Digestibility Of Wheat Straw Research Articles

Enhancing anaerobic digestion of wheat straw through multistage milling

Enhancing anaerobic digestion of wheat straw through multistage milling

Improving enzymatic digestibility of wheat straw pretreated by a cellulase-free xylanase-secreting Pseudomonas boreopolis G22 with simultaneous production of bioflocculants

BackgroundXylan removal by bacterial pretreatments has been confirmed to increase the digestibility of biomass. Here, an effective xylan removal technique has been developed to enhance the digestibility of wheat straw and simultaneously produce bioflocculants by a cellulase-free xylanase-secreting strain, Pseudomonas boreopolis G22.ResultsThe results indicated that P. boreopolis G22 is an alkaliphilic strain which can secrete abundant amounts of xylanase. This xylanase had activity levels of 2.67–1.75 U mL−1 after an incubation period of 5–25 days. The xylanase showed peak activity levels at pH 8.6, and retained more than 85% relative activity in the pH range of 7.2–9.8. After 15 days of cultivation, the hemicellulose contents of the wheat straw were significantly decreased by 32.5%, while its cellulose contents were increased by 27.3%, compared to that of the control. The maximum reducing sugars released from the 15-day-pretreated wheat straw were 1.8-fold higher than that of the untreated wheat straw, under optimal enzymatic hydrolysis conditions. In addition, a maximum bioflocculant yield of 2.08 g L−1 was extracted from the fermentation broth after 15 days of incubation. The aforementioned bioflocculants could be used to efficiently decolorize a dye solution.ConclusionsThe results indicate that the cellulase-free xylanase-secreting P. boreopolis G22 may be a potential strain for wheat straw pretreatments. The strain G22 does not only enhance the enzymatic digestibility of wheat straw, but also simultaneously produces a number of bioflocculants that can be used for various industrial applications.

Effect of thermal pretreatment on chemical composition, physical structure and biogas production kinetics of wheat straw

Hard lignocellulosic structure of wheat straw is the main hindrance in its anaerobic digestion. Thus, a laboratory scale batch experiment was conducted to study the effect of thermal pretreatment on anaerobic digestion of wheat straw. For this purpose, different thermal pretreatment temperatures of 120, 140, 160 and 180 °C were studied and the results were compared with raw wheat straw. Significant differences in biogas production were observed at temperature higher than 160 °C. Highest biogas yield of 615 Nml/gVS and volatile solids reduction of 69% was observed from wheat straw pretreated at 180 °C. Wheat straw pretreated at 180 °C showed 53% higher biogas yield as compared to untreated. Further, FTIR analysis revealed change in chemical bonds of lignocellulosic structure of wheat straw. Modified Gompertz model was best fitted on biogas production data and predicted shorter lag phase time and higher biogas production as the pretreatment temperature increased. Overall, change in lignocellulosic structure and increase in cellulose content were the main reason in enhancing biogas production.

Bioaugmentation of anaerobic digesters treating lignocellulosic feedstock by enriched microbial consortia.

Three different bioaugmentation cultures enriched from natural and engineered cellulolytic environments (cow and goat rumen, a biogas reactor digesting sorghum biomass) were compared for their enhancement potential on the anaerobic digestion of wheat straw. Methane yields were determined in batch tests using the Automatic Methane Potential Test System operated for 30 days under mesophilic conditions. All cultures had positive effects on substrate degradation, and higher methane yields were observed in the bioaugmented reactors compared to control reactors set up with standard inoculum. However, the level of enhancement differed according to the type of the enrichment culture. Methane yield in batch reactors augmented with 2% cow rumen derived enrichment culture was increased by only 6%. In contrast, reactors amended with 2% goat rumen derived enrichment culture or with the bioaugmentation culture obtained from the biogas reactor digesting sorghum biomass produced 27 and 20% more methane, respectively. The highest methane yield was recorded in reactors amended with 6% goat rumen derived enrichment culture, which represented an increase by 36%. The microbial communities were quite similar at the end of the batch tests independently of the bioaugmentation sources, indicating that the introduced microbial communities of the enrichment cultures did not dominate the reactors.

Enhanced methane production from wheat straw with the assistance of lignocellulolytic microbial consortium TC-5

The major obstacle of methane production from lignocellulose lies in the inefficient deconstruction of biomass. In this study, an anaerobic microbial consortium TC-5 was enriched with high lignocellulose-degradation capacity to enhance methane production from wheat straw. High degradation ratio of 45.7% of un-pretreated wheat straw was achieved due to a multi-species lignocellulolytic enzyme presented in the crude culture supernatant. The specific activity of xylanase, xylan esterase and β-xylosidase reached the highest level of 4.23, 0.15 and 0.48 U/mg, while cellobiohydrolase, endoglucanase and β-glucosidase showed the highest specific activity of 0.36, 0.22 and 0.41 U/mg during 9 days’ degradation. Inoculation of TC-5 in digestion sludge during anaerobic digestion of wheat straw resulted in remarkable enhancement of 22.2% and 36.6% in methane yield under mesophilic and thermophilic conditions, respectively. This work demonstrates the potential of TC-5 for enhancing the production of biogas and other chemicals through biomass based biorefinery.

Influence of white-rot fungus Polyporus brumalis BRFM 985 culture conditions on the pretreatment efficiency for anaerobic digestion of wheat straw

For the first time, Polyporus brumalis BRFM985 was cultivated on wheat straw to investigate the simultaneous effects of pretreatment parameters on anaerobic digestion: these include initial substrate humidity, temperature, duration, and metal supplementation. Surface response methodology was applied to quantify the importance of each parameter, as well as the synergistic effects between them. Firstly, metal addition and secondly, pretreatment duration, both resulted in a positive impact. According to calculations, the highest methane production (182 dm3 of methane per kilogram of initial Total Solids) is associated to pretreatment with metal addition during 20 days. In comparison with the least optimal conditions (118 dm3.kg−1 without metal addition, during 15 days), this result implies a 52% increase.

Increased biogas production from wheat straw by chemical pretreatments

Abstract This work investigated the effect of three different chemical pretreatment methods on the biogas production from the anaerobic digestion of wheat straw. The lignocellulosic material was separately pretreated using i) the organic solvent N-methylmorpholine N-oxide (NMMO) at 120 °C for 3 h, ii) the organosolv method, employing ethanol as the organic solvent at 180 °C for 1 h and iii) using an alkaline pretreatment with NaOH at 30 °C for 24 h. All the pretreatments were effective in increasing the biomethane production yield of wheat straw. In particular, the cumulative biomethane production yield of 274 mL CH4/g VS obtained with the untreated feedstock was enhanced by 11% by the NMMO pretreatment and by 15% by both the organosolv and alkaline pretreatment. The three pretreatment methods had a different impact on the chemical composition of the straw. NMMO hardly changed the amount of carbohydrates and lignin present in the original feedstock. Organosolv had a major impact on dissolving the hemicellulose component, whereas the alkaline pretreatment was the most effective in removing the lignin fraction. In addition to the increased biogas yields, the applied pretreatments enhanced the kinetics of biomethane production.

Characterization of the Microbial Communities in Rumen Fluid Inoculated Reactors for the Biogas Digestion of Wheat Straw

The present study investigated the effect of rumen fluid (RF) concentration on the methane production through anaerobic digestion of wheat straw in batch mode, and compared the microbial communities in RF and RF inoculated reactors by 16S rRNA genes sequencing. Six levels of RF concentration including 1%, 5%, 10%, 15%, 20% and 25% (v/v) were used in reactors R1, R5, R10, R15, R20 and R25 respectively. The results revealed that lower than or equal to 5% RF concentrations resulted in reactor acidification and low methane production. The highest methane yield of 106 mL CH4 g VS−1 was achieved in R10, whereas higher RF concentrations than 10% could not improve the methane production significantly. Methanosarcina barkeri was abundant in the well-working reactors, and Methanobacterium was dominant in the poor-working reactors, implying the archaeal communities in reactors had changed greatly from the Methanobrevibacter-dominated RF. Although the relative abundance of Clostridium and Ruminococcus were greatly different between RF and reactors, the Bacteroidetes and Firmicutes communities were dominant in all the tested samples. The results indicated that the in vitro anaerobic conditions had altered the rumen methanogenic communities significantly and the facultative acetoclastic Methanosarcina was important for the methane production in the RF seeded reactors.

Effect of Hydraulic Retention Time on Anaerobic Digestion of Wheat Straw in the Semicontinuous Continuous Stirred-Tank Reactors.

Three semicontinuous continuous stirred-tank reactors (CSTR) operating at mesophilic conditions (35°C) were used to investigate the effect of hydraulic retention time (HRT) on anaerobic digestion of wheat straw. The results showed that the average biogas production with HRT of 20, 40, and 60 days was 46.8, 79.9, and 89.1 mL/g total solid as well as 55.2, 94.3, and 105.2 mL/g volatile solids, respectively. The methane content with HRT of 20 days, from 14.2% to 28.5%, was the lowest among the three reactors. The pH values with HRT of 40 and 60 days were in the acceptable range compared to that with HRT of 20 days. The propionate was dominant in the reactor with HRT of 20 days, inhibiting the activities of methanogens and causing the lower methane content in biogas. The degradation of cellulose, hemicellulose, and crystalline cellulose based on XRD was also strongly influenced by HRTs.

Isolation and identification of termite gut symbiotic bacteria with lignocellulose-degrading potential, and their effects on the nutritive value for ruminants of some by-products

The termite gut contains different kinds of lignin and lignocellulose degrading microbes. This study was conducted to isolate and identify termite gut symbiotic bacteria with lignocellulose-degrading potential, and evaluate their effects on the chemical composition and in vitro digestibility of wheat straw and date leaves. Termite gut contents were extracted and cultured in 9 different culture media containing lignin and lignocellulosic materials that had been prepared from water-extracted sawdust and wheat straw. Three superior bacteria capable of growing on all media, and with higher lignin peroxidase activity, were selected and subjected to molecular identification. Following this, wheat straw and date leaves were incubated with the isolated bacteria in liquid medium for 6 weeks. 16S rRNA sequence analysis showed that these isolates possessed 97, 99 and 97% similarity with Bacillus licheniformis, Ochrobactrum intermedium and Microbacterium paludicola, respectively. The highest (P<0.05) dry matter (DM) loss in wheat straw and date leaves was observed following treatment with B. licheniformis. In the case of wheat straw, the organic matter (OM) and neutral detergent fiber (NDF), and for date leaves OM, NDF and acid detergent lignin (ADL) contents were not influenced by the treatments (P>0.05). The greatest and lowest (P<0.05) ADF content of wheat straw was observed as a result of treatment with B. licheniformis and O. intermedium, respectively. However, bacterial treatments decreased (P<0.05) ADF content of date leaves when compared to the control. Acid detergent lignin content of wheat straw was decreased (P<0.05) by bacterial treatments in comparisons to the control. For wheat straw, the highest and lowest (P<0.05) value of crude protein (CP) was observed in the case of M. paludicola and O. intermedium treatments, respectively. For date leaves, the CP content of the control treatment was highest (P<0.05) among treatments. For wheat straw, bacterial treatments enhanced (P<0.05) DM, OM and ADF digestibility when compared to the control. However, highest and lowest (P<0.05) CP digestibility was observed using O. intermedium and M. paludicola, respectively. For date leaves, treatment with B. licheniformis significantly increased (P<0.05) digestibility of DM, OM and NDF when compared to the others. However, CP and ADF digestibility was not different (P>0.05) between experimental groups. Overall, the results of this study showed that the isolated bacteria partially changed the chemical composition of wheat straw and date leaves while, they improved digestibility of nutrients. These bacteria are suitable candidates for increasing nutritive value of by-products for ruminants.

Effect of supplementing essential oils on the in vitro methane production and digestibility of wheat straw

The study was taken up to assess the effect of the pure essential oils (EOs) viz. cinnamaldehyde, carvacrol, carvone and limonene supplemented individually at 1 to 5% levels of the substrate DM (wheat straw) on the in vitro methane production and fiber degradation in a 4 × 7 factorial design. Supplementation of cinnamaldehyde and carvon, irrespective of their level had significantly (P < 0.01) higher net gas production (NGP), digestibility of neutral detergent fiber (NDFD) and true organic matter (TOMD), metabolizable energy (ME) availability and volatile fatty acids (VFAs) production from the substrate. The methane production was lowest (P < 0.01) in carvacrol followed by limonene and highest (P < 0.01) in carvone supplemented groups. Irrespective of the type of EO, the NGP and ME availability at 1% level of supplementation was comparable with control, while values of all other parameters were significantly (P < 0.01) lower than control and positive control. The NGP, NDFD and TOMD, ME availability, methane production and total and individual VFAs production was depressed significantly (P < 0.01) beyond 1% level of supplementation of EO. It was concluded that carvacrol or limonene supplementation beyond 1% level reduced the methane production but the digestibility of nutrients, volatile fatty acid production and ME availability from the substrate were also depressed significantly.

Effect of thermal, acid, alkaline and alkaline-peroxide pretreatments on the biochemical methane potential and kinetics of the anaerobic digestion of wheat straw and sugarcane bagasse

The effect of thermal, acid, alkaline and alkaline-peroxide pretreatments on the methane produced by the anaerobic digestion of wheat straw (WS) and sugarcane bagasse (SCB) was studied, using whole slurry and solid fraction. All the pretreatments released formic and acetic acids and phenolic compounds, while 5-hydroxymetilfurfural (HMF) and furfural were generated only by acid pretreatment. A remarkable inhibition was found in most of the whole slurry experiments, except in thermal pretreatment which improved methane production compared to the raw materials (29% for WS and 11% for SCB). The alkaline pretreatment increased biodegradability (around 30%) and methane production rate of the solid fraction of both pretreated substrates. Methane production results were fitted using first order or modified Gompertz equations, or a novel model combining both equations. The model parameters provided information about substrate availability, controlling step and inhibitory effect of compounds generated by each pretreatment.

The effect of increased atmospheric temperature and CO2 concentration during crop growth on the chemical composition and in vitro rumen fermentation characteristics of wheat straw.

This experiment was conducted to investigate the effects of increased atmospheric temperature and CO2 concentration during crop growth on the chemical composition and in vitro rumen fermentation characteristics of wheat straw. The field experiment was carried out from November 2012 to June 2013 at Changshu (31°32′93″N, 120°41′88″E) agro-ecological experimental station. A total of three treatments were set. The concentration of CO2 was increased to 500 μmol/mol in the first treatment (CO2 group). The temperature was increased by 2 °C in the second treatment (TEM group) and the concentration of CO2 and temperature were both increased in the third treatment (CO2 + TEM group). The mean temperature and concentration of CO2 in control group were 10.5 °C and 413 μmol/mol. At harvesting, the wheat straws were collected and analyzed for chemical composition and in vitro digestibility. Results showed that dry matter was significantly increased in all three treatments. Ether extracts and neutral detergent fiber were significantly increased in TEM and CO2 + TEM groups. Crude protein was significantly decreased in CO2 + TEM group. In vitro digestibility analysis of wheat straw revealed that gas production was significantly decreased in CO2 and CO2 + TEM groups. Methane production was significantly decreased in TEM and CO2 + TEM groups. Ammonia nitrogen and microbial crude protein were significantly decreased in all three treatments. Total volatile fatty acids were significantly decreased in CO2 and CO2 + TEM groups. In conclusion, the chemical composition of the wheat straw was affected by temperature and CO2 and the in vitro digestibility of wheat straw was reduced, especially in the combined treatment of temperature and CO2.

Effects of grinding processes on anaerobic digestion of wheat straw

Lignocellulosic biomass represents an important part of the agricultural wastes that can be transformed into a renewable energy. The biodegradability and biodegradation kinetics of ultra-finely ground wheat straw was studied under mesophilic anaerobic conditions. Biological methane potential (BMP) tests and batch reactors were performed on samples resulting from successive grinding processes (759–48μm). The main conclusion is that micronization do not improve methane yield but has a positive effect on the biodegradation kinetics. In addition, the results presented here showed for the first time that no significant increase of kinetics was observed below a size threshold value around 200μm. This can be explained by the modifications in the lignocellulosic network from 759 to 200μm but not below 200μm. Therefore, micronization, increasing significantly the kinetics of anaerobic digestion, can decrease the retention time or the size of the digesters to treat the same quantity of waste.

Enhanced biomethane potential from wheat straw by low temperature alkaline calcium hydroxide pre-treatment

A factorially designed experiment to examine the effectiveness of Ca(OH)2 pre-treatment, enzyme addition and particle size, on the mesophilic (35°C) anaerobic digestion of wheat straw was conducted. Experiments used a 48h pre-treatment with Ca(OH)2 7.4% (w/w), addition of Accellerase®-1500, with four particle sizes of wheat straw (1.25, 2, 3 and 10mm) and three digestion time periods (5, 15 and 30days). By combining particle size reduction and Ca(OH)2 pre-treatment, the average methane potential was increased by 315% (from 48NmL-CH4 g-VS−1 to 202NmL-CH4 g-VS−1) after 5days of anaerobic digestion compared to the control. Enzyme addition or Ca(OH)2 pre-treatment with 3, 2 and 1.25mm particle sizes had 30-day batch yields of between 301 and 335NmL-CH4 g-VS−1. Alkali pre-treatment of 3mm straw was shown to have the most potential as a cost effective pre-treatment and achieved 290NmL-CH4 g-VS−1, after only 15days of digestion.

Digestate liquor recycle in minimal nutrients-supplemented anaerobic digestion of wheat straw

Anaerobic digestion (AD) of minimal nutrient-supplemented wheat straw and digestate liquor recycle was evaluated in semi-continuous processes using a novel BioReactor Simulator developed for easy accurate online normalised-gas measurement. Three scenarios (i) no recycle (NR), (ii) recycle of soluble nutrient (RSN), and (iii) recycle of nutrient and microbes (RNM) were investigated in order to evaluate their respective efficiencies. Although mono-digestion of lignocellulosic biomasses are often performed with very long solid retention times (SRT), the present study demonstrated an efficient process operating with a 30-day SRT and an organic loading rate of 4gVS/Ld. The best methane yield was 303mLCH4/g VS achieved in the RSN process showing a 21% improvement as compared to the NR process. The methanogenic potential of the digestates from the RSN and RNM processes was comparable to fresh inoculum indicating efficient processes. The RNM and RSN processes showed superior process stability evidenced by minimal volatile fatty acid accumulation (˂0.5g/L). As compared to the RNM process, RSN demonstrated the best performance. The improved process performance was probably due to higher nutrient and microbial concentration in the digestate-recycled processes. This study confirms the feasibility of digestate recycle in AD as an appropriate technology for treating nutrient-deficient substrates.

Diverse cell wall composition and varied biomass digestibility in wheat straw for bioenergy feedstock

Wheat straw has a vast potential as feedstock for biofuel production in China. However, little information is available regarding variation in cell wall composition and enzymatic digestibility of wheat straw. This study investigated cell wall compositions and biomass digestibility of the straw of 115 wheat accessions from central China using a 1% NaOH pretreatment and mixed enzymatic hydrolysis. Significant variation in cell wall composition and sugar release was observed, with a coefficient variation (CV) ranging from 4.7% to 21.2%. Cellulose, hemicelluloses, alkali detergent hemicelluloses (ADH), and acid insoluble lignin (AIL) positively correlated with each other, and they all negatively correlated with acid soluble lignin (ASL). Hexose yields had a negative correlation with ADH and AIL, and positive correlation with ASL. No apparent undesirable correlation was found between sugar release and grain yield, thus yield and biomass convertibility can be potentially improved simultaneously. Furthermore, the features of the cell wall constitutions were compared with other plants and their implication in determining the best possible conversion strategy was discussed. This initial study is essential to understand the cell wall composition of wheat straw and to explore the potential of wheat straw as feedstock for biofuel production.

Screening of ecologically diverse fungi for their potential to pretreat lignocellulosic bioenergy feedstock

A widespread and hitherto by far underexploited potential among ecologically diverse fungi to pretreat wheat straw and digestate from maize silage in the future perspective of using such lignocellulosic feedstock for fermentative bioenergy production was inferred from a screening of nine freshwater ascomycetes, 76 isolates from constructed wetlands, nine peatland isolates and ten basidiomycetes. Wheat straw pretreatment was most efficient with three ascomycetes belonging to the genera Acephala (peatland isolate) and Stachybotrys (constructed wetland isolates) and two white-rot fungi (Hypholoma fasciculare and Stropharia rugosoannulata) as it increased the amounts of water-extractable total sugars by more than 50 % and sometimes up to 150 % above the untreated control. The ascomycetes delignified wheat straw at rates (lignin losses between about 31 and 40 % of the initial content) coming close to those observed with white-rot fungi (about 40 to 57 % lignin removal). Overall, fungal delignification was indicated as a major process facilitating the digestibility of wheat straw. Digestate was generally more resistant to fungal decomposition than wheat straw. Nevertheless, certain ascomycetes delignified this substrate to extents sometimes even exceeding delignification by basidiomycetes. Total sugar amounts of about 20 to 60 % above the control value were obtained with the most efficient fungi (one ascomycete of the genus Phoma, the unspecific wood-rot basidiomycete Agrocybe aegerita and one unidentified constructed wetland isolate). This was accompanied by lignin losses of about 47 to 56 % of the initial content. Overall, digestate delignification was implied to be less decisive for high yields of fermentable sugars than wheat straw delignification.

Pretreatments to Enhance the Digestibility of Wheat Straw

Wheat straw is a sufficient agricultural by-product with a low market price. The biofuel produced from lignocellulosic material exhibits energetic, economic and environmental benefits in contrast to bio-ethanol from starch or sugar. Until now, physical and chemical difficulty caused by the close connection of the main components of lignocellulosic biomass, discourage the hydrolysis of cellulose and hemicellulose to fermentable sugars. The main purpose of pretreatment is to enhance the enzyme accessibility improving digestibility of cellulose. Every pretreatment has a particular effect on the fraction of cellulose, hemicellulose and lignin, thus different pretreatment methods and conditions should be selected for the development of subsequent hydrolysis and fermentation steps. This paper reviews the most importance technologies for ethanol production from lignocellulose and its represent several vital qualities that should be marked for low-price and promote pretreatment processes.

Nutritional evaluation of wheat straw treated with white-rot fungus Crinipellis sp. RCK-SC in Sahiwal calves

Digestibility of wheat straw is limited mainly by lignin in ruminants, and fungal treatment is known to improve its nutritional worth. In the present study, wheat straw, subjected to solid state fermentation with ligninolytic white-rot basidiomycetes fungus Crinipellis sp. RCK-SC for 10 days, was studied with untreated wheat straw for in vitro nutritional parameters like chemical composition, digestibility, gas production and ruminal parameters, followed by in vivo feeding trial in Sahiwal calves. The fungal treatment after 10 days led to significant (P<0.05) decrease in cell wall constituents viz. neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose, lignin and cellulose to the extent of 104.0, 121.9, 64.2, 29.97 and 73.9g/kgDM, respectively. Crude protein (CP) and ash contents were increased (P<0.05) by 502.7 and 526.1g/kgDM, respectively, in fungal treated wheat straw (FT-WS) than untreated straw (UT-WS). Further, in vitro gas production (GP24h), in vitro true dry matter digestibility and organic matter digestibility for 48h, calculated metabolizable energy (ME) content, microbial biomass production and short chain fatty acids production were significantly (P<0.05) higher in FT-WS, while in vitro methane production (L) per kg of digestible dry matter was lower (P<0.05) in FT-WS. Ammonia nitrogen and total volatile fatty acids values were also significantly (P<0.05) higher in FT-WS. For in vivo feeding trial, ten healthy male Sahiwal calves (8–12 months) were divided into two groups based on comparable body weights following randomized block design. Control group (T1) was fed with ad libitum chopped wheat straw, whereas in treatment (T2), it was substituted with ad libitum chopped fungal treated wheat straw. Animals in both the groups were supplemented with groundnut cake to meet nitrogen requirement and green berseem (Trifolium alexandrium) forage to fulfill their vitamin A requirements. Digestibility of nutrients for DM, OM, CP, ether extract, NDF, ADF, hemicellulose, cellulose and total carbohydrates were significantly (P<0.05) higher in T2 compared to T1 group. Moreover, daily DM, digestible crude protein (P<0.01) and ME intakes were also higher (P<0.05) in T2 with higher (P<0.05) nitrogen retention (P<0.05), higher average daily gain in body weight and feed conversion ratio. This study suggested that the bioconversion of wheat straw using Crinipellis sp. RCK-SC holds potential in upgrading its nutritional value for feeding growing calves.