Biological saccharification by Clostridium thermocellum and two-stage hydrogen and methane production from hydrogen peroxide-acetic acid pretreated sugarcane bagasse

The present work aimed at establishing an efficient degradation and energy recovery system form sugarcane bagasse (SCB) through hydrogen peroxide-acetic acid (HPAC) pretreatment, thermophilic hydrogen production and mesophilic methane production. The degradation ratio of HPAC pretreated SCB (HPAC-SCB, 2%, w/v) exceeded 90% under the biological hydrolysis of C. thermocellum without enzyme addition. The hydrogen yield in the co-culture fermentation of T. thermosaccharolyticum and C. thermocellum from HPAC-SCB (2%, w/v) reached 226 mL/g substrate. The long-term hydrogen fermentation was successfully established with 1.59 L/(L·d), 0.159 L/g substrate for average hydrogen productivity and yield, respectively. Methane production of 0.341 L/g COD (chemical oxygen demand)_added was recovered by semi-continuous methane fermentation from hydrogen-producing effluent at 12 days of hydraulic retention time (HRT). Average energy recovery of 8.79 MJ/kg SCB was obtained under the optimal conditions. The present work indicated the promising application of the established process in valorization of lignocellulosic bio-waste.     

Identification of new critical points for logistics model in cumulative methane yield curves after co-digestion of apple pulp and chicken manure with sulphuric acid pretreatment and a new modelling study

In this study, anaerobic co-digestion of apple pulp (AP) with high carbon content and chicken manure (CM) with high nitrogen content was evaluated with regard to sulphuric acid pretreatment conditions in the concentration range of 1%-6% v/v. The best mixing ratio of CM:AP was determined as 3:1 w/w under untreated conditions for which the methane yield was 255.88 ± 11.55 mL/g VS (volatile solid). Sulphuric acid pretreatments were applied to this mixture ratio. The highest methane yield after pretreatment was 466.01 ± 10.85 mL/g VS in the reactor, where the sulphuric acid pretreatment concentration was 3.0% v/v. Control of acid pretreatment results were achieved by analysis of lignocellulosic degradation and increase in soluble chemical oxygen demand. The highest cellulose, hemicellulose and lignin degradation after pretreatment were 27.5% ± 1.4%, 35.9% ± 2.9% and 14% ± 1.5% w/w, respectively. The cumulative methane yields (CMY) were analysed by the modified logistic model, modified Bertalanffy model (MBM), modified Gompertz model (MGM) and modified Holling model (MHM). The MBM and MGM were found to fit the experimental data better than other models. The MHM has not previously been applied to CMY. In addition to the kinetic studies, new critical points for CMYs were identified in the logistics model (lm). The importance and critical properties of these points with regard to CMY are introduced. The differences and superior properties of these critical points compared to other modelling methods are discussed.     

Simultaneous saccharification and fermentation of sweet sorghum after acid pretreatment

The sweet sorghum bagasse pretreated with 5% (w/w) acetic acid at an accumulated solid concentration of 20% (w/v) during the 96-h fed-batch simultaneous saccharification and fermentation achieved a maximum ethanol concentration of 53.1 g/L and ethanol yield of 88.7%, compared to 25.7 g/L and 86.7% for the 96-h batch simultaneous saccharification and fermentation at a solid concentration of 10% (w/v), respectively. For comparison, the bagasse pretreated with 0.5% (w/w) sulfuric acid and water under the same fed-batch simultaneous saccharification and fermentation conditions produced maximum ethanol concentrations of 44.3 and 36.5 g/L, and ethanol yields of 77.6 and 69.7%, respectively.     

Evaluation of dilute acid and alkaline pretreatments,enzymatic hydrolysis and fermentation of napiergrass for fuel ethanol production

Napiergrass (Pennisetum purpureum Schum.) is a promising low cost raw material which does not compete with food prices, has attractive yields and an environmentally friendly farming. Dilute sulfuric acid pretreatment of napiergrass was effective to obtain high yields of sugars and low level of degradation by-products from hemicellulose. Detoxification with Ca(OH)₂ removed inhibitors but showed sugars loss. An ethanol concentration of 21 g/L after 176 h was found from the hydrolyzate using Pichia stipitis NBRC 10063 (fermentation efficiency 66%). An additional alkaline pretreatment applied to the solid fraction remaining from the diluted acid pretreatment improved the lignin removal. The highest cellulose hydrolysis values were found with the addition of β-glucosidase and PEG 6000. The simultaneous hydrolysis and fermentation of the cellulosic fraction with Saccharomyces cerevisiae, 10% (w/v) solid concentration, β-glucosidase and PEG 6000, showed the highest ethanol concentration (24 g/L), and cellulose hydrolysis values (81%). 162 L ethanol/t of dry napiergrass were produced (overall efficiency of 52%): 128 L/t from the cellulosic fraction and 34 L/t from the hemicellulosic fraction.     

Coproduction of hydrogen and volatile fatty acid via thermophilic fermentation of sweet sorghum stalk from co-culture of Clostridium thermocellum and Clostridium thermosaccharolyticum

This study was focused on investigating the potential of hydrogen and volatile fatty acid (VFA) coproduction. Sweet sorghum stalks (SS) were used as substrate along with Clostridium thermocellum and Clostridium thermosaccharolyticum as production microbes. Inoculation ratio of C. thermosaccharolyticum to C. thermocellum (0:1–1.5:1 and 1:0 v/v), substrate concentrations (2.5–15.0 g/L) and inoculation time intervals of C. thermosaccharolyticum followed by C. thermocellum (0–48 h) were investigated. Experimental data showed that higher yields of hydrogen and VFA were obtained in the co-culture than their individual cultures. The optimum conditions for the highest yield of products found as 1:1 inoculation ratio of both strains, 24 h of time gap between C. thermosaccharolyticum followed by C. thermocellum after the first inoculation and 5 g/L of substrate concentration. The maximum yield of products was observed as hydrogen (5.1 mmol/g-substrate), acetic acid (1.27 g/L) and butyric acid (1.05 g/L) at optimum conditions. The results suggest that SS can be used for simultaneous production of hydrogen and VFA employing co-culture of C. thermocellum and C. thermosaccharolyticum strains. This approach can contribute to the sustainability of biorefinery.     

Optimization of batch dilute-acid hydrolysis for biohydrogen production from red algal biomass

Marine algae are promising alternative sources for bioenergy including hydrogen. Their polymeric structure, however, requires a pretreatment such as dilute-acid hydrolysis prior to fermentation. This study aimed to optimize the control variables of batch dilute-acid hydrolysis for dark hydrogen fermentation of algal biomass. The powder of Gelidium amansii was hydrolyzed at temperatures of 120–180 °C, solid/liquid (S/L) ratios of 5–15% (w/v), and H₂SO₄ concentrations of 0.5–1.5% (w/w), and then fed to batch hydrogen fermentation. Among the three control variables, hydrolysis temperature was the most significant for hydrogen production as well as for hydrolysis efficiency. The maximum hydrogen production performance of 0.51 L H₂/L/hr and 37.0 mL H₂/g dry biomass was found at 161–164 °C hydrolysis temperature, 12.7–14.1% S/L ratio, and 0.50% H₂SO₄. The optimized dilute-acid hydrolysis would enhance the feasibility of the red algal biomass as a suitable substrate for hydrogen fermentation.     

Enhanced hydrogen and volatile fatty acid production from sweet sorghum stalks by two-steps dark fermentation with dilute acid treatment in between

This study investigated the potential of hydrogen and volatile fatty acid coproduction from two steps dark fermentation with dilute acid treatments of the residual slurry after 1st step fermentation. Sweet sorghum stalks (SS) was used as substrate along with Clostridium thermosaccharolyticum as production microbe. Residual lignocelluloses after 1st step fermentation were treated for 1 h by sulfuric acid concentration of 0.25, 0.5, 1.0, 1.5, 2.0 and 2.5% (w/v) with different reaction temperature of 120, 90 and 60 °C were studied. The optimum severity conditions for the highest yield of products found from the treatment acid concentration of 1.5% (w/v) at 120 °C for 10 g/L of substrate concentration. Experimental data showed that two-step fermentation increased 76% hydrogen, 84% acetic acid and 113% of butyric acid production from single step. Maximum yields of hydrogen, acetic acid and butyric acid were 5.77 mmol/g-substrate, 2.17 g/L and 2.07 g/L respectively. This two-step fermentation for hydrogen and VFA production using the whole slurry would be a promising approach to SS biorefinery.     

Biotoxicity assessment and lignocellulosic structural changes of phosphoric acid pre-treated young coconut husk hydrolysate for biohydrogen production

Major sugar constituents in young coconut husk were found to be glucans (0.30 g/g husk), while xylans were 0.10 g/g husk. Pre-treatments were carried out using phosphoric acid with dried coconut husk powder under steam heating. The effect of phosphoric acid on coconut husk hydrolysis was observed using acid concentrations of 0%, 1%, 5% and 10% (v/v). Soluble sugar concentration in hydrolysate was increasing proportional to acid concentration, as the total recovered solid decreases. FTIR and XRD analysis showed that acid hydrolysis led to the disruption of internal chemical bonds, causing coconut husk structural sugars to be released into the hydrolysate. Highest soluble sugar concentration, 29.9 g/L with a total suspended solid of 75.1 g/L, was obtained when the coconut husk was pre-treated with 10% phosphoric acid, and can be utilised for biohydrogen fermentation. Biotoxicity testing of the hydrolysates shows that half-maximal inhibition concentration of phosphoric acid was around 4.41% for a 24-h incubation and 3.80% for a 96-h incubation.     

有机酸和路易斯酸对玉米芯和玉米秸秆生物质水热法制备木糖影响研究

为确定有机酸和路易斯酸水热法处理玉米芯和玉米秸秆制备木糖的影响因素显著性顺序及最优工艺条件,设计正交实验,考察酸种类、酸浓度、固液比、水解时间和水解温度对木糖得率的影响.对酸种类和酸浓度进行单因素实验设计,采用高效液相色谱对水解液进行分析.结果表明:各因素影响主次顺序为水解时间>固液比>酸种类>水解温度>酸浓度;最佳处...     

Batch-based enzymatic saccharification of sweet sorghum bagasse

To improve enzymatic digestibility and sugar concentration, sweet sorghum bagasse was pretreated with alkali and liquid hot water, and then subjected to fed-batch enzymatic hydrolysis. Scanning electron microscopy assay suggested that different pretreatment methods resulted in different composition and structure of residues; these changes had a significant influence on cellulose hydrolysis. Fresh substrate was pretreated and then added at different amounts during the first 48 h to yield a final dry matter content of 30% (w/v). For liquid hot water pretreatment, a maximal glucose concentration of 95.71 g/L, corresponding to 52.85% xylan removal, was obtained with the sweet sorghum bagasse pretreated at 184°C for 18 min. NaOH soaking at ambient conditions removed lignin up to 60%, and the subsequent hydrolysis with cellulase loading of less than 10 FPU/g DM, and substrate supplementation every few hours yield the high glucose and xylose concentrations of 114.89L and 29.93 g/L, respectively after 144 h.     

Utilization of palm kernel cake as a renewable feedstock for fermentative hydrogen production

Fermentative hydrogen generation was studied using palm kernel cake (PKC) as sustainable cellulosic biomass. PKC was subjected to an acid hydrolysis approach using dilute H₂SO₄ (7% v/v). PKC hydrolysate obtained was then diluted (70%) and used as a substrate for hydrogen generation. Chemical analysis showed that the main fermentable sugars in diluted PKC hydrolysate were glucose, xylose and mannose with the concentrations of 2.75 g/L, 2.60 g/L and 27.75 g/L, respectively. Hydrogen production was carried out by the cultivation of Clostridium acetobutylicum YM1 on PKC hydrolysate. The effect of incubation temperature, the initial pH of culture medium and microbial inoculum size on hydrogen production was studied using a statistical model. The analysis of the model generated showed that the initial pH value of the culture medium and inoculum size had significant effects on the hydrogen production. The study showed that the optimum conditions for the biohydrogen production were 30.57 °C temperature, pH 5.5 and 20% inoculum size. A verification experiment was performed in the optimum conditions determined. Experimental results of the verification test showed that a cumulative hydrogen volume of 1575 ml/L was generated with consuming 2.75 g/L glucose, 2.20 g/L xylose and 16.31 g/L mannose.     

高活力木聚糖酶菌株的筛选、酶学性质及酶解应用

实验分离鉴定了高产木聚糖酶曲霉菌株,研究其固态发酵产酶条件及酶学性质。经菌落形态观察、ITS基因序列分析菌株在系统分类中的地位。通过单因素固态发酵实验确定其最佳产酶条件。结果表明,高产木聚糖酶曲霉菌株鉴定为黑曲霉（Aspergillus niger）。其最佳产酶条件为：玉米芯与麸皮比例为1∶3、氮源为尿素、初始pH为3.5、料水比为1∶3.5和接种量为10.0%。在此条件下发酵120 h,木聚糖酶酶活最高可达10 446.92 IU/g。酶学性质研究表明,在pH为5.0、温度为45℃条件下木聚糖酶处于最优条件。糠醛（23.0 g /L）和5-羟甲基糠醛（25.7 g/L）对木聚糖酶的激活率分别达到15.9%和18.4%。Aspergillus niger SM751可以作为木聚糖酶潜在的生产菌株用于木质纤维素的酶解领域。     

玉米秸秆的渗滤式稀酸预处理

对玉米秸秆的渗滤式稀酸预处理进行了考察,通过对温度、酸浓度、渗滤速度、液固比等影响因素的实验分析,得到了优化的工艺条件:反应温度170℃,硫酸浓度0.25%,液固比为10:1,渗滤速度150mL/min,70%水解液排出后,渗滤速度降为100mL/min。水解液中木糖浓度达到22g/L,糖得率达到约80%。经过稀酸预处理后的玉米秸秆进行酶水解,纤维素转化率达到80%。     

Enzymatic hydrolysis of pretreated soybean straw

In order to produce lactic acid, from agricultural residues such as soybean straw, which is a raw material for biodegradable plastic production, it is necessary to decompose the soybean straw into soluble sugars. Enzymatic hydrolysis is one of the methods in common use, while pretreatment is the effective way to increase the hydrolysis rate. The optimal conditions of pretreatment using ammonia and enzymatic hydrolysis of soybean straw were determined. Compared with the untreated straw, cellulose in straw pretreated by ammonia liquor (10%) soaking for 24 h at room temperature increased 70.27%, whereas hemicellulose and lignin in pretreated straw decreased to 41.45% and 30.16%, respectively.The results of infrared spectra (IR), scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis also showed that the structure and the surface of the straw were changed through pretreatment that is in favor of the following enzymatic hydrolysis. maximum enzymatic hydrolysis rate of 51.22% was achieved at a substrate concentration of 5% (w/v) at 50 °C and pH 4.8 using cellulase (50 fpu/g of substrate) for 36 h.     

Pretreatment of sweet sorghum bagasse for hydrogen production by Caldicellulosiruptor saccharolyticus

Pretreatment of sweet sorghum bagasse, an energy crop residue, with NaOH for the production of fermentable substrates, was investigated. Optimal conditions for the alkaline pretreatment of sweet sorghum bagasse were realized at 10% NaOH (w/w dry matter). A delignification of 46% was then observed, and improved significantly the efficiency of enzymatic hydrolysis. Under hydrolysis conditions without pH control, up to 50% and 41% of the cellulose and hemicellulose contained in NaOH-pretreated sweet sorghum bagasse were converted by 24 h enzymatic hydrolysis to soluble monomeric sugars. The extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus showed normal growth on hydrolysates of NaOH-pretreated biomass up to a sugar concentration of 20 g/L. Besides hydrogen, the main metabolic products detected in the fermentations were acetic and lactic acid. The maximal hydrogen yield observed in batch experiments under controlled conditions was 2.6 mol/mol C6 sugar. The maximal volumetric hydrogen production rate ranged from 10.2 to 10.6 mmol/(L h). At higher substrate concentrations the production of lactic acid increased at the expense of hydrogen production.     

Comparison of steam-alkali-chemical and microwave-alkali pretreatment for enhancing the enzymatic saccharification of oil palm trunk

This paper demonstrates two different pretreatment protocols for oil palm trunks (OPT); steam-alkali-chemical (SAC) and microwave-alkali (Mw-A) method. The composition, morphology, structure and crystallinity of OPT before and after pretreatment were analyzed. The effectiveness of the pretreated methods was investigated by performing enzymatic saccharification on the OPT. The physiochemical factors namely: enzyme ratio (cellulase to β-glucosidase), pH, temperature and substrate loading (w/v) on enzymatic saccharification were also investigated. The pre-determined optimal conditions were then used for further enzymatic hydrolysis of raw and pretreated OPT substrates. The results revealed a huge degree of reduction in lignin, up to 89% for SAC treated OPT and at least 15% for Mw-A treated OPT sample as compared to untreated ones. High glucose accumulation (79.4%) was obtained after 72 h saccharification for both pretreated OPT samples.     

Performance evaluation of artificial neural network coupled with generic algorithm and response surface methodology in modeling and optimization of biodiesel production process parameters from shea tree (Vitellaria paradoxa) nut butter

This work investigated the potential of shea butter oil (SBO) as feedstock for synthesis of biodiesel. Due to high free fatty acid (FFA) of SBO used, response surface methodology (RSM) was employed to model and optimize the pretreatment step while its conversion to biodiesel was modeled and optimized using RSM and artificial neural network (ANN). The acid value of the SBO was reduced to 1.19 mg KOH/g with oil/methanol molar ratio of 3.3, H₂SO₄ of 0.15 v/v, time of 60 min and temperature of 45 °C. Optimum values predicted for the transesterification reaction by RSM were temperature of 90 °C, KOH of 0.6 w/v, oil/methanol molar ratio of 3.5, and time of 30 min with actual shea butter oil biodiesel (SBOB) yield of 99.65% (w/w). ANN combined with generic algorithm gave the optimal condition as temperature of 82 °C, KOH of 0.40 w/v, oil/methanol molar ratio of 2.62 and time of 30 min with actual SBOB yield of 99.94% (w/w). Coefficient of determination (R²) and absolute average deviation (AAD) of the models were 0.9923, 0.83% (RSM) and 0.9991, 0.15% (ANN), which demonstrated that ANN model was more efficient than RSM model. Properties of SBOB produced were within biodiesel standard specifications.     

Characterization of cell wall structure in dilute acid-pretreated biomass by confocal Raman microscopy and enzymatic hydrolysis

The chemical and ultrastructural properties of cell walls were investigated to determine the effect of dilute acid pretreatment on the hydrolysis of lignocellulosic biomass. Confocal Raman microscopy was used to gain a clear understanding of how dilute acid pretreatments destroy lignocellulosic cell walls. Total fermentable sugar (glucose and xylose) was high in oxalic acid hydrolysate (26.18 g/L) compared to that in sulfuric acid hydrolysate (24.34 g/L). Chemical composition of the pretreated biomass differed slightly according to the acid catalyst used. Oxalic acid pretreatment was effective for enzymatic hydrolysis, with 29.46 g/L of total fermentable sugar after 96 h. Optical microscopy showed that dilute acid pretreatment significantly changed cell wall structure, and broken and crushed cell walls could be clearly seen during pretreatment. Based on confocal Raman peak intensity, the ratio of lignin/cellulose [I(1600)/I(900)] was low for oxalic acid-pretreated biomass compared to sulfuric acid-pretreated biomass.     

A comparative study of vegetable oil methyl esters (biodiesels)

In the present study, rubber seed oil, coconut oil and palm kernel oil, which are locally available especially in Kerala (India), are chosen and their transesterification processes have been investigated. The various process variables like temperature, catalyst concentration, amount of methanol and reaction time were optimized. Biodiesel from rubber seed oil (with high free fatty acid) was produced by employing two-step pretreatment process (acid esterification) to reduce acid value from 48 to 1.72 mg KOH/g with 0.40 and 0.35 v/v methanol-oil ratio and 1.0% v/v H₂SO₄ as catalyst at a temperature of 63(±2) °C with 1 h reaction time followed by transesterification using methanol-oil ratio of 0.30 v/v, 0.5 w/v KOH as alkaline catalyst at 55(±2) °C with 40 min reaction time to yield 98-99% biodiesel. Coconut oil and palm oil, being edible oils, transesterification with 0.25 v/v methanol-oil ratio, 0.50% w/v KOH as at 58(±2) °C, 20 min reaction time for coconut oil and 0.25% v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 60(±2) °C for palm kernel oil will convert them to 98-99% biodiesel. The brake thermal efficiency of palm oil biodiesel was higher with lower brake specific fuel consumption, but rubber seed oil biodiesel(ROB) showed less emission (CO and NO_x) compared to other biodiesels.     

Optimization of sugar release from banana peel powder waste (BPPW) using box-behnken design (BBD): BPPW to biohydrogen conversion

Optimization of pre-treatment conditions has been achieved for total sugar release from banana peel powder waste (BPPW) feedstock modelled through a three-level Box-Behnken design (BBD) of the response surface methodology (RSM). A series of various runs were executed at varied acid (H₂SO₄) concentrations (0.05%–0.15% v/v), incubation periods (1 h–3 h) in water bath at 95 °C and alkali (NaOH) concentrations (0.05%–0.15% v/v) according to the Box-Behnken design (BBD). From RSM the significant values of incubation period, acid concentration and alkali concentration were obtained as 3 h, 0.095% v/v, and 0.05% v/v respectively. The maximum total sugar release was reported as 5243.62 μg/ml which was highly close to the predicted value (5010.07 μg/ml). The model P- value (0.001), R-sq (98.26%), (adj) R-sq (95.14%) and (pred) R-sq (79.56%) obtained through ANOVA justified the results. The mutual impact of alkali and incubation period had the highest effect on total sugar release from dried banana peel powder, followed by mutual impact of acid and incubation period based on ANOVA (Analysis of Variance) results.Under optimized conditions of pre-treatment six different substrate concentrations (1%, 3%, 5%, 7% and 9% w/v) of BPPW was hydrolyzed and used to obtain volumetric bio-hydrogen evolution. The highest cumulative volumetric bio hydrogen gas 43 ml H₂/30 ml media was achieved at 5% w/v of pretreated BPPW. The substrate concentration above 5% w/v resulted in lowered fermentation process owing to product and substrate inhibition.