interactions in DEHP adsorption. The extracted peptidoglycan from LGG and MTCC 25,433 adsorbed 45% and 68% of DEHP, respectively, revealing the imperative role of peptidoglycan and its integrity in DEHP adsorption. These findings indicated that DEHP removal was based on physico-chemical adsorption and cell wall proteins, polysaccharides or peptidoglycan played a primary role in its adsorption. Owing to the high binding efficiency, L. rhamnosus GG and L. plantarum MTCC 25,433 were considered to be a potential detoxification strategy to mitigate the risk associated with the consumption of DEHP-contaminated foods.

Application of a new strategy for time-efficient laser treatment of galvanized steel substrates to improve the adhesion properties

Laser structuring to improve the adhesion properties of steel substrates in fiber-metal laminates offers many advantages that are highly suitable for modern industrial requirements. Maintenance and energy costs are relatively low, it is easy to automate, and there are no by-products such as chemicals or abrasives to dispose of or recycle. This makes laser structuring a particularly environmentally friendly process, which is nowadays more important than ever. On the other hand, the process time for laser structuring is much higher than for chemical pre-treatment, for example. In past studies, the time and cost efficiency of the laser structuring process has tended to play a minor role. However, there are approaches in which laser structured surfaces are adapted to the shear stress peaks occurring within the adhesive layer, thus requiring only partial structuring of the area to be bonded, potentially saving process time. In this experimental study, electrolytically galvanized steel substrates were partially laser structured to match the shear stress distribution and then bonded to a carbon fiber-reinforced plastic. The adhesion properties achieved were characterized using shear tensile tests and compared with the properties of the fully structured ones. With the partial laser structuring, a saving of 66 % of the conventional process time was achieved while maintaining 95 % of the same shear strength.

A new evaluation system of iron bioavailability in seaweed

In marine ecosystems, the avid binding of iron (Fe) to organic ligands influences Fe bioavailability in seaweed. This study aimed to elucidate Fe's biological availability to seaweed and develop a simple and rapid bioassay method as a new evaluation system. Undaria pinnatifida was used as a model seaweed species and the actual seaweed samples were collected using the 0.5 m × 0.5 m quadrat from the Mashike Bay area of Hokkaido, Japan. Chlorophyll fluorescence measurements were utilized as an index to evaluate the biological -effectiveness of Fe and compared with the results of culture tests based on growth. The effect of Fe content on media, pre-culture, concentrations and types of chelating and reducing agents in clearing solutions, cleaning time, Fe removal effect, and resistance to seaweed were systematically optimized to obtain the maximum efficacy of the washing solution. A bioassay was developed to evaluate the Fe environment by combining chlorophyll fluorescence measurements. The findings suggest that the tolerance of seaweeds to the wash solution is strongly influenced by the concentrations of the chelating and reducing agents than their types. Washing with 0.02 M Ti-Citrate/EDTA solution for 80 s was the most effective in terms of maximum Fe removal with minimum cell damage. The application of pre-culture and chemical pre-treatment methods under Fe deficiency to the culture strain confirmed the maximum reproducibility in the culture test. Finally, the developed method was applied to actual seaweed samples and was found to be applicable to many seaweed species. However, the method was less robust for some seaweed species and depended on the seaweed growth stage.

Impact of eco-friendly chemical pretreatment on physicochemical and surface mechanical properties of sustainable lignocellulosic agricultural waste

This research aimed to investigate the impact of glycerol (Gly) and choline chloride (ChCl) pretreatments on physico-chemical and mechanical properties of rice husk (RH) at a submicron scale. Gly (75 wt%) and ChCl (25 wt%) were used to pretreat RH at 110 °C for 4 h in a water bath (150 rpm). Physico-chemical and surface mechanical (elastic modulus and hardness) properties of treated RH were determined and compared with untreated ones. The impacts of Gly and ChCl pretreatments on RH, surface morphology, structure, thermal stability, elastic modulus, and hardness were investigated using scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), x-rays diffractometry (XRD), thermogravimetric analysis (TGA) and nanoindentation technique, respectively. Experimental results depicted that pretreatment of RH with Gly and ChCl produced cellulosic-rich fiber, increase crystallinity, and enhanced thermal stability. In contrast to the untreated (35 %) RH, the ChCl and Gly-treated RH had cellulose contents of 49 % and 45 %, respectively. The degree of crystallinity was increased after the treatment of RH with 37 % and 35 % in ChCl RH, respectively, as compared to the untreated one. Elastic modulus and hardness of ChCl-treated RH were decreased by 67 % and 70 %, respectively, compared to the untreated one. Similarly, reductions in elastic modulus and hardness were noted in the case of Gly treatment. According to current research, lignocellulosic biomass can be pretreated with green solvents to produce cellulosic-rich fiber for engineered composite applications.

Influence of common palynological extraction treatments on ultraviolet absorbing compounds (UACs) in sub-fossil pollen and spores observed in FTIR spectra

IntroductionBiological life, atmospheric circulation and the Earth’s climate may be influenced by UV-B radiation. In plants, Ultraviolet Absorbing Compounds (UACs) are an indicator of UV-B exposure, and the abundance of UACs in pollen and spores of embryophytes is measurable using Fourier Transform Infrared (FTIR) micro-Spectroscopy. However, understanding the influence of common chemical pre-treatments on sub-fossil pollen and spores with a view to UV-B reconstruction still requires investigation.MethodsHere, peat samples collected from a Late Holocene raised bog were treated with different chemicals (HCl, KOH, and acetolysis) for varying treatment times (up to 210 min). Pollen or spores of three common taxa (Alnus, Calluna and Sphagnum) were isolated and FTIR spectra obtained on individual grains. The spectra were compared to modern pollen and spore samples collected nearby.ResultsSpectra of modern and sub-fossil samples show several visible differences related to lipid and protoplast contents. The results of chemical treatments on sub-fossil pollen and spores reveal that HCl produced limited changes, while KOH and acetolysis altered several peaks, including the UAC-related aromatic peak at 1516 cm−1. We observe that all treatments modify the FTIR spectra to some degree, from weakest (HCl) to strongest (acetolysis). With respect to reduction of UAC peak area and treatment time, we observe in some cases a significant log-decay relationship, notably for KOH treatment on Calluna pollen and acetolysis on Sphagnum spores. Compared to untreated control samples, UAC peak area in Alnus, Calluna and Sphagnum reduced by 68%, 69% and 60% respectively, after only 3 min of acetolysis treatment. After 60 minutes of acetolysis treatment UAC peaks were reduced by 77%, 84% and 88%.DiscussionDue to the potential for taxon-specific effects and significant reductions in UAC peak area even within short treatment times, our recommendation for future applications in palaeoecological studies on palynomorph chemistry is to avoid chemical digestions in the pollen extraction process in favour of separation methods including micro-sieving and density separation.

Environmental Sustainable Cement Mortars Based on Polyethylene Terephthalate from Recycling Operations.

The building and construction industry is a key sector behind the ecological transition in that it is one of the main responsible factors in the consumption of natural resources. Thus, in line with circular economy, the use of waste aggregates in mortars is a possible solution to increase the sustainability of cement materials. In the present paper, polyethylene terephthalate (PET) from bottle scraps (without chemical pretreatment) was used as aggregate in cement mortars to replace conventional sand aggregate (20%, 50% and 80% by weight). The fresh and hardened properties of the innovative mixtures proposed were evaluated through a multiscale physical-mechanical investigation. The main results of this study show the feasibility of the reuse of PET waste aggregates as substitutes for natural aggregates in mortars. The mixtures with bare PET resulted in less fluid than the specimens with sand; this was ascribed to the higher volume of the recycled aggregates with respect to sand. Moreover, PET mortars showed a high tensile strength and energy absorption capacity (with Rf = 1.9 ÷ 3.3 MPa, Rc = 6 ÷ 13 MPa); instead, sand samples were characterized by a brittle rupture. The lightweight specimens showed a thermal insulation increase ranging 65-84% with respect to the reference; the best results were obtained with 800 g of PET aggregate, characterized by a decrease in conductivity of approximately 86% concerning the control. The properties of these environmentally sustainable composite materials may be suitable for non-structural insulating artifacts.

Proficient bioconversion of rice straw biomass to bioethanol using a novel combinatorial pretreatment approach based on deep eutectic solvent, microwave irradiation and laccase

Current study is the first report of the combined application of chemical (deep eutectic solvent), physical (microwave irradiation) and biological (laccase) pretreatment strategies for enhancing the enzymatic digestibility of rice straw biomass. Pretreated rice straw biomass was saccharified by cellulase/xylanase from Aspergillus japonicus DSB2 to get a sugar yield of 252.36 mg/g biomass. Design of Experiment based optimization of pretreatment and saccharification variables increased the total sugar yield by 1.67 times (421.5 mg/g biomass, saccharification efficiency 72.6%). Sugary hydrolysate was ethanol-fermented by Saccharomyces cerevisiae and Pichia stipitis to achieve an ethanol yield of 214 mg/g biomass (bioconversion efficiency 72.5%). Structural/chemical aberrations induced in the biomass due to pretreatment were elucidated by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and 1H nuclear magnetic resonance techniques to unravel the pretreatment mechanisms. Combined application of various physico-chemical/biological pretreatment may be a promising approach for proficient bioconversion of rice straw biomass.

Designing 3D fractal morphology of eco-friendly nanocellulose-based composite aerogels for water remediation

The renewable and economic aspects of cellulose nanofibril (CNF)-based aerogels are reviving interest in green adsorbents for water remediation. However, the combination of CNF chemical pre-treatment, fibrillation processes, and a solvent-free hydrophobization route to obtain structurally wet-resilient and eco-friendly porous adsorbent is lacking in the literature. Herein, the oxidation/fibrillation approaches to isolating CNF from sugarcane bagasse and producing CNF-based aerogels were investigated. These porous materials were designed through ice-templating, followed by a freeze-drying method. Oxidated CNF aerogels containing 3-times-microfluidization (TMI3) exhibited the most homogeneous interconnected regular structure, with micro- and nanoporous structures achieving robust compressive mechanical properties (Young’s modulus ∼400 kPa). Natural rubber latex (NR) was combined with TMI3, yielding a water-resilient and hydrophobic composite aerogel (TMI/NR). The removal capacity of TMI/NR ranged from 108 to 420 mg·g−1 for Cu (II) and 159–334 mg·g−1 for methylene blue (MB) dye, with reuse performance ranging from 66 to 98 % over the reuse cycles. Furthermore, TMI/NR aerogel showed its effectiveness for Cu (II) removal from water in an environmentally relevant concentration (20 and 60 µg·L−1 Cu(II)) without posing additional toxicity to Daphnia similis aquatic model organisms. These findings indicate TMI/NR composite aerogels as promising and efficient green adsorbents of pollutants from contaminated water.

Biorationals and Chemical Treatments to Overcome the Dormancy in Tree spp.

Dormancy in seeds is defined as the failure of seeds to germinate despite the presence of all necessary conditions for germination. It is caused by the impermeability of the hard seed coat or a lack of availability and activity of germination-essential enzymes. Seeds undergo a variety of physical and chemical pre-treatments to break their dormancy. It results into lower seed germination rate and poor growth. To overcome this drawback various treatments are given to the seeds before sowing this study reviews some of the pre-sowing practices and the effects they have on seed germination and growth. Scientists are quite concerned about seed dormancy; hence it is a research topic of interest to develop an effective solution. All viable seeds are capable of germinating if the proper pre-sowing treatment is used.

Stretchable and wash durable reactive silver ink coatings for electromagnetic interference shielding, Joule heating, and strain sensing textiles

In this paper, we demonstrate a highly conductive, stretchable, and wash-durable fabric for a variety of electronic textile applications such as electromagnetic interference (EMI) shielding, Joule heating, and strain sensing by utilizing a chemical etchant pretreatment that promotes covalent bonding, a reactive silver ink with conformal in situ silver reduction, and the use of a polymer coating for a protective barrier. Reactive ink coated on polyethylene terephthalate (PET) knitted textiles exhibit an average EMI shielding efficiency of 74.8 dB in the X band (frequency range of 8–12 GHz) and 76.6 dB in the Ku band (12–18 GHz). The conductive textiles show high Joule heating performance, where a temperature of 152 °C can be achieved at only 1.3 V DC applied voltage. This Joule heating performance is maintained after stretching and washing. Furthermore, the textile may be used for strain sensing and monitoring human movement. As prepared silver films do not degrade after 1000 stretching cycles at 50 % strain and maintain EMI SE higher than 70 dB after 300 min washing. The demonstrated textiles may be used for wearable electronics, personal medical devices, and next generation communications.

Current Development of Chemical Penetration Enhancers for Transdermal Insulin Delivery.

The use of the transdermal delivery system has recently gained ample recognition due to the ability to deliver drug molecules across the skin membrane, serving as an alternative to conventional oral or injectable routes. Subcutaneous insulin injection is the mainstay treatment for diabetes mellitus which often leads to non-compliance among patients, especially in younger patients. Apart from its invasiveness, the long-term consequences of insulin injection cause the development of physical trauma, which includes lipohypertrophy at the site of administration, scarring, infection, and sometimes nerve damage. Hence, there is a quest for a better alternative to drug delivery that is non-invasive and easily adaptable. One of the potential solutions is the transdermal delivery method. However, the stratum corneum (the top layer of skin) is the greatest barrier in transporting large molecules like insulin. Therefore, various chemical enhancers have been proposed to promote stratum corneum permeability, or they are designed to increase the permeability of the full epidermis, such as the use of ionic liquid, peptides, chemical pre-treatment as well as packaging insulin with carriers or nanoparticles. In this review, the recent progress in the development of chemical enhancers for transdermal insulin delivery is discussed along with the possible mechanistic of action and the potential outlook on the proposed permeation approaches in comparison to other therapeutical drugs.

Dithiotreitol pre-treatment of synovial fluid samples improves microbiological counts in peri-prosthetic joint infection

PurposeSynovial fluid cultures of periprosthetic joint infections (PJI) may be limited by bacteria living in the fluids as biofilm-aggregates. The antibiofilm pre-treatment of synovial fluids with dithiotreitol (DTT) could improve bacterial counts and microbiological early stage diagnosis in patients with suspected PJI.MethodsSynovial fluids collected from 57 subjects, affected by painful total hip or knee replacement, were divided into two aliquots, one pre-treated with DTT and one with normal saline. All samples were plated for microbial counts. Sensitivity of cultural examination and bacterial counts of pre-treated and control samples were then calculated and statistically compared.ResultsDithiothreitol pre-treatment led to a higher number of positive samples, compared to controls (27 vs 19), leading to a statistically significant increase in the sensitivity of the microbiological count examination from 54.3 to 77.1% and in colony-forming units count from 1884 ± 2.129 CFU/mL with saline pre-treatment to 20.442 ± 19.270 with DTT pre-treatment (P = 0.02).ConclusionsTo our knowledge, this is the first report showing the ability of a chemical antibiofilm pre-treatment to increase the sensitivity of microbiological examination in the synovial fluid of patients with peri-prosthetic joint infection. If confirmed by larger studies, this finding may have a significant impact on routine microbiological procedures applied to synovial fluids and brings further support to the key role of bacteria living in biofilm-formed aggregates in joint infections.

Spent Mushroom Substrate Hydrolysis and Utilization as Potential Alternative Feedstock for Anaerobic Co-Digestion

Valorization of lignocellulosic biomass, such as Spent Mushroom Substrate (SMS), as an alternative substrate for biogas production could meet the increasing demand for energy. In view of this, the present study aimed at the biotechnological valorization of SMS for biogas production. In the first part of the study, two SMS chemical pretreatment processes were investigated and subsequently combined with thermal treatment of the mentioned waste streams. The acidic chemical hydrolysate derived from the hydrothermal treatment, which yielded in the highest concentration of free sugars (≈36 g/100 g dry SMS, hydrolysis yield ≈75% w/w of holocellulose), was used as a potential feedstock for biomethane production in a laboratory bench-scale improvised digester, and 52 L biogas/kg of volatile solids (VS) containing 65% methane were produced in a 15-day trial of anaerobic digestion. As regards the alkaline hydrolysate, it was like a pulp due to the lignocellulosic matrix disruption, without releasing additional sugars, and the biogas production was delayed for several days. The biogas yield value was 37 L/kg VS, and the methane content was 62%. Based on these results, it can be concluded that SMS can be valorized as an alternative medium employed for anaerobic digestion when pretreated with both chemical and hydrothermal hydrolysis.

Novel alternative pretreatment approaches for production of quality raisins from grapes: Opportunities and future prospects

AbstractRaisins are high‐value products obtained by drying grape berries. Natural drying of grapes is difficult because a hydrophobic waxy cuticle is present on the berry surface. Pretreatment is an important operation in raisin production in which the waxy layer is dissolved or removed for enhancing the drying rate of grapes. Chemical pretreatment consisting of dipping grape bunches in a solution of alkali and oil emulsion is commonly followed for raisin production. However, the threat of chemicals to human health, the environment, and longer processing time lead to the development of an alternative to chemical pretreatment. Various alternative methods have been explored including the abrasive pretreatment and some novel thermal and nonthermal techniques. The potential of these alternative pretreatments has been discussed in this review along with a critical analysis of literature on grape drying. The fundamentals of grape drying and unit operations of the chemical and abrasive process of raisin production have also been narrated. An abrasive process as the best alternative to chemicals in raisin production has been described in detail along with future prospects of different physical pretreatments. This review provides comprehensive information on raisin production with a focus on chemical‐free processing of grape for raisin production.Practical applicationsRaisins are dried grapes rich in nutritional and functional ingredients that are beneficial for human health. A predrying treatment to remove or to dissolve the waxy layer from surface of grapes is an important operation in raisin production. The chemical method of pretreatment is prevalent among raisin processors. However, a chemical method has some limitations like longer processing time, intense use of chemicals, food safety issues, and so forth. Many novel pretreatments like superficial abrasion, thermal, and nonthermal techniques have been explored by researchers and it has the potential to produce safe raisins without use of any chemicals. These alternative techniques can be adopted for industrial‐scale processing of raisins. A lot of literature is available on the grape drying process, modeling, and quality aspects of raisins. All this information has been summarized in this comprehensive review with a comparison of unit operations, analysis of findings, and future aspects for the production of safe raisins. This review will be very useful for industrial‐scale processing of raisins adopting novel processes and it will also provide in‐depth knowledge to the academician and research scholars.