Microbial biopolymer production from waste streams

Abstract: Burgeoning concerns on the adverse environmental impacts of fossil-derived products are propelling the pursuit of material production from sustainable resources. Resource recovery from waste is a key component of meeting the environmental sustainability agendas set by the United Nations. Municipal organic wastes present a significant opportunity for resource recovery due to their inherent organic content. Volatile fatty acids (VFAs), the intermediary products of anaerobic digestion of waste streams, can serve as building block chemicals with a wide range of applications. Meanwhile, microbiologically produced biopolymers called polyhydroxyalkanoates (PHAs) hold an enormous potential as an alternative to petrochemical-based plastics, given their comparable physiochemical properties, biodegradability and biocompatibility. In view of this, the focus of this thesis was on bio-based VFA production from food waste (FW) and PHA production from municipal organic waste by exploring process optimization and microbial community dynamics of mono and co-cultures as well as mixed microbial cultures (MMCs).The link between different inocula, retention time and pH on VFA production from FW was elucidated. This part of the study employed three distinct inocula under initial acidic (pH 5) and alkaline (pH 10) conditions for a period of 30 days. Waste-derived VFAs were employed for mono and co-culture PHA biosynthesis with bacteria, Cupriavidus necator, Burkholderia cepacia and Bacillus megaterium. The highest PHA yields of 78 ± 5.7% of cell dried weight (CDW) was obtained with C. necator and a PHA yield of 55 ± 3.7% of CDW was achieved with B. cepacia. In the next part of the study, activated sludge MMC was enriched over short (3 and 5 days) periods in combination with bioaugmentation of C. necator and B. cepacia in both mono and co-culture modes. While bioaugmentation did not increase the total PHA accumulation capacity, the microbial composition of the different bioreactors was modified. This Ph.D. project provided insights on recovery of biobased materials from waste. Manipulation of the microbial communities in the MMCs can be a critical parameter to enhance the overall efficacy as well as to tailor the composition of the end products.