Poly-hydroxyalkanoates production from mixed microbial cultures: effect of dissolved oxygen and pH.

Abstract

The accumulation potential of poly-hydroxyalkanoates (PHAs) produced from an acclimated mixed microbial culture (MMC) under different dissolve oxygen (DO) levels and pH was investigated, using volatile fatty acids (VFAs) as carbon source. Specifically, the PHAs production potential of the MMC was evaluated in batch mode in a 5L bioreactor under controlled high aeration (DO level set at 25% saturation, DO25) and low aeration (DO level set at 5% saturation, DO5). The effect of the controlled DO level on the PHAs yield expressed in % PHAs/DCW (w/w) and also the monomeric composition was evaluated in comparison to the results obtained during constant aeration at 2L/min/L rector i.e. with highly varying DO (DOv). The optimal yield of 79.5±0.14% PHAs/DCW was achieved for DO25, while in the cases of DO5 results were similar to those from DOv, i.e. 60 % PHAs/DCW and 65 % PHAs/DCW, respectively . In all cases, P(3HB-co-3HV) was produced whereas the assimilation of propionate to HV in the polymers did not seem to be correlated to the DO changes, with HV content being above 5% in all cases. The subsequent simultaneous advantageous for the process, indicating that control of DO and not of pH proved to be even more advantageous for the process enhancing the assimilation rates as well, indicating that the production of PHAs from MMCs may be quite efficient if the cultivation conditions are properly controlled.