Tailoring microbial communities for medium chain fatty acid production from waste activated sludge: Comparative performance of endogenous vs. exogenous consortia

Optimizing medium chain fatty acid (MCFA) production from waste activated sludge (WAS) requires tailoring microbial communities, yet it remains unclear whether combining substrate sterilization with exogenous caproate-synthesizing bacteria (CSB) can enhance chain elongation. Here, we compared the MCFA production achieved using this strategy with that driven by the endogenous microbiomes in both the solid residue and the supernatant. Among all experimental groups, this strategy achieved the highest MCFA production in the supernatants (3935 ± 21 mg COD/L). This strategy increased CSB abundance in both the solid residue and the supernatant relative to the abundance in the endogenous microbiome systems. Notably, in supernatant systems, this strategy not only enriched acidogens but also led to the highest soluble protein utilization rate, maximal CO₂ release/uptake, and an increased gene abundance related to pyruvate generation. Life cycle assessment confirmed economic and environmental benefits. This work provides new insights into optimizing MCFA recovery from WAS.