Microbial conversion of lignocellulose-derived carbohydrates into bioethanol and lactic acid

Houtachtige biomassa (rest)stromen kan één van de duurzame alternatieven gaan worden voor aardolie omdat het kan dienen als grondstof voor de productie van biobrandstoffen en bulkchemicaliën. Belangrijk voordeel van deze technologie is dat er geen gebruik hoeft te worden gemaakt van plantaardige producten die geschikt zijn voor voedseldoeleinden. Binnen het huidige onderzoek zijn we erin geslaagd om op grote schaal houtachtige biomassa zoals stro via verschillende fysisch-chemische behandelingen en een enzymatische hydrolyse af te breken tot enkelvoudige suikers. Deze suikers werden door verschillende soorten micro-organismen omgezet naar gewenste producten zoals ethanol voor biobrandstoftoepassing of melkzuur als bouwsteen voor de productie van biologisch afbreekbaar plastic. De delen van het stro welke niet door de micro-organismen konden worden omgezet werden gebruikt voor biogasproductie of fungeerden als brandstof voor het verkrijgen van warmte en elektriciteit. Een productieproces waarbij, via een combinatie van verschillende voorbehandelingen, stro door bacteriën efficiënt werd omgezet naar melkzuur werd gepatenteerd

Xylose metabolism in the fungus Rhizopus oryzae : effect of growth and respiration on l (+)-lactic acid production

The fungus Rhizopus oryzae converts both glucose and xylose under aerobic conditions into chirally pure l(+)-lactic acid with by-products such as xylitol, glycerol, ethanol, carbon dioxide and fungal biomass. In this paper, we demonstrate that the production of lactic acid by R. oryzae CBS 112.07 only occurs under growing conditions. Deprivation of nutrients such as nitrogen, essential for fungal biomass formation, resulted in a cessation of lactic acid production. Complete xylose utilisation required a significantly lower C/N ratio (61/1) compared to glucose (201/1), caused by higher fungal biomass yields that were obtained with xylose as substrate. Decreasing the oxygen transfer rate resulted in decline of xylose consumption rates, whereas the conversion of glucose by R. oryzae was less affected. Both results were linked to the fact that R. oryzae CBS 112.07 utilises xylose via the two-step reduction/oxidation route. The consequences of these effects for R. oryzae as a potential lactic acid producer are discussed

Lactic acid production from xylose by the fungus Rhizopus oryzae

Lignocellulosic biomass is considered nowadays to be an economically attractive carbohydrate feedstock for large-scale fermentation of bulk chemicals such as lactic acid. The filamentous fungus Rhizopus oryzae is able to grow in mineral medium with glucose as sole carbon source and to produce optically pure l(+)-lactic acid. Less is known about the conversion by R. oryzae of pentose sugars such as xylose, which is abundantly present in lignocellulosic hydrolysates. This paper describes the conversion of xylose in synthetic media into lactic acid by ten R. oryzae strains resulting in yields between 0.41 and 0.71 g g¿1. By-products were fungal biomass, xylitol, glycerol, ethanol and carbon dioxide. The growth of R. oryzae CBS 112.07 in media with initial xylose concentrations above 40 g l¿1 showed inhibition of substrate consumption and lactic acid production rates. In case of mixed substrates, diauxic growth was observed where consumption of glucose and xylose occurred subsequently. Sugar consumption rate and lactic acid production rate were significantly higher during glucose consumption phase compared to xylose consumption phase. Available xylose (10.3 g l¿1) and glucose (19.2 g l¿1) present in a mild-temperature alkaline treated wheat straw hydrolysate was converted subsequently by R. oryzae with rates of 2.2 g glucose l¿1 h¿1 and 0.5 g xylose l¿1 h¿1. This resulted mainly into the product lactic acid (6.8 g l¿1) and ethanol (5.7 g l¿1

Biofuel production from acid-impregnated willow and switchgrass

As part of a broader technical and economic feasibility study, we studied production of bioethanol from two types of lignocellulosic biomass by way of concentrated acid impregnation at low temperature. Willow chips and switchgrass were submitted to various impregnation techniques with concentrated sulfuric acid at varying acid: biomass ratios and impregnation times. Goal of the experiments was to investigate the technical feasibility of concentrated acid pretreatment technology as part of an industrial process that employs recycling of acid through biological means. Experimental results showed that significant amounts of fermentable sugars including glucose (up to 78 f max. obtainable glucose) and xylose can be obtained by relatively simple impregnation techniques at room temperature. Fermentation of willow-derived hydrolysates with S. Cerevisiae yielded 0.45 - 0.49 g ethanol/g glucose. Ethanol production rates however were 38 ower compared to standard glucose fermentation, prompting the need for further optimization to reduce the formation of acetic acid and furfural, two fermentation inhibitors. Novel impregnation techniques, including employment of sulfur trioxide, were also investigated but require more work to assess technical feasibilit

Biotechnological application of enzymes for making paper pulp from green jute/kenaf

The objectives of the tasks of Agrotechnology & Food Innovation (formerly ATO) in the project are: to determine at laboratory level the best conditions for producing high-yield pulps from whole jute for utilisation in wood containing papers; to test the potential of using recommended enzyme recipes in both extruder and refiner processes in terms of pulp quality, chemicals and energy consumption, brightness and production cost; to evaluate the potential of a micro-biological pre-treatment with selected strains of fungi; to establish process conditions for pilot confirmatory trials

Modelling ethanol production from cellulose: separate hydrolysis and fermentation versus simultaneous saccharification and fermentation

In ethanol production from cellulose, enzymatic hydrolysis, and fermentative conversion may be performed sequentially (separate hydrolysis and fermentation, SHF) or in a single reaction vessel (simultaneous saccharification and fermentation, SSF). Opting for either is essentially a trade-off between optimal temperatures and inhibitory glucose concentrations on the one hand (SHF) vs. sub-optimal temperatures and ethanol-inhibited cellulolysis on the other (SSF). Although the impact of ethanol on cellobiose hydrolysis was found to be negligible, formation of glucose and cellobiose from cellulose were found to be significantly inhibited by ethanol. A previous model for the kinetics of enzymatic cellulose hydrolysis was, therefore, extended with enzyme inhibition by ethanol, thus allowing a rational evaluation of SSF and SHF. The model predicted SSF processing to be superior. The superiority of SSF over SHF (separate hydrolysis and fermentation) was confirmed experimentally, both with respect to ethanol yield on glucose (0.41 g g-1 for SSF vs. 0.35 g g-1 for SHF) and ethanol production rate, being 30% higher for an SSF type process. High conversion rates were found to be difficult to achieve since at a conversion rate of 52% in a SSF process the reaction rate dropped to 5% of its initial value. The model, extended with the impact of ethanol on the cellulase complex proved to predict reaction progress accurately

A generic model for glucose production from various cellulose sources by a commercial cellulase complex

The kinetics of cellulose hydrolysis by commercially available Cellubrix were described mathematically, with Avicel and wheat straw as substrates. It was demonstrated that hydrolysis could be described by three reactions: direct glucose formation and indirect glucose formation via cellobiose. Hydrolysis did not involve any soluble oligomers apart from low amounts of cellobiose. Phenomena included in the mathematical model were substrate limitation, adsorption of enzyme onto substrate, glucose inhibition, temperature dependency of reaction rates, and thermal enzyme inactivation. In addition, substrate heterogeneity was described by a recalcitrance constant. Model parameters refer to both enzyme characteristics and substrate-specific characteristics. Quantitative model development was carried out on the basis of Avicel hydrolysis. In order to describe wheat straw hydrolysis, wheat straw specific parameter values were measured. Updating the pertinent parameters for wheat straw yielded a satisfactory description of wheat straw hydrolysis, thus underlining the generic potential of the model.

Biofuel production from acid-impregnated willow and switchgrass

As part of a broader technical and economic feasibility study, we studied production of bioethanol from two types of lignocellulosic biomass by way of concentrated acid impregnation at low temperature. Willow chips and switchgrass were submitted to various impregnation techniques with concentrated sulfuric acid at varying acid: biomass ratios and impregnation times. Goal of the experiments was to investigate the technical feasibility of concentrated acid pretreatment technology as part of an industrial process that employs recycling of acid through biological means. Experimental results showed that significant amounts of fermentable sugars including glucose (up to 78 f max. obtainable glucose) and xylose can be obtained by relatively simple impregnation techniques at room temperature. Fermentation of willow-derived hydrolysates with S. Cerevisiae yielded 0.45 - 0.49 g ethanol/g glucose. Ethanol production rates however were 38 ower compared to standard glucose fermentation, prompting the need for further optimization to reduce the formation of acetic acid and furfural, two fermentation inhibitors. Novel impregnation techniques, including employment of sulfur trioxide, were also investigated but require more work to assess technical feasibilit