Production of biodegradable polymer from microbial mixed culture (MMC)

Polyhydroxyalkanoates (PHAs) are biodegradable, biocompatible, non-toxic and cost effective polyesters that provide alternative to conventional petroleum based plastics. PHA polymers are composed of fatty acids monomers with attached hydroxyl groups and naturally produced as intracellular carbon and energy storage material by many microorganisms. Owing to its environmental-friendly characteristics and being derived from renewable sources, PHA production strategies are being a hot topic for both research-scale and industrial scale. Since Microbial Mixed Culture approach does not require aseptic conditions and can be operated by using cheaper substrates, it is preferred instead of pure culture cultivation for PHA production. The main goal of this study is increasing the PHA storage capacity of activated sludge by two steps strategy; culture enrichment and PHA production processes. For the culture enrichment, synthetic wastewater, which contains acetate as carbon source and peptone as carbon and nitrogen source, was fed to the system under aerobic dynamic feeding (ADF) conditions in SBR. Also, for the PHA production process, Volatile Fatty Acids (VFA)-rich industrial wastewater was used for 6 hours of batch operation. In order to maximize the production, different food-to-microorganism ratios (F/M) were performed with VFA-rich industrial wastewater and the results were compared with reference acetate containing synthetic wastewater of F/M=4. Additionally, investigation of microbial community structure in enrichment reactor was also aimed. In order to observe the changes in microbial community profile 16S rRNA based DGGE finger printing analyses were operated. Besides the DGGE analyses, 16S-based Next Generation Sequencing were also analysed for three samples of enrichment process. Due to the enrichment process, weight percentages of accumulated PHA were increased by nine fold, from 0.47% to 4.1% (g PHA/ g dry biomass). The efficiency of enrichment process was also proved by batch operations with VFA-rich industrial wastewater that were performed for both enriched and non-enriched cultures. While the maximum produced PHA content of non-enriched culture which fed by VFA-rich industrial wastewater was 4.44% of cell dry weight; 43% PHA of dry biomass was accumulated by enriched culture batches. The produced PHA level in VFA-rich industrial wastewater industrial wastewater after enrichment reached to a level as high as the one obtained in pure culture processes. Furthermore, enrichment process of microbial mixed culture was also analysed in taxonomic level. After the 12 months of enrichment process, SBR was become dissimilar with 76,4 % . This differentiation ratio was also proved by NGS analyses. According to the taxonomy classification of NGS analyses, Shinella genus of Alphaproteobacteria emerged as the most abundant group as they occupied 49% ofsample from the end of 20 months-enrichment process while they were not detected in inoculation sample of enrichment. Fundamentally, it can be postulated that PHA production in mixed culture has been successfully optimized. By the using of two steps enrichment-production strategy, PHA production capacity has been increased by ten times.