Ultrasonication-assisted polyhydroxyalkanoate production from mixed sewage sludge: Exploring the feast-famine regime and microbial resilience

This study examines the production of polyhydroxyalkanoates (PHAs) from municipal sludge using an innovative ultrasonication-assisted microbial acclimatization strategy. By employing mixed microbial cultures (MMCs) under a controlled feast/famine regime, the research explores the use of ultrasonicated fermented surplus mixed sludge as the primary feedstock. Fermentation was conducted at three energy input levels - 2500, 10,000, and 20,000 kJ/kg - to evaluate the impact of energy input on substrate solubilization and volatile fatty acid (VFA) production. The process yielded a VFA-rich effluent containing significant concentrations of 114 mM acetate, 39.04 mM propionate, and 10.11 mM butyrate, resulting in a total VFA concentration of 13.3 gCOD/L. This enriched effluent was utilized to cultivate an acclimatized MMC in a lab-scale sequencing batch reactor (SBR), with 4.5 g/L acetate serving as the primary carbon source to optimize PHA accumulation. Our findings revealed PHA yields ranging from 0.415 to 0.482 gPHA/gCOD of total VFA, corresponding to an accumulation efficiency of 41.5 % to 48.2 %. The produced PHAs were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). This study underscores the potential of municipal sludge as a sustainable and cost-effective feedstock for bioplastic production.