The effects of the ratio of propionate to acetate on the transformation and composition of polyhydroxyalkanoates with enriched cultures of glycogen‐accumulating organisms

Abstract

Studies on the synthesis of polyhydroxyalkanoates (PHA) mainly focus on the enriched cultures of phosphorus‐accumulating (PAO) or glycogen‐accumulating organisms (GAO) with acetate or propionate as the sole carbon source. However, PHA production with a mixture of propionate and acetate by enriched cultures of GAO has not been reported. It is well known that the physical and mechanical properties of PHA can be improved by incorporating 3‐hydroxyvalerate (3HV) into the polymer. To synthesize PHA with a high 3HV percentage, five laboratory‐scale sequencing batch reactors were operated with the enriched cultures of GAO using different ratios of propionate and acetate (P/A) as the carbon sources in this study. The effects of P/A ratio on the anaerobic and aerobic transformations, composition and synthesis rate of PHA were studied. The results showed that with the increase in the P/A ratio, the anaerobic yields of total PHA declined from 4.226 to 2.469 mmol‐C per gram of volatile suspended solids (VSS), and the 3‐hydroxybutyrate (3HB) fraction in PHA decreased from approximately 70 to 10%, along with an increase in 3HV and 3‐hydroxy‐2‐methylvalerate (3H2MV) percentages. When there were equal quantities (mmol‐C L−1) of propionate and acetate, 3HB was produced more quickly than 3H2MV. By increasing P/A ratio from 1/10 to 10/1, the initial synthesis rate of 3H2MV rose from 0.002 to 0.029, while 3HB and the total PHA declined from 0.083 to 0.007 and 0.110 to 0.071 mmol‐C g‐VSS−1 min−1, respectively. Also, it was observed that more 3HV was incorporated into PHA with increasing P/A ratio. This study suggested that when the enriched cultures of GAO were applied to the synthesis of PHA, the composition, yield and synthesis rate of PHA could be manipulated by varying the feed composition.