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Abstract: A major problem with fermentative ethanol production is the formation of large amounts of numerous organic pollutants. In an industrial distillery, stillage, fermenter and condenser cooling water are the main sources of wastewater. However, the selection of a proper technology makes it possible to almost completely avoid emissions of such kind of wastewater to the environment. This study examines the effect of stillage recirculation on fuel ethanol production. It is based on the use of Saccharomyces cerevisiae and a granular starch hydrolyzing enzyme in a simultaneous saccharification and fermentation process using a native starch obtained from corn flour. It was shown that the yield of the ethanol production was not influenced by the recycled stillage, a mean yield being 83.38% of the theoretical value. No significant trend for change in the ethanol concentration or in the residual starch was observed during any particular run, even after the 75% of fresh water was replaced with stillage. Thus, by applying this new clean technology it is possible to significantly reduce the rate of water consumption and in this way the production of by-products such as stillage. [Copyright &y& Elsevier]

Background. The most important innovations in boethanol production in the last decade were: simultaneous saccharification and fermentation processes (SSF), high gravity fermentation, the use of new enzyme preparation able to hydrolyse native granular starch and construction of genetically modified strains of microorganisms able to carry out simultaneous production of hydrolytic enzymes and fermentation of C6 and C5 sugars. The aim of this study was to assess the efficiency of ethanol fermentation using new type of amylolytic enzymes able to hydrolyse native corn starch in a SSF process. Material and methods. The simultaneous saccharification and fermentation of raw corn flour by fed-batch processes using Saccharomyces cerevisiae strain Red Star Ethanol Red and Stargen 001 enzyme preparation was performed. As experimental variable were investigated: fermentation temperature (35-37-40°C), rate of mash stirring (100 and 200 rpm), fermentation time (0-92 h) and dosage of corn flour (different portion and different time). Results. It was found that optimal temperature for fed-batch SSF process was 37°C at initial pH of 5.0. However, the yeast intensively fermented the saccharides also at 40°C. The fermentation stirring rate has significant effect on starch utilization and fermentation production. The prolongation of fermentation time over 72 h has no substantiation in additional ethanol production. In all experimental fermentations the level of produced organic acids was very low, significantly below toxic concentration for the yeast. Conclusions. It was stated that the use of new method of starch raw material preparation resulted in satisfied fermentation yield and allowed to reduce energy requirements for starch liquefaction. [ABSTRACT FROM AUTHOR]

This study demonstrated the importance of fermentation broth pretreatment and dewatering by forward osmosis (FO) before keto carboxylic acid recovery. The most effective and profitable pretreatment procedure was a combination of centrifugation, ceramic ultrafiltration of molecular weight cut-off of 15 kDa, and ceramic nanofiltration of molecular weight cut-off of 450 Da. By applying the complex pretreatment and FO as a pre-concentration step of fermentation broth dewatering, the keto acid enrichment of two times was achieved for alpha-ketoglutaric acid and pyruvic acid. Extensive fouling analysis performed in this study confirmed that the proposed pretreatment procedure was sufficient to avoid severe fouling of the FO dewatering process. A techno-economic analysis of the proposed keto acid extraction scheme shown that by using FO for fermentation broth dewatering, the total capital investment was reduced and the payback time was shortened by 0.83 yr. [Display omitted] • FO fouling reduction & keto acid enrichment governed pretreatment selection. • The best pretreatment was a combination of centrifugation, UF, and loose NF. • Keto acid enrichment of 2 times was achieved by pretreatment and FO dewatering. • FO dewatering reduced capital investment & shortened the payback time by 0.83 yr. [ABSTRACT FROM AUTHOR]

Abstract: Cross-flow microfiltration of fermented mash containing native corn starch granules from a simultaneous saccharification and fermentation process, was investigated with respect to the process performance. Influence of transmembrane pressure and cross-flow velocity on normalized permeate flux rate decline and membrane fouling were examined. The microfiltration system was equipped with a tubular ceramic membrane with 0.45μm pore size. A combined pore-blockage–cake-filtration model was successfully used to determine the process performance and identify principal fouling mechanisms. Experimental results revealed that the fouling phenomenon taking place during microfiltration of the fermented mash follows a pattern of initial complete pore blockage and subsequent cake formation. As a result, initial rapid flux decline is followed by gradual flux decline. Fouled membranes were characterized using scanning electron microscopy (SEM). The membrane surface characteristics examined by SEM images evidenced formation of dense deposit on the upper membrane surface. Rinsing the fouled membrane with water followed by investigation of the permeate flux rate indicated occurrence of increased fouling, when microfiltration was carried out at high transmembrane pressure. The highest normalized flux decline was observed for microfiltration operated at the highest transmembrane pressure (1.4bar) and the lowest cross flow velocity (1ms−1). It is recommended to use high cross-flow velocity (4.55ms−1) and low transmembrane pressure (0.35bar) to minimize membrane fouling, triggered by components of the fermented mash. [Copyright &y& Elsevier]