Propionate-oriented kitchen waste fermentation for polyhydroxyalkanoate production by mixed microbial cultures

Kitchen waste fermentation can provide a low-cost carbon source rich in volatile fatty acids (VFAs) for polyhydroxyalkanoate (PHA) production by mixed microbial cultures (MMCs), while the effects of VFA composition on process performance remain unclear. This study compared the enrichment of PHA-producing microorganisms and PHA production performances of MMCs supplied with acetate-, propionate-, and butyrate-dominant VFAs. Although the three systems achieved similar maximum PHA contents (PHA_m) of about 70%, the propionate-type system showed better substrate-switching adaptability and biomass retention, achieving the highest PHA productivity of 0.94 g PHA/(L·d). It indicates that increasing the propionate fraction in the feed may be a promising strategy for MMC-based PHA production. Glycerol-assisted kitchen waste fermentation was therefore investigated to enhance propionate formation. Under the optimized conditions of maintaining pH 6.5 and 35 °C, propionate accounted for approximately 41% of total VFAs. The actual fermentation broth supported a PHA content of 42.5% and a carbon conversion efficiency of 48.3% in the propionate-type system. Further analysis indicated that elevated nutrient and salinity levels were important factors limiting its performance relative to the simulated fermentation broth group. Overall, this study presents a feasible strategy for enhancing MMC-based PHA production through propionate-oriented kitchen waste fermentation.