Enrichment of a mixed microbial culture for polyhydroxyalkanoates production: Effect of pH and N and P concentrations

© 2017 Elsevier B.V. Polyhydroxyalkanoates (PHA) are biopolymers that can be an alternative against conventional plastics. The study reported herein evaluated the enrichment of a mixed microbial culture (MMC) operated under feast/famine regime and different pHs in a sequencing batch reactor (SBR) using acetate as sole carbon source to produce polyhydroxyalkanoates (PHAs). The enrichment step was evaluated at controlled pH of 7.5 and also without pH control (averaged value of 9.0). The acetate uptake rate (− qS) of both enrichments at the end of the experimental period exhibited similar behaviour being about 0.18 Cmol Ac Cmol X− 1 h− 1 and 0.19 Cmol Ac Cmol X− 1 h− 1 for SBR-A and SBR-B, respectively. However, the PHA-storing capacity of the biomass enriched without pH control was better, exhibiting a maximum PHA content of 36% (gPHA g− 1 VSS) with a PHA production rate (qPHA) of 0.16 Cmol PHA Cmol X− 1 h− 1. Batch experiments were performed to evaluate PHA-storing capacity of the enriched culture at different pHs and nutrients concentrations. In the pH experiments (without nutrient limitation), it was found that in the absence of controlled pH, the enriched biomass exhibited a PHA content of 44% gPHA g− 1 VSS with − qS and PHA to substrate yield (YPHA/Ac) of 0.57 Cmol Ac Cmol X− 1 h− 1 and 0.33 Cmol PHA Cmol Ac− 1, respectively. Regarding the experiments at variable nutrients concentration (pH ranging 8.8 to 9.2), the results indicate that the PHA content in the enriched biomass is significantly higher being around 51% gPHA g− 1 VSS under nitrogen limitation. This work demonstrated the feasibility of the enrichment of a MMC with PHA storage ability without pH control. Results also suggest that better PHAs contents and substrate uptake rates are obtained without controlling the pH in the accumulation step. Finally, this work also highlights the importance of understanding the role of nutrients concentration during the accumulation step.