Fixed-bed biofilm reactor for single-stage bioconversion of organic waste to medium-chain carboxylic acids

Biofilm-based systems can enhance medium-chain carboxylic acids (MCCAs) production by retaining slow-growing microorganisms and increasing biomass density. This study investigated a novel single-stage fixed-bed biofilm system for the co-fermentation of food waste and sewage sludge. Significant enhancements in stability and metabolic efficiency were achieved without external pH control or the addition of external electron donors, as the process relied on the endogenous in-situ production of lactate and ethanol. Using a 1:1 support-to-inoculum ratio with porous sintered glass as solid support, the system reached a caproic acid yield of 62 ± 5 gC6/kgVSfed, significantly higher than the control (43.4 ± 2.1 gC6/kgVSfed) over the entire seventy-day continuous trial. Analytical profiling and sequencing confirmed the selective enrichment of specialized chain elongators, primarily Caproiciproducens and Pseudoramibacter, within the biofilm. This study establishes the single-stage fixed-bed biofilm reactor as a robust and efficient strategy for valorising complex organic waste into high-value chemicals.