ABSTRACT
Anaerobe fermentation of sugar beet pressed pulp was investigated in pilot-scale digesters. Thermophilic adaptation of mesophilic culture was monitored using chemical analysis and metagenomic characterization of the sludge. Temperature adaptation was achieved by increasing the temperature gradually (2 °C day(-1)) and by greatly decreasing the OLR. During stable run, the OLR was increased gradually to 11.29 kg VS m(-3)d(-1) and biogas yield was 5% higher in the thermophilic reactor. VFA levels increased in the thermophilic reactor with increased OLR (acetic acid 646 mg L(-1), propionic acid 596 mg L(-1)), then VFA decreased and the operation was manageable beside the relative high tVFA (1300-2000 mg L(-1)). The effect of thermophilic adaptation on the microbial communities was studied using a sequencing-based metagenomic approach. Connections between physico-chemical parameters and populations of bacteria and methanogen archaea were revealed.
Subject(s)
Adaptation, Physiological/physiology , Bacteria, Anaerobic/physiology , Beta vulgaris/metabolism , Biofuels , Bioreactors , Methane/biosynthesis , Bacteria, Anaerobic/genetics , Bacteria, Anaerobic/metabolism , Base Sequence , Beta vulgaris/chemistry , Chromatography, High Pressure Liquid , Computational Biology , Fermentation , Metagenome , Molecular Sequence Data , Pilot Projects , Sequence Analysis, DNA , Species Specificity , TemperatureABSTRACT
The anaerobic digestion of pure glycerol, which produces a baseline acetic acid to propionic acid ratio of 0.2, was studied in laboratory scale reactors (3 l working volume) at mesophilic temperature (37 °C) with 3000 mg chemical oxygen demand (COD)l(-1) d(-1). During the experiment tVFA and C2-C6 VFA analysis and daily biogas yield measurement were carried out. Following 10 days of a 15% d(-1) increase in the organic loading rate (OLR) of 3.0-10.5 g COD l(-1) d(-1), the concentration of propionic acid increased to 6200-8000 mg l(-1). Then the inoculum was divided into three parts feeding with 100% glycerol, 50% glycerol + 50% acetic acid, and 50% glycerol + 50% thick stillage, (presented in % of 2.60 g COD l(-1) d(-1) OLR), respectively. The application of co-substrates reduced the recovery period by 5 days compared to feeding with pure glycerol. When the reactors were loaded with glycerol again (10% OLR raise per day) the previously applied co-substrates had a positive effect on the VFA composition and the biogas yield as well.
