Glutamic acid removal and PHB storage in the activated sludge process under dynamic conditions

Glutamic acid removal in the activated sludge process is studied herein, primarily the formation of storage polymers under dynamic conditions. The activated sludge process was operated by using a sequencing batch reactor (sludge age of 6 d) fed with a synthetic mixture of readily available carbon sources, including glutamic acid. Removal of glutamic acid as the only carbon sources was studied in batch tests, along with oxygen consumption, ammonia uptake-release, and formation of storage polymers. It was found that poly-3-hydroxybutyrate (PHB) was stored and that the storage also occurred simultaneously to biomass growth. PHB storage accounted for 16% of the overall solids that were formed from glutamic acid, as the average value of nine batch tests. Neither other Polyhydroxyalkanoates nor polyglutamic acid were detected. Nuclear magnetic resonance analysis, performed on biomass extracts, allowed us to clarify the main metabolic pathways involved in glutamic acid removal and, in particular, the pathways involved in PHB storage. It was found that glutamic acid enters the Krebs cycle as alpha-ketoglutaric acid and exits to form pyruvic acid and then acetyl-CoA, which is the starting point of PHB production pathway.