Effects of bio-surfactants combined with alkaline conditions on volatile fatty acid production and microbial community in the anaerobic fermentation of waste activated sludge

• Bio-surfactants & pH 9 stimulated VFA production from WAS fermentation.
• Bio-surfactants & pH 9 were optimal in organics conversion and hydrolysis.
• Saponin & pH 9 achieved the highest VFA accumulation of 425.2 mg COD/g VSS.
• Saponin & pH 9 maintained microbial metabolic ability.
• The relative abundances of acidogens detected in Saponin & pH 9 were more abundant.

This study investigated the effects of three types of bio-surfactants (BS), namely, saponin (SP), surfactin (SF), and rhamnolipid (RL), with alkaline conditions on volatile fatty acid (VFA) production and microbial community in sludge fermentation. BS combined with a pH of 9 significantly enhanced hydrolase activities, promoted VFA production and inhibited methanation. SP & pH 9 was more efficient in converting organics to VFAs and thus achieved the highest yield of 425.2 mg COD/g VSS, which was 1.5 times that at pH 10. The lower negative effect of SP on metabolic potential and diversity than that of SF or RL was confirmed through a Biolog assay. Illumina-sequencing further proved that the relative abundances of acidogens in SP & pH 9 were higher than those in other tests, including Proteiniclasticum, Fusibacter, Macellibacteroides and Petrimonas et al. This study provided a strategy for plant-derived SP applications in sludge moderate alkaline fermentation to enhance VFA production.

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