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Table 6 Summary of microbial populations and end product profiles under various operating conditions

From: Effect of pH and temperature on microbial community structure and carboxylic acid yield during the acidogenic digestion of duckweed

Conditions Key findings
Acidic mesophilic Susceptible to VFA loss due to acetoclastic methanogenic activity (Methanosarcina, 2.03%)
High biogas-CO2 content, suggesting fast hydrolysis, resulting in TAN release
Low CH4 yield (26.6 ± 3.8 ml g duckweed VS −1added ) compared to literature, likely because the very high ammonium concentrations required as buffer were inhibitory
Acidic thermophilic H2 recovery up to 23.5 ± 0.5 ml g−1 duckweed solids added
Least diverse microbial communities (α diversity)
Acetate and butyrate were predominant VFA species
Basic mesophilic Highest VFA yields (388 ± 28 mg VFA as HAceq g VS −1added )
Competition between homoacetogenesis and hydrogenotrophic methanogenesis over H2
Low biogas recovery (23.7 ± 6.2 ml g duckweed VS −1added ) compared to literature, suggesting presence of internal sinks for headspace H2 and CO2
Basic thermophilic Highest final particulate matter formation (18.6% of initial total carbon) in the absence of inoculum, suggesting chemical (alkaline) pretreatment augmented VFA production
Low biogas recovery (29.7 ± 6.3 ml g duckweed VS −1added ), suggesting presence of internal sinks for headspace H2 and CO2
Overall conclusions Within 9 days, more than 80% of the final day VFA concentrations were achieved
Species richness (α diversity) was higher in basic reactors
pH has a more significant impact than temperature on both the composition of microbial communities (β diversity) and VFA production