The aim of this work was the optimization of the enzyme hydrolysis of potato peel residues (PPR) for bioethanol production. The process included a pretreatment step followed by an enzyme hydrolysis using crude enzyme system composed of cellulase, amylase and hemicellulase, produced by a mixed culture of Aspergillus niger and Trichoderma reesei. Hydrothermal, alkali and acid pretreatments were considered with regards to the enhancement of enzyme hydrolysis of potato peel residues. The obtained results showed that hydrothermal pretreatment lead to a higher enzyme hydrolysis yield compared to both acid and alkali pretreatments. Enzyme hydrolysis was also optimized for parameters such as temperature, pH, substrate loading and surfactant loading using a response surface methodology. Under optimized conditions, 77 g/L of reducing sugars were obtained. Yeast fermentation of the released reducing sugars led to an ethanol titer of 30g/L after supplementation of the culture medium with ammonium sulfate. Moreover, a comparative study between acid and enzyme hydrolysis of potato peel residues was investigated. Results showed that enzyme hydrolysis offers higher yield of bioethanol production than acid hydrolysis. These results highlight the potential of second generation bioethanol production from potato peel residues treated with onsite produced hydrolytic enzymes.

International audienceSyrup resulting from date by-products constitutes a favorable medium for yeast development, owing to its sugar composition; it was hence tested for ethanol production. Three yeasts, Saccharomyces cerevisiae, Zygosaccharomyces rouxii and Candida pelliculosa, were selected for ethanol production on dates syrup. In batch fermentation, the ethanol concentration depended on the initial sugar concentration and the yeast strain. For an initial sugar concentration of 174.0 ± 0.2 kg m−3, maximum ethanol concentration was 63.0 ± 0.1 kg m−3 during S. cerevisiae growth, namely higher than the amounts achieved during Z. rouxii and C. pelliculosa growth, 33.0 ± 2.0 kg m−3 and 41.0 ± 0.3 kg m−3 respectively. Contrarily, only Z. rouxii was able to grow on 358.0 ± 1.0 kg m−3 initial sugar amount, resulting in 55.0 ± 1.0 kg m−3 ethanol produced

Ethanol production from by-products of dates in very high gravity was conducted in batch fermentation using two yeasts, Saccharomyces cerevisiae and Zygosaccharomyces rouxii, as well as a native strain: an osmophilic strain of bacteria which was isolated for the first time from the juice of dates (Phoenix dactylifera L.). The phylogenetic analysis based on the 16S ribosomal RNA and gyrB sequence and physiological analysis indicated that the strain identified belongs to the genus of Bacillus, B. amyloliquefaciens. The ethanol yields produced from the syrup of dates (175 g L and 360 g L of total sugar) were 40.6% and 29.5%, respectively. By comparing the ethanol production by the isolated bacteria to that obtained using Z. rouxii and S. cerevisiae, it can be concluded that B. amyloliquefaciens was suitable for ethanol production from the syrup of dates and can consume the three types of sugar (glucose, fructose, and sucrose). Using Z. rouxii, fructose was preferentially consumed, while glucose was consumed only after fructose depletion. From this, B. amyloliquefaciens was promising for the bioethanol industry. In addition, this latter showed a good tolerance for high sugar concentration (36%), allowing ethanol production in batch fermentation at pH 5.0 and 28 °C in date syrup medium. Promising ethanol yield produced to sugar consumed were observed for the two osmotolerant microorganisms, Z. rouxii and B. amyloliquefaciens, nearly 32-33%, which were further improved when they were cocultivated, leading to an ethanol to glucose yield of 42-43%.

Recently, achieving to a cost-effective method of treating industrial wastes with maximum level of removing contaminant and microorganism has been researched by many scientists. Anaerobic bioreactors are important tools and platforms in biological and microbiological technology to manage such kind of huge quantity waste. Today is widely used in purification of factories' waste due to their being low energy consumption. In this review article, benefits and defects of anaerobic process and 3 main properties of bioreactors i.e. uniformity, instability of time and location reviews. In order to increase the efficiency, parameters of waste refining like temperature, pH, retention time, organic loading rate and reproduction of bacteria are calculated and controlled. Internal parts can improve retention time even mass transfer.

No abstract

Three yeasts, Saccharomyces cerevisiae, Zygosaccharomyces rouxii and Candida pelliculosa, were tested for ethanol production on dates’syrup. In batch fermentation, the ethanol concentration depended on the initial sugar concentration and the yeast strain. For an initial sugar concentration of 17.4°Brix, maximum ethanol concentration was 63 g/L during S. cerevisiae growth, higher than the amounts achieved during Z. rouxii and C. pelliculosa growth, 33 g/L and 41 g/L respectively. On 35.8°Brix initial sugar amount, only Z. rouxii was able to grow, resulting in 50 g/L ethanol production, showing an inhibitory effect on S.cerevisae and C. Pelliculosa due to the osmotic stress resulting from the high sugar concentration.

The optimal extraction conditions were determined for by-product of date fruit by using the response surface design method. The obtained juice was used for the production of ethanol by fermentation of free cells of Saccharomyces cerevisiae. Optimal conditions for date juice extraction were found to be 80°C, 60 min, 1:2 dilution (fruit on water ratio) according to the result of response surface analysis (Equivalents glucose: 219 g.L-1). Saccharomyces cerevisiae showed a preference for glucose over fructose and among the tested total sugar concentrations, namely 50, 100, 174 and 358 g.L-1, 174 g.L-1 appeared to be the optimal amount, leading to 70 g.L-1 ethanol concentration after 66 h of fermentation,; while an inhibitory effect of a high sugar content, 358 g.L-1 of total sugars, namely about 2 mol/L of monosaccharide like glucose or fructose was also shown. Overall, this study suggested that date juice can be utilized for ethanol production.