Effect of Endogenous Carbon Source on Biological Denitrification Rate

Abstract

Post-anoxic denifitrication process can remove nitrogen from wastewater at a lower cost than pre-anoxic denitrification process since the nitrified water is not circulated during this process unless exogenous carbon addition is required. However, the denitrification rate is generally lower than that of a pre-anoxic process because endogenous carbon sources within the denitrifying bacteria are used as electron donors. The objective of this study was to develop a better understanding of this endogenous denitrification rate. A sequencing batch reactor fed with propionate was operated under variable anaerobic-aerobic conditions for 26 days to allow the biomass to accumulate polyhydroxyalkanoate (PHA) and glycogen stores. Sludge samples were collected from the reactor periodically, and nitrate removal rates were measured in the absence of any external carbon sources. Nitrate reduction rates ranged from 1.20 to 2.74 mgN/gMLSS/h. Meanwhile, PHA consumption (1.04 - 8.01 mgC/gMLSS/h) and glycogen synthesis (0 - 4.74 mgC/gMLSS/h) and consumption (0 - 1.54 mgC/gMLSS/h) were observed. The PHA consumption correlated positively with the nitrate reduction rate. Furthermore, glycogen consumption seemed to reduce both PHA consumption and nitrate reduction.