Study on the microbial community shift during co-fermentation of substrates

Abstract

Some of the core issues faced today in developed and developing countries are global energy protection and better utilisation of natural resources. Anaerobic digestion is currently one of the options available that may assist in this regard and research has been done on a wide variety of substrates for anaerobic digestion. Several phases can be observed during a typical batch setup for anaerobic digestion, with the lag phase being of particular interest as the microbial communities present typically adapts to substrate during this phase. The lag phase is also typically one of the longest phases observed in batch reactor setups. Pig slurry is readily available and poses a threat to environmental, including over-fertilisation and eutrophication. The aim of the current study was to determine whether back inoculation will reduce the observed lag time before biogas production occurs in batch reactors using pig slurry as the primary substrate. Batch reactors were used in this study, during which back inoculation was done and sample were taken at key intervals. Samples taken from the batch reactors were subjected to physical and chemical analysis, as well as molecular analysis of the microbial communities present during the sample times using metabarcoding on the MiSeq next generation sequencing (NGS) platform. From the NGS data community composition and predicted metabolic activities were derived. Low biogas yields were observed in this study and could be attributed to factors such as imbalanced nutrient levels and ratios between the main functional groups. Methanogenesis was not optimal as the abundance of methane producing microorganism was inhibited The major phyla observed in the microbiomes in the current study included Firmicutes, Bacteroidetes, Proteobacteria, Synergistetes, Euryarchaeota, Chloroflexi, Actinobacteria and Atribacteria, and the major families were Clostridiaceae 1, Synergistaceae, Ruminococcaceae, Rikenellaceae, Marinilabiaceae, Porphyromonadaceae, Erysipelotrichiaceae and Methanosarcinaceae. These are typically phyla and families associated with the AD processes. The predicted metabolic activities indicated the highest metabolic activity to be unknown, followed by ammonia oxidation. These issues primarily relate to the small size of the bench-top reactors and the state of the seeding sludge. The back inoculation was successful in reducing the observed lag phase, even though the C:N ratio was not optimal.