Abstract

Polyhydroxyalkanoates are bio-based and biodegradable plastics, stored under growth-limiting conditions. Their lower environmental impact -in comparison to the conventional plastic production- make them the perfect candidates for commercial plastic replacement. Many attempts have been made the last decade for scaling-up the PHA production process, but the high energy and cost requirements are some of the constraining factors. Lately, the new adapted approach is the mixed culture biotechnology. More specifically, for PHA-producers selection, the most common strategy applied is the cyclic feast/famine conditions. Previous research reported PHA accumulation 90wt% in open environment from single substrate (acetate). However, in order to make the process even more sustainable, wastewater could be used as the substrate (resource recovery approach). The main bottleneck of using that substrate is the presence of different carbon sources within the wastewater, some of which can lead to PHA storage, while others are used for growth of non-PHA producers. A substrate that can simulate that behaviour of the wastewater is acetate-methanol. Previous study from our group has proved that in the abovementioned substrate, acetate is quickly converted to PHA by the PHA-producers (40%), while methanol is used slowly only for growth of the methanol-consumers (60%). The present work is focused on increasing the fraction of the PHA-producers in that mixed substrate in a sequence batch reactor, under feast/famine conditions. In order to increase the fraction of the PHA-producers and enhance the PHA production, a sedimentation step was implemented after the fast acetate uptake (feast) phase, followed by discharge of the supernatant. Considering the much slower methanol uptake rate, a significant amount of methanol is removed with the supernatant, and eventually less non-PHA producers were retained in the system. Experimental results obtained from the systems with and without sedimentation, show an increase in the PHA content within the cells at a range of 10%. These results are closely related to the theoretical ones and demonstrate the success of the approach implemented.