Potential of Potassium Hydroxide Pretreatment of Switchgrass for Fermentable Sugar Production

Chemical pretreatment of lignocellulosic biomass has been extensively investigated for sugar generation and subsequent fuel production. Alkaline pretreatment has emerged as one of the popular chemical pretreatment methods, but most attempts thus far have utilized NaOH for the pretreatment process. This study aimed at investigating the potential of potassium hydroxide (KOH) as a viable alternative alkaline reagent for lignocellulosic pretreatment based on its different reactivity patterns compared to NaOH. Performer switchgrass was pretreated at KOH concentrations of 0.5–2 % for varying treatment times of 6–48 h, 6–24 h, and 0.25–1 h at 21, 50, and 121 °C, respectively. The pretreatments resulted in the highest percent sugar retention of 99.26 % at 0.5 %, 21 °C, 12 h while delignification up to 55.4 % was observed with 2 % KOH, 121 °C, 1 h. Six pretreatment conditions were selected for subsequent enzymatic hydrolysis with Cellic CTec2® for sugar generation. The pretreatment condition of 0.5 % KOH, 24 h, 21 °C was determined to be the most effective as it utilized the least amount of KOH while generating 582.4 mg sugar/g raw biomass for a corresponding percent carbohydrate conversion of 91.8 %.     

Thermal Pretreatment of Harvest Residues and Their Use in Anaerobic Co-digestion with Dairy Cow Manure

Several batch experiments were conducted on the anaerobic co-digestion of dairy cow manure (DCM) with three harvest residues (HR) (soybean straw, sunflower stalks, and corn stover). The influence of thermal pretreatment of HR on biogas production was investigated, where the HR were thermally pretreated at two different temperatures: T = 121 °C and T = 175 °C, during t = 30 and t = 90 min, respectively. All anaerobic co-digestion batch experiments were performed simultaneously under thermophilic regime, at T = 55 °C. Biogas and methane yields were significantly improved in experiments performed with corn stover thermally pretreated at 175 °C for 30 min (491.37 cm³/g VS and 306.96 cm³/g VS, respectively), if compared to experiments performed with untreated corn stover. The highest VS and COD removal rates were also observed in the same group of experiments and were 34.5 and 50.1%, respectively. The highest biogas and methane yields with soybean straw (418.93 cm³/g VS and 261.44 cm³/g VS, respectively) were obtained when soybean straw pretreated at 121 °C during 90 min. The highest biogas and methane yields with sunflower stalk (393.28 cm³/g VS and 245.02 cm³/g VS, respectively) were obtained when sunflower stalk was pretreated at 121 °C during 90 min.     

Microbial Lipid Production from Enzymatic Hydrolysate of Pecan Nutshell Pretreated by Combined Pretreatment

Biodiesel is a fuel composed of monoalkyl esters of long-chain fatty acids derived from renewable biomass sources. In this study, biomass waste pecan nutshell (PS) was attempted to be converted into microbial oil. For effective utilization of PS, sequential pretreatment with ethylene glycol–H₂SO₄–water (78:2:20, wt:wt:wt) at 130 °C for 30 min and aqueous ammonia (25 wt%) at 50 °C for 24 h was used to enhance its enzymatic saccharification. Significant linear correlation was obtained about delignification-saccharification (R ² = 0.9507). SEM and FTIR results indicated that combination pretreatment could effectively remove lignin and xylan in PS for promoting its enzymatic saccharification. After 72 h, the reducing sugars from the hydrolysis of 50 g/L pretreated PS by combination pretreatment could be obtained at 73.6% yield. Using the recovered PS hydrolysates containing 20 g/L glucose as carbon source, microbial lipids produced from the PS hydrolysates by Rhodococcus opacus ACCC41043. Four fatty acids including palmitic acid (C16:0; 23.1%), palmitoleic acid (C16:1; 22.4%), stearic acid (C18:0; 15.3%), and oleic acid (C18:1; 23.9%) were distributed in total fatty acids. In conclusion, this strategy has potential application in the future.     

Effects of Low Moisture Anhydrous Ammonia (LMAA) Pretreatment at Controlled Ammoniation Temperatures on Enzymatic Hydrolysis of Corn Stover

Corn stover was treated using low-moisture anhydrous ammonia (LMAA) at controlled ammoniation temperature. Moisturized corn stover (50 % moisture) was contacted with anhydrous ammonia (0.1 g NH₃/g-biomass) in a batch reactor at various temperatures (ambient to 150 °C). After ammoniation at elevated and controlled temperature, ammoniated corn stover was pretreated at various temperatures (60–150 °C) for 72–144 h. Change in composition was marginal at low pretreatment temperature but was relatively severe with pretreatment at high temperature (130–150 °C). The latter resulted in low enzymatic digestibility. It was also observed that extreme levels (either high or low) of residual ammonia affected enzymatic digestibility, while residual ammonia improved by 1.0–1.5 %. The LMAA method enhanced enzymatic digestibility compared to untreated corn stover (29.8 %). The highest glucan and xylan digestibility (84.1 and 73.6 %, respectively) was obtained under the optimal LMAA conditions (i.e., ammoniation at 70 °C for 20 min, followed by pretreatment at 90 °C for 48 h).     

Sequential Extrusion-Ozone Pretreatment of Switchgrass and Big Bluestem

Pretreatment is one of the biggest challenges in utilizing lignocellulosic feedstocks to meet the mandatory requirements for biofuels around the world. Earlier researchers evaluated extrusion and ozone pretreatment separately and found that sugar recovery can be improved significantly from 15–20 to 40–75 % for different feedstocks. To further improve sugar recoveries, extrusion-ozone sequential pretreatment was explored. Accordingly, optimal extruded switchgrass (176?°C, 155 rpm, 20 % moisture, and 8 mm) and big bluestem (180?°C, 155 rpm, 20 % moisture, and 8 mm) at 25–75 % moisture content were exposed to an ozone flow rate of 37–365 mg/h for 2.5 to 10 min. Pretreated samples were then subjected to enzymatic hydrolysis to determine sugar recovery. Statistical analyses confirmed significant effects of the independent variables and their interactions on sugar recoveries for both feedstocks. Maximum glucose, xylose, and total sugar recovery of 66.4, 82.3, and 70.4 %, respectively, were obtained when a low-moisture (25 %) extruded switchgrass was ozonated for 2.5 min at a flow rate of 37 mg/h. Respectively, this represents increases of 3.42, 5.01, and 3.42 times that of the control. When big bluestem at 25 % moisture was extruded and then ozonated for 2.5 min at a flow rate of 365 mg/h, resulting glucose, xylose, and total sugar recoveries of 90.8, 92.2, and 87.5 %, respectively, were obtained. These represent increases of 4.5, 2.7, and 3.9 times than that of the control. It is also noteworthy that furfural and hydroxymethyl furfural were not detected in any of the pretreatments, and only low levels (0.14–0.18 g/l) of acetic acid were measured. The results show that sequential pretreatment using extrusion and ozone is an efficient way to improve sugar recovery from herbaceous biomass feedstocks.     

Bioethanol Production Using Waste Seaweed Obtained from Gwangalli Beach,Busan, Korea by Co-culture of Yeasts with Adaptive Evolution

Conditions for ethanol production were evaluated using waste seaweed obtained from Gwangalli beach, Busan, Korea, after strong winds on January 15, 2015. Eleven types of seaweed were identified, and the proportions of red, brown, and green seaweed wastes were 26, 46, and 28%, respectively. Optimal pretreatment conditions were determined as 8% slurry content, 286 mM H₂SO₄ for 90 min at 121 °C. Enzymatic saccharification with 16 units/mL Celluclast 1.5L and Viscozyme L mixture at 45 °C for 48 h was carried out as optimal condition. A maximum monosaccharide concentration of 30.2 g/L was obtained and used to produce ethanol. Fermentation was performed with single or mixed yeasts of non-adapted and adapted Saccharomyces cerevisiae KCTC 1126 and Pichia angophorae KCTC 17574 to galactose and mannitol, respectively. The maximum ethanol concentration and yield of 13.5 g/L and Y_EtOH of 0.45 were obtained using co-culture of adapted S. cerevisiae and P. angophorae.     

Effect of Bovine Serum Albumin (BSA) on Enzymatic Cellulose Hydrolysis

Bovine serum albumin (BSA) was added to filter paper during the hydrolysis of cellulase. Adding BSA before the addition of the cellulase enhances enzyme activity in the solution, thereby increasing the conversion rate of cellulose. After 48 h of BSA treatment, the BSA adsorption quantities are 3.3, 4.6, 7.8, 17.2, and 28.3 mg/g substrate, each with different initial BSA concentration treatments at 50 °C; in addition, more cellulase was adsorbed onto the filter paper at 50 °C compared with 35 °C. After 48 h of hydrolysis, the free-enzyme activity could not be measured without the BSA treatment, whereas the remaining activity of the filter paper activity was approximately 41 % when treated with 1.0 mg/mL BSA. Even after 96 h of hydrolysis, 25 % still remained. Meanwhile, after 48 h of incubation without substrate, the remaining enzyme activities were increased 20.7 % (from 43.7 to 52.7 %) and 94.8 % (from 23.3 to 45.5 %) at 35 and 50 °C, respectively. Moreover, the effect of the BSA was more obvious at 35 °C compared with 50 °C. When using 15 filter paper cellulase units per gram substrate cellulase loading at 50 °C, the cellulose conversion was increased from 75 % (without BSA treatment) to ≥90 % when using BSA dosages between 0.1 and 1.5 mg/mL. Overall, these results suggest that there are promising strategies for BSA treatment in the reduction of enzyme requirements during the hydrolysis of cellulose.     

Hybrid SSF/SHF Processing of SO<Subscript>2</Subscript> Pretreated Wheat Straw—Tuning Co-fermentation by Yeast Inoculum Size and Hydrolysis Time

Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO₂ as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO₂ (based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion.     

Pretreatment of Chicken Feather Waste for Improved Biogas Production

This study deals with the utilization of chicken feather waste as a substrate for anaerobic digestion and improving biogas production by degradation of the compact structure of the feather keratin. In order to increase the digestibility of the feather, different pretreatments were investigated, including thermal pretreatment at 120 °C for 10 min, enzymatic hydrolysis with an alkaline endopeptidase [0.53–2.66 mL/g volatile solids (VS) feathers] for 0, 2, or 24 h at 55 °C, as well as a combination of these pretreatments. The effects of the treatments were then evaluated by anaerobic batch digestion assays at 55 °C. The enzymatic pretreatment increased the methane yield to 0.40 Nm³/kg VS_added, which is 122 % improvement compared to the yield of the untreated feathers. The other treatment conditions were less effective, increasing the methane yield by 11–50 %. The long-term effects of anaerobic digestion of feathers were examined by co-digestion of the feather with organic fraction of municipal solid waste performed with and without the addition of enzyme. When enzyme was added together with the feed, CH₄ yield of 0.485 Nm³/kg VS^?1 d^?1 was achieved together with a stable reactor performance, while in the control reactor, a decrease in methane production, together with accumulation of undegraded feather, was observed.     

Ethanol Production from the Organic Fraction Obtained After Thermal Pretreatment of Municipal Solid Waste

In this work, the use of organic fraction from municipal solid waste (MSW) as substrate for ethanol production based on enzymatic hydrolysis was evaluated. MSW was subjected to a thermal pretreatment (active hygienization) at 160?°C from 5 to 50 min. The organic fiber obtained after 30 min was used as substrate in a simultaneous saccharification and fermentation (SSF) and fed-batch SSF process using cellulases and amylases. In a fed-batch mode with 25% (w/w) substrate loading, final ethanol concentration of 30 g/L was achieved (60% of theoretical). In these conditions, more than 160 L of ethanol per ton of dry matter could be produced from the organic fraction of MSW.     

Enhancement of enzymatic hydrolysis of corncob by microwave-assisted alkali pretreatment and its effect in morphology

Bioethanol produced from a conventional fermentation process using Saccharomyces cerevisiae utilizing pretreated and hydrolyzed corncob as a substrate was studied. It was found that the morphology of corncob was significantly changed after microwave-assisted alkali pretreatment was applied. An increase in the crystallinity index and surface area of the pretreated corncob was also observed. The highest total sugar concentration of 683.97 mg/g of pretreated corncob, or 45.60 g L^?1, was obtained from the optimum pretreatment conditions of 2 % NaOH at 100 °C for 30 min in a microwave oven. Microwave-assisted alkali pretreatment was an efficient way to improve the enzymatic hydrolysis accessibility of corncob in a shorter amount of time and at a lower temperature, compared to other methods.     

Sequential Aqueous Ammonia Extraction and LiCl/<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethyl Formamide Pretreatment for Enhancing Enzymatic Saccharification of Winter Bamboo Shoot Shell

Effective utilization of winter bamboo shoot shell (BSS) is of great interest, since BSS provides a renewable and inexpensive bioresource for the production of biofuels. In this study, an effective combination pretreatment by the sequential aqueous ammonia (25 wt%) extraction at 50 °C for 24 h and LiCl/N,N-dimethyl formamide (LiCl/DMF) (6 wt% of LiCl) pretreatment at 50 °C for 8 h was used for pretreating BSS. SEM, FTIR, and XRD results indicated that combination pretreatment could effectively remove lignin and change the crystal structure of cellulose for promoting enzymatic saccharification. Additionally, significant linear correlations were found about solid recovery-delignification (R ² = 0.9235), delignification-reducing sugars (R ² = 0.9552), and delignification-hemicellulose removal (R ² = 0.9779) during the combination pretreatment. The reducing sugars and glucose from the hydrolysis of 100 g/L pretreated BSS could be obtained at 72.3 and 40.5 g/L, respectively. Using the recovered BSS-hydrolysates containing 20–50 g/L glucose as carbon source, the ethanol yields at 48 h could be obtained at 84.5–86.1% of the theoretical yield. In conclusion, the sequential ammonia extraction and LiCl/DMF pretreatment has high potential application in future.     

Tailoring Wet Explosion Process Parameters for the Pretreatment of Cocksfoot Grass for High Sugar Yields

The pretreatment of lignocellulosic biomass is crucial for efficient subsequent enzymatic hydrolysis and ethanol fermentation. In this study, wet explosion (WEx) pretreatment was applied to cocksfoot grass and pretreatment conditions were tailored for maximizing the sugar yields using response surface methodology. The WEx process parameters studied were temperature (160–210 °C), retention time (5–20 min), and dilute sulfuric acid concentration (0.2–0.5 %). The pretreatment parameter set E, applying 210 °C for 5 min and 0.5 % dilute sulfuric acid, was found most suitable for achieving a high glucose release with low formation of by-products. Under these conditions, the cellulose and hemicellulose sugar recovery was 94 % and 70 %, respectively. The efficiency of the enzymatic hydrolysis of cellulose under these conditions was 91 %. On the other hand, the release of pentose sugars was higher when applying less severe pretreatment conditions C (160 °C, 5 min, 0.2 % dilute sulfuric acid). Therefore, the choice of the most suitable pretreatment conditions is depending on the main target product, i.e., hexose or pentose sugars.     

Acetylcholinesterase immobilised eggshell membrane-based optical biosensor for organophosphate detection

The development of an optical biosensor for the determination of malathion based on acetylcholinesterase (AChE) inhibition using Ellman’s reagent is reported. The AChE has been immobilised onto the eggshell membrane (ESM) using glutaraldehyde as a cross-linking agent. Scanning Electron Microscopic (SEM) studies and Fourier Transformed Infra-Red (FTIR) characterisations have been carried out to affirm the successful immobilisation of AChE onto the ESM. Under optimum conditions, the developed biosensor estimated the pesticide concentration in the range of 0.1–50 ng/mL with a limit of detection (LOD) of 0.1 ng/mL within 30 min. Parameters affecting the biosensor response such as concentration of enzyme, substrate and inhibition time were optimised. The stability and reusability of the AChE/ESM sensor have been observed as 31 days at 4°C and two times, respectively.     

Biodiesel Synthesis via Esterification of Feedstock with High Content of Free Fatty Acids

The objective of this work was to study the synthesis of ethyl esters via esterification of soybean oil deodorizer distillate with ethanol, using solid acid catalysts and commercial immobilized lipases, in a solvent-free system. Three commercially immobilized lipases were used, namely, Lipozyme RM-IM, Lipozyme TL-IM, and Novozym 435, all from Novozymes. We aimed for optimum reaction parameters: temperature, enzyme concentration, initial amount of ethanol, and its feeding technique to the reactor (stepwise ethanolysis). Reaction was faster with Novozym 435. The highest conversion (83.5%) was obtained after 90 min using 3 wt.% of Novozym 435 and two-stage stepwise addition of ethanol at 50°C. Four catalysts were also tested: zeolite CBV-780, SAPO-34, niobia, and niobic acid. The highest conversion (30%) was obtained at 100°C, with 3 wt.% of CBV-780 after 2.5 h. The effects of zeolite CBV 780 concentration were studied, resulting in a conversion of 49% using 9 wt.% of catalyst.     

The uranium recovery from aqueous solutions using amidoxime modified cellulose derivatives. III. Modification of hydroxypropylmethylcellulose with amidoxime groups

Grafting of acrylonitrile on hydroxypropyl methylcellulose films has been carried out by means of ⁶⁰Co-γ radiation, using a constant amount of hydroxypropyl methylcellulose films, at different concentrations of acrylonitrile in dimethylformamide. Grafting percentage—dose curves were obtained. 63 % of grafting yield were reached at around 3 kGy dose. Conversion of nitrile groups to amidoxime groups were achieved by aqueous solutions of NH₂OH·HCl–NaOH at 50 °C. The amidoxime conversion was followed by using FTIR spectrophotometer and determined as percentage. 98 % amidoxime conversion was achieved within 50 h. The structural, morphological and thermal evaluations of acrylonitrile grafted hydroxypropyl methylcellulose films, before and after amidoxime conversion, were performed using FTIR, AFM, Contact Angle, SEM and TGA analyses.     

Improving anti-UV performances of cotton fabrics via graft modification using a reactive UV-absorber

In this study, a reactive UV-absorber (UV-DTHM) was synthesized by the reaction of 2,4-dihydroxy benzophenone with 2,4,6-trichlorotriazine and showed excellent ultraviolet absorption property and good thermostability. Using pad-dry-steam process, UV-DTHM was grafted into bleached cotton fabric through the covalent surface modification of the cotton fibers. The optimal finishing conditions, such as amount of the catalyst, temperature of the finishing bath, steaming time and concentration of UV-DTHM, were discussed. The UV-DTHM-modified cotton fabrics were characterized by FTIR spectroscopy, SEM and ultraviolet protection factor (UPF), etc. It was found that the highest value of UPF, 46.5, can be obtained in the conditions of 60 °C, 2 % owf UV-DTHM and dipping 60 min, and that UPF remained constant and was still more than 30 after thirty consecutive launderings, which showed strong anti-UV performance and fairly good durability.     

Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods

Forest biomass is a promising resource for future biofuels and bioproducts. Pre-pulping extraction of hemicellulose by alkaline (Green Liquor) pretreatment produces a neutral-pH extract containing hemicellulose-derived oligomers. A near-term option for use of this extract is to hydrolyze the oligomers to fermentable monomer sugars. Chips of mixed northern hardwoods were cooked in a rocking digester at 160 °C for 110 min in Green Liquor at a concentration of 3% Na₂O equivalent salts on dry wood. The mass of wood extracted into the Green Liquor extract was approximately 11.4% of the debarked wood mass, which resulted in a dilute solution of oligomeric hemicelluloses sugars. The concentration of the extract was increased through partial evaporation prior to hydrolysis. Dilute sulfuric acid hydrolysis was applied at conditions ranging from 100 to 160 °C, 2% to 6% (w/v) H₂SO₄, and 2- to 258-min residence time. The maximum fermentable sugar concentration achieved from evaporated extract was 10.7 g/L, representing 90.7% of the maximum possible yield. Application of the biomass pretreatment severity function to the hydrolysis results proved to offer a relatively poor prediction of temperature and reaction time interaction. The combined severity function, which incorporates reaction time, temperature, and acid concentration, did prove to provide a useful means of trading off the combined effects of these three variables on total sugar yields.     

Two-Stage Acidic–Alkaline Hydrothermal Pretreatment of Lignocellulose for the High Recovery of Cellulose and Hemicellulose Sugars

The focus of this work was to develop a combined acid and alkaline hydrothermal pretreatment of lignocellulose that ensures high recovery of both hexose and pentose. Dilute sulfuric acid and lime pretreatments were employed sequentially. Process performance was optimized in terms of catalyst concentration, retention time, and temperature using response surface methodology. Medium operational conditions in the acid stage and harsh conditions in the alkaline stage were desirable with optimal performance at 0.73 wt% H₂SO₄, 150 °C, 6.1 min in the first stage, and 0.024 g lime/g biomass, 202 °C, 30 min in the second stage. In comparison to single-stage pretreatments with high recovery of either glucose or xylose, two-stage process showed great promises with >80 % glucose and >70 % xylose recovery. In addition, the method greatly improved ethanol fermentation with yields up to 0.145 g/g Miscanthus, due to significantly reduced formation of inhibitory by-products such as weak acids, furans, and phenols. Supplementing biomimetic acids would further increase glucose yield by up to 15 % and xylose yield by 25 %.     

Comparative potentiality of Kans grass (Saccharum spontaneum) and Giant reed (Arundo donax) as lignocellulosic feedstocks for the release of monomeric sugars by microwave/chemical pretreatment

Two-stage microwave (microwave/NaOH pretreatment followed by microwave/H₂SO₄ pretreatment) was used to release monomeric sugars from Kans grass (Saccharum spontaneum) and Giant reed (Arundo donax). The optimum pretreatment conditions were investigated, and the maximum monomeric sugar yields were compared. The microwave-assisted NaOH and H₂SO₄ pretreatments with a 15:1 liquid-to-solid ratio were studied by varying the chemical concentration, reaction temperature, and reaction time to optimize the amount of monomeric sugars. The maximum amounts of monomeric sugars released from microwave-assisted NaOH pretreatment were 6.8 g/100 g of biomass [at 80 °C/5 min, 5 % (w/v) NaOH for S. spontaneum and at 120 °C/5 min, 5 % (w/v) NaOH for A. donax]. Furthermore, the maximum amounts of monomeric sugars released from microwave-assisted H₂SO₄ pretreatment of S. spontaneum and A. donax were 33.8 [at 200 °C/10 min, 0.5 % (w/v) H₂SO₄] and 31.9 [at 180 °C/30 min, 0.5 % (w/v) H₂SO₄] g/100 g of biomass, respectively. The structural changes of S. spontaneum and A. donax were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy.