Bioethanol production from mahula (Madhuca latifolia L.) flowers by solid-state fermentation

There is a growing interest worldwide to find out new and cheap carbohydrate sources for production of bioethanol. In this context, the production of ethanol from mahula (Madhuca latifolia L.) flowers by Saccharomyces cerevisiae in solid-state fermentation was investigated. The moisture level of 70%, pH of 6.0 and temperature of 30 °C were found optimum for maximum ethanol concentration (225.0 ± 4.0 g/kg flower) obtained from mahula flowers after 72 h of fermentation. Concomitant with highest ethanol concentration, the maximum ethanol productivity (3.13 g/kg flower/h), yeast biomass (18.5 × 10⁸ CFU/g flower), the ethanol yield (58.44 g/100 g sugar consumed) and the fermentation efficiency (77.1%) were also obtained at these parametric levels.     

Fungal solid-state fermentation of food waste for biohydrogen production by dark fermentation

The dark fermentation process was evaluated for biohydrogen production from food waste through fungal solid-state fermentation (SSF). Three fungal cultures (one strain of Aspergillus tubingensis and two strains of Meyerozyma caribbica) were compared, being A. tubingensis the best hydrolyser culture for releasing soluble carbohydrates. The biochemical hydrogen potential of food waste hydrolysate (FWH) at different substrate-inoculum ratios obtained a lower hydrogen yield than untreated food waste (RFW). The highest hydrogen yield value corresponded to treatments RFW-20 and RFW-30 with 77.0 ± 2.6 and 76.9 ± 1.4 mL H₂ normalized by per gram volatile solid added (NmL H₂/gVS_added), respectively. The microbial community of food waste was analysed, being detected lactic-acid bacteria genera as Latilactobacillus and Leuconostoc. The presence of actively growing bacteria during the SSF could explain the lowest hydrogen yield (20.1–36.0 NmL H₂/gVS_added) in the FWH treatment due to the substrate competition between lactic-acid bacteria and hydrogen-producing bacteria, where the lactic-acid bacteria were favoured by their faster growth rate.     

Biohydrogen production by extracted fermentation from sugar beet

In the study, the production of biohydrogen by extracted fermentation from sugar beet was evaluated. Effects of initial amount of sugar beet, biomass and particle size of sugar beet on biohydrogen formation were investigated. The hydrogen (H₂) gas was predicted to be 78.6 mL at initial dry weight of sugar beet 24.6 g L^?1 and H₂ yield was calculated as 81.9 mLH₂ g^?1TOC while biomass concentration (1 g L^?1) and particle size (0.3 cm) were constant. The peak H₂ gas volume was predicted to be 139.9 mL at the low particle size of 0.1 cm. Hydrogen gas production potential was predicted as 143.6 mL h^?1. The peak value of 197.9 mLH₂ g^?1TOC was obtained with particle size of 0.1 cm when dry weight of sugar beet and initial amount of biomass was kept constant at 24.6 g L^?1 and 1 g L^?1, respectively.     

A sequential process of anaerobic solid-state fermentation followed by dark fermentation for bio-hydrogen production from Chlorella sp.

Microalgal biomass has recently been one of the most widely studied feedstocks for bio-hydrogen production, owing to its richness in fermentable components, e.g. polysaccharides and proteins, and high biomass productivity. In this study, biomass of microalga Chlorella sp. TISTR 8411 was converted to hydrogen through a sequential process consisting of an anaerobic solid-state fermentation (ASSF) followed by a dark fermentation. The microalga was grown photoautothrophically in 80-L rectangular glass tanks and then scaled-up to a 240-L open pond for the production of biomass. The highest biomass concentration attained was 4.45 g L⁻¹. The biomass was harvested with over 90% flocculation efficiency at pH 11.5 and a biomass concentration of 2.6 g/L. The sequential process gave a total hydrogen yield (HY) of 16.2 mL/g-volatile-solid (VS), of which 11.6 mL/g-VS was from ASSF. The high HY obtained from the ASSF indicated that it was effective and could be integrated with a conventional hydrogen production process to improve energy recovery from biomass.     

Bioethanol production from thick juice as intermediate of sugar beet processing

The aims of this study were to investigate the bioethanol production of thick juice as intermediate from sugar beet processing in batch culture by free Saccharomyces cerevisiae cells and the effect of sugar concentration on ethanol yield and CO₂ weight loss rate. Thick juice and molasses of sugar beet from a domestic sugar factory were diluted with distilled water to give a total sugar concentration of 5, 10, 15, 20 and 25% (w w^?1). Initial concentration of fermentable sugars of 20% (w w^?1) in culture medium can be taken as optimal, enabling maximal ethanol yield (68%) and maximal CO₂ evolution rate was realized, amounting to more than 90 g L^?1 h^?1. The optimal concentration of fermentable sugar from thick juice for bioethanol production by free S. cerevisiae cells was 20% (w w^?1) at 30 °C, pH 5 and agitation rate 200 rpm gave maximum ethanol concentration of 12% (v v^?1).     

Life cycle analysis for bioethanol production from sugar beet crops in Greece

The main aim of this study is to evaluate whether the potential transformation of the existing sugar plants of Northern Greece to modern bioethanol plants, using the existing cultivations of sugar beet, would be an environmentally sustainable decision. Using Life Cycle Inventory and Impact Assessment, all processes for bioethanol production from sugar beets were analyzed, quantitative data were collected and the environmental loads of the final product (bioethanol) and of each process were estimated. The final results of the environmental impact assessment are encouraging since bioethanol production gives better results than sugar production for the use of the same quantity of sugar beets. If the old sugar plants were transformed into modern bioethanol plants, the total reduction of the environmental load would be, at least, 32.6% and a reduction of more than 2 tons of CO₂e/sugar beet of ha cultivation could be reached. Moreover bioethanol production was compared to conventional fuel (gasoline), as well as to other types of biofuels (biodiesel from Greek cultivations).     

Bioethanol production from sweet sorghum: Evaluation of post-harvest treatments on sugar extraction and fermentation

Three experimental sweet sorghum varieties (M81, Topper and Theis) and three post-harvest conditions were evaluated for ethanol production: juices extracted by milling were obtained from the whole plant, plant without panicle, and stalk (plant without panicle and leaves), respectively. A linear relationship was found between the total fermentable sugar concentrations and Brix degrees of the juices, which can predict the potential ethanol yield by field analytical tests. The juice extractability presented different behavior among the sweet sorghum varieties with respect to the treatments studied. However such treatments did not affect the level of sugar concentration of the juices obtained and the fermentation efficiency. Topper and Theis showed the best performance in terms of ethanol concentration, fermentation efficiency and ethanol yield. The variety used and its post-harvest treatment should be appropriately selected in order to improve the ethanol production from sweet sorghum.     

Optimization of very high gravity fermentation process for ethanol production from industrial sugar beet syrup

In order to reduce production costs and environmental impact of bioethanol from sugar beet low purity syrup 2, an intensification of the industrial alcoholic fermentation carried out by Saccharomyces cerevisiae is necessary. Two fermentation processes were tested: multi-stage batch and fed-batch fermentations with different operating conditions. It was established that the fed-batch process was the most efficient to reach the highest ethanol concentration. This process allowed to minimize both growth and ethanol production inhibitions by high sugar concentrations or ethanol. Thus, a good management of the operating conditions (initial volume and feeding rate) could produce 15.2% (v/v) ethanol in 53 h without residual sucrose and with an ethanol productivity of 2.3 g L h⁻¹.     

Bioethanol production from pretreated Miscanthus floridulus biomass by simultaneous saccharification and fermentation

The production of ethanol from the fast-growing perennial C4 grass Miscanthus floridulus by simultaneous saccharification and fermentation (SSF) was investigated. M. floridulus biomass was composed of 36.3% glucan, 22.8% hemicellulose, and 21.3% lignin (based on dried mass). Prior to SSF, harvested stems of M. floridulus were pretreated separately by alkali treatment at room temperature, alkali treatment at 90 °C, steam explosion, and acid-catalyzed steam explosion. The delignification rates were determined to be 73.7%, 61.5%, 42.7%, and 63.5%, respectively, by these four methods, and the hemicellulose removal rates were 51.5%, 85.1%, 70.5%, and 97.3%, respectively. SSF of residual solids after various pretreatments was performed with dried yeast (Saccharomyces cerevisiae) and cellulases (Accellerase 1000) by using 10% water-insoluble solids (WIS) of the pretreated M. floridulus as the substrate. The ethanol yields from 72-h SSF of M. floridulus biomass after these pretreatments were 48.9 ± 3.5, 78.4 ± 1.0, 46.4 ± 0.1, and 69.0 ± 0.1% (w/w), respectively, while the ethanol concentrations after 72-h SSF were determined to be 15.4 ± 1.1, 27.5 ± 0.3, 13.9 ± 0.1, and 30.8 ± 0.1 g/L, respectively. Overall, the highest amount of ethanol (0.124 g/g-dried raw material) was generated from dried raw material of M. floridulus after alkaline pretreatment at 90 °C. The acid-catalyzed steam explosion pretreatment also resulted in a high ethanol yield (0.122 g/g-dried raw material). Pretreatment resulting in high lignin and hemicellulose removal rates could make biomass more accessible to enzyme hydrolysis and lead to higher ethanol production.     

Isolation of fermentative microbial isolates from sugar cane and beet molasses and evaluation for enhanced production of bioethanol

In an attempt to produce bioethanol as a renewable and natural energy resource and as a promising alternative/complement to conventional petrol (i.e., gasoline), 44 microbial isolates (12 yeast and 32 bacterial strains) were isolated from molasses samples obtained from some of the sugar factories in Egypt. Among the microbial isolates obtained, only two yeast isolates (HSC-22 and HSC-24) were selected from sugarcane molasses (SCM) for their high bioethanol fermentation capabilities, recording bioethanol production of ≈9.6 and 8.2 g/L with actual yield of 0.48 and 0.41 g ethanol/g SCM, respectively, within 48-h incubation period at 30°C. Phylogenetic identification of these isolates was performed based on the analysis of the nucleotide sequence of the 18S rDNA gene, which indicated that these isolates can be identified as Pichia veronae and Candida tropicalis, respectively, with similarity of 99%.     

Bioethanol production from tuber crops using fermentation technology: a review

Bioethanol, an alcohol produced by fermentation of plant biomass containing starch and sugars by micro-organisms, considered as a dominant form of fuel for future. Production of this renewable fuel, especially from starchy materials such as tuber crops, holds a remarkable potential to meet the future energy demand because of its high production and comparitively less demand for use as food and fodder. This review focuses on the world bioethanol production scenario from various tuber crops, namely cassava, sweet potato, potato, yam, aroids, sugar beet, etc., fermentation techniques and micro-organisms used in fermentation process along with its future prospects. The advances in metabolic pathway engineering and genetic engineering techniques have led to the development of micro-organisms capable of efficiently converting biomass sugars into ethanol. Several biotechnological tools that are also available for the improvement of microorganisms to meet the harsh environments typically met with certain industrial fermentation process are also discussed.     

Hydrogen-rich syngas fermentation for bioethanol production using Sacharomyces cerevisiea

Bioethanol is an eco-friendly biofuel due to its merit that makes it a top-tier fuel. The present study emphasized on bioethanol production from hydrogen-rich syngas through fermentation using Sacharomyces cerevisiea. Syngas fermentation was performed in a tar free fermenter using a syngas mixture of 13.05% H₂, 22.92% CO, 7.9% CO₂, and 1.13% CH₄, by volume. In the fermentation process, effects of various parameters including syngas impurity, temperature, pH, colony forming unit, total organic carbon and syngas composition were investigated. The yield of bioethanol was identified by Gas chromatography-Mass spectrometry analysis and further, it was confirmed by Nuclear magnetic resonance (¹H) analysis. From GC-MS results, it is revealed that the concentration of bioethanol using Saccharomyces cerevisiae was 30.56 mmol from 1 L of syngas. Thus, hydrogen-rich syngas is suited for bioethanol production through syngas fermentation using Saccharomyces cerevisiae. This research may contribute to affordable and environment-friendly bioethanol-based energy to decrease the dependency on fossil fuels.     

Bioethanol production from bamboo (Dendrocalamus sp.) process waste

Bamboo as a feed stock for bioethanol production is interesting due to the relatively higher growth rate of these plants and their abundant and sustainable availability in the tropics. Dendrocalamus are bamboo varieties common in India, of which large amounts of biomass is generated annually as byproducts of bamboo processing industries. In the current study, process waste from bamboo industry was evaluated as a feedstock for bioethanol production by enzymatic saccharification. Dilute alkali pretreatment of the biomass resulted in efficient removal of lignin, effectively increasing the concentration of cellulose to 63.1% from 46.7%. Enzymatic saccharification of pretreated biomass was optimized following a response surface methodology and the optimal set of parameters for maximal saccharification was derived. Pretreatment method could recover 64.31% of the total sugar polymers and a hydrolysis efficiency of 82.36% was achieved. Direct fermentation of the enzymatic hydrolysate was efficient with ethanol production being 71.34% of theoretical maximum (3.08% v/v ethanol yield). Material balances were calculated for the entire process from raw biomass to ethanol and the overall process efficiency was found to be ∼43%. The process has the potential to generate 143 L of ethanol per dry ton of bamboo process waste.     

A simple rule for bioenergy conversion plant size optimisation: Bioethanol from sugar cane and sweet sorghum

Fuel ethanol from agricultural crops, “bioethanol”, is more expensive than petrol. Here we consider ways to reduce ethanol costs, by using mixed crops to extend the processing season and by optimising plant capacity. We derive a simple model of general applicability by balancing crop transport costs (which increase with plant size) against the (decreasing) production costs. We show that at the optimum, the cost of transporting crop, per unit quantity of alcohol, must be a predictable proportion of the unit cost of production, generally in the range 0.4–0.6. Under current Australian conditions, cane sugar and cane plus sweet sorghum bioethanol plants have optimum capacities around 245,000 and 175,000 kl/year, respectively. the model is equally applicable to any other bioenergy conversion plant which requires biomass to be transported from surrounding areas. The model also shows quantitatively how more efficient transport allows larger scale production, while lower production costs make smaller plants more economic.     

Bioconversion of sugar industry by-products—molasses and sugar beet pulp for single cell protein production by yeasts

In the bioconversion studies of molasses and sugarbeet pulp to single cell protein by four Candida spp. (utilis, tropicalis, parapsilosis and solani) maximum protein content of 37.5 and 43.4% was achieved from the two substrates, respectively, in 48 h. Candida utilis and C. tropicalis performed better than the other yeasts. The maximum bioconversion efficiency for molasses (43%) was given by C. parapsilosis and for beet pulp (46%) by C. tropicalis in 48 h batch flask fermentations. The bioconversion of beet pulp under controlled conditions was studied using C. tropicalis in a 51 fermentor, which gave 29 and 48% product recovery with 39 and 25% protein level, in a two- and one-stage process, respectively. The one-stage process (simultaneous saccharification and fermentation) was also run in a larger volume and gave 50% product recovery with 29% protein content. The results are discussed in terms of biomass yield, protein content and bioconversion efficiency of yeasts under each condition.     

Modeling of rotating drum bioreactor for anaerobic solid-state fermentation

Solid-state fermentation (SSF) has received more attention and has been applied to production of different products in recent years, especially biofuel production. The major problems to overcome in large-scale SSF are heat accumulation and heterogeneous distribution in a complex gas–liquid–solid multiphase bioreactor (or fermenter) system. In this work, a mathematical model of a rotating drum bioreactor for anaerobic SSF is developed considering the radial temperature distribution in the substrate bed. Validation experiments were conducted in a 5 m³ pilot plant fermenter for production of fuel ethanol from milled sweet sorghum stalks. The model that was developed fit well with the experimental data. From these results, it was concluded that this mathematical model is a powerful tool to investigate the design and scale-up of an anaerobic SSF fermenter in the application of bioethanol production using cellulosic materials such as sweet sorghum stalks.     

纤维素酶固态发酵动力学的研究

以稻壳和麸皮混合物为基质,进行纤维素酶固态发酵动力学的研究.以氨基葡萄糖含量表征生物量,建立了纤维素酶固态发酵过程中细胞生长、产酶和二氧化碳释放速率动力学模型,并得到模型参数.动力学分析结果表明,在不同培养温度和基质配比下,最大菌体量与最大酶活呈正相关;在适宜培养温度下,预期最大酶活与最大CO2释放速率也呈一定的正相关关系.     

Effect of ammonia on biohydrogen production from food waste via anaerobic fermentation

The effect of different additive ammonia (0–10 g/l as nitrogen) on hydrogen production from the anaerobic batch mesophilic fermentation of food waste was studied at two feed-to-microorganism ratios (F/M), 3.9 and 8.0. Anaerobic sludge taken from an anaerobic digester was used as inoculum. The hydrogen yield at F/M 3.9 and 8.0 without additive ammonia was 77.2 and 51.0 ml-H₂/gVS, respectively. At F/M 3.9, the hydrogen production was enhanced by adding additive ammonia in the system when the total ammonia nitrogen (TAN) concentration was no higher than 6.0 g/l. A maximum hydrogen yield of 121.4 ml-H₂/gVS was obtained at a TAN concentration of 3.5 g/l. At F/M 8.0, the enhancement of hydrogen production was found in a narrower range of additive TAN concentrations, with a highest yield of 60.9 ml-H₂/gVS at the TAN of 1.5 g/l. Hydrogen production was inhibited at higher additive TAN concentrations for both F/M ratios. This study provides a novel strategy for controlling ammonia for production of hydrogen from food waste via anaerobic fermentation.     

Fungal solid-state fermentation and various methods of enhancement in cellulase production

Cellulase serves vast applications in the industries of biofuel, pulp and paper, detergent and textile. With the presence of its three components i.e. endoglucanase, exoglucanase and β-glucosidase, the enzyme can effectively depolymerize the cellulose chains in lignocellulosic substrate to produce smaller sugar units that consist of cellobiose and glucose. Fungi are the most suitable cellulase producers attributing to its ability to produce a complete cellulase system. Solid state fermentation (SSF) by fungi is a preferable production route for cellulase as it imposes lower cost and enables the production of cellulase with higher titre. This article gives an overview on the major aspects of cellulase production via SSF by applying white-rot fungi (WRF) and brown-rot fungi (BRF), which include the type of lignocellulosic substrates for cellulase production, inoculum preparation and process conditions applied in SSF. The parameters that affect SSF production of cellulase such as fermentation medium, duration, pH, temperature and moisture content are highlighted. In addition, potential methods that can improve cellulase production, namely genetic modification, co-culture of different fungal strains, and development of bioreactors are also discussed.