Fermentative hydrogen production from hydrolyzed cellulosic feedstock prepared with a thermophilic anaerobic bacterial isolate

Hydrogen gas was produced via dark fermentation from natural cellulosic materials and α-cellulose via a two-step process, in which the cellulosic substrates were first hydrolyzed by an isolated cellulolytic bacterium Clostridium strain TCW1, and the resulting hydrolysates were then used as substrate for fermentative H₂ production. The TCW1 strain was able to hydrolyze all the cellulosic materials examined to produce reducing sugars (RS), attaining the best reducing sugar production yield of 0.65 g reducing sugar/g substrate from hydrolysis of α-cellulose. The hydrolysates of those cellulosic materials were successfully converted to H₂ via dark fermentation using seven H₂-producing bacterial isolates. The bioH₂ production performance was highly dependent on the type of cellulosic feedstock used, the initial reducing sugar concentration (C_RS,o) (ranging from 0.7 to 4.5 mg/l), as well as the composition of sugar and soluble metabolites present in the cellulosic hydrolysates. It was found that Clostridium butyricum CGS5 displayed the highest H₂-producing efficiency with a cumulative H₂ production of 270 ml/l from α-cellulose hydrolysate (C_RS,o = 4.52 mg/l) and a H₂ yield of 7.40 mmol/g RS (or 6.66 mmol/g substrate) from napier grass hydrolysate (C_RS,o = 1.22 g/l).     

Cellulase production using biomass feed stock and its application in lignocellulose saccharification for bio-ethanol production

A major constraint in the enzymatic saccharification of biomass for ethanol production is the cost of cellulase enzymes. Production cost of cellulases may be brought down by multifaceted approaches which include the use of cheap lignocellulosic substrates for fermentation production of the enzyme, and the use of cost efficient fermentation strategies like solid state fermentation (SSF). In the present study, cellulolytic enzymes for biomass hydrolysis were produced using solid state fermentation on wheat bran as substrate. Crude cellulase and a relatively glucose tolerant BGL were produced using fungi Trichoderma reesei RUT C30 and Aspergillus niger MTCC 7956, respectively. Saccharification of three different feed stock, i.e. sugar cane bagasse, rice straw and water hyacinth biomass was studied using the enzymes. Saccharification was performed with 50 FPU of cellulase and 10 U of β-glucosidase per gram of pretreated biomass. Highest yield of reducing sugars (26.3 g/L) was obtained from rice straw followed by sugar cane bagasse (17.79 g/L). The enzymatic hydrolysate of rice straw was used as substrate for ethanol production by Saccharomyces cerevisiae. The yield of ethanol was 0.093 g per gram of pretreated rice straw.     

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

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

Comparative study on the production of biohydrogen from rice mill wastewater

This study presents the production of biohydrogen from rice mill wastewater. The acid hydrolysis and enzymatic hydrolysis operating conditions were optimized, for better reducing sugar production. The effect of pH and fermentation time on biohydrogen production from acid and enzymatic hydrolyzed rice mill wastewater was investigated, using Enterobacter aerogenes and Citrobacter ferundii. The enzymatic hydrolysis produced the maximum reducing sugar (15.8 g/L) compared to acid hydrolysis (14.2 g/L). The growth data obtained for E. aerogenes and C. ferundii, fitted well with the Logistic equation. The hydrogen yields of 1.74 mol H₂/mol reducing sugar, and 1.40 mol H₂/mol reducing sugar, were obtained from the hydrolyzate obtained from enzymatic and acid hydrolysis, respectively. The maximum hydrogen yield was obtained from E. aerogenes compared to C. ferundii, and the optimum pH for better hydrogen production was found to be in the range from 6.5 to 7.0. The chemical oxygen demand (COD) reduction obtained was around 71.8% after 60 h of fermentation.     

Ethanol production from enzymatic hydrolysis of sugarcane bagasse pretreated with lime and alkaline hydrogen peroxide

In this work we evaluated ethanol production from enzymatic hydrolysis of sugarcane bagasse. Two pretreatments agents, lime and alkaline hydrogen peroxide, were compared in their performance to improve the susceptibility of bagasse to enzymatic action. Mild conditions of temperature, pressure and absence of acids were chosen to diminish costs and to avoid sugars degradation and consequent inhibitors formation. The bagasse was used as it comes from the sugar/ethanol industries, without grinding or sieving, and hydrolysis was performed with low enzymes loading (3.50 FPU g⁻¹ dry pretreated biomass of cellulase and 1.00 CBU g⁻¹ dry pretreated biomass of ??-glucosidase). The pretreatment with alkaline hydrogen peroxide led to the higher glucose yield: 691 mg g⁻¹ of glucose for pretreated bagasse after hydrolysis of bagasse pretreated for 1 h at 25 °C with 7.35% (v/v) of peroxide. Fermentation of the hydrolyzates from the two pretreatments were carried out and compared with fermentation of a glucose solution. Ethanol yields from the hydrolyzates were similar to that obtained by fermentation of the glucose solution. Although the preliminary results obtained in this work are promising for both pretreatments considered, reflecting their potential for application, further studies, considering higher biomass concentrations and economic aspects should be performed before extending the conclusions to an industrial process.     

Hydrolysis of pretreated rice straw by an enzyme cocktail comprising acidic xylanase from Aspergillus sp. for bioethanol production

The most crucial enzyme involved in xylan hydrolysis is endoxylanase which cleaves the internal glycosidic bonds of xylan. The aim of this work was to study the production of extracellular xylanase by a locally isolated strain of Aspergillus sp. under solid-state fermentation (SSF) and to evaluate the potential of the enzyme in enzymatic hydrolysis of pretreated rice straw. Xylanase production reached maximum with incubation period (96 h), moisture level (80%), inoculum size (3 × 10⁶ spores/mL), pH (4.8), temperature (25 °C), carbon source (wheat bran) and nitrogen source (yeast extract). Under optimized conditions, xylanase production reached to 5059 IU/gds. Crude xylanase was used for supplementing the enzyme cocktail comprising cellulases (Zytex, India), β-glucosidase (In-house) and xylanase (In-house) for the saccharification of alkali-pretreated rice straw to get the maximum reducing sugar production. The cocktail containing the three enzymes resulted a maximum of 574.8 mg/g of total reducing sugars in comparison to 430.2 mg/g sugars by the cocktail without xylanase. These results proved that the crude xylanase preparation from Aspergillus sp. could be a potent candidate for the enzyme cocktail preparation for biomass hydrolysis in lignocellulosic bioethanol program.     

Comparison between heterofermentation and autofermentation in hydrogen production from Arthrospira (Spirulina) platensis wet biomass

Hydrogen production from Arthrospira (Spirulina) platensis wet biomass through heterofermentation by the [FeFe] hydrogenase of hydrogenogens (hydrogen-producing bacteria) and autofermentation by the [NiFe] hydrogenase of Arthrospira platensis was discussed under dark anaerobic conditions. In heterofermentation, wet cyanobacterial biomass without pretreatment was hardly utilized by hydrogenogens for hydrogen production. But the carbohydrates in cyanobacterial cells released after cell wall disruption were effectively utilized by hydrogenogens for hydrogen production. Wet cyanobacterial biomass was pretreated with boiling and bead milling, ultrasonication, and ultrasonication and enzymatic hydrolysis. Wet cyanobacterial biomass pretreated with ultrasonication and enzymatic hydrolysis achieved the maximum reducing sugar yield of 0.407 g/g-DW (83.0% of the theoretical reducing sugar yield). Different concentrations (10 g/l to 40 g/l) of pretreated wet cyanobacterial biomass were used as substrate to produce fermentative hydrogen by hydrogenogens, which were domesticated with the pretreated wet cyanobacterial biomass as carbon source. The maximum hydrogen yield of 92.0 ml H₂/g-DW was obtained at 20 g/l of wet cyanobacterial biomass. The main soluble metabolite products (SMPs) in the residual solutions from heterofermentation were acetate and butyrate. In autofermentation, hydrogen yield decreased from 51.4 ml H₂/g-DW to 11.0 ml H₂/g-DW with increasing substrate concentration from 1 g/l to 20 g/l. The main SMPs in the residual solutions from autofermentation were acetate and ethanol. The hydrogen production peak rate and hydrogen yield at 20 g/l of wet cyanobacterial biomass in heterofermentation showed 110- and 8.4-fold increases, respectively, relative to those in autofementation.     

Biohydrogen production from pure and natural lignocellulosic feedstock with chemical pretreatment and bacterial hydrolysis

Pretreatment and saccharification of lignocellulosic materials is the key technology affecting the efficiency of cellulosic biohydrogen production. In this work, two pure cellulosic materials (i.e., carboxymethyl-cellulose (CMC) and xylan) were directly hydrolyzed (without pretreatment) by a cellulolytic isolate Cellulomonas uda E3-01 able to release extracellular cellulolytic enzymes. Natural cellulosic feedstock (i.e., sugarcane bagasse) was chemically pretreated prior to the bacterial hydrolysis.A temperature-shift strategy (35 °C for cellulolytic enzymes production and 45 °C for hydrolysis reaction) was used to increase the production of reducing sugars during the bacterial hydrolysis. The hydrolysates of CMC, xylan, and bagasse were efficiently converted to H₂ via dark fermentation with Clostridium butyricum CGS5. The maximum hydrogen yield was 8.80 mmol H₂/g reducing sugar (i.e., 1.58 mol H₂/mol hexose) for CMC, 6.03 mmol H₂/g reducing sugar (i.e., 0.91 mol H₂/mol pentose) for xylan, and 6.01 mmol H₂/g reducing sugar for bagasse.     

Hydrogen production from water hyacinth through dark- and photo- fermentation

This article discusses the method of producing hydrogen from water hyacinth. Water hyacinth was pretreated with microwave heating and alkali to enhance the enzymatic hydrolysis and hydrogen production in a two-step process of dark- and photo- fermentation. Water hyacinth with various concentrations of 10–40 g/l was pretreated with four methods: (1) steam heating; (2) steam heating and microwave heating/alkali pretreatment; (3) steam heating and enzymatic hydrolysis; (4) steam heating, microwave heating/alkali pretreatment and enzymatic hydrolysis. Water hyacinth (20 g/l) pretreated with method 4 gave the maximum reducing sugar yield of 30.57 g/100 g TVS, which was 45.6% of the theoretical reducing sugar yield (67.0 g/100 g TVS). The pretreated water hyacinth was used to produce hydrogen by mixed H₂-producing bacteria in dark fermentation. The maximum hydrogen yield of 76.7 ml H₂/g TVS was obtained at 20 g/l of water hyacinth. The residual solutions from dark fermentation (mainly acetate and butyrate) were used to further produce hydrogen by immobilized Rhodopseudomonas palustris in photo fermentation. The maximum hydrogen yield of 522.6 ml H₂/g TVS was obtained at 10 g/l of water hyacinth. Through a combined process of dark- and photo- fermentation, the maximum hydrogen yield from water hyacinth was dramatically enhanced from 76.7 to 596.1 ml H₂/g TVS, which was 59.6% of the theoretical hydrogen yield.     

Sequencing batch reactor enhances bacterial hydrolysis of starch promoting continuous bio-hydrogen production from starch feedstock

Bio-hydrogen production from starch was carried out using a two-stage process combining thermophillic starch hydrolysis and dark H₂ fermentation. In the first stage, starch was hydrolyzed by Caldimonas taiwanensis On1 using sequencing batch reactor (SBR). In the second stage, Clostridium butyricum CGS2 was used to produce H₂ from hydrolyzed starch via continuous dark hydrogen fermentation. Starch hydrolysis with C. taiwanensis On1 was operated in SBR under pH 7.0 and 55 °C. With a 90% discharge volume, the reducing sugar (RS) production from SBR reactor reached 13.94 g RS/L, while the reducing sugar production rate and starch hydrolysis rate was 0.92 g RS/h/L and 1.86 g starch/h/L, respectively, which are higher than using other discharge volumes. For continuous H₂ production with the starch hydrolysate, the highest H₂ production rate and yield was 0.52 L/h/L and 13.2 mmol H₂/g total sugar, respectively, under a hydraulic retention time (HRT) of 12 h. The best feeding nitrogen source (NH₄HCO₃) concentration was 2.62 g/L, attaining a good H₂ production efficiency along with a low residual ammonia concentration (0.14 g/L), which would be favorable to follow-up photo H₂ fermentation while using dark fermentation effluents as the substrate.     

Feasibility of reed for biobutanol production hydrolyzed by crude cellulase

The aim of this study was to efficiently utilize reed for both cellulase and biobutanol production. The unprocessed cellulase blend produced under solid-state fermentation using reed as the substrate showed a similar reducing sugar yield using Whatman filter paper to the commercial enzyme blend (38.61%). Organosolv pretreatment method could efficiently reduce hemicellulose (29.3%–14.6%) and lignin (17.2%–14.1%) content and increase cellulose content (42.5%–62.3%) from reed. Enzymatic hydrolysis of organosolv-pretreated reed using the crude cellulase with enzyme loading of 25 FPU/g reed, 20% solid content at 50 °C and pH 5.5 resulted in a reed hydrolysate containing 40.01 g/L glucose and 3.55 g/L xylose after 72 h. Fermentation of the hydrolysate medium by Clostridium acetobutylicum produced 9.07 and 14.24 g/L of biobutanol and ABE with yield of 0.21 g/g and 0.33 g/g, respectively. This study proved that crude cellulase complex produced under solid state fermentation and organsolv pretreatment can efficiently provide reed hydrolysate that can be converted to biobutanol without any commercial cellulase usage.     

18S rDNA integration of the exo-inulinase gene into chromosomes of the high ethanol producing yeast Saccharomyces sp. W0 for direct conversion of inulin to bioethanol

Inulin and inulin-containing materials are good substrates for bioethanol production. In order to construct genetically stable recombinant yeast cells carrying the inulinase gene for bioethanol production from inulin, a new 18S rDNA integration vector was constructed in this study. After the INU1 gene encoding exo-inulinase was ligated into the 18S rDNA integration vector, transformed into uracil mutant of Saccharomyces sp. W0 and integrated into its chromosomes, the transformant MguINU1-04 obtained could produce 34.8 U cm⁻³ of inulinase activity within 72 h. The transformant could stably produce high activity of inulinase after five sequential batch cultivations. During 5-l fermentation, ethanol concentration in the fermentation medium containing 30.0% inulin was 14.7% (v/v) and the ethanol productivity was over 0.386 g of ethanol per g of inulin. When the tuber meal of Jerusalem artichoke (50.0%) was fermented into ethanol by the transformant MguINU1-04, 12.6% (v/v) ethanol was produced within 120 h and the ethanol productivity was over 0.331 g of ethanol per g of sugar. Therefore, inulin and inulin in the tuber meal of Jerusalem artichoke could be directly converted into high concentrations of ethanol by the engineered Saccharomyces sp. W0 carrying the inulinase gene.     

Conversion of paper sludge to ethanol by separate hydrolysis and fermentation (SHF) using Saccharomyces cerevisiae

The conversion of ethanol from paper sludge using the separate hydrolysis and fermentation (SHF) process with cellulase and Saccharomyces cerevisiae GIM-2 were investigated in this paper. Optimization strategy based on statistical experimental designs was employed to enhance degree of saccharification by enzymatic hydrolysis of paper sludge. Based on the Plackett-Burman design, hydrolysis time, substrate concentration and cellulase dosage were selected as the most significant variable on the degree of saccharification. Subsequently, the optimum combination of the selected factors was investigated by a Box-Behnken approach. A mathematical model was developed to show the effects of each factor and their combinatorial interactions on the degree of saccharification. The optimal conditions were hydrolysis time 82.7 h, substrate concentration 40.8 g L⁻¹ and cellulase dosage 18.1 FPU g⁻¹ substrate, and a degree of saccharification of 82.1% can be achieved. When hydrolysate was further fermented with S. cerevisiae GIM-2, the conversion rate of sugar to ethanol was 34.2% and the ethanol yield was 190 g kg⁻¹ of dry paper sludge, corresponding to an overall conversion yield of 56.3% of the available carbohydrates on the initial substrate. The results derived from this study indicate that the response surface methodology is a useful tool for optimizing the hydrolysis conditions to converse paper sludge to ethanol.     

Lipid production from sweet sorghum bagasse through yeast fermentation

Cryptococcus curvatus has great potential in fermenting unconditioned hydrolysates of sweet sorghum bagasse. With hydrolysates obtained by enzymatic hydrolysis of the solid pretreated by microwave with lime, the maximal yeast cell dry weight and lipid content were 10.83 g/l and 73.26%, respectively. For hydrolysates obtained in the same way but without lime, these two parameters were 15.50 g/l and 63.98%, respectively. During yeast fermentation, glucose and xylose were consumed simultaneously while cellobiose was released from the residual bagasse. The presence of lime, on one hand, made cellulose more accessible to enzymes as evidenced by higher total reducing sugar release compared to that without during enzymatic hydrolysis step; on the other hand, it caused the degradation of sugars to non-sugar chemicals during pretreatment step. As a result, higher lipid yield of 0.11 g/g bagasse or 0.65 ton/hectare of land was achieved from the pathway of microwave pretreatment and enzymatic hydrolysis while 0.09 g/g bagasse or 0.51 ton/hectare of land was attained from the process of lime-assisted microwave pretreatment followed by the same enzymatic saccharification.     

Evaluation of an adapted inhibitor-tolerant yeast strain for ethanol production from combined hydrolysate of softwood

In order to evaluate the potential of an adapted inhibitor-tolerant yeast strain developed in our lab to produce ethanol from softwood, the effect of furfural and HMF presented in defined medium and pretreatment hydrolysate on cell growth was investigated. And the efficiency of ethanol production from enzymatic hydrolysate mixed with pretreatment hydrolysate of softwood by bisulfite and sulfuric acid pretreatment process was reported. The results showed that in the combined treatments of the two inhibitors, cell growth was not affected at 1 g/L each of furfural and HMF. When 3 g/L each of furfural and HMF was applied, the adapted strain responded with an extended lag phase of 24 h. Both in batch and fed-batch runs of combined hydrolysate fermentation, the final ethanol concentrations were above 20.0 g/L and the ethanol yields (Y_p/s) on the total amount of fermentable sugar presented in the pretreated materials were above 0.40 g/g. It implies the great promise of the yeast strain for improving ethanol production from softwood due to its high ability of metabolizing inhibitor compounds of furfural and HMF.     

Biohydrogen and 5-aminolevulinic acid production from waste barley by Rhodobacter sphaeroides O.U.001 in a biorefinery concept

The production of biohydrogen and 5-aminolevulinic acid (5-ALA) by Rhodobacter sphaeroides O.U.001 was investigated in a biorefinery concept. Waste barley was used as a substrate after acid hydrolysis. The hydrolysate was analyzed in terms of its total simple sugar, organic acid, ammonium, element and total phenol contents. Four different growth media having 5 g/L, 7 g/L, 9 g/L and 11 g/L sugar content were prepared using the waste barley hydrolysate to produce biohydrogen and 5-ALA. The increased sugar concentrations resulted in higher cell density and hydrogen accumulation. Accordingly, the highest cell density (OD₆₆₀: 1.78) and hydrogen production (0.4 L H₂/L culture) were observed in the 11 g/L sugar-containing medium. A 67.4 μM 5-ALA was produced upon vitamin B₁₂ and levulinic acid additions. These results showed that waste barley can be used as a substrate for R. sphaeroides for biohydrogen and 5-ALA production within a biorefinery concept.     

Sweet sorghum as a whole-crop feedstock for ethanol production

The potential of sweet sorghum as an alternative crop for ethanol production was investigated in this study. Initially, the enzymatic hydrolysis of sorghum grains was optimized, and the hydrolysate produced under optimal conditions was used for ethanol production with an industrial strain of Saccharomyces cerevisiae, resulting in an ethanol concentration of 87 g L⁻¹. From the sugary fraction (sweet sorghum juice), 72 g L⁻¹ ethanol was produced. The sweet sorghum bagasse was submitted to acid pretreatment for hemicellulose removal and hydrolysis, and a flocculant strain of Scheffersomyces stipitis was used to evaluate the fermentability of the hemicellulosic hydrolysate. This process yielded an ethanol concentration of 30 g L⁻¹ at 23 h of fermentation. After acid pretreatment, the remaining solid underwent an alkaline extraction for lignin removal. This partially delignified material, known as partially delignified lignin (PDC), was enriched with nutrients in a solid/liquid ratio of 1 g/3.33 mL and subjected to simultaneous saccharification and fermentation (SSF) process, resulting in an ethanol concentration of 85 g L⁻¹ at 21 h of fermentation. Thus, from the conversion of starchy, sugary and lignocellulosic fractions approximately 160 L ethanol.ton⁻¹ sweet sorghum was obtained. This amount corresponds to 13,600 L ethanol.ha⁻¹.     

Effect of cornstalk hydrolysis on photo-fermentative hydrogen production by R. capsulatus

Cornstalk is a typical cellulose material, which can be used by photo-fermentative H₂ production after pretreatment. However, the pretreatment methods have different influence on photo fermentation. In this study, 25.0 g cornstalk was pretreated by HCl/NaOH/cellusase. The hydrolysis rates increased from 45.51% by ddH₂O-treatment to 60.79% by diluted HCl-treatment and 51.6% by NaOH-treatment. The corresponding reducing sugar yields were 0.13 g/g, 0.42 g/g and 0.01 g/g, respectively. Enzymatic treatment enhanced the corresponding cornstalk hydrolysis rates to 50.81%, 67.60% and 64.10% with reducing sugar yields of 0.22 g/g, 0.62 g/g and 0.26 g/g. The sorts and concentrations of carbon source for H₂ production vary among different hydrolysates. Photo-fermentative H₂ production of strain R. capsulatus JL1 and mutant JL1601 (cheR2^-) with hydrolysates were investigated. The maximum H₂ yield of 123.8 ± 14.2 mL/g by strain JL1 was obtained from alkali-enzyme pretreated cornstalk, while the H₂ yield of 224.9 ± 5.2 mL/g by mutant JL1601 (cheR2^-) was obtained with acid-enzyme hydrolysate as the substrates. Meanwhile, the alkali pretreated cornstalk was the worst for photo-fermentation of both strain JL1 and mutant JL1601 (cheR2^-). Nevertheless, the highest substrate conversion efficiencies for both strains were obtained from ddH₂O-pretreated hydrolysate. Two-step pretreated hydrolysates were more beneficial to H₂ production for mutant JL1601 (cheR2^-) but not for strain JL1.     

Enzymatical hydrolysis of food waste and ethanol production from the hydrolysate

The aim of present paper was to investigate the prospect for the use of food waste, an important municipal waste, as a potential substrate to generate hydrolysates for fuel ethanol production. The critical variables that affected reducing sugar production from food waste were identified by Plackett–Burman design (glucoamylase loud, time, temperature and pH) and further optimized by using a four factor central composite design of response surface methodology. According to the results of response surface analysis, the optimum conditions for reducing sugar production were determined to be glucoamylase loud of 142.2 u/g, saccharification pH of 4.82, enzyme reaction temperature of 55 °C, enzyme reaction time of 2.48 h. Reducing sugar production (164.8 g/L) in the optimized condition was in good agreement with the value predicted by the quadratic model (164.3 g/L), thereby confirming its validity. Furthermore, the obtained liquid phase of food waste hydrolysate was utilized for production of ethanol by using Saccharomyces cerevisiae H058 fermentation. In order to develop an economical process for transforming food waste hydrolysates to ethanol, non-sterilized and sterilized processes were compared in the experiments. The result shows non-sterilized fermentation without undergoing heat treatment was better due to the unspoiled nutrients inside. These results helped to find the effective strategies to utilize food waste for ethanol production.     

Pretreatment of cassava stems and peelings by thermohydrolysis to enhance hydrolysis yield of cellulose in bioethanol production process

The potential of wastes obtained from the cultivation of Manihot esculenta Crantz as raw material for bioethanol production was studied. The objective was to determine the optimal conditions of hemicellulose thermohydrolysis of cassava stems and peelings and evaluate their impact on the enzymatic hydrolysis yield of cellulose. An experimental design was conducted to model the influence of factors on the pentose, reducing sugar and phenolic compound contents. Residues obtained from the optimal pretreatment conditions were hydrolysed with cellulase (filter paper activity 40 FPU/g). The hydrolysates from pretreatment and enzymatic hydrolysis were fermented respectively using Rhyzopus spp. and Sacharomyces cerevisiae. The yield of enzymatic hydrolysis obtained under the optimal conditions were respectively 73.1% and 86.6% for stems and peelings resulting in an increase of 39.84% and 55.40% respectively as compared to the non-treated substrates. The ethanol concentrations obtained after fermentation of enzymatic hydrolysates were 1.3 and 1.2 g/L respectively for the stem and peeling hydrolysates. The pentose and phenolic compound concentrations obtained from the multi-response optimization were 10.2 g/L; 0.8 g/L and 10.1 g/L; 1.3 g/L respectively for stems and peelings. The hydrolysates of stems and peelings under these optimal conditions respectively gave ethanol concentrations of 5.27 g/100 g for cassava stems and 2.6 g/100 g for cassava peelings.