Short- and long-term temperature effects on aerobic polyhydroxybutyrate producing mixed cultures

Short- and long-term temperature effects on polyhydroxybutyrate (PHB) producing mixed cultures enriched in feast-famine sequencing batch reactors (SBRs) were investigated in a temperature range of 15-35 degrees C and 15-30 degrees C, respectively. After short-term temperature changes (i.e. 1 cycle) from the steady state temperature of 20 degrees C, reaction rate changes in the famine phase could be described over the whole temperature range with the Arrhenius equation with one temperature coefficient. For the feast phase different temperature coefficients were identified for acetate uptake, PHB production and growth. These were only valid for temperatures 5 degrees C higher or lower than the steady state temperature. Long-term temperature changes (i.e. new steady states) influenced not only the reaction rates but also the selective pressure in the SBR. At higher temperatures (30 degrees C) the SBR feast phase was short and the rates of acetate uptake and PHB storage were very high. This culture was characterized by a storage strategy with high yields of PHB and low yields of biomass in the feast phase. The PHB storage capacity of this culture was 84 wt% as evaluated in fed-batch experiments. At lower temperatures (15 degrees C) the feast phase was longer due to a lower rate of acetate uptake and the culture followed a strategy of direct growth on acetate rather than on PHB. This culture had a low maximal PHB storage capacity (about 35 wt%). The SBR culture enriched at 20 degrees C was able to store up to about 70 wt% PHB. The temperature at which fed-batch experiments were conducted did not influence the maximal PHB storage capacity. The SBR temperature was found to be an important factor to consider when designing a mixed culture PHB production process.