Ethanol and value‐added byproducts from rice straw by dimorphic fungus Mucor hiemalis

Different morphologies of Mucor hiemalis were induced and used for the production of ethanol and biomass from rice straw through a separate hydrolysis and fermentation process. The yield of enzymatic hydrolysis was improved from 40.4% for the untreated straw to 80–93% by employing sodium hydroxide and concentrated phosphoric acid pretreatments with or without ultrasonication. The best hydrolysis performance was achieved after pretreatment by sodium hydroxide assisted with ultrasonication. The ethanol yields from the hydrolysates were 0.39–0.44 g/g depending on the pretreatment method and the fungus morphology. The yeast‐like form of the fungus showed faster glucose assimilation and slightly higher ethanol yield compared to the other morphologies. The biomass yield of mostly yeast‐like cells was more than the other morphologies (0.202–0.282 g/g glucose). Moreover, the biomass of the yeast‐like cells had more protein content (46.7–52.4 %) compared to filamentous cells (37.7–46.3 %). The cell wall, alkali‐insoluble material (AIM) of the biomass, represented 16.3–20.1% of the biomass. On average, total chitin‐chitosan content of AIM of the biomass of purely filamentous, mostly filamentous, mostly yeast‐like, and purely yeast‐like forms of the fungus was 0.460, 0.373, 0.330, and 0.336 g/g AIM of the biomass, respectively.     

Microbial Fermentation of Rice Straw: Nutritive Composition and In Vitro Digestibility of the Fermentation Products

Rice straw was fermented with Cellulomonas sp. and Alcaligenes faecalis. Microbial cells and undigested residue, as well as chemically treated (NaOH or NH₄OH) and untreated straws, were analyzed for nutrient composition and in vitro digestibility. In a typical fermentation, 75% of the rice straw substrate was digested, and 18.6% of the total substrate weight that disappeared was recovered as microbial protein. The microbial cell fraction was 37% protein and 5% crude fiber; the residue was 12% protein and 45% crude fiber. The microbial protein amino acid profile was similar to alfalfa, except for less cysteine. The microbial cells had more thiamine and less niacin than Torula yeast. In vitro digestibility of the microbial protein was 41.2 to 55%; that of cellulose was 52%.     

Semisolid fermentation of ryegrass straw

Candida utilis, Aureobasidium pullulans, and Trichoderma viride were grown on pretreated ryegrass straw. The pretreatment consisted of hydrolysis of straw with 0.5 N H₂SO₄ (water-substrate, 3:1) at 121 C, 100 C, and room temperature and adjustment of the hydrolysate to pH 4.5 to 5.0 with 5 N NH₄OH. The 121 C pretreatment yielded a material containing 30% sugar and 2.3% N. The fermentation was carried on semisolid substrate (moisture level, 75%) in rotating jars for 2 to 3 days at room temperature. The organisms grew rapidly during the period from 18 to 42 h of incubation. During this period the number of microbial cells increased by 20- to 200-fold, and the level of NH₃-N decreased from 1.3 to 0.9%. The fermentation resulted in a fourfold increase in protein, fivefold increase in crude fat, and 40% increase in the digestibility of straw. The best result in terms of increasing protein and digestibility of straw was obtained when C. utilis was grown on straw preheated at 121 C.     

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.     

Pollution control of swine manure and straw by conversion to Chaetomium cellulolyticum SCP feed

Swine manure has a very high pollution potential and obnoxious odor. Large farms particularly are confronted with a manure disposal problem since environmentally acceptable solutions are now required by government regulations. Swine manure was found to be a good source of supplementary nutrients to ferment wheat straw into single-cell protein (SCP) with Chaetomium cellulolyticum when 0.13g (NH₄)₂SO₄/g solid was used as an additional source of N. In batch fermentations, inhibitory effects, possibly due to soluble released from the straw during alkali or acid pretreatment, were overcome by starting the fermentation at about pH 7.0 and then reducing it to 5.0 during growth. An overall protein productivity of up to 66 mg/L h was obtained from a slurry mixture of 1% w/v solids of manure and straw. This compares favorably with 99 mg/L h when manure was fermented with glucose instead of straw as the main carbon source. A high protein productivity of 200 mg/L h was obtained from a slurry mixture containing anaerobically prefermented swine manure liquor and 1.5% w/v solids from straw. The final products of the manure and straw fermentations contained 25–30% DW crude protein and 6–20% DW cellulose and the materials were free of the original obnoxious odor and undesirable microbial contamination.     

不同培养料和发酵次数栽培巴氏菇比较

分别以玉米秸秆和稻草为培养料栽培巴氏菇,对菌丝生长性状进行对比;同时,在我国传统发酵栽培方法的基础上,将三次发酵法与二次发酵法进行了对比。试验结果表明:利用玉米秸秆栽培的巴氏菇在发菌速度及子实体质量和产量上均优于稻草;培养料经过3次发酵更适宜巴氏菇生长。经过3次发酵的玉米秸秆培养料栽培的巴氏菇产量和生物学效率分别为7.7 kg/m2和27.5%,子实体粗蛋白含量44.89%,可溶性糖含量44.01%,18种氨基酸总量31.70%,明显高于2次发酵的玉米秸秆培养料及2次、3次发酵的稻草培养料。     

Comparison between solid-state and powder-state alkali pretreatment on saccharification and fermentation for bioethanol production from rice straw

The efficacy of different concentrations of NaOH (0.25%, 0.50%, 0.75%, and 1.00%) for the pretreatment of rice straw in solid and powder state in enzymatic saccharification and fermentation for the production of bioethanol was evaluated. A greater amount of biomass was recovered through solid-state pretreatment (3.74 g) from 5 g of rice straw. The highest increase in the volume of rice straw powder as a result of swelling was observed with 1.00% NaOH pretreatment (48.07%), which was statistically identical to 0.75% NaOH pretreatment (32.31%). The surface of rice straw was disrupted by the 0.75% NaOH and 1.00% NaOH pretreated samples as observed using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). In Fourier-transform infrared (FT-IR) spectra, absorbance of hydroxyl groups at 1,050 cm^?1 due to the OH group of lignin was gradually decreased with the increase of NaOH concentration. The greatest amounts of glucose and ethanol were obtained in 1.00% NaOH solid-state pretreated and powder-state hydrolyzed samples (0.804 g g^?1 and 0.379 g g^?1, respectively), which was statistically similar to the use of 0.75% NaOH (0.763 g g^?1 and 0.358 g g^?1, respectively). Thus, solid-state pretreatment with 0.75% NaOH and powder-state hydrolysis appear to be suitable for fermentation and bioethanol production from rice straw.     

Optimisation of the biological pretreatment of wheat straw with white-rot fungi for ethanol production

The biological pretreatment of lignocellulosic biomass for the production of bioethanol is an environmentally friendly alternative to the most frequently used process, steam explosion (SE). However, this pretreatment can still not be industrially implemented due to long incubation times. The main objective of this work was to test the viability of and optimise the biological pretreatment of lignocellulosic biomass, which uses ligninolytic fungi (Pleurotus eryngii and Irpex lacteus) in a solid-state fermentation of sterilised wheat straw complemented with a mild alkali treatment. In this study, the most important parameters of the mechanical and thermal substrate conditioning processes and the most important parameters of the fungal fermentation process were optimised to improve sugar recovery. The largest digestibilities were achieved with fermentation with I. lacteus under optimised conditions, under which cellulose and hemicellulose digestibility increased after 21 days of pretreatment from 16 to 100 % and 12 to 87 %, respectively. The maximum glucose yield (84 %) of cellulose available in raw material was obtained after only 14 days of pretreatment with an overall ethanol yield of 74 % of the theoretical value, which is similar to that reached with SE.     

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.     

Enhanced saccharification of rice straw using hypochlorite-hydrogen peroxide

Rice straw is a lignocellulosic biomass, and has been recognized as a renewable organic substance and alternative energy source. In this study, rice straw was pretreated with hypochlorite-hydrogen peroxide (Ox-B) solution. The optimal pretreatment conditions were determined via response surface methodology, and the pretreated rice straw was hydrolyzed with exo-glucanase, endoglucanase, hemicellulase, and β-glucosidase Accellerase 1000? (endo-glucanase equivalent activity of 1,250 carboxy methyl cellulose (CMC) U/g of rice straw pretreated for 24 h). The optimal conditions were as follows: 60 min pretreatment using Ox-B solution containing 0.6% hypochlorite and 25% hydrogen peroxide for 1 g of rice straw in a total reaction volume of 240 mL. Under these conditions, 406.8 mg of d-glucose and 224.0 mg of d-xylose were obtained from 1 g of rice straw. The fermentation of enzymatic hydrolysates containing 8.14 g/L d-glucose and 4.49 g/L d-xylose with Pichia stipitis generated 3.65 g/L of ethanol with a corresponding yield of 0.37 g/g. The maximum possible ethanol conversion rate is 72.54%.     

Production of a cellulolytic enzyme system in mixed-culture solid-state fermentation of soybean hulls supplemented with wheat bran

Solid-state fermentation of soybean hulls supplemented with wheat bran using a co-culture of Trichoderma reesei and Aspergillus oryzae was performed. Three parameters — initial moisture content, incubation temperature, and initial pH — were optimized in culture flasks using response surface methodology. Parameter optimization was carried out with respect to filter paper activity and β-glucosidase activity in the culture. Temperature of 30 °C, pH of 5, and moisture content of 70% were found to be optimum. Optimized parameters were used for laboratory scale-up in static tray fermenters. The maximum filter paper activity of 10.7 FPU/g-ds and β-glucosidase of 10.7 IU/g-ds were obtained after 96-h incubation period in static tray fermenters in agreement with optimized activities at shake flask level. The results of static tray fermentation also highlighted the importance of mixed-culture fermentation. Both enzyme activities and volumetric productivities of enzyme produced were significantly higher in mixed-culture fermentation as compared to mono-culture static tray fermentation. Expression profile of cellulase system was characterized using SDS-PAGE and it indicated the presence of all the five major activities corresponding to β-glucosidase, CBH I, CBH II, EG I and xylanase. Enzyme broth was centrifuged and concentrated in an ultrafiltration cell. The concentrate was used for enzymatic saccharification of pretreated wheat straw and the potential of an indigenously developed enzyme concoction was reported in terms of saccharification efficiency. Pretreatment using both acid and alkali was carried out, and differences in sugar yield due to differences in composition as a result of pretreatment were reported. Results showed that alkali treatment generated higher sugars as compared to acid pretreatment. This was due to lignin removal and concentration of the cellulosic fraction. Present work showed that solid-state fermentation in a static tray bioreactor is a valuable technique for producing a system of enzymes with balanced activities that can efficiently saccharify lignocellulosic biomass like wheat straw.     

Comparison of the kinetics of lipopeptide production by Bacillus amyloliquefaciens XZ-173 in solid-state fermentation under isothermal and non-isothermal conditions

This study aimed to compare the kinetics of lipopeptide production in solid-state fermentation (SSF) under isothermal and non-isothermal conditions. Models based on the logistic, modified Gompertz and Luedeking–Piret-like equations were developed to describe the time course of fermentation under different conditions. The experiments were conducted in 250 mL flasks and a 50 L fermenter. The results showed that the non-isothermal process had higher levels of product formation rate and substrate utilization rate compared to the isothermal process. The part of substrate carbon to meet microbial maintenance—energy, biomass and lipopeptides formation requirements got increased using the non-isothermal technique. In addition, fermenter conditions positively influenced the lipopeptides formation rate with significantly higher levels of substrate for the microbial growth and product formation, though the product productivity and biomass both decreased as compared to flask. This is the first report that investigates the effects of temperature changing on the kinetics of lipopeptide production by Bacillus amyloliquefaciens strain under SSF condition using soybean flour and rice straw as major substrates in flask and in fermenter.     

Hemicellulose bioconversion

Various agricultural residues, such as corn fiber, corn stover, wheat straw, rice straw, and sugarcane bagasse, contain about 20–40% hemicellulose, the second most abundant polysaccharide in nature. The conversion of hemicellulose to fuels and chemicals is problematic. In this paper, various pretreatment options as well as enzymatic saccharification of lignocellulosic biomass to fermentable sugars is reviewed. Our research dealing with the pretreatment and enzymatic saccharification of corn fiber and development of novel and improved enzymes such as endo-xylanase, β-xylosidase, and α-l-arabinofuranosidase for hemicellulose bioconversion is described. The barriers, progress, and prospects of developing an environmentally benign bioprocess for large-scale conversion of hemicellulose to fuel ethanol, xylitol, 2,3-butanediol, and other value-added fermentation products are highlighted.     

Organosolvent pretreatment and enzymatic hydrolysis of rice straw for the production of bioethanol

The present study investigates the operational conditions for organosolvent pretreatment and hydrolysis of rice straw. Among the different organic acids and organic solvents tested, acetone was found to be most effective based on the fermentable sugar yield. Optimization of process parameters for acetone pretreatment were carried out. The structural changes before and after pretreatment were investigated by scanning electron microscopy, X-ray diffraction and Fourier transform infrared (FTIR) analysis. The X-ray diffraction profile showed that the degree of crystallinity was higher for acetone pretreated biomass than that of the native. FTIR spectrum also exhibited significant difference between the native and pretreated samples. Under optimum pretreatment conditions 0.458 g of reducing sugar was produced per gram of pretreated biomass with a fermentation efficiency of 39%. Optimization of process parameters for hydrolysis such as biomass loading, enzyme loading, surfactant concentration and incubation time was done using Box–Benhken design. The results indicate that acetone pretreated rice straw can be used as a good feed stock for bioethanol production.     

Alkali treatment and fermentation of straw for animal feed

The feed value of annual ryegrass straw was improved by treatment with various concentrations of NaOH or NH₃ followed by fermentation of the treated straw with a mixed culture of Cellulomonas sp. and Alcaligenes faecalis. Laboratory feeding trials with voles showed that NaOH or NH₃ treatment considerably increased the feed efficiency of straw, but apparently gave a poorly palatable product. Fermentation tended to decrease the in vitro rumen digestibility (IVRD) of alkali-treated straw. The fermentations were carried out aerobically on a semisolid straw matrix having 11–86% moisture. Treatment by both NaOH and NH₃ increased the IVRD of straw. NH₃ also increased the nitrogen content in straw. The optimum condition for alkaline treatment of the straw was 4–6% NaOH for 1 hr or with 3% NH₃ for four weeks at room temperature. A minimum of 63% moisture was needed for significant fermentation of the straw. The combined effects of NaOH treatment and fermentation more than doubled crude protein, doubled crude fat, and increased IVRD by 75%. The NH₃ plus fermentation treatment tripled crude protein, doubled crude fat, and increased IVRD by 60%. Acetic acid was the main volatile fatty acid in the fermented straw.     

Microbial biomass production from rice straw hydrolysate in airlift bioreactors

Rice straw is a by-product of rice production, and a great bioresource as raw biomass material for manufacturing value-adding protein for animal feedstock, which has been paid more and more attention. In the present work, utilizing rice straw hydrolysate as a substrate for microbial biomass production in 11.5L external-loop airlift bioreactors was investigated. Rice straw hydrolysate obtained through acid-hydrolyzing rice straw was used for the culture of yeast Candida arborea AS1.257. The influences of gas flow rate, initial liquid volume, hole diameter of gas sparger and numbers of sieve plates on microbial biomass production were examined. The best results in the external-loop airlift bioreactor were obtained under 9.0 L initial liquid volume, 1.1 (v/v)/min gas flow rate during culture time of 0-24 h and 1.4 (v/v)/min gas flow rate of 24-48 h at 29+/-1 degrees C. The addition of the sieve plates in the riser of the external-loop airlift bioreactor increased productivity. After 48 h, under optimized operation conditions, crude protein productivity with one sieve and two sieves were 13.6 mg/mL and 13.7 mg/mL, respectively, comparing 12.7 mg/mL without sieves in the airlift bioreactor and 11.7 mg/mL in the in the 10-L mechanically stirred tank bioreactor. It is feasible to operate the external-loop airlift bioreactors and possible to reduce the production cost for microbial biomass production from the rice straw hydrolysate.     

Effect of physicochemical pre-treatment of rice straw on its digestibility by <Emphasis Type="Italic">Clostridium cellulolyticum</Emphasis>

Rice straw (RS) may serve as a low-cost biomass for the production of biofuels and biochemicals, but its native structure is resistant to enzymatic and microbial deconstruction. Therefore, an efficient pre-treatment method is required to modify crystalline cellulose to a more reactive amorphous form. This work investigated pre-treatments of rice straw involving size reduction (S) followed by either sodium hydroxide (NaOH) or diluted sulfuric acid (H₂SO₄) and liquid hot water (LHW). The shrinkage of the vascular bundles in the rice straw structure pre-treated with NaOH–LHW–S was higher than that with LHW–S and H₂SO₄–LHW–S pre-treatments. The highest levels of total fermentative products and residual sugars were obtained at the concentrations of 7.8 ± 0.2 and 2.1 ± 0.3 g/L, respectively, after fermentation by Clostridium cellulolyticum for NaOH–LHW–S pre-treated rice straw at 121 °C for 120 min. Overall, the combined physicochemical pre-treatment of RS led to improved microbial hydrolysis during cellulose degradation at the percentage of 85.5 ± 0.5.     

混合菌群发酵秸秆合成菌体蛋白及其动力学分析

混合菌群发酵秸秆可有效提高秸秆纤维的降解率及菌体蛋白的转化率,对拓广蛋白饲料来源、减少环境污染起到积极的作用。本研究以小麦秸秆为原料,在纤维素酶水解预处理的基础上,以米曲霉作为先导菌,进一步分解残留的粗纤维,为后期发酵提供充足的碳源。根据不同微生物的代谢特征和协同机理,试验确定了发酵阶段混合菌群的组成为:米曲霉、产朊假丝酵母和枯草芽胞杆菌;接种顺序为:先接种米曲霉,再接种产朊假丝酵母,最后接种枯草芽胞杆菌。正交试验表明,影响发酵主要因素的主次顺序为:秸秆与麸皮配比>接种比例>发酵时间>接种量>发酵温度;发酵的最适条件为:米曲霉的接种量2.5%,发酵12h后接入5%的产朊假丝酵母,继续发酵8h后接入2.5%的枯草芽胞杆菌,发酵温度为28℃,秸秆与麸皮的配比为4∶1,尿素添加量为1.2%;结合动力学分析,将混合菌群的发酵时间优化为35h,发酵产物中粗蛋白含量由原来的5.47%提高到25%左右。对最适发酵条件下的动力学过程进行了探讨,建立了以Logistic方程为基础的数学模型和动力学方程。本研究表明,混合菌群发酵秸秆提高了发酵产物中的粗蛋白含量。动力学分析对于了解发酵机理、掌握整个发酵过程中混合菌群生长的动态变化、优化发酵工艺具有重要的指导意义。     

Efficient bioconversion of rice straw to ethanol with TiO2/UV pretreatment

Rice straw is a lignocellulosic biomass that constitutes a renewable organic substance and alternative source of energy; however, its structure confounds the liberation of monosaccharides. Pretreating rice straw using a TiO(2)/UV system facilitated its hydrolysis with Accellerase 1000(?), suggesting that hydroxyl radicals (OH·) from the TiO(2)/UV system could degrade lignin and carbohydrates. TiO(2)/UV pretreatment was an essential step for conversion of hemicellulose to xylose; optimal conditions for this conversion were a TiO(2) concentration of 0.1% (w/v) and an irradiation time of 2 h with a UV-C lamp at 254 nm. After enzymatic hydrolysis, the sugar yields from rice straw pretreated with these parameters were 59.8 ± 0.7% of the theoretical for glucose (339 ± 13 mg/g rice straw) and 50.3 ± 2.8% for xylose (64 ± 3 mg/g rice straw). The fermentation of enzymatic hydrolysates containing 10.5 g glucose/L and 3.2 g xylose/L with Pichia stipitis produced 3.9 g ethanol/L with a corresponding yield of 0.39 g/g rice straw. The maximum possible ethanol conversion rate is 76.47%. TiO(2)/UV pretreatment can be performed at room temperature and atmospheric pressure and demonstrates potential in large-scale production of fermentable sugars.     

选择性抑菌剂对添加稻草红壤旱土团聚体磷素微生物转化的影响

为了进一步探明红壤旱土磷素微生物固持的机理,采用室内模拟培养试验研究了微生物类群对红壤旱土团聚体(0.2～2mm)磷素转化的作用.结果表明:在培养90d期间,添加稻草处理能显著提高红壤旱土团聚体的微生物生物量碳、生物量磷、提取磷(Olsen法)和有机磷的含量.在培养前期(5～30d),与添加稻草处理比较,稻草+真菌抑制剂(放线菌酮)、稻草+细菌抑制剂(四环素+链霉素硫酸盐)处理团聚体微生物生物量碳含量分别降低10.5%～31.8%和6.8%～11.6%,前者的降低幅度显著大于后者(P0.01),此后加入抑菌剂处理团聚体微生物生物量碳基本保持稳定.添加细菌抑制剂处理团聚体微生物生物量磷含量在培养5～20d期间比加真菌抑制剂处理高10.0%～28.8%,差异显著(P0.01).表明真菌和细菌均参与红壤旱土团聚体磷素的固持,但真菌的作用明显大于细菌.