Higher bacterial diversity in two-phase thermophilic anaerobic digestion of food waste after micronutrient supplementation

Deficiency of trace metals exacerbates instability in the methanogenic phase of two-phase thermophilic AD. The addition of a micronutrient supplement containing calcium, magnesium, cobalt and nickel was found to help process recovery, increasing methane production by up to 40%. In this study, next gen sequencing was used to identify the changes brought by addition of the micronutrients in the bacterial community of the methanogenic phase of food waste processing. The diversity of the community before supplementation was considerably low and a single species of Phylum Thermotogae was the sole dominant bacterial group. The addition of a micronutrient supplement comprising of Ca, Mg, Co and Ni caused a potent increase in the diversity of the community and species belonging to Arcobacter, Clostridium, Pseudomonas, Bacteroides and Coprothermobacter were particularly enriched. This suggested that the action of the micronutrients resulted in an increase in the functional diversity and redundancy of the bacterial community and limiting hydrogenotrophic methanogenesis in favour of acetotrophic methanogenesis. These factors would contribute to the observed increased stability and higher productivity in the micronutrient supplemented thermophilic AD process.