Metagenomic analysis revealed the microbiota and metabolic function during co-composting of food waste and residual sludge for nitrogen and phosphorus transformation.

This paper used bagasse as a composting additive and bulking agent in order to investigate the aerobic composting process of food waste and residual sludge. Accordingly, the variations of nitrogen and phosphorus nutrients, microbiota and metabolic function during the composting process were systematically explored. Three piles with residual sludge, food waste and bagasse mass ratios of 1:1:1, 2:1:1 and 4:1:1 were set. The ammonia nitrogen content in the three compost piles were 3.18 mg/g, 4.68 mg/g and 5.84 mg/g at the end of composting. The final available phosphorus content of the three piles were 3.42 mg/g, 6.70 mg/g and 11.21 mg/g, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that absorption peaks attributed to amines, amino acids and amides appeared in the 1:1:1 pile. Metagenomic analysis of the glycolysis and ammonia transformation pathways showed that the total relative abundance of key enzyme genes for the conversion of glucose to glucose-6-phosphate in the three plies were 0.326%, 0.213% and 0.248%, respectively. The total relative abundance of 2 glutamate dehydrogenase (GDH2), glud1-2 and E1,4,1,4 dehydrogenases in the three piles was 0.125%, 0.151% and 0.160%, respectively, as the main enzymes for the mutual conversion of ammonia and glutamate.

Effect of excess sludge and food waste feeding ratio on the nutrient fractions, and bacterial and fungal community during aerobic co-composting.

The effect of excess sludge and food waste feeding ratio on the co-composting process was explored using 5% bagasse biochar as an additive and conditioner. Results showed that when the mass ratio was 1:1, nitrogen fixation ability was the strongest and ammonia nitrogen increment in the pile reached 2.31 mg/g. The increase in excess sludge content/food waste ratio during composting was conducive to the accumulation of H2O-P, BD-P, HCl-P, NaOH-P and NaOH85-P. When the ratio of excess sludge to food waste mass was 1:1, the relative abundance of Firmicutes was the largest in the compost, which corresponded to 72.77% at the phylum level. Food waste mass was more beneficial to the growth and reproduction of microorganisms and to the metabolic activities related to membrane transport. Considering the fungal content, Ascomycota and Basidiomycota were maximum, with relative abundance of 69.53% and 20.91%, respectively, at the mass ratio of 1:1.