Ultrasound-assisted Alkaline Pretreatment Research Articles

Ultrasound-Assisted Alkaline Pretreatment of Biomass to Enhance the Extraction Yield of Valuable Chemicals

As a renewable and sustainable resource, lignocellulosic biomass serves as a crucial raw material for the production of biofuels, biochemicals, and various value-added products. This paper aims to develop and optimize a mild alkaline treatment of sawdust assisted by ultrasound, along with enzymatic hydrolysis of the pretreated material. The alkaline sonochemical pretreatment emerged as the optimal approach to enhance the susceptibility of cellulose to subsequent enzymatic hydrolysis to improve the yield of reducing sugars. A comparative study was performed using various ultrasonic applicators (horn and bath) and conventional assisted alkaline pretreatment. The ultrasonic-assisted pretreatment revealed a higher delignification of 68% (horn) and 57% (bath) compared with conventional pretreatment. Processes were optimized using a statistical analysis based on a 23 factorial design. The ratios between sawdust and alkaline solution (RSL = 0.5–1.5 g/100 mL), US amplitude (A = 20–60%), and working temperature (t = 30–50 °C) were selected as process factors. The optimal operating conditions to maximize the reducing sugar yield (138.15 mg GE/gsubstrate) were found as follows: a solid/liquid ratio of RSL,opt = 1.25 g/100 mL, US amplitude of Aopt = 60%, and pretreatment temperature of topt = 50 °C. The overall outcomes clearly confirmed the intensification of delignification by ultrasound-assisted alkaline pretreatment.

Enzymatic digestibility of lignocellulosic wood biomass: Effect of enzyme treatment in supercritical carbon dioxide and biomass pretreatment

Energy and resource intensive mechanical and chemical pretreatment along with the use of hazardous chemicals are major bottlenecks in widespread lignocellulosic biomass utilization. Herein, the study investigated different pretreatment methods on spruce wood namely supercritical CO2 (scCO2) pretreatment, ultrasound-assisted alkaline pretreatment, and acetosolv pulping-alkaline hydrogen peroxide bleaching, to enhance the enzymatic digestibility of wood using optimized enzyme cocktail. Also, the effect of scCO2 pretreatment on enzyme cocktail was investigated after optimizing the concentration and temperature of cellulolytic enzymes. The impact of scCO2 and ultrasound-assisted alkaline pretreatments of wood were insignificant for the enzymatic digestibility, and acetosolv pulping-alkaline hydrogen peroxide bleaching was the most effective pretreatment that showed the release of total reducing sugar yield (TRS) of ∼95.0 wt% of total hydrolyzable sugars (THS) in enzymatic hydrolysis. The optimized enzyme cocktail showed higher yield than individual enzymes with degree of synergism 1.34 among the enzymes, and scCO2 pretreatment of cocktail for 0.5–1.0 h at 10.0–22.0 MPa and 38.0–54.0 °C had insignificant effect on the enzyme's primary and global secondary structure of cocktail and its activity.

Ultrasound-assisted alkaline pretreatment of Parthenium hysterophorus for fermentable sugar production using a response surface approach

Parthenium hysterophorus is a lignocellulosic material with a high potential for fermentable sugar production due to its high availability and adaptability. The current investigation aims at studying the effectiveness of KOH-assisted ultrasonication on the pretreatment of P. hysterophorus biomass. Ultrasonication is a new hydrolysis technology that can provide a higher fermentable sugar yield in less time and at a lower temperature while using less alkali. The combination of KOH and ultrasound has been applied with a detailed study into the effects of various parameters such as sonication time (operating range of 10–50 min), KOH concentration (0.5–2.5%), and temperature (20–50 °C). A higher reducing sugar yield (128.15±0.06 mg/g) was obtained in US-KOH-pretreated biomass as compared with that of the KOH-pretreated biomass. The optimised pretreatment (using a 1:10 bath ratio, 1% (w/v) KOH, and 15-min sonication times) reduced lignin content (delignification) by 58.72% (w/w) and increased the available cellulose content (27.97% w/w) over untreated biomass, which was confirmed by compositional analysis of treated biomass. Further US-KOH-pretreatment was investigated for the liberation of maximum reducing sugar (325.51 mg/g) using the response surface methodology (RSM) approach. Following statistical optimization using response surface methodology, the yield of enzymatic hydrolysis was increased by 3.2-fold compared to the control. According to the investigations, P. hysterophorus can be used as a promising and affordable biomass source for the production of commercial bioethanol.

Pathways of lignocellulosic biomass deconstruction for biofuel and value-added products production

As the world attempts to transition from fossil fuels, lignocellulosic biomass (LCB) serves as a promising alternative due to its high abundance. Hydrolysing LCB can generate various bioproducts, such as biofuels and value-added chemicals. However, the presence of lignin inhibits the solubilization of LCBs, presenting a major techno-economic challenge in the biorefinery concept. Therefore, this paper addresses the gaps left by most of the recent review works that fail to comprehensively review different pretreatment methods and the full scope of applications of LCBs, and do not incorporate techno-economic considerations of the technologies, the latter being the greatest bottleneck in the commercialization of the processes. The literature review revealed that while many of the physical and chemical pretreatment methods exhibit great effectiveness, they have a huge dependence on energy, chemicals, water, and/or specialized equipment, and produce harmful waste and inhibitory compounds. The pretreatment of lignocellulosic biomass can account for 40% of total production costs. Biological pretreatment can address these challenges but is limited by long incubation times. For instance, the bacterial pretreatment can noticeably reduce sawdust cellulose, hemicelluloses, and lignin contents by 35.8%, 37.1%, and 46.2%, respectively. Recently, integrated/coupling (hybrid) methods, such as chemical-assisted liquid hot water/steam and microwave or ultrasound-assisted alkaline pretreatment, have been gaining popularity due to their potential to improve chemical yield, but at the expense of the high cost of operation. To make pretreatment processes more techno-economically feasible, there is a need for process integration and the standardization and optimization of process parameters.

Xylitol Production from Sugarcane Bagasse Through Ultrasound-Assisted Alkaline Pretreatment and Enzymatic Hydrolysis Followed by Fermentation

This study focused on the optimization of xylitol production from sugarcane bagasse by using response surface methodology. Xylitol was produced through a series of processes, firstly, optimization of ultrasound-assisted mild alkaline pretreatment for the xylan extraction from sugarcane bagasse followed by enzymatic hydrolysis of xylan to xylose by enzyme β-1,4-xylanase and finally microbial fermentation of xylose to xylitol using yeast (Candida guilliermondii), bacteria (Corynebacterium glutamicum) and their mixed culture for different time periods (0–96 h). Maximum xylan recovery of 12.059% (w/w) was observed at pretreatment; 0.73 M NaOH, 1:38.55 solid-to-liquid ratio and 34.77 min ultrasonication. The enzyme concentration of 400 U/g xylan at 48 h of incubation showed the highest xylose production (81.51 mg/g bagasse). Yeast (C. guilliermondii) resulted in the highest xylitol yield (Yp/s = 0.43 g/g) after 72 h. This bioprocess route can contribute as a suitable alternative for chemical methods of xylitol production.

Intensification of delignification and enzymatic hydrolysis of orange peel waste using ultrasound for enhanced fermentable sugar production

The present study focuses on using orange peel as a lignocellulosic substrate for fermentable reducing sugar production with intensification studies for delignification and enzymatic hydrolysis steps. The orange peel exposed to conventional and ultrasound-assisted alkaline pretreatment under ambient temperature for delignification resulted in around 86% delignification and 92% delignification in 4 h respectively. Subsequently, the effect of the enzyme concentration, ultrasonic power and duty cycle on reducing sugar production in the enzymatic hydrolysis has been investigated. Maximum concentration of reducing sugar as 1.30 g/L was obtained in 6 h treatment under 60W as power and 70% duty cycle, which was higher and much faster as compared to the conventional method where the sugar concentration was 0.814 g/L in 24 h. Studies involving advanced oxidation pretreatment based on hydrogen peroxide, Fenton, and ozone performed under ambient temperature demonstrated that the optimum conditions for best pretreatment efficacy are 3% H2O2 loading, 0.5g as FeSO4 loading and 2 L/min as the ozone flow rate as applicable, yielding a sugar concentration of 1.528 g/L, 2.069 g/L and 0.472 g/L respectively. Overall, the work has established that application of ultrasound and advanced oxidation pretreatment benefits the delignification and subsequent enzymatic hydrolysis of orange peel waste.

Polyhydroxybutyrate production from ultrasound-aided alkaline pretreated finger millet straw using Bacillus megaterium strain CAM12

In this study, finger millet straw (FMS) was utilized for the production of Polyhydroxybutyrate (PHB) by Bacillus megaterium strain CAM12. Ultrasound-assisted alkaline (NaOH) pretreatment of FMS under optimized conditions followed by enzymatic saccharification resulted in the maximum delignification (72%), hydrolysis yield (84%), glucose yield (86%) and xylose yield (61%). The effects of different pH, temperature, incubation period, inoculum concentration, agitation speed and FMS enzymatic hydrolysates concentration were investigated to improve the PHB production. Under optimized conditions, strain CAM12 used the FMS hydrolysates as the sole carbon source for their growth and produced 8.31 g L−1 of PHB. The extracted polymer on Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Nuclear magnetic resonance (NMR) analyses were confirmed to be PHB. These results suggest the potential of combined ultrasound and alkaline pretreated FMS hydrolysates as a promising feedstock for PHB production.

Ultrasound-assisted alkaline pre-treatment and its sequential combination with microwave for fractionation of pistachio shell

Ultrasound-assisted alkaline pre-treatment (UAAP) and its sequential combination with microwave (SUMAAP) were performed for fractionation of pistachio shell and compared with conventional alkaline pre-treatment (CAP). The pre-treatment conditions were investigated and optimized using Box-Behnken design for maximum hemicellulose and cellulose recoveries. Under optimum conditions, the hemicellulose and cellulose recoveries were 57.67% and 94.05% for UAAP and 66.14% and 90.78% for SUMAAP, while these values were 16.28% and 98.70% after CAP, respectively. The compositional analysis showed that the xylo-oligosaccharides were the main components in liquid phases, while the solid phases were enriched in cellulose. Furthermore, a significant increase in enzymatic hydrolysis yield of pre-treated solids was obtained compared to the raw pistachio shell. Thus, the UAAP was proved to be a reliable and efficient process for pistachio shell pre-treatment and its sequential combination with microwave provide further increase in pre-treatment efficiency while reducing the processing time and alkali requirement.

Evaluation and characterization of novel sources of sustainable lignocellulosic residues for bioethanol production using ultrasound-assisted alkaline pre-treatment

In recent years, research is focused on finding a sustainable and eco-friendly lignocellulosic biomass for the effective production of bioethanol to meet the world’s energy demand. The present study investigates the bioethanol production potential of four different lignocellulosic biomass residues viz., Saccharum arundinaceum (hardy sugar cane), Arundo donax (giant reed), Typha angustifolia (narrow-leaved cattail), and Ipomoea carnea (pink morning glory). The maximum reducing sugar release showed 185.00 ± 1.57, 213.73 ± 3.47, 187.57 ± 2.14, 294.08 ± 3.98 mg/g and fermentation efficiency of 72.60 ± 8.17%, 82.59 ± 7.42%, 77.45 ± 7.35%, and 85.04 ± 8.37% which was analyzed by estimating the percentage of bioethanol yield were achieved for Saccharum arundinaceum, Arundo donax, Typha angustifolia, and Ipomoea carnea, respectively. The chemical composition of biomass was characterized using National Renewable Energy Limited (NREL) protocol. The effect of ultrasound (US)-assisted alkaline pre-treatment on the four biomasses was characterized by different techniques. The cavitation phenomena of US-assisted alkaline pre-treatment was evident from the decreased value of lignin percentage, increased surface porosity and area, changes in crystallinity index (CrI) values and in the functional groups of biomass. The results revealed that all the four lignocellulosic biomass residues could be utilized as an effective and sustainable source for the production of bioethanol using US-assisted sodium hydroxide as a pre-treatment tool.

Ultrasound-assisted alkaline pretreatment to intensify enzymatic saccharification of Crotalaria juncea using a statistical method

Sunn hemp as a non-woody fiber crop was selected to determine the effect of ultrasound-assisted alkali pretreatment on enzymatic hydrolysis. We hypothesized that ultrasound-assisted alkali pretreatment (US-NaOH) was more efficient than alkali pretreatment alone; maximum fermentable sugars were released in US-NaOH-pretreated biomass by enzymatic hydrolysis. In this study, sunn hemp was pretreated with NaOH and US-NaOH at 121 °C. A higher cellulose content of 67% was obtained in US-NaOH-pretreated biomass (1% NaOH, 10-min sonication, 121 °C) as compared with that of the alkali-pretreated biomass. After ultrasound-assisted alkaline pretreatment, the crystallinity index of cellulose and the solubilization of pentose and lignin increased from 39 to 53%, leading to a significant increase in enzyme accessibility to cellulose to release reducing sugars. Scanning electron microscopy showed that the biomass underwent erosion after ultrasound pretreatment. Response surface methodology was chosen to study the individual effects of variables on enzymatic hydrolysis and their inter-dependence. The quantity of reducing sugars released was optimized using a response surface methodology, and the experimental results with optimized process variables gave 5.17 mg/mL glucose and 2.08 mg/mL xylose.

Ultrasound assisted alkaline pre-treatment of sugarcane filter mud for performance enhancement in biogas production

Sugar cane filter mud pre-treated by combined ultrasound-alkaline pre-treatment at different NaOH loading rates (0.25%-6%) and pre-treatment time (5 min to 60 min) performed in batch reactors under mesophilic conditions ((37±1)°C). Central composite design (CCD) was used to assess the effects on the chemical oxygen demand (COD) solubilisation, volatile fatty acid (VFA) concentration and methane yield. All pre-treatments were found significant to enhance methane yield (up to 39.49%) compared to the untreated filter mud. In general, results demonstrated the effectiveness of ultrasound assisted alkaline pre-treatment while increasing both NaOH loadings and pre-treatment time. Pre-treatment also increased the CODs solubilisation as well as VFA concentration, the optimal Initial CODs and VFA of 12 212 mg/L and 5830.97 mg/L, as determined by response surface methodology were noted on E9. Finally, modified Gompertz model was applied successfully to study kinetic of biogas production data, and showed an excellent fit. Keywords: anaerobic digestion, ultrasound-alkaline pre-treatment, biogas production, filter mud, enzymatic hydrolysis DOI: 10.25165/j.ijabe.20181101.3441 Citation: Talha Z, Hamid A, Guo D, Hassan M, Mehryar E, Okinda C, et al. Ultrasound assisted alkaline pre-treatment of sugarcane filter mud for performance enhancement in biogas production. Int J Agric & Biol Eng, 2018; 11(1): 226–231.

Ultrasound assisted alkaline pre-treatment of sugarcane filter mud for performance enhancement in biogas production

Ultrasound assisted alkaline pre-treatment of sugarcane filter mud for performance enhancement in biogas production

Ultrasound assisted alkaline pretreatment to enhance enzymatic saccharification of grass clipping

Grass clipping, a cellulose-rich raw material, has great potential to produce biofuels, but must be firstly hydrolyzed to liberate fermentable sugars. In this study, grass clipping was pretreated with ultrasound (US), Ca(OH)2, NaOH, US-Ca(OH)2 and US-NaOH at relatively low temperature to enhance its enzymatic hydrolysis. The solubilization of hemicellulose and lignin, and crystallinity index of cellulose increased after US-alkaline pretreatment, leading to a significant increase of enzyme accessibility to cellulose. Compared with another four pretreatments, US-Ca(OH)2 pretreatment of grass clipping showed the best improvement for reducing sugar yield. X-ray diffraction (XRD) determination and scanning electron microscope (SEM) observation showed that the crystallinity index of grass clipping increased and the grass clipping surface suffered from serious erosion after US-Ca(OH)2 pretreatment. Then, the operating conditions of US-Ca(OH)2 pretreatment and enzymatic hydrolysis were systematically optimized, and the suitable operating conditions were as follows: US power density of 0.65W/ml, US pretreatment time of 30min, Ca(OH)2 concentration of 0.75%, pretreatment temperature of 75°C, enzyme loading of 125FPU/g, and hydrolysis time of 72h. The reducing sugar yield of grass clipping pretreated by US-Ca(OH)2 reached 414mg/g, increasing by 3.5 times compared with that of raw grass clipping. The US-Ca(OH)2 pretreatment of grass clipping at low temperature significantly enhanced the potential of grass clipping as a promising raw material to produce biofuels.

Ultrasound-assisted alkaline pretreatment for enhancing the enzymatic hydrolysis of rice straw by using the heat energy dissipated from ultrasonication

Rice straw samples were exposed to ultrasound-assisted alkaline (NaOH) pretreatment by using the heat energy dissipated from ultrasonication to increase their enzymatic digestibility for saccharification. The characterization shows that the pretreatment could selectively remove lignin and hemicellulose without degrading cellulose, and increase porosity and surface area of rice straw. The porosity, surface area and cellulose content of rice straw increased with the increasing concentration of NaOH used. The rice straw sample pretreated by using the heat energy dissipated from ultrasonication has a higher surface area and a lower crystallinity index value than that pretreated by using the external source of heating, and the amount of reducing sugar released from the former sample at 48h of enzymatic saccharification, which is about 3.5 times as large as that from the untreated rice straw sample (2.91vs. 0.85gL−1), is slightly larger than that from the latter sample (2.91vs. 2.73gL−1). The ultrasound-assisted alkaline pretreatment by using the heat energy dissipated from ultrasonication was proved to be a reliable and effective method for rice straw pretreatment.

Effect of alkaline ultrasonic pretreatment on crystalline morphology and enzymatic hydrolysis of cellulose

In this study, ultrasound-assisted alkaline pretreatment is developed to evaluate the morphological and structural changes that occur during pretreatment of cellulose, and its effect on glucose production via enzymatic hydrolysis. The pretreated samples were characterized using scanning electron microscopy, infrared spectroscopy, and X-ray diffraction to understand the change in surface morphology, crystallinity and the fraction of cellulose Iβ and cellulose II. The combined pretreatment led to a great disruption of cellulose particles along with the formation of large pores and partial fibrillation. The effects of ultrasound irradiation time (2, 4 h), NaOH concentration (1–10 wt%), initial particle size (20–180 μm) and initial degree of polymerization (DP) of cellulose on structural changes and glucose yields were evaluated. The alkaline ultrasonic pretreatment resulted in a significant decrease in particle size of cellulose, besides significantly reducing the treatment time and NaOH concentration required to achieve a low crystallinity of cellulose. More than 2.5 times improvement in glucose yield was observed with 10 wt% NaOH and 4 h of sonication, compared to untreated samples. The glucose yields increased with increase in initial particle size of cellulose, while DP had no effect on glucose yields. The glucose yields exhibited an increasing tendency with increase in cellulose II fraction as a result of combined pretreatment.

Alkaline and ultrasound assisted alkaline pretreatment for intensification of delignification process from sustainable raw-material

Alkaline and ultrasound-assisted alkaline pretreatment under mild operating conditions have been investigated for intensification of delignification. The effect of NaOH concentration, biomass loading, temperature, ultrasonic power and duty cycle on the delignification has been studied. Most favorable conditions for only alkaline pretreatment were alkali concentration of 1.75N, solid loading of 0.8% (w/v), temperature of 353K and pretreatment time of 6h and under these conditions, 40.2% delignification was obtained. In case of ultrasound-assisted alkaline approach, most favorable conditions obtained were alkali concentration of 1N, paper loading of 0.5% (w/v), sonication power of 100W, duty cycle of 80% and pretreatment time of 70min and the delignification obtained in ultrasound-assisted alkaline approach under these conditions was 80%. The material samples were characterized by FTIR, SEM, XRD and TGA technique. The lignin was recovered from solution by precipitation method and was characterized by FTIR, GPC and TGA technique.

Ultrasound-assisted alkaline pretreatment of sugarcane bagasse for fermentable sugar production: Optimization through response surface methodology

Ultrasound-assisted alkaline pretreatment of sugarcane bagasse (SCB) for fermentable sugar production was carried out and the influence of particle size, liquid to solid ratio (LSR), NaOH concentration, temperature and sonication time on delignification and reducing sugar production was ascertained with Placket–Burman design. The best combination of each significant factor was determined by a central composite design (CCD) and optimum pretreatment conditions for maximum reducing sugar yield (96.27%) were particle size of 0.27mm, LSR of 25ml/g, NaOH concentration of 2.89% (w/v), temperature of 70.15°C and pretreatment time of 47.42min. Under these conditions, 92.11% of theoretical reducing sugar yield was observed experimentally. The substantial reduction in pretreatment time and temperature with improved efficiency is the most attractive features of the ultrasound-assisted alkaline pretreatment.