Abstract
Photo-hydrogen and lipid production from individual synthetic volatile fatty acids (VFAs) and sugar manufacturing wastewater (SMW) by Rhodobacter sp. KKU-PS1 with sodium glutamate or Aji-L (i.e., waste from the process of crystallizing monosodium glutamate) as a nitrogen source was investigated. Using individual synthetic VFAs, the maximum hydrogen production was achieved with Aji-L as a nitrogen source rather than sodium glutamate. The maximum hydrogen production was 1,727, 754 and 1,353 mL H2/L, respectively, using 25 mM of lactate, 40 mM of acetate and 15mM of butyrate as substrates. Under these conditions, lipid was produced in the range of 10.6–16.9% (w/w). Subsequently, photo-hydrogen and lipid production from SMW using Aji-L as nitrogen source was conducted. Maximal hydrogen production and hydrogen yields of 1,672 mL H2/L and 1.92 mol H2/mol substrate, respectively, were obtained. Additionally, lipid content and lipid production of 21.3% (w/w) and 475 mg lipid/L were achieved. The analysis of the lipid and fatty acid components revealed that triacyglycerol (TAG) and C18:1 methyl ester were the main lipid and fatty acid components, respectively, found in Rhodobacter sp. KKU-PS1 cells.
Highlights
The unsustainability of fossil fuel consumption and the climate change resulting from fossil fuel combustion have stimulated strategies for developing alternative energy sources that are renewable and eco-friendly (Sagnak & Kargi, 2011)
Purple non-sulfur photosynthetic bacteria (PNSB) such as Rhodobacter sphaeroides KKU-PS5, R. sphaeroides KD131, R. sphaeroides O.U. 001, and Rhodopseudomonas palustris WP3-5 have the capacity to convert hydrogen from a single organic acid (Assawamongkholsiri, Plangklang & Reungsang, 2016; Assawamongkholsiri & Reungsang, 2015; Laocharoen & Reungsang, 2014) and mixed volatile fatty acids (VFAs), which are the major substrates in dark fermentation effluents (Lo et al, 2011; Uyar et al, 2009; Yang et al, 2012)
The effect of various carbon sources, i.e., lactate, acetate and butyrate, which are the primary organic acids contained in Sugar manufacturing wastewater (SMW), on hydrogen production was investigated using glutamate or Aji-L as a nitrogen source by Rhodobacter sp
Summary
The unsustainability of fossil fuel consumption and the climate change resulting from fossil fuel combustion have stimulated strategies for developing alternative energy sources that are renewable and eco-friendly (Sagnak & Kargi, 2011). The limitations of photofermentation are its low hydrogen production rate and high raw material costs (Levin, Pitt & Love, 2004) For these reasons, the efficiency of photo-hydrogen production has to be improved as well as developing ways to use alternative carbon sources, such as lactate, acetate and butyrate, which can be obtained from wastes containing VFAs. Wastewater from sugar manufacturing processes (SMW) is an attractive feedstock for photo-hydrogen production due to its abundance and high VFAs content. The effect of a medium containing various VFAs components, and their concentrations on photo-hydrogen fermentation should be investigated
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