RESUMO
Wastewater from cider factories (losses during transfers, products discarded due to quality policies, and products returned from the market) exhibit a Chemical Oxygen Demand greater than 170,000 mg O2/l, mainly due to the ethanol content and carbohydrates that are added to obtain the finished product. These effluents can represent up to 10% of the volume of cider produced, and they must be treated to meet environmental regulations. In this work, a process was developed, based on alcoholic fermentation of the available carbohydrates present in ciders. The impact of inhibitors at different pH, size and reuse of inoculums and different nutrient supplementation on the ethanol yield were evaluated. The use of a 0.5 g/l yeast inoculum and corn steep water as the nutrient source allowed for depletion of the sugars in less than 48 h, which increased the content of ethanol to more than 70 g/l.
Assuntos
Bebidas Alcoólicas , Biocombustíveis , Etanol/metabolismo , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Metabolismo dos Carboidratos , Etanol/análise , Estudos de Viabilidade , Fermentação , Concentração de Íons de Hidrogênio , Saccharomyces cerevisiae/crescimento & desenvolvimento , Saccharomyces cerevisiae/metabolismo , Açúcares/análise , Açúcares/metabolismo , Zea mays/metabolismoRESUMO
This work focuses on the performance of ten commercial Saccharomyces yeast strains in the batch alcoholic fermentation of sugars contained in selected industrial wastewaters from the soft drink industry. Fermentation has been applied successfully to treat these effluents prior to their disposal. Although many strains were investigated, similar behaviour was observed between all of the Saccharomyces strains tested. When media were inoculated with 2gL-1 of yeast, all strains were able to completely consume the available sugars in less than 14h. Thus, any of the strains studied in this work could be used in non-conventional wastewater treatment processes based on alcoholic fermentation. However, ethanol production varied between strains, and these differences could be significant from a production point of view. Saccharomyces bayanus produced the most ethanol, with a mean yield of 0.44gethanolgsugarconsumed-1 and an ethanol specific production rate of 5.96gethanol (Lh)-1. As the assayed soft drinks wastewaters contain about 105gsugar/L of fermentable sugars, the concentration of ethanol achieved after the fermentations process was 46.2gethanol/L. A rigorous kinetic modelling methodology was used to model the Saccharomyces bayanus fermentation process. The kinetic model included coupled mass balances and a minimal number of parameters. A simple unstructured model based on the Andrews equation (substrate inhibition) was developed. This model satisfactorily described biomass growth, sugar consumption and bioethanol production. In addition to providing insights into the fermentative performance of potentially relevant strains, this work can facilitate the design of large-scale ethanol production processes that use wastewaters from the sugar-sweetened beverage industry as feedstock.
Assuntos
Etanol/metabolismo , Saccharomyces/metabolismo , Edulcorantes/metabolismo , Águas Residuárias/química , Biocombustíveis , Biomassa , Biotecnologia , Metabolismo dos Carboidratos , Fermentação , Microbiologia Industrial , Cinética , Modelos Biológicos , Saccharomyces/crescimento & desenvolvimento , Saccharomyces cerevisiae/crescimento & desenvolvimento , Saccharomyces cerevisiae/metabolismo , Especificidade da EspécieRESUMO
In bioethanol production processes, the media composition has an impact on product concentration, yields and the overall process economics. The main purpose of this research was to develop a low-cost mineral-based supplement for successful alcoholic fermentation in an attempt to provide an economically feasible alternative to produce bioethanol from novel sources, for example, sugary industrial wastewaters. Statistical experimental designs were used to select essential nutrients for yeast fermentation, and its optimal concentrations were estimated by Response Surface Methodology. Fermentations were performed on synthetic media inoculated with 2.0 g L(-1) of yeast, and the evolution of biomass, sugar, ethanol, CO2 and glycerol were monitored over time. A mix of salts [10.6 g L(-1) (NH4)2HPO4; 6.4 g L(-1) MgSO4·7H2O and 7.5 mg L(-1) ZnSO4·7H2O] was found to be optimal. It led to the complete fermentation of the sugars in less than 12h with an average ethanol yield of 0.42 g ethanol/g sugar. A general C-balance indicated that no carbonaceous compounds different from biomass, ethanol, CO2 or glycerol were produced in significant amounts in the fermentation process. Similar results were obtained when soft drink wastewaters were tested to evaluate the potential industrial application of this supplement. The ethanol yields were very close to those obtained when yeast extract was used as the supplement, but the optimized mineral-based medium is six times cheaper, which favorably impacts the process economics and makes this supplement more attractive from an industrial viewpoint.
Assuntos
Biocombustíveis/economia , Custos e Análise de Custo , Meios de Cultura/economia , Etanol/metabolismo , Fermentação , Resíduos Industriais/análise , Águas Residuárias/química , Fermentação/efeitos dos fármacos , Magnésio/farmacologia , Minerais/farmacologia , Fosfatos/farmacologia , Saccharomyces cerevisiae/efeitos dos fármacos , Saccharomyces cerevisiae/metabolismo , Zinco/farmacologiaRESUMO
Wastewaters from the soft drinks industry were examined as media for producing bioethanol using yeast-mediated fermentation. Fermentation assays were performed using cola-type, orange and lemon-lime soft drinks and the biomass, sugar and ethanol levels were monitored over time. The effect of the addition of yeast extract was evaluated; the results indicated that 15 g/L is a suitable value for successful fermentation. Depletion of the sugars contained in the soft drinks (10-12% w/v) was achieved in less than 12 h when the medium was inoculated with 2 g/L of Saccharomyces cerevisiae var. Windsor. Ethanol yields were close to the theoretical values. The performance of several kinetic models was evaluated, and their parameters were determined. A model including inhibition by ethanol enabled the best adjustment of the experimental results in all assayed media. Some soft drinks include sodium benzoate in their formulae, the effect of which on yeast metabolism is discussed.