Enhanced polyhydroxyalkanoate (PHA) production by a combined growth and storage response in waste activated sludge

Municipal wastewater treatment plants (WWTPs) offer a ubiquitous source of microbial biomass for PHA production. When an endogenously respiring activated sludge is exposed to a sudden substrate exposure, substrate is principally consumed and initially metabolized in the biomass just for PHA production. This selectively allows PHA-storing microorganisms in waste activated sludge (WAS) to rapidly accumulate intracellular substrate. In this work, it is proposed that if ATP is also produced in sufficient excess of the demands for PHA storage and cell maintenance, those PHA storers will also be able to grow concurrently, leading to a combined growth and storage response. Experiments showed that such a combined growth and storage response can significantly enhance direct PHA accumulation on municipal WAS. Due to selective growth of PHA-storing microorganisms in a direct accumulation process, both PHA content in the product biomass and PHA yields on substrate were significantly increased. PHA contents of 0.61 gPHA/gVSS and PHA yields on substrate of 0.47 gCODPHA/gCOD were obtained in PHA accumulation experiments with butyrate as the sole carbon source. Four times more PHA mass was produced due to selective growth using only butyrate compared to only acetate as substrate over the same accumulation time and with all other factors, including nutrient availability, being the same.