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Table 2 Distribution of fermentative products for the six conditions

From: Total solids content: a key parameter of metabolic pathways in dry anaerobic digestion

Categories Unit (molar %) Wet (W) Dry (D) Highly dry (HD) Similarity Similarity
   10% ≤ TS ≤14% 19% < TS <28% 28% < TS ≤33% W-D group W-D group
Gas products Total products 63% ± 2 63% ± 5 57% ± 5 Similar (P = 0.34, ns) Different (P = 1e-2*)
Hydrogen Gas products 51% ± 3 31% ± 3 18% ± 6 Different (P = 3e-7***) Different (P = 2e-4***)
Carbon dioxide 49% ± 3 69% ± 3 82% ± 6 Different (P = 3e-7***) Different (P = 2e-4***)
Hydrogen associated with VFAs Total products 30% ± 3 23% ± 5 29% ± 2 Different (P = 3e-2*) Different (P = 2e-4***)
Acetic acid Hydrogen associated with VFAs 62% ± 12 62% ± 10 29% ± 5 Similar (P = 0.12, ns) Different (P = 5e-7***)
Butyric acid 38% ± 10 38% ± 12 71% ± 5 Similar (P = 0.12, ns) Different (P = 5e-7***)
Other metabolites Total products 7% ± 2 14% ± 2 13% ± 4 Different (P = 3e-5***) Similar (P = 0.26, ns)
Propionic acid Concurrent metabolite 23% ± 4 26% ± 3 26% ± 13 Similar (P = 0.54, ns) Similar (P = 0.39, ns)
Valeric acid 7% ± 3 12% ± 3 14% ± 3 Different (P = 7e-4*) Different (P = 2e-2*)
Caproic acid 15% ± 7 1% ± 2 0% ± 0 Different (P = 2e-7***) Similar (P = 0.07, ns)
Lactic acid 0% ± 0 0% ± 0 12% ± 13 Similar (P = 0.27, ns) Different (P = 2e-3*)
Ethanol 55% ± 7 60% ± 7 52% ± 10 Similar (P = 0.71, ns) Similar (P = 0.12, ns)
  1. The three groups of TS contents are classified in three categories: gaseous products, VFAs associated with the production of hydrogen, and other metabolites. The similarity between group wet and dry and group dry and highly dry is indicated based on ANOVA. P value levels of significance: * < 0.05; ** < 0.01; *** < 0.001; and ns, >0.05. D, dry; HD, highly dry; ns, not significant; TS, total solids; VFA, volatile fatty acid; W, wet.