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

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 ⁻¹_added ) 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 HAc_eq g VS ⁻¹_added )

Competition between homoacetogenesis and hydrogenotrophic methanogenesis over H₂

Low biogas recovery (23.7 ± 6.2 ml g duckweed VS ⁻¹_added ) 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 ⁻¹_added ), 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