The Effect of Organic Loading and Mode of Operation in a Sequencing Batch Reactor Producing PHAs from a Medium Corresponding to Condensate from Food Waste Drying

This study evaluated polyhydroxyalkanoates (PHAs) production from a medium corresponding to the condensate derived from food waste drying, using a mixed microbial culture in a 15 L Sequencing Batch Reactor (SBR). The reactor operation comprised two distinct periods to investigate the impact of varying organic loading rates on biomass performance and polymer accumulation. In Period 1, when the soluble Chemical Oxygen Demand (sCOD) was 6.8 ± 1.4 g/L, efficient nitrogen limitation promoted complete urea consumption and stable biomass growth, yielding higher intracellular PHA accumulation (11.74 ± 6.01%). The microbial community exhibited a balanced copolymer production (HB:HV ratio of approximately 54:46). Conversely, Period 2, characterized by higher organic loads (sCOD 12.1 ± 2.9 g/L), displayed incomplete urea utilization, reduced biomass viability, and significantly lower PHA accumulation (5.26 ± 2.53%). A second set of experiments aiming at the assessment of the impact of operation mode (with and without inclusion of a settling phase) demonstrated that removal of settling leads to a stable long-term steady-state operation with enriched PHA-accumulating bacteria and increased polymer storage capacity.