Enzymatic hydrolysis of sugarcane bagasse and straw mixtures pretreated with diluted acid

Abstract

In Brazil, sugarcane biomass is generated in large amounts. Sugarcane bagasse and straw are considered as an important feedstock for renewable energy and biorefinery. This paper aims to study the generation of monosaccharides (C5 and C6) from sugarcane biomass via processing bagasse or straw and mixtures of both materials (bagasse:straw 3:1, 1:1 and 1:3). Samples were pretreated with sulfuric acid which resulted in approximately 90% of hemicellulose solubilization, corresponding to around 58 g L^{? 1} of xylose. Pretreated straw showed greater susceptibility to enzymatic hydrolysis in comparison to bagasse, as shown by glucose yields of 76% and 65%, respectively, whereas the mixtures showed intermediate yields. Thus, one strategy to balance sugarcane biomass availability and possibly increasing 2G ethanol production would be to use bagasse–straw mixtures in appropriate ratios according to market fluctuations. Untreated and pretreated samples were analyzed using X-ray diffraction, but there was no relationship to enzymatic hydrolysis.     

An Analysis of the Energy Potential of Anaerobic Digestion of Agricultural By-Products and Organic Waste

Anaerobic digestion is a promising option for recycling agricultural by-products and some organic wastes. While both agricultural by-products and wastes have no direct commercial value, their management is both complicated and costly. One option to simplify by-product management and reduce the costs associated with biogas plant feedstock is to substitute dedicated crops with vegetal by-products. Given that the chemical composition of some of these by-products can differ considerably from more typical biogas plant feedstock (such as maize silage), more complete knowledge of these alternatives to produce environmentally friendly energy is warranted. To this end, batch trials under mesophilic conditions were conducted to evaluate the potential biogas yield of many agricultural by-products: maize stalks, rice chaff, wheat straw, kiwi fruit, onions, and two expired organic waste products (dairy and dry bread) from the retail mass-market. Among the considered biomasses, the highest methane producer was the expired dairy product mixture, which yielded 554 l_NCH₄ kg⁻¹ volatile solids (VS). Maize stalks and wheat straw produced the lowest yields of 214 and 285 l_NCH₄ kg⁻¹VS, respectively. An assessment of the biogas and methane yields of each biomass was also undertaken to account for the specific chemical composition of each biomass as it can affect the anaerobic digestion operating system. Finally, the total Italian green energy production that might be derived from feeding all these biomasses to a biogas digester was estimated, in order to understand its potential impact.     

Biogas production from the brown seaweed Saccharina latissima: thermal pretreatment and codigestion with wheat straw

Saccharina latissima is a carbohydrate-rich fast-growing seaweed (SW) which may be utilized as a marine energy crop. In this study, S. latissima was anaerobically digested for biogas production, and the effects of thermal pretreatment and codigestion with wheat straw (WS) were investigated. Batch experiments showed that pretreatment of SW increased the methane yield from 223 to 268 mL g^-1 VS. Codigestion of SW and steam-exploded WS had a clear positive effect on biogas production, giving yields that were considerably higher than what would be expected on the basis of the yields obtained with either of the individual feedstocks. Thus, anaerobic digestion of blends of SW and lignocellulosic substrates provides a promising strategy for biogas production. Although thermal pretreatment increased the yield of biogas from SW such a harsh pretreatment is probably more relevant for the more recalcitrant lignocellulosic substrates.     

Bioethanol,biohydrogen and biogas production from wheat straw in a biorefinery concept

The production of bioethanol, biohydrogen and biogas from wheat straw was investigated within a biorefinery framework. Initially, wheat straw was hydrothermally liberated to a cellulose rich fiber fraction and a hemicellulose rich liquid fraction (hydrolysate). Enzymatic hydrolysis and subsequent fermentation of cellulose yielded 0.41 g-ethanol/g-glucose, while dark fermentation of hydrolysate produced 178.0 ml-H₂/g-sugars. The effluents from both bioethanol and biohydrogen processes were further used to produce methane with the yields of 0.324 and 0.381 m³/kg volatile solids (VS)_added, respectively. Additionally, evaluation of six different wheat straw-to-biofuel production scenaria showed that either use of wheat straw for biogas production or multi-fuel production were the energetically most efficient processes compared to production of mono-fuel such as bioethanol when fermenting C6 sugars alone. Thus, multiple biofuels production from wheat straw can increase the efficiency for material and energy and can presumably be more economical process for biomass utilization.     

Biogas production and saccharification of Salix pretreated at different steam explosion conditions

Different steam explosion conditions were applied to Salix chips and the effect of this pretreatment was evaluated by running both enzymatic hydrolysis and biogas tests. Total enzymatic release of glucose and xylose increased with pretreatment harshness, with maximum values being obtained after pretreatment for 10 min at 210 °C. Harsher pretreatment conditions did not increase glucose release, led to degradation of xylose and to formation of furfurals. Samples pretreated at 220 and 230 °C initially showed low production of biogas, probably because of inhibitors produced during the pretreatment, but the microbial community was able to adapt and showed high final biogas production. Interestingly, final biogas yields correlated well with sugar yields after enzymatic hydrolysis, suggesting that at least in some cases a 24 h enzymatic assay may be developed as a quick method to predict the effects of pretreatment of lignocellulosic biomass on biogas yields.     

Production of Ligninolytic Enzymes by Phlebia Floridensis

Summary The present work reports the production of laccase, lignin peroxidase and manganese peroxidase by the little studied white-rot fungus Phlebia floridensis under a variety of nutritional and physicochemical conditions. Among the different media and supplements the highest yields of laccase, lignin peroxidase and manganese peroxidase were recorded in the presence of sugarcane bagasse, wheat straw and rice straw, respectively. Laccase and manganese peroxidase activities were best expressed at a pH of 4.5 while lignin peroxidase was optimally active at a lower pH. Laccase proved to be much more thermostable as compared to the other two enzymes.     

Effect of reactor configuration on biogas production from wheat straw hydrolysate

The potential of wheat straw hydrolysate for biogas production was investigated in continuous stirred tank reactor (CSTR) and up-flow anaerobic sludge bed (UASB) reactors. The hydrolysate originated as a side stream from a pilot plant pretreating wheat straw hydrothermally (195 °C for 10–12 min) for producing 2nd generation bioethanol [Kaparaju, P., Serrano, M., Thomsen, A.B., Kongjan, P., Angelidaki, I., 2009. Bioethanol, biohydrogen and biogas production from wheat straw in a biorefinery concept. Bioresource Technology 100 (9), 2562–2568]. Results from batch assays showed that hydrolysate had a methane potential of 384 ml/g-volatile solids (VS)_added. Process performance in CTSR and UASB reactors was investigated by varying hydrolysate concentration and/or organic loading rate (OLR). In CSTR, methane yields increased with increase in hydrolysate concentration and maximum yield of 297 ml/g-COD was obtained at an OLR of 1.9 g-COD/l d and 100% (v/v) hydrolysate. On the other hand, process performance and methane yields in UASB were affected by OLR and/or substrate concentration. Maximum methane yields of 267 ml/g-COD (COD removal of 72%) was obtained in UASB reactor when operated at an OLR of 2.8 g-COD/l d but with only 10% (v/v) hydrolysate. However, co-digestion of hydrolysate with pig manure (1:3 v/v ratio) improved the process performance and resulted in methane yield of 219 ml/g-COD (COD removal of 72%). Thus, anaerobic digestion of hydrolysate for biogas production was feasible in both CSTR and UASB reactor types. However, biogas process was affected by the reactor type and operating conditions.     

Utilization of spent agro-residues from mushroom cultivation for biogas production

Summary Various spent agro-residues obtained after cultivation of the edible mushroom Pleurotus sajor-caju were used in anaerobic digestors for production of biogas. The changes that take place in the residues during bioconversion were quantified in terms of composition of cellulose, hemicellulose, lignin, carbon and nitrogen. These mycostraws resulted in increased biogas production over the untreated ones, which varied from 21.5% in the case of spent bagasse to 38.8% in the case of spent paddy straw. The increased biogas generation by the spent residues seems to be due to the increased susceptibility to digestion and more favourable C/N ratio of the residues. Offprint requests to: V. S. Bisaria     

牲畜粪便与麦秆混合厌氧发酵的产气量、发酵时间及最优温度

探索牲畜粪便与作物秸秆混合发酵的产气量和发酵时间与发酵温度之间的关系,是解决农村户用沼气原料选择、确定最优发酵温度和提高农作物秸秆资源化利用效率的关键.采用可控型恒温发酵装置,以猪粪、牛粪和麦秆作为发酵原料,以常温厌氧发酵池的底物为接种物,在总固体（total solid,TS）质量分数为8%的条件下进行批量试验,研究了混合发酵的产气量、发酵时间及最优温度.结果表明：粪便与麦秆混合发酵明显提高了原料的产气效率,其中猪粪与麦秆混合发酵的累积产气量比猪粪作为单一发酵原料高24倍,而牛粪与麦杆混合发酵的累积产气量与单一牛粪无显著差异.猪粪、牛粪与麦秆混合发酵的最优温度均在30 ℃以上,发酵时间在60 d左右.厌氧发酵的发酵时间不总是随着温度的升高而缩短,单一以温度来断定厌氧发酵时间的长短是不可行的.     

Comparative evaluations of cellulosic raw materials for second generation bioethanol production

Aims: To evaluate sugar recoveries and fermentabilities of eight lignocellulosic raw materials following mild acid pretreatment and enzyme hydrolysis using a recombinant strain of Zymomonas mobilis. Methods and Results: Dilute acid pretreatment (2% H₂SO₄) with 10% (w/v) substrate loading was performed at 134°C for 60 min followed by enzyme hydrolysis at 60°C. The results demonstrated that hydrolysis of herbaceous raw materials resulted in higher sugar recoveries (up to 60–75%) than the woody sources (<50%). Fermentation studies with recombinant Z. mobilis ZM4 (pZB5) demonstrated that final ethanol concentrations and yields were also higher for the herbaceous hydrolysates. Significant reduction in growth rates and specific rates of sugar uptake and ethanol production occurred for all hydrolysates, with the greatest reductions evident for woody hydrolysates. Further studies on optimization of enzyme hydrolysis established that higher sugar recoveries were achieved at 50°C compared to 60°C following acid pretreatment. Conclusions: Of the various raw materials evaluated, the highest ethanol yields and productivities were achieved with wheat straw and sugarcane bagasse hydrolysates. Sorghum straw, sugarcane tops and Arundo donax hydrolysates were similar in their characteristics, while fermentation of woody hydrolysates (oil mallee, pine and eucalyptus) resulted in relatively low ethanol concentrations and productivities. The concentrations of a range of inhibitory compounds likely to have influence the fermentation kinetics were determined in the various hydrolysates. Significance and Impact of the Study: The study focuses on lignocellulosic materials available for second generation ethanol fermentations designed to use renewable agricultural/forestry biomass rather than food‐based resources. From the results, it is evident that relatively good sugar and ethanol yields can be achieved from some herbaceous raw materials (e.g. sugarcane bagasse and sorghum straw), while much lower yields were obtained from woody biomass.     

Characterization of dilute acid pretreatment of silvergrass for ethanol production

Pretreatment with dilute sulfuric acid of silvergrass was compared with the pretreatment's effect on other commonly used lignocellulosic materials, namely rice straw and bagasse, in order to evaluate the potential of this feedstock for ethanol production. The highest yield of xylose from silvergrass was between 70% and 75%, which was similar to bagasse. However, silvergrass gave a higher level of fermentability than bagasse using the hydrolysate because less acetic acid was formed. The release of sugars resulted in an about 2.0-fold increase in specific surface area of the pretreated silvergrass. Increasing the specific surface area did not obviously enhance enzymatic digestibility. The hydrophilicity of the acid pretreated silvergrass was characterized using its Fourier transform infrared (FTIR) spectra. The increase in hydrophilicity may enhance enzymatic adsorption onto lignin and increase the accumulation of cellobiose for enzymatic hydrolysis as pretreatment severity increases.     

Production of bioactive polysaccharides by Inonotus obliquus under submerged fermentation supplemented with lignocellulosic biomass and their antioxidant activity

The effect of lignocellulose degradation in wheat straw, rice straw, and sugarcane bagasse on the accumulation and antioxidant activity of extra- (EPS) and intracellular polysaccharides (IPS) of Inonotus obliquus under submerged fermentation were first evaluated. The wheat straw, rice straw, and sugarcane bagasse increased the EPS accumulation by 91.4, 78.6, and 74.3 % compared with control, respectively. The EPS and IPS extracts from the three lignocellulose media had significantly higher hydroxyl radical- and 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity than those from the control medium. Of the three materials, wheat straw was the most effective lignocellulose in enhancing the mycelia growth, accumulation and antioxidant activity of I. obliquus polysaccharides (PS). The carbohydrate and protein content, as well as the monosaccharide compositions of the EPS and IPS extracts, were correlated with sugar compositions and dynamic contents during fermentation of individual lignocellulosic materials. The enhanced accumulation of bioactive PS of cultured I. obliquus supplemented with rice straw, wheat straw, and bagasse was evident.     

Methane production through anaerobic digestion of various energy crops grown in sustainable crop rotations

Biogas production is of major importance for the sustainable use of agrarian biomass as renewable energy source. Economic biogas production depends on high biogas yields. The project aimed at optimising anaerobic digestion of energy crops. The following aspects were investigated: suitability of different crop species and varieties, optimum time of harvesting, specific methane yield and methane yield per hectare. The experiments covered 7 maize, 2 winter wheat, 2 triticale varieties, 1 winter rye, and 2 sunflower varieties and 6 variants with permanent grassland. In the course of the vegetation period, biomass yield and biomass composition were measured. Anaerobic digestion was carried out in eudiometer batch digesters. The highest methane yields of 7500-10200 m(N)(3)ha(-1) were achieved from maize varieties with FAO numbers (value for the maturity of the maize) of 300 to 600 harvested at "wax ripeness". Methane yields of cereals ranged from 3200 to 4500 m(N)(3)ha(-1). Cereals should be harvested at "grain in the milk stage" to "grain in the dough stage". With sunflowers, methane yields between 2600 and 4550 m(N)(3)ha(-1) were achieved. There were distinct differences between the investigated sunflower varieties. Alpine grassland can yield 2700-3500 m(N)(3)CH(4)ha(-1). The methane energy value model (MEVM) was developed for the different energy crops. It estimates the specific methane yield from the nutrient composition of the energy crops. Energy crops for biogas production need to be grown in sustainable crop rotations. The paper outlines possibilities for optimising methane yield from versatile crop rotations that integrate the production of food, feed, raw materials and energy. These integrated crop rotations are highly efficient and can provide up to 320 million t COE which is 96% of the total energy demand of the road traffic of the EU-25 (the 25 Member States of the European Union).     

Improved bio-energy yields via sequential ethanol fermentation and biogas digestion of steam exploded oat straw

Using standard laboratory equipment, thermochemically pretreated oat straw was enzymatically saccharified and fermented to ethanol, and after removal of ethanol the remaining material was subjected to biogas digestion. A detailed mass balance calculation shows that, for steam explosion pretreatment, this combined ethanol fermentation and biogas digestion converts 85-87% of the higher heating value (HHV) of holocellulose (cellulose and hemicellulose) in the oat straw into biofuel energy. The energy (HHV) yield of the produced ethanol and methane was 9.5-9.8 MJ/(kg dry oat straw), which is 28-34% higher than direct biogas digestion that yielded 7.3-7.4 MJ/(kg dry oat straw). The rate of biogas formation from the fermentation residues was also higher than from the corresponding pretreated but unfermented oat straw, indicating that the biogas digestion could be terminated after only 24 days. This suggests that the ethanol process acts as an additional pretreatment for the biogas process.     

Optimization of biogas production from co-digestion of whey and cow manure

Anaerobic co-digestion is effective and environmentally attractive technology for energy recovery from organic waste. Organic, agricultural and industrial wastes are good substrates for anaerobic co-digestion because they contain high levels of easily biodegradable materials. In this paper enhancement of biogas production from codigestion of whey and cow manure was investigated in a series of batch experiments. The influence of whey ratio on specific biogas production in a mixture with cow manure was analyzed at 35 and 55°C, for different initial pH values and for different concentrations of supplemental bicarbonate in experiments carried out over 12 days. Good biogas production (6.6 dm³/dm³), methane content (79.4%) in a biogas mixture and removal efficiencies for total solids (16%) were achieved at optimum process conditions (temperature of 55°C, 10% v/v of whey and 5 g/dm³ NaHCO₃ in the initial mixture). In order to validate optimized conditions for co-digestion of whey and cow manure in the one-stage batch process, the experiments were performed within 45 days. The high biogas production (21.8 dm³/dm³), a good methane content (78.7%) in a biogas mixture as well as maximum removal efficiencies for total solids (32.3%), and chemical oxygen demand (56.3%), respectively indicate that whey could be efficiently degraded to biogas in a onestage batch process when co-digested with cow manure.     

Biogas production by microbial communities via decomposition of cellulose and food waste

Several active microbial communities that form biogas via decomposition of cellulose and domestic food waste (DFW) were identified among 24 samples isolated from different natural and anthropogenic sources. The methane yield was 190–260 ml CH₄/g from microbial communities grown on cellulose substrates, office paper, and cardboard at 37°C without preprocessing. Under mesophilic conditions, bioconversion of paper waste yields biogas with a methane content from 47 to 63%; however, the rate of biogas production was 1.5–2.0 times lower than under thermophilic conditions. When microbial communities were grown on DFW under thermophilic conditions, the most stable and effective of them produced 230–353 ml CH₄/g, and the methane content in biogas was 54–58%. These results demonstrates the significance of our studies for the development of a technology for the biotransformation of paper waste into biogas and for the need of selection of microbial communities to improve the efficiency of the process.     

Microwave-assisted preparation of bagasse and rice straw for the removal of emulsified oil from wastewater

The present study was carried out to examine modified bagasse and rice straw as absorbents for the removal of emulsified oil by a microwave-assisted technique. The raw adsorbents were chemically modified with sodium hydroxide and surfactant solution for better adsorption of oil. The surface modification was confirmed through Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis. Batch studies were performed to identify the influence of contact time, pH, dosage, speed, and temperature on the percentage of removal of emulsified oil from the wastewater. A maximum oil removal of 98.07% and 98.72% was achieved in microwave-assisted bagasse and rice straw at 313 K. The obtained data were compared with isotherm and kinetic models to understand the mechanism behind the adsorption. From the Langmuir isotherm model, a maximum adsorption capacity of 192.58 and 276.82 mg/g was observed for modified bagasse and rice straw. The oil-loaded raw and microwave-assisted adsorbents can act as a potential energy source for renewable energy.     

Biogas production with horse dung in solid-phase digestion systems

Experiments on methanogenesis from horse dung were conducted in laboratory-scale batch reactors in order to determine the substrate performance in a solid-phase digestion process, more specifically in terms of potential energy recovery and suitable process technology. Dung from a horse stable with straw bedding was used. The temperature was kept in the mesophilic range. In the percolation process (with process water sprinkled over the stacked biomass) a proportion of 10-20% of solid inoculum (pre-digested horse dung) was found to be suitable. Comparative experiments with both percolation and flooding revealed a higher biogas production per volume for the flooded process, as no addition of solid inoculum was necessary. Methane yield from fresh material was similar in both processes: around 170 L(N) CH(4) per kg VS added was obtained in six-week cycles with untreated material under optimized conditions. Methane production was increased after chopping the substrate. Pre-aeration resulted in decreased methane production.     

Effect of biological pretreatments in enhancing corn straw biogas production

A biological pretreatment with new complex microbial agents was used to pretreat corn straw at ambient temperature (about 20°C) to improve its biodegradability and anaerobic biogas production. A complex microbial agent dose of 0.01% (w/w) and pretreatment time of 15 days were appropriate for biological pretreatment. These treatment conditions resulted in 33.07% more total biogas yield, 75.57% more methane yield, and 34.6% shorter technical digestion time compared with the untreated sample. Analyses of chemical compositions showed 5.81-25.10% reductions in total lignin, cellulose, and hemicellulose contents, and 27.19-80.71% increases in hot-water extractives; these changes contributed to the enhancement of biogas production. Biological pretreatment could be an effective method for improving biodegradability and enhancing the highly efficient biological conversion of corn straw into bioenergy.     

Alkali-explosion pretreatment of straw and bagasse for enzymic hydrolysis

Sugarcane bagasse and wheat straw were subjected to alkali treatment at 200 degrees C for 5 min and at 3.45 MPa gas pressure (steam and nitrogen), followed by an explosive discharge through a defibrating nozzle, in an attempt to improve the rate and extent of digestibility. The treatment resulted in the solubilization of 40-45% of the components and in the production of a pulp that gave saccharification yields of 80 and 65% in 8 h for bagasse and wheat straw, respectively. By comparison, alkali steaming at 200 degrees C (1.72 MPa) for 5 min gave saccharification yields of only 58 and 52% in 48 h. The increase in temperature from 140 to 200 degrees C resulted in a gradual increase in in vitro organic matter digestibility (IVOMD) for both the substrates. Also, the extent of alkalinity during pretreatment appears to effect the reactivity of the final product towards enzymes. Pretreatment times ranging from 5 to 60 caused a progressive decline in the IVOMD of bagasse and wheat straw by the alkali explosion method and this was accompanied by a progressive decrease in pH values after explosion. In the alkali-steaming method, pretreatment time had no apparent effect with either substrate. An analysis of the alkali-exploded products showed that substantial amounts of hemicellulose and a small proportion of the lignin were solubilized. The percentage crystallinity of the cellulose did not alter in either substrate but there was a substantial reduction in the degree of polymerization. The superiority of the alkali-explosion pretreatment is attributed to the efficacy of fiber separation and disintegration; this increases the surface area and reduces the degree of polymerization.