Abstract
In this study, we investigated the operational performance and product spectrum of glucose‐fermenting anaerobic granular sludge reactor at pH 4. A selective environment for the growth of granules was implemented by the introduction of a 2 min settling phase, a hydraulic retention time of 6 h and a solid retention time of 12 ± 3 days. The fermentation products were ethanol, lactate, and volatile fatty acids (VFA) with yields of 0.55 ± 0.03, 0.15 ± 0.02, and 0.20 ± 0.04 gram chemical oxygen demand (gCOD)/gCOD glucose, respectively. The obtained product spectrum was remarkably different from the VFA‐dominated product spectrum reported in a previous study when the same system was operated at higher pH (4.5–5.5). The shift in product spectrum coincided with a shift in the microbial community structure with the dominance of eukaryotic Candida tropicalis, Pichia jaroonii, and prokaryotic Lactobacillus species instead of the Clostridia species obtained at higher pH‐values. The control of the microbiomes and the associated product spectra provides bioprocess engineers with the option to tailor a suitable precursor compound mixture for subsequent chain elongation fermentation or PHA biopolymer production.
Highlights
Anaerobic fermentation is a method to convert the multitude of compounds present in organic residue streams into a more defined range of products while largely maintaining the energy content of the substrates
We investigate the effect of low pH on the product spectrum of anaerobic glucose fermentation in a sequencing batch reactor (SBR)
Phase 2 was a reaction phase of 157 min; phase 3 was a settling phase of 2 min, and phase 4 was a 3 min effluent phase in which half of the reactor liquid (1.3 L/cycle) was decanted, resulting in a hydraulic retention time (HRT) of 6 h and a chemical oxygen demand (COD) loading rate of 45 gram chemical oxygen demand/(L·d)
Summary
Anaerobic fermentation is a method to convert the multitude of compounds present in organic residue streams into a more defined range of products while largely maintaining the energy content of the substrates. It was proposed that at lower pH, microorganisms cannot sustain themselves if they produce VFA and should switch to the production of compounds that do not lead to exhibit increased toxicity with lower pH, that is, ethanol (Rodríguez et al, 2006) Contrary to these predictions, studies on open culture fermentation of sugar at moderately low pH (4.5–5.5) have reported acetate and butyrate and main products instead of ethanol (Fang & Liu, 2002; Temudo et al, 2007). Industrial yeast fermentations seem to rely on the addition of dedicated pure cultures to establish high ethanol yields (Siqueira et al, 2008) In this manuscript, we investigate the ethanol production in open cultures using low pH as a selective pressure
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