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Microorganisms 2016, 4(1), 2;

Influence of pH Regulation Mode in Glucose Fermentation on Product Selection and Process Stability

Faculty of Civil Engineering, Universiti Teknologi MARA (Pulau Pinang), 13500 Permatang Pauh, Pulau Pinang, Malaysia
Institute Center for Energy (iEnergy), Masdar Institute of Science and Technology, 54224 Abu Dhabi, United Arab Emirates
Advanced Water Management Centre, The University of Queensland, St. Lucia, QLD 4072, Australia
Author to whom correspondence should be addressed.
Academic Editor: Willy Verstraete
Received: 27 October 2015 / Revised: 26 November 2015 / Accepted: 8 December 2015 / Published: 4 January 2016
(This article belongs to the Special Issue Microbial Resource Management)
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Mixed culture anaerobic fermentation generates a wide range of products from simple sugars, and is potentially an effective process for producing renewable commodity chemicals. However it is difficult to predict product spectrum, and to control the process. One of the key control handles is pH, but the response is commonly dependent on culture history. In this work, we assess the impact of pH regulation mode on the product spectrum. Two regulation modes were applied: in the first, pH was adjusted from 4.5 to 8.5 in progressive steps of 0.5 and in the second, covered the same pH range, but the pH was reset to 5.5 before each change. Acetate, butyrate, and ethanol were produced throughout all pH ranges, but there was a shift from butyrate at pH < 6.5 to ethanol at pH > 6.5, as well as a strong and consistent shift from hydrogen to formate as pH increased. Microbial analysis indicated that progressive pH resulted in dominance by Klebsiella, while reset pH resulted in a bias towards Clostridium spp., particularly at low pH, with higher variance in community between different pH levels. Reset pH was more responsive to changes in pH, and analysis of Gibbs free energy indicated that the reset pH experiments operated closer to thermodynamic equilibrium, particularly with respect to the formate/hydrogen balance. This may indicate that periodically resetting pH conforms better to thermodynamic expectations. View Full-Text
Keywords: fermentation; mixed culture; glucose; pH control; pH regulation method fermentation; mixed culture; glucose; pH control; pH regulation method

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Mohd-Zaki, Z.; Bastidas-Oyanedel, J.R.; Lu, Y.; Hoelzle, R.; Pratt, S.; Slater, F.R.; Batstone, D.J. Influence of pH Regulation Mode in Glucose Fermentation on Product Selection and Process Stability. Microorganisms 2016, 4, 2.

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