Combining Phototrophic Polyhydroxybutyrate Production by Cyanobacteria with Anaerobic Digestion for Providing Nutrients and Utilizing Residual Biomass

摘要

In recent years, the interest in producing high value compounds (Chew et al., 2017) or biodegradable polymers (Singh et al., 2016) with algae/cyanobacteria steadily increased. Reasons for this are, in case of fossil based and persistent plastics, therising environmental pollutions (Lechner et al., 2014), which can be avoided by using biodegradable materials like poly-ls-hydroxybutyrate (PHB). Currently, PHB-production is based on heterotrophic bacteria (Panda et al., 2006) using organic carbon sources from agricultural crops. As alternative and to avoid competition with food and feed production cyanobacteria, metabolising PHB from CO2 e.g. from exhaust gas, can be used (Drosg et al., 2015). Due to the comparable low PHB concentrations accumulated by cyanobacteria (Drosg et al., 2015) it is necessary to increase the economic efficiency of photoautotrophic PHB production. A possibility is to use effluent streams (e.g. digestate) instead of fertilizers to provide nitrogen and phosphorous sources (Morales-Amaral et al, 2015) and to recycle process water of algae/cyanobacteria cultivation (Sing et al. 2014). Other options are to gain further high-value products from the cyanobacterial biomass (e.g. pigments, proteins; Koller et al. 2014) or to recycleresidual biomass into an anaerobic digestion process. Considering all these options a biorefinery concept was designed, where digestate and process water are used as nutrient source for cyanobacteria cultivation, additional products are gained and the residual biomass as well as the produced methane (CH4) and carbon dioxide (CO2) are utilized. Literature (Bhati et al. 2016) and previous experiments (Meixner et al. 2016) already demonstrate that effluent streams can be used as nutrient source for producing PHB with cyanobacteria. The current issue of research is to investigate further high-value products as well as the biochemical methane potential of residual biomass.