Quality evaluation of co-composted wheat straw, poultry droppings and oil seed cakes

Poultry droppings, neem cake, castor cake, jatropha cake and grass clippings were used separately as organic nitrogen additives to decrease the high C:N ratio of wheat straw. Composting was carried out aerobically in presence of fungal consortium developed by including Aspergillus awamori, Aspergillus nidulans, Trichoderma viride and Phanerochaete chrysosporium. The degraded product was characterized to assess the technical viability of organic nitrogen supplements as well as fungal consortium in improving the quality of compost and hastening the process of decomposition of high lignocellulolytic waste. Evaluation of maturity showed that mixture of wheat straw, poultry dropping and jatropha cake had the lowest C:N ratio of 10:1, the highest humic acid fraction of 3.15%, the lowest dehydrogenase activity and a germination index exceeding 80% in 60 days of decomposition. Inoculated and grass clipping amended wheat straw–poultry dropping mixture resulted in compost with highest humus content of 11.8% and C:N ratio of 13.5, humic acid fraction of 2.84% and germination index of 59.66%. Fungal consortium was effective in improving the humus content of all the composted mixtures. In some treatments, germination index could not be correlated with C:N ratio. Non edible oil seed cake supplemented substrate mixtures did not respond to fungal inoculation as far as C:N ratio was concerned.     

Optimization of solid substrate fermentation of wheat straw

Optimal conditions for solid substrate fermentation of wheat straw with Chaetomium cellulolyticum in laboratory-scale stationary layer fermenters were developed. The best pretreatment for wheat straw was ammonia freeze explosion, followed by steam treatment, alkali treatment, and simple autoclaving. The optimal fermentation conditions were 80% (w/w) moisture content; incubation temperature of 37 degrees C; 2% (w/w) unwashed mycelial inoculum; aeration at 0.12 L/h/g; substrate thickness of 1 to 2 cm; and duration of three days. Technical parameters for this optimized fermentation were: degree of substance utilization, 27.2%; protein yield/substrate, 0.09 g; biomass yield/bioconverted substrate, 0.40 g; degree of bioconversion of total available sugars in the substrate, 60.5%; specific efficiency of bioconversion, 70.8%; and overall efficiency of biomass production from substrate, 42.7%. Mixed culturing of Candida utilis further increased biomass production by 20%. The best mode of fermentation was a semicontinuous fed-batch fermentation where one-half of the fermented material was removed at three-day intervals and replaced by fresh substrate. In this mode, protein production was 20% higher than in batch mode, protein productivity was maintained over 12 days, and sporulation was prevented.     

Pretreatment of wheat straw for fermentation to methane

The effects of pretreating wheat straw with gamma-ray irradiation, ammonium hydroxide, and sodium hydroxide on methane yield, fermentation rate constant, and loss of feedstock constituents were evaluated using laboratory-scale batch fermentors. Results showed that methane yield increased as pretreatment alkali concentration increased, with the highest yield being 37% over untreated straw for the pretreatment consisting of sodium hydroxide dosage of 34 g OH(-)/kg volatile solids, at 90 degrees C for 1 h. Gamma-ray irradiation had no significant effect on methane yield. Alkaline pretreatment temperatures above 100 degrees C caused a decrease in methane yield. After more than 100 days of fermentation, all of the hemi-cellulose and more than 80% of the cellulose were degraded. The loss in cellulose and hemicellulose accounted for 100% of the volatile solids lost. No consistent effect of pretreatments on batch fermentation rates was noted. Semicontinuous fermentations of straw-manure mixtures confirmed the relative effectiveness of sodium and ammonium-hydroxide pretreatments.     

Biological upgrading of wheat straw through solid-state fermentation with Streptomyces cyaneus

The biological upgrading of wheat straw with Streptomyces cyaneus was examined through the analysis of chemical and structural changes of the transformed substrate during solid-state fermentation. Analysis of enzymes produced during the growth of S. cyaneus showed that phenol oxidase was the predominant enzyme. The reduction in Klason lignin content (16.4%) in the transformed substrate indicated the ability of this strain to delignify lignocellulose residues and suggests a role for phenol oxidase in the bacterial delignification process. Microscopic examination of the transformed substrate showed that the initial attack occurred at the less lignified cell walls (phloem and parenchyma), while xylem and sclerenchyma were slowly degraded. The pattern of degradation of sclerenchymatic tissues by S. cyaneus showed delamination between primary and secondary walls and between S₁ and S₂ due to partial removal of lignin. In the later stages of the decay a disorganization of the secondary walls was detected on account of fibrillation of this layer. A comparison of the properties of the pulp from wheat straw transformed by S. cyaneus with untreated wheat straw showed that pretreatment improved the characteristics that determine the quality of pulp. This was indicated by an increase in pulp brightness and by a decrease in the kappa number. These changes occurred without significantly affecting the viscosity, a measure of the quality of the cellulose fibres. These results support the potential application of this organism or its oxidative enzymes in biopulping. Received: 01 February 2000 / Received revision: 25 May 2000 / Accepted: 30 May 2000     

Solid substrate fermentation of wheat straw to fungal protein

Steam-treated wheat straw at a 70% (w/w) moisture level was subjected to solid substrate fermentation (SSF) with Trichoderma reesei (Riga, USSR) or a mixed culture of T. reesei and Endomycopsis fibuliger (R-574) in fermentation equipment of various design: some with mixing, some with stationary layers, including a mixedlayer 1.5-m(3) pilot plant scale fermenter. The best protein productivity was obtained in stationary layer fermenters with a product containing 13% protein. The main limitations of lignocellulose SSF, such as hindrance of fungal growth, limiting accessibility and availability of substrate, and difficulty in moisture and heat control, were analyzed. The technological parameters of SSF, submerged fermentation, and alternate lignocellulose conversion processes were compared. The SSF had lower overall efficiency but higher product concentration per reaction volume than other conversion schemes.     

Modification of wheat straw lignin by solid state fermentation with white-rot fungi

The potential of crude enzyme extracts, obtained from solid state cultivation of four white-rot fungi (Trametes versicolor, Bjerkandera adusta, Ganoderma applanatum and Phlebia rufa), was exploited to modify wheat straw cell wall. At different fermentation times, manganese-dependent peroxidase (MnP), lignin peroxidase (LiP), laccase, carboxymethylcellulase (CMCase), avicelase, xylanase and feruloyl esterase activities were screened and the content of lignin as well as hydroxycinnamic acids in fermented straw were determined. All fungi secreted feruloyl esterase while LiP was only detected in crude extracts from B. adusta. Since no significant differences (P > 0.05) were observed in remaining lignin content of fermented straw, LiP activity was not a limiting factor of enzymatic lignin removal process. The levels of esterified hydroxycinnamic acids degradation were considerably higher than previous reports with lignocellulosic biomass. The data show that P. rufa, may be considered for more specific studies as higher ferulic and p-coumaric acids degradation was observed for earlier incubation times.     

The enzymatic hydrolysis and fermentation of pretreated wheat straw to ethanol

Autohydrolysis and ethanol-alkali pulping were used as pretreatment methods of wheat straw for its subsequent saccharification by Trichoderma reesei cellulase. The basic hydrolysis parameters, i.e., reaction time, pH, temperature, and enzyme and substrate concentration, were optimized to maximize sugar yields from ethanol-alkali modified straw. Thus, a 93% conversion of 2.5% straw material to sugar syrup containing 73% glucose was reached in 48 h using 40 filter paper units/g hydrolyzed substrate. The pretreated wheat straw was then fermented to ethanol at 43 degrees C in the simultaneous saccharification and fermentation (SSF) process using T. reesei cellulase and Kluyveromyces fragilis cells. From 10% (w/v) of chemically treated straw (dry matter), 2.4% (w/v) ethanol was obtained after 48 h. When the T. reesei cellulase system was supplemented with beta-glucosidase from Aspergillus niger, the ethanol yield in the SSF process increased to 3% (w/v) and the reaction time was shortened to 24 h.     

Thermophilic and thermotolerant fungi in poultry droppings in Nigeria.

Ten species of fungi were obtained from poultry droppings in Nigeria. Six of these are true thermophiles while the other four are thermotolerant. Aspergillus fumigatus Fresenius, Mucor pusillus Lindt and Thermoascus aurantiacus Stolk are known human pathogens. Except for M. pusillus, all the thermotolerant species had a higher occurrence at 45 degrees C while the thermophilic varieties were readily obtained at 50 degrees C.     

Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol

Wheat straw consists of 48.57 ± 0.30% cellulose and 27.70 ± 0.12% hemicellulose on dry solid (DS) basis and has the potential to serve as a low cost feedstock for production of ethanol. Dilute acid pretreatment at varied temperature and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from wheat straw (7.83%, w/v, DS) by dilute H₂SO₄ (0.75%, v/v) pretreatment and enzymatic saccharification (45 °C, pH 5.0, 72 h) using cellulase, β-glucosidase, xylanase and esterase was 565 ± 10 mg/g. Under this condition, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per litre) from acid pretreated enzyme saccharified wheat straw (78.3 g) hydrolyzate by recombinant Escherichia coli strain FBR5 was 19 ± 1 g with a yield of 0.24 g/g DS. Detoxification of the acid and enzyme treated wheat straw hydrolyzate by overliming reduced the fermentation time from 118 to 39 h in the case of separate hydrolysis and fermentation (35 °C, pH 6.5), and increased the ethanol yield from 13 ± 2 to 17 ± 0 g/l and decreased the fermentation time from 136 to 112 h in the case of simultaneous saccharification and fermentation (35 °C, pH 6.0).     

Anaerobic fermentation of sheep droppings for biogas production

Production of biogas in batch digesters at 30°C from sheep droppings produced 93 l gas/kg dry matter whereas cattle dung yielded 234 l/kg dry matter. When the sheep droppings and cattle dung were used at 25:75 (w/w), gas production per kg dry matter was equal to that of cattle dung only. The methane content of the biogas obtained from sheep droppings was 70 to 72% as compared to 56 to 60% from cattle dung.     

Degradation of alkali-lignin residues from solid-state fermentation of wheat straw by streptomycetes

The ability of three Streptomyces strains to degradealkali-lignin, produced from the treatment of wheat straw by the same organisms, was examined. Decolourisation and loss of alkali-lignin was only detected in cultures supplemented with ammonium as an inorganic N source. The pH of cultures supplemented with inorganic N reached lower pH than in those supplemented with yeast extract. From FT-IR spectra corresponding to the alkali-lignin obtained from the same cultures, a degradation of carbohydrate component concomitant with a modification in the aromatic moiety of lignin could be inferred. The results indicate that streptomycetes are suitable for use in the treatment of alkali-lignin effluents from the biological treatment of wheat straw by the same organisms and therefore support the role for these organisms in the development of clean technologies in pulp and paper industry.     

Solid state fermentation of a Mycelia Sterilia laccase using steam-exploded wheat straw

Mycelia Sterilia YY-5, an endophytic fungus isolated from Rhus Chinensis Mill, was used in SSF for laccase production using steam-exploded wheat straw (SEWS). The fermentation period of YY-5 in solid state fermentation (SSF) shortened to 4 days compared with 5 days of submerged liquid fermentation (SmF) and the maximum laccase activity was 678.1 IU g⁻¹ substrate. The steam-explosion intensity (Log₁₀ R ₀) of SEWS had a significant effect on the growth of YY-5 and laccase activity, since SEWS could provide enough carbon source for YY-5 and inducers for laccase. The optimum SSF conditions using SEWS with Log₁₀ R ₀ = 3.597 as substrate were: inoculating with liquid inocula, keeping the solid-to-liquid ratio (S/L) for 1:4 and cultivating at 26°C. Under the optimum fermentation condition the laccase activity of YY-5 reached 849.5 ± 42.5 IU g⁻¹ substrate. The enzyme composition analysis indicated that laccase was the dominant enzyme of YY-5. Assayed with SDS-PAGE and active PAGE electrophoresis, the molecular weight of YY-5 laccase was approximately 45 kDa.     

Effect of wilting and the additives,straw, molasses and urea on the fermentation pattern of maize silage

The process of ensiling was studied in fresh maize (15% dry matter (DM)), wilted maize (18 and 24% DM) and maize mixed with 5–20% of wheat straw (18, 25 and 29% DM). Silages with 24% DM were preserved better than those with lower dry matter content. There was a significant change, with time, in pH, titrable acidity, volatile fatty acids, lactic acid, number of lactic acid bacteria, volatile nitrogen and soluble sugars in all the treatments. There was a significant decline in volatile fatty acids (P<0.05) and ammonia (P<0.01) production, and a significant increase in soluble sugar (P<0.01) in silages made after wilting. A significant decline in titrable acidity (P<0.01), volatile fatty acid production (p<0.05) and ammonia nitrogen (P<0.01), and a significant increase in pH (P<0.01) were found in silages of maize mixed with wheat straw. The overall rate of fermentation decreased during the first few days of fermentation in wilted and wheat straw silages, but the final products had characteristics of a good silage. In the second experiment the effect of urea and molasses was studied on wheat straw plus maize (15:85) silage with an initial DM content of 31–34%. Three levels of molasses (0, 3 and 6% of fresh weight) and two levels of urea (0 and 0.5% of fresh weight) were studied. Urea treatment with 3% molasses was found to be the best on the basis of silage characteristics.     

Fermentation characteristics and feeding value of ensiled poultry litter containing wheat straw,bagasse or sawdust

Poultry excreta substantially increased the crude protein (CP) content and the calcium and phosporus content of the base bedding materials. The crude fibre (CF) content of sawdust (52.3%) was higher than that of wheat straw (38.9%) and bagasse (30.2%). Dry matter digestibility in vitro (IVDMD) of wheat straw, bagasse and sawdust poultry litters (PL) was 65.4, 64.5 and 48.1%, respectively. Green sorghum fodder when ensiled alone or with 20% wheat straw PL, sawdust PL or bagasse PL on fresh basis contained 4.67, 7.80, 10.00 and 7.55% CP, respectively. Nitrogen-free extract (NFE) content of PL silages was lower than that of the control. Apart from wheat straw PL, all silages accumulated considerable amounts of lactic acid. The total volatile fatty acids (TVFA) concentrations were similar for all silages. The addition of PL caused an increase in the proportion of ammonia nitrogen. A feeding trial with crossbred adult male cattle revealed no significant difference in dry matter (DM), CP and ether extract (EE) digestibility of wheat straw and bagasse PL silages. The CF digestibility was similar for all the silages. Sawdust PL silage, however, was significantly lower (P < 0.05) in digestibility of DM, EE and NFE compared to other PL based silages. The DCP and TDN values for the control, wheat straw, bagasse and sawdust PL silages were 2.0, 60.1; 4.3, 45.3; 6.1, 50.3 and 2.9, 41.9 kg/100 kg DM, respectively.     

Single cell oil production in solid-state fermentation by Microsphaeropsis sp. from steam-exploded wheat straw mixed with wheat bran

Microsphaeropsis sp. was used to produce SCO in solid-state fermentation (SSF) from a substrate consisting of steam-exploded wheat straw (SEWS) and wheat bran (WB). The yield of SCO was 42 mg/g dry substrate (gds) without adding cellulase. To achieve a higher SCO yield, cellulase was added to the solid-state medium, resulting in an increase of SCO from 42 to 74 mg/gds with a cellulase loading of 10 FPU/gds. Other SSF parameters such as ratio of SEWS to WB of the dry substrate, initial moisture content, and incubation temperature were optimized under the condition of cellulase loading of 10 FPU/gds. So optimized, the SCO yield was 80 mg/gds, and the SCO content of the dry fermented mass was 10.2%. This research explored a novel method to produce SCO from the abundant and cheap agricultural residues - wheat straw and wheat bran.     

Bioconversion of wheat straw and wheat straw components into single-cell protein.

Several fungi (Aspergillus niger, A. terreus, Cochliobolus specifer, Myrothecium verrucaria, Rhizoctonia solani, Spicaria fusispora, Penicillium sp., and Gliocladium sp.) were isolated from decomposing wheat straw and tested for their ability to utilize whole straw and its components, holocellulose (hemicellulose and cellulose) and cellulose, for the production of single-cell protein (SCP). It was found that C. specifer was the most efficient fungus for protein synthesis with the three substrates. Using potassium nitrate as N source in mixtures of 0.04 g N/g substrate (0.04% wt./vol.) at pH 4.5, it was found that incubation periods of 3, 4, and 5 days were optimal for protein production on cellulose and holocellulose fractions, and whole straw, respectively. Whole native straw was found to be the most recalcitrant to bioconversion into SCP; however, protein production was almost doubled when the lignin component was removed using a mixture of sodium chlorite and acetic acid.     

Lactic acid bacteria active during the fermentation of wheat silage in small scale silos

Summary Wheat was ensiled and periodically analyzed for lactic acid bacteria present. Initially Lactobacillus plantarum, Leuconostoc mesenteroides, Lactobacillus cellobiosus and Streptococcus lactis predominated. After two to four days enterococci including S. faecium and S. bovis were present in high populations as well as Lactobacillus plantarum. It was concluded that mixed populations of enterococci and L. plantarum are active in the successful fermentation of wheat silage.     

Steric hindrance of growth of filamentous fungi in solid substrate fermentation of wheat straw

Cellulolytic fungi, such as Trichoderma reesei, T. lignorum, and Chaetomium cellulolyticum reach a low packing density of mycelia when grown on straw under conditions of solid substrate fermentation. The low packing density is shown to be caused partially by the geometric limitation of the growth of mycelia in the substrate and particularly in its pores, but the exact contribution of this limitation and other limitations such as mass transfer and substrate availability cannot be easily distinguished. The combined effect of such limitations is called steric hindrance. This steric hindrance is associated with and may be the principal cause of low biomass concentration in SSF.     

Bioconversion of wheat straw to ethanol: Chemical modification,enzymatic hydrolysis,and fermentation

Native wheat straw (WS) was pretreated with various concentrations of H₂SO₄ and NaOH followed by secondary treatments with ethylene diamine (EDA) and NH₄OH prior to enzymatic saccharification. Conversion of the cellulosic component to sugar varied with the chemical modification steps. Treatment solely with alkali yield 51–75% conversion, depending on temperature. Acid treatment at elevated tempeatures showed a substantial decrease in the hemicellulose component, whereas EDA-treated WS (acid pretreated) showed a 69–75% decrease in the lignin component. Acid-pretreated EDA-treated straw yielded a 98% conversion rate, followed by 83% for alkali–NH₄OH treated straws. In other experiments, WS was pretreated with varying concentration of H₂SO₄ or NaOh followed by NH₄OH treatment prior to enzymatic hydrolysis. Pretreatment of straw with 2% NaOH for 4 h coupled to enzymatic hydrolysis yield a 76% conversion of the cellulosic component. Acid–base combination pretreatment yielded only 43% conversions. A reactor column was subsequently used to measure modification–saccharification–fermentation for wheat straw conversion on a larger scale. Thirty percent conversions of wheat straw cellulosics to sugar were observed with subsequent fermentation to alcohol. The crude cellulase preparation yielded considerable quantities of xylose in addition to the glucose. Saccharified materials were fermented directly with actively proliferating proliferating yeast cells without concentration of the sugars.