Physicochemical Pretreatment Research Articles

Acidic and thermal pre-treatments for anaerobic digestion inoculum to improve hydrogen and volatile fatty acid production using xylose as the substrate

Xylose is a by-product of lignocellulosic biomass processing for production of second-generation biofuels and could be suitable for bioproduct manufacturing. This paper describes an innovative approach that enables the system to achieve high yielding for hydrogen production. The study compared 4 physicochemical pre-treatments performed in an anaerobic mixed culture (acidic, thermal, acidic-thermal and thermal acidic) to achieve an inoculum with a high-efficiency xylose to hydrogen conversion under mesophilic conditions (30 °C). The acidic pre-treatment was the most efficient to select microorganisms able to produce hydrogen and volatile acid from xylose. Kinetics has shown that acidic pre-treatment had a hydrogen/xylose molar yielding factor of 1.57 (molar base) and a hydrogen maximum production rate of 253 mL H2 h−1. Mass balance considered all possible metabolic pathways using xylose as a substrate. Anaerobic degradation of ethanol was the most active pathway for hydrogen production in all experiments, except for the control. Each pre-treatment performed for the original inoculum resulted in different microbiological profiles, but the genus Clostridium was the most abundant in all assays. Acidic pre-treatment stimulated the growth of organisms from the genera Peptostreptococcaceae, Truepera and Kurthia, which could be related to the better results in hydrogen production found in this condition.

Mesta (Hibiscus spp.) – a potential feedstock for bioethanol production

ABSTRACT Mesta crop biomass is one of the unexplored lignocellulosic feedstocks for second-generation bioethanol production. The compositional analysis of two mesta species, namely Hibiscus sabdariffa and H. cannabinus were carried out which revealed that the mesta contains 41.89–46.50% cellulose that can be saccharified to release fermentative sugar. Among different physical and physico-chemical pretreatment methods employed, cold alkali (2%) treatment showed maximum cellulose enrichment (38.71%) and significant lignin removal (27.27% of total). Optimization of saccharification process for pretreated mesta biomass was carried out using Box–Behnken design. Based on the observations, use of 4.02% substrate loading, 15.02 FPU/mL of cellulase from psychrotolerant Aspergillus niger SH3, and 5.01 IU/gds of β-glucosidase from Pseudomonas lutea BG8, led to 533.25 mg/gds sugar release from the pretreated biomass. Simultaneous saccharification and fermentation was carried out using efficient thermotolerant yeast strain Saccharomyces cerevisiae LN that resulted in 4.1 g/L ethanol production. It can be concluded that mesta crop can be a good source for the production of second-generation biofuel and the ethanol yield can be further improved by use of accessory enzymes and co-fermenting yeast.

Analysis of Techniques for Improving the Adsorption Capacity of Talc

Mineral adsorbents, such as talc, are materials that are abundant in nature and used as scavengers, binding agents, fillers, etc. Mechanical and physicochemical pretreatment creates new opportunities for the production of highly effective mineral materials with a wide range of destinations. The possibility of using various techniques to enhance the adsorption properties of dispersed talc, namely, enrichment and use in a mixture with another mineral, treatment with various reagents, and changing the temperature and acidity conditions, is demonstrated. Phenomena and trends having an effect on the adsorption ability of talc are considered. Surface modification of talc can significantly increase its technological capability of absorbing resinous components of wood pulp in the manufacture of paper. It is shown that the adsorption and structural characteristics of dispersed talc change significantly after modifying it with organic reagents. The best effect is achieved when pretreating talc with cationic surfactant N-cetylpyridinium chloride. The resulting adsorbent is characterized by a high value of rosin adsorption, reaching 200 mg/g, which is commensurate with the data on the absorption of rosin by talc pretreated with a Penta-416 industrial mixture. Substantial changes in the surface properties due to an increase in the temperature, a change in the acidity, and a shift in the hydrophilic-hydrophobic balance occur when using the accessible, affordable, and safe anionic surfactants. The highest value of adsorption of rosin (160–170 mg/g) is typical for samples of talc modified with sodium oleate and enriched with zinc oxide. The importance of pretreatment of talc with solutions of mineral acids and salts that promote settling of suspensions and the formation of a compact precipitate is shown.

Biodegradability study of Egeria densa biomass using acid and basic pre-treatments for use in bioprocessing of energy products

Egeria densa is a submerged aquatic plant species, with a high capacity for colonization and growth. Its proliferation has caused serious problems in hydroelectricity generation, due to biomass accumulation in turbine containment grids. Bioprocessing of macrophytes may be an alternative for using this biomass to produce bioenergetic products such as biofuels. The cell wall of macrophytes is a lignocellulosic material with a complex lignin-hemicellulose-cellulose network, which may require pretreatment to provide the fermentable sugars as substrate prior further processing. This work aims to evaluate a physicochemical pretreatment of E. densa, with the objective of making its structure suitable for bioprocessing. Full factorial 23 analysis was performed for different concentrations of the reagents and reaction times. The variable responses were delignification, total carbohydrate yield and crystallinity grade. Results showed greater efficiency for alkaline hydrolysis, but both processes were viable for removing amorphous compounds and for increasing bundling of cellulose molecules.

Evaluation of physicochemical pretreatment of tomato plant for aerobic and anaerobic biodegradation

This study evaluates different hydrothermal pretreatment conditions for the tomato plant. Since these plants produce abundant waste due to their lignocellulosic content, biodegradation through anaerobic digestion is difficult. Hydrothermal pretreatment of the tomato plant was carried out at different times (0, 10, 15, 20, 30, and 60 min), with pressure and temperature conditions maintained at 394 K and 202,650 total Pa. In addition, acid and base were added to determine if they favored the hydrolysis of the lignocellulosic material. After determining the most appropriate pretreatment time for the different options (with or without chemical reagent), aerobic biodegradability was evaluated, as well as the structural changes caused by the pretreatment. From this stage of pretreatment evaluation, it was concluded that the conditions of greatest interest were 15 min (t15) hydrothermal pretreatment without the addition of chemical reagents (TPWH (t15)). The anaerobic digestion process was subsequently evaluated by comparing TPWH (t15) with the untreated tomato plant, obtaining a mean value of 0.125 ± 0.006 and 0.097 ± 0.010 m3STP CH4/kg TVS (total volatile solids) (STP standard temperature and pressure conditions, 273 K and 101,325 Pa), respectively, once the methane production is stabilized.

Efficient nutrient recovery/removal from real source-separated urine by coupling vacuum thermal stripping with activated sludge processes

Separation and treatment of human urine from domestic wastewater have been recognized as a sustainable alternative to conventional urban sanitation system, but the unique water quality of source-separated urine, such as high nutrient, insufficient alkalinity and low COD/nitrogen ratio, poses challenges to the biological nitrogen removal process. It was hypothesized that a physicochemical pre-treatment should be adopted to not only reduce nitrogen load but adjust water quality suitable for biological treatment. In this study, a vacuum thermal stripping process coupled to acid absorption was used as a pre-treatment to recover ammonia from hydrolyzed urine in the form of ammonium sulphate. The maximal ammonia mass transfer coefficient of 17.6 mm/h was obtained under 60 °C and 21.3 kPa 80% of the nitrogen in hydrolyzed urine was recovered in 3 h batch stripping experiments without pH adjustment, corresponding to a nitrogen recovery loading rate of 36 kg N/m3⋅d. The majority of organic matters were retained in urine solutions, thus COD/N and alkalinity/NH4+N ratios were elevated to 4.75 and 4.37, respectively. Phosphorus recovery could be simultaneously obtained in stripping process by adding MgCl2. The remaining nitrogen was effectively removed via short-cut nitrification and denitrification in an anoxic/oxic membrane bioreactor. More than 95% of overall nutrient recovery/removal from urine was achieved with a minimal consumption of external resources. The economic assessment of the technique showed that the recovery/removal of nutrients from 1 m3 of urine can make a profit of € 0.26.

Effect of physicochemical pretreatments plus enzymatic hydrolysis on the composition and morphologic structure of corn straw

In order to decrease corn straw crystallinity for improving reducing sugar yield, physicochemical pretreatments plus enzymatic hydrolysis were investigated. The results showed that hemicellulose and lignin degradation rates in corn straw treated with physical method (ultrasound wave (group 12), extrusion + ultrasound wave (group 14), extrusion + ultrasound wave + microwave (group 15)) combined with chemical compounds (lime + sodium hydroxide + hydrogen peroxide) were significantly higher than the untreated corn straw (P < 0.05). After the above three physicochemical pretreatments were fulfilled and followed by enzymatic hydrolysis, the cellulose, hemicelluloses, lignin degradation rates and reducing sugar yield were respectively increased by 51.38%, 82.44%, 64.63% and 378.86% in group 12, 69.61%, 86.05%, 62.88% and 421.77% in group14, 61.59%, 74.51%, 56.19% and 425.98% in group 15, compared with the untreated corn straw (P < 0.05). The scanning electron microscope showed that straw structure treated with extrusion + ultrasonic + chemical pretreatment was more seriously damaged than that with single physical or chemical pretreatment. The different sequences of physicochemical treatments had different effects on corn straw degradation. It could be concluded that the optimal physicochemical pretreatments plus enzymatic hydrolysis were effective for corn straw degradation and reducing sugar yield.

Effects of autohydrolysis on rice biomass for reducing sugars production

Abstract The current improper disposal methods of rice biomass either by incinerating or open burning has led to an environmental problem due to smoke release to the air. Regarding this issue, much works have been carried out to utilize rice biomass for value-added products but its commercial utilization is hindered due to the lack of clear understanding on the energy conversion that meets the overall environmental friendly standardAbundant of rice biomass production from rice industry has created environmental issues to the surrounding localities primarily due to the inefficient disposal and incineration. Nevertheless, rice biomass has a great potential as a renewable feedstock. Autohydrolysis (a physico-chemical pretreatment method) is one of the options that offers a lot of benefits for the subsequent process such as allow excellent selectivity towards biomass degradation in mild operational conditions. Autohydrolysis pretreatment which were the hydrothermal (HT) and the saturated steam (ST) were analyzed in term of the reducing sugars and the degradation products production. In overall, combined rice biomass in ratio of 3(rice straws):1(rice husks) has been identified to be the best selection with chemical composition of 42.5%, 26.5% and 10.0 % for cellulose, hemicellulose and lignin respectively. This combination of biomass yielded the highest reducing sugars when extracted under HT pretreatment (14.4 g/L) at 210°C for 5 min with 0.58 g/L furfural, 0.27 g/L Hydroxymetylfurfural (HMF), 0.10 g/L total phenolic compounds (TPC). The result obtained by the ST pretreatment is lower about 4.5 times than the HT system. ST needs higher temperature for maximum production of reducing sugars and the production was only 3.19 g/L at 230°C for 15 min with 1.16 g/L furfural, 0.73 g/L HMF, 0.04 g/L TPC.

Effect of Various Pretreatment Methods on Bioethanol Production from Cotton Stalks

Cotton stalks (CS) are considered a good candidate for fuel-ethanol production due to its abundance and high carbohydrate content, but the direct conversion without pretreatment always results in extremely low yields due to the recalcitrant nature of lignocelluloses. The present study was undertaken to investigate the effect of various chemical and physicochemical pretreatment methods, i.e., alkali, microwave-assisted acid, organosolv, hydrothermal treatment, and sequentially organosolv and hydrothermal pretreatment, on chemical composition of CS and subsequent ethanol production applying pre-hydrolysis and simultaneous saccharification and fermentation (PSSF) at high solid loading. The best results in terms of ethanol production were achieved by the sequential combination of organosolv and hydrothermal pretreatment (32.3 g/L, using 15% w/v substrate concentration and 6 h pre-hydrolysis) with an improvement of 32% to 50% in ethanol production compared to the other pretreatments. Extending pre-hydrolysis time to 14 h and increasing substrate concentration to 20% w/v, ethanol production reached 47.0 g/L (corresponding to an ethanol yield of 52%) after 30 h of fermentation.

Pulp and Paper Mill Effluent Treated by Combining Coagulation-Flocculation-Sedimentation and Fenton Processes

Pulp and paper industries face serious environmental challenges, especially with regard to the conservation of water resources. Chemical thermal mechanical pulping (CTMP) is a process of pulping that combines chemical and mechanical pulping. This reduces the volume of water used in the process. But on the other hand, CTMP generates an effluent with high concentration of organic matter and is difficult to treat. This study evaluated the efficiency in the combination of physicochemical pretreatment by coagulation-flocculation-sedimentation (CFS) process and advanced oxidation process (AOP) by Fenton in sequence to treat CTMP effluent of a Brazilian industry. At first, the best treatment conditions for this type of effluent were determined. To evaluate the efficiency, pH, chemical oxygen demand, biochemical oxygen demand, total organic carbon, lignin contents, color, total phenolic contents, turbidity, and solids were measured before and after treatment. The acute toxicity on Daphnia magna was also determined. The treatment with CFS showed better results in the removal of solids and Fenton in the removal of recalcitrant compounds, such as lignin, demonstrating the need to use them in sequence. Combining CFS and Fenton to treat CTMP effluent allowed to achieve a removal efficiency of 95% for TOC, 61% for COD, and 76% for lignin contents.

Understanding biomass recalcitrance in grasses for their efficient utilization as biorefinery feedstock

One of the main challenges for the deployment of lignocellulosic biorefineries in future years is to find renewable and secured biomass sources in order to obtain bio-sourced products, as an alternative to petroleum-based commodities. Grass biomass, considering its characteristics (availability, composition, productivity, possibility of being harvested from both arable (post-harvest residues) and non-agricultural lands), can be considered as a biomass source for the future. Nevertheless, because of its complex structure and composition, which need deconstructive pre-treatments to render possible further biological conversions, grasses utilisation in biorefinery is today not widespread. Indeed, recalcitrance to polymers degradation in grasses concerns structural and compositional characteristics and can result in costly and complicated biorefinery processes. Grass recalcitrance is due to various natural factors strongly related and difficult to dissociate: rind and vascular structures; composition (lignin content is a key factor for cellulose hydrolysis acting like a physical barrier while hemicelluloses seem to play a more significant role in woody biomass than in grass plants); physical structures (crystalline nature and insoluble surface of cellulose, specific surface area, particle size), etc. Physico-chemical pretreatments are efficient solutions to overcome recalcitrance, while phenotypic selections are interesting but not efficient enough to obtain an optimal enzymatic hydrolysis. In some cases, the structural elements of grass biomass can be negatively affected by physico-chemical pretreatments, causing pre-treatment-induced recalcitrance, like cellulose hornification (irreversible alteration of cellulose microfibers), vascular structure collapsed and reduced cellulose bioaccesibility to enzymes due to cellulose covering by lignin, following lignin solubilisation.

Combined Ball Milling and Ethanol Organosolv Pretreatment to Improve the Enzymatic Digestibility of Three Types of Herbaceous Biomass

A combined ball milling and ethanol organosolv process is proposed for the pretreatment of three types of herbaceous biomass, giant miscanthus, corn stover, and wheat straw. The combined pretreatment was effective at both removing lignin and increasing the glucan content. After 120 min pretreatment, the glucan content increased to 63.09%, and 55.89% of the acid-insoluble lignin was removed from the giant miscanthus sample. The removal of cellulose, hemicellulose, and acetyl groups were correlated with the removal of lignin. The pretreatment of corn stover showed the highest removal of cellulose, but this was dependent on the removal of acid-insoluble lignin. The slope of the regression lines, which shows the correlation between the removal of lignin and cellulose, was lower than other correlations. The changes in biomass size were analyzed using size distribution graphs. With increasing pretreatment time, the particle size reduction improved in the three types of herbaceous biomass. Because of the combined physicochemical pretreatment, the enzymatic digestibility improved, and a maximum of 91% glucan digestibility was obtained from the pretreated corn stover when 30 FPU/g-glucan enzyme was added. Finally, compositional analysis of the recovered lignin from the remaining black liquor was investigated.

Industrial potato peel as a feedstock for biobutanol production

Potato peel from a snack factory was assessed as possible feedstock for biobutanol production. This lignocellulosic biomass was subjected to various physicochemical pretreatments (autohydrolysis and hydrolysis with dilute acids, alkalis, organic solvents or surfactants) under different conditions of time, temperature and reagent concentrations, in order to favour the release of sugars and reduce the generation of fermentation inhibitors. Thereafter, the pretreated potato peel was treated enzymatically to complete the hydrolysis. Autohydrolysis at 140 °C and 56 min was the most effective pretreatment, releasing 37.9 ± 2.99 g/L sugars from an aqueous mixture containing 10% (w/w) potato peel (sugar recovery efficiency 55 ± 13%). The fermentability of the hydrolysates was checked with six strains of Clostridium beijerinckii, C. acetobutylicum, C. saccharobutylicum and C. saccaroperbutylacetonicum. C. saccharobutylicum DSM 13864 produced 2.1 g/L acetone, 7.6 g/L butanol and 0.6 g/L ethanol in 96 h (0.186 gB/gS), whereas C. saccharoperbutylacetonicum DSM 2152 generated 1.8 g/L acetone, 8.1 g/L butanol and 1.0 g/L ethanol in 120 h (0.203 gB/gS). Detoxification steps of the hydrolysate before fermentation were not necessary. Potato peel may be an interesting feedstock for biorefineries focused on butanol production.

Thermal degradation behavior of ball-milled Miscanthus plants and its relationship to enzymatic hydrolysis

Correlations were determined between the thermal degradation behaviors of ball-milled Miscanthus plants and their enzymatic digestibilities. Overall, thermal degradation temperatures of Miscanthus giganteus were higher than those of M. sinensis. The differential thermogravimetric (DTG) curve of M. giganteus had a characteristic shoulder peak near 292 °C as opposed to that of M. sinensis. The thermal degradation temperatures of both ball-milled samples decreased with increased ball-milling time, although the composition was not changed by ball milling. Remarkable changes in the DTG curves of M. sinensis and M. giganteus occurred with ball milling for more than 60 min and 120 min, respectively. These thermal degradation results were similar to the results for physicochemical pretreatments and enzymatic digestibilities. The thermal decomposition temperatures of both ball-milled samples at 20% weight loss were most negatively correlated with the enzymatic digestibilities with a value of approximately -1.0.

An Overview of Current Pretreatment Methods Used to Improve Lipid Extraction from Oleaginous Micro-Organisms.

Microbial oils, obtained from oleaginous microorganisms are an emerging source of commercially valuable chemicals ranging from pharmaceuticals to the petroleum industry. In petroleum biorefineries, the microbial biomass has become a sustainable source of renewable biofuels. Biodiesel is mainly produced from oils obtained from oleaginous microorganisms involving various upstream and downstream processes, such as cultivation, harvesting, lipid extraction, and transesterification. Among them, lipid extraction is a crucial step for the process and it represents an important bottleneck for the commercial scale production of biodiesel. Lipids are synthesized in the cellular compartment of oleaginous microorganisms in the form of lipid droplets, so it is necessary to disrupt the cells prior to lipid extraction in order to improve the extraction yields. Various mechanical, chemical and physicochemical pretreatment methods are employed to disintegrate the cellular membrane of oleaginous microorganisms. The objective of the present review article is to evaluate the various pretreatment methods for efficient lipid extraction from the oleaginous cellular biomass available to date, as well as to discuss their advantages and disadvantages, including their effect on the lipid yield. The discussed mechanical pretreatment methods are oil expeller, bead milling, ultrasonication, microwave, high-speed and high-pressure homogenizer, laser, autoclaving, pulsed electric field, and non-mechanical methods, such as enzymatic treatment, including various emerging cell disruption techniques.

Improvement of Delignification, Desilication and Cellulosic Content Availability in Paddy Straw via Physico-chemical Pretreatments

Improvement of Delignification, Desilication and Cellulosic Content Availability in Paddy Straw via Physico-chemical Pretreatments

Innovative Nanofibrillated Cellulose from Rice Straw as Dietary Fiber for Enhanced Health Benefits Prepared by a Green and Scale Production Method

Increased focus has been directed toward the use of agricultural residues. Conversion of lignocellulosic biomass to nanocellulose, such as nanofibrillated cellulose (NFC) has prompted a revolution in biobased materials for diverse applications. Currently used chemical methods for the preparation of NFC are not environmentally friendly and even exhibit toxicity, limiting the application of NFC in food. The present study proposes an innovative NFC as dietary fiber, prepared using a green and scale production method. This technique provides an integrated approach that combines physicochemical pretreatment (high-density steam flash-explosion, HDSF at 2.0 MPa) and successively enzymatic catalysts (45 U/g xylanase for 3 h, 60 U/g laccase for 4 h, and 150 U/g cellulose for 12 h) for the conversion of rice straw into NFC which is characterized by long and distinct fibrillated cellulose with widths of 30–200 nm, exhibiting excellent water retention capacity (20 g water/g) and swelling capacity (105 mL/g). Based on...

Physico-Chemical Conversion of Lignocellulose: Inhibitor Effects and Detoxification Strategies: A Mini Review.

A pretreatment of lignocellulosic biomass to produce biofuels, polymers, and other chemicals plays a vital role in the biochemical conversion process toward disrupting the closely associated structures of the cellulose-hemicellulose-lignin molecules. Various pretreatment steps alter the chemical/physical structure of lignocellulosic materials by solubilizing hemicellulose and/or lignin, decreasing the particle sizes of substrate and the crystalline portions of cellulose, and increasing the surface area of biomass. These modifications enhance the hydrolysis of cellulose by increasing accessibilities of acids or enzymes onto the surface of cellulose. However, lignocellulose-derived byproducts, which can inhibit and/or deactivate enzyme and microbial biocatalysts, are formed, including furan derivatives, lignin-derived phenolics, and carboxylic acids. These generation of compounds during pretreatment with inhibitory effects can lead to negative effects on subsequent steps in sugar flat-form processes. A number of physico-chemical pretreatment methods such as steam explosion, ammonia fiber explosion (AFEX), and liquid hot water (LHW) have been suggested and developed for minimizing formation of inhibitory compounds and alleviating their effects on ethanol production processes. This work reviews the physico-chemical pretreatment methods used for various biomass sources, formation of lignocellulose-derived inhibitors, and their contributions to enzymatic hydrolysis and microbial activities. Furthermore, we provide an overview of the current strategies to alleviate inhibitory compounds present in the hydrolysates or slurries.

Use of green fluorescent protein to monitor fungal growth in biomass hydrolysate.

A reporter gene encoding green fluorescent protein (GFP) was introduced into the ascomycete Coniochaeta ligniaria NRRL30616, and fluorescence of cultures was monitored as a measure of cell growth. Fluorescence in the GFP-expressing strain was measured during growth of cells in defined and complex media as well as in the liquor derived from pretreatment of corn stover, an agricultural residue. Fluorescence mirrored growth of cultures, as measured by optical density and counts of colony forming units. Because traditional methods to monitor growth cannot be used in biomass liquors due to its fibrous, dark-colored nature, the speed and convenience of using GFP to monitor growth is advantageous. Fluorescence of cultures in biomass hydrolysate also correlated with the concentration of furfural in hydrolysate. Furfural and other compounds, present in hydrolysate due to physico-chemical pretreatment of biomass, are inhibitory to fermenting microbes. Therefore, measurement of fluorescence in GFP-expressing C. ligniaria is a proxy for measures of microbial growth and furfural consumption, and serves as a convenient indicator of metabolism of fermentation inhibitors in biomass hydrolysate.

Biological and Physicochemical Pretreatment of Sweet Sorghum Bagasse to Liberate Reducing Sugars

Biological and Physicochemical Pretreatment of Sweet Sorghum Bagasse to Liberate Reducing Sugars