Fermentation of deproteinized cheese whey powder solutions to ethanol by engineered Saccharomyces cerevisiae : effect of supplementation with corn steep liquor and repeated-batch operation with biomass recycling by flocculation

The lactose in cheese whey is an interesting substrate for the production of bulk commodities such as bio-ethanol, due to the large amounts of whey surplus generated globally. In this work, we studied the performance of a recombinant Saccharomyces cerevisiae strain expressing the lactose permease and intracellular ß-galactosidase from Kluyveromyces lactis in fermentations of deproteinized concentrated cheese whey powder solutions. Supplementation with 10 g/l of corn steep liquor significantly enhanced whey fermentation, resulting in the production of 7.4% (v/v) ethanol from 150 g/l initial lactose in shake-flask fermentations, with a corresponding productivity of 1.2 g/l/h. The flocculation capacity of the yeast strain enabled stable operation of a repeated-batch process in a 5.5-l air-lift bioreactor, with simple biomass recycling by sedimentation of the yeast flocs. During five consecutive batches, the average ethanol productivity was 0.65 g/l/h and ethanol accumulated up to 8% (v/v) with lactose-toethanol conversion yields over 80% of theoretical. Yeast viability (>97%) and plasmid retention (>84%) remained high throughout the operation, demonstrating the stability and robustness of the strain. In addition, the easy and inexpensive recycle of the yeast biomass for repeated utilization makes this process economically attractive for industrial implementation.Fundação para a Ciência e a Tecnologia (FCT)LACTOGAL-Produtos Alimentares S.A.Companhia Portuguesa de Amidos, S.A

Comparison of adsorption performances of powdered activated sludge and powdered activated carbon for removal of turquoise blue dyestuff

Effective treatment of dyestuff containing wastewaters require advanced treatment technologies such as adsorption for the removal of dyestuffs. Powdered activated carbon (PAC) has been the most widely used adsorbent for the removal of dyestuffs from wastewaters. As an alternative to PAC, powdered activated sludge (PAS) was used as adsorbent for dyestuff removal from synthetic wastewater in this study. The colour removal performance of PAS was compared with that of PAC under the same experimental conditions. Turquoise Blue-G was used as the dyestuff and the effects of adsorbent concentration on the rate and extent of colour removal were investigated for both adsorbents. The colour removal performance of PAS was comparable with that of PAC at high adsorbent concentrations above 4 g 1(-1), resulting in nearly 95% colour removal with 200 mg 1(-1) initial dyestuff concentration. The rates of dyestuff removal were comparable for both adsorbents when initial adsorbent concentration was larger then 4 g 1(-1). Maximum dyestuff removal rates obtained with 6 g 1(-1) adsorbent concentration were 85 and 80 mg 1(-1) h(-1) for PAS and PAC, respectively. Three different isotherms were tested for correlation of the equilibrium adsorption data and the Langmuir isotherm was found to be the most suitable one. The maximum adsorption capacities of PAC and PAS were approximately 100 and 92 mg g(-1), respectively. (c) 2004 Elsevier Ltd. All rights reserved

Biosorption performance of powdered activated sludge for removal of different dyestuffs

Removal of dyestuffs from industrial wastewaters require special advanced technologies since dyes are usually difficult to remove by biological methods. Adsorption of dyestuffs on solid adsorbents such as powdered activated carbon (PAC) is one of the methods commonly used for the removal of these compounds. As an alternative to PAC, a new adsorbent material, powdered activated sludge (PAS) was used for removal of different dyestuffs from aqueous media in this study. The rate and extent of dyestuff removal by acid washed powdered activated sludge were evaluated for six different dyestuffs. Dyestuff removal performance of PAS increased with increasing concentrations of PAS for all dyestuffs tested. Removal of Direct Yellow 12 was superior to the other dyes tested and the lowest removal efficiency was obtained with Levafix rot. Different adsorption isotherms were tested to represent the equilibrium adsorption data and the Freundlich isotherm was found to be the most suitable isotherm. Adsorption isotherm constants of Direct Yellow 12 were determined for all isotherms tested. (C) 2004 Elsevier Inc. All rights reserved

Utilization of cheese whey powder (CWP) for ethanol fermentations: Effects of operating parameters

Cheese whey powder (CWP) solution was used for ethanol fermentation by Kluyveromyces marxianus NRRL-1195 in batch experiments. Effects of initial pH. CWP concentration and external nutrient (N, P) supplementation on ethanol formation rate and extent were investigated. The initial pH was varied between 3 and 7. The most suitable initial pH maximizing the final ethanol yield was found to be 5. Nutritional requirements of the organisms were investigated by supplementing the CWP solution with external nitrogen and phosphate sources. The rate and extent of ethanol formation did not increase with external nutrient addition indicating the fact that the nitrogen and phosphorous content of CWP was sufficient for ethanol fermentation. CWP concentration was varied between 50 and 300 g l(-1) with total sugar concentrations between 25 and 150 g l(-1). Final ethanol concentration and the rate of ethanol formation increased with increasing CWP concentration indicating no substrate or product inhibitions, but substrate limitations. The yield coefficient of ethanol varied between 0.35 and 0.54 g ethanol g sugar I and reached the theoretical level (0.54 a EtOH a sugar(-1)) at 300 g l(-1) CWP concentration. (c) 2005 Elsevier Inc. All rights reserved

Batch biological treatment of nitrogen deficient synthetic wastewater using Azotobacter supplemented activated sludge

Biological treatment of nitrogen deficient wastewaters are usually accomplished by external addition of nitrogen sources to the wastewater which is an extra cost item. As an alternative for effective biological treatment of nitrogen deficient wastewaters, the nitrogen fixing bacterium, Azotobacter vinelandii, was used in activated sludge and also in pure culture. Total organic carbon (TOC) removal performances of Azotobacter-added and free activated sludge cultures were compared at different initial TN/TOC ratios. The rate and extent of TOC removal were comparable for all cultures when initial TN/TOC ratio was larger than 0.12; however, both the rate and extent of TOC removal from nitrogen deficient (TN/TOC <12%) synthetic wastewater were improved by using Azotobacter-added activated sludge as compared to the Azotobacter-free activated sludge culture. More than 90% TOC removal was obtained with pure Azotobacter or Azotobacter-added activated sludge culture from a nitrogen deficient synthetic wastewater. (C) 2004 Elsevier Ltd. All rights reserved

Performance of azotobacter supplemented activated sludge in biological treatment of nitrogen deficient wastewater

External addition of nitrogenous compounds is the most common practice used in biological treatment of nitrogen deficient wastewaters. However, this method adds an extra cost to the treatment. As an alternative for effective biological treatment of nitrogen deficient wastewaters, nitrogen fixing bacteria, Azotobacter vinelandii was used in activated sludge culture in this study. COD removal performance of Azotobacter-supplemented activated sludge was compared with Azotobacter-free activated sludge culture for biological treatment of nitrogen deficient synthetic wastewater. Effects of important process variables such as N/COD ratio, sludge age, hydraulic residence time, feed COD concentration and the COD loading rate on the COD removal performance were investigated. Kinetic constants of the system were determined. Azotobacter addition to the activated sludge in biological treatment of nitrogen deficient wastewater (N/COD < 0.06) improved the COD removal performance significantly. (C) 2002 Elsevier Science Ltd. All rights reserved

Comparison of yeast strains for batch ethanol fermentation of cheese-whey powder (CWP) solution

Aims: To test the suitability of cheese whey powder (CWP) solution for ethanol fermentation and to compare performances of different Kluyveromyces marxianus strains for ethanol fermentation from CWP solution