Factors Affecting Nitrous Oxide Production: A Comparison of Biological Nitrogen Removal Processes with Partial and Complete Nitrification

Abstract

Nitrous oxide (N(2)O) emission from biological nitrogen removal (BNR) processes has recently received more research attention. In this study, two lab-scale BNR systems were used to investigate the effects of various operating parameters including the carbon to nitrogen (C/N) ratio, ammonia loading, and the hydraulic retention time on N(2)O production. The first system was operated in a conventional BNR mode known as the Ludzack-Ettinger (LE) process, consisting of complete denitrification and nitrification reactors, while the second one was operated in a shortcut BNR (SBNR) mode employing partial nitrification and shortcut denitrification, which requires less oxygen and carbon sources. As the C/N ratio was decreased, a significant increase in N(2)O production was observed only in the anoxic reactor of the LE process, indicating that N(2)O was released as an intermediate of the denitrification reaction under the carbon-limited condition. However, the SBNR process did not produce significant N(2)O even at the lowest C/N ratio of 0.5. When the SBNR process was subjected to increasing concentrations of ammonia, N(2)O production from the aerobic reactor was rapidly increased. Furthermore, the increasing production of N(2)O was observed mostly in the aerobic reactor of the SBNR process with a decline in hydraulic retention time. These experimental findings indicated that the increase in N(2)O production was closely related to the accumulation of free ammonia, which was caused by an abrupt increase of the ammonium loading. Consequently, the partial nitrification was more susceptible to shock loading conditions, resulting in a high production of N(2)O, although the SBNR process was more efficient with respect to nitrogen removals as well as carbon and oxygen requirements.

Potential of Aerobic Denitrification by Pseudomonas stutzeri TR2 To Reduce Nitrous Oxide Emissions from Wastewater Treatment Plants

“…Among the new microbial nitrogen removal processes, nitrification and denitrification via the nitrite pathway have been investigated with a view to introducing the process into wastewater plants (12,20). However, the process produces a significant amount of N 2 O, probably because of the toxicity of nitrite (14). The results of this study showing that strain TR2 can rapidly denitrify nitrite even under aerobic conditions (Fig.…”

“…The first decrease in N 2 O should depend on dissolution of N 2 O into the liquid phase. All oxygen was consumed within 3 h; however, 14 On the other hand, strain TR2 started to consume 14 N 2 O before the complete consumption of O 2 , and it almost exhausted it within 3 h (Fig. 3B) Effects of nitrate and nitrite on aerobic cultures of P. denitrificans and strain TR2.…”

Survival of the Aerobic DenitrifierPseudomonas stutzeriStrain TR2 during Co-Culture with Activated Sludge under Denitrifying Conditions

“…It can be concluded that the application of strain TR2 to reduce N 2 O emissions 18) is most effective when the strain is used to augment sewage disposal of wastewater that contains low COD and high levels of ammonium, such as DLMF. The strain is best used in conjunction with a partial nitrification technique, such as a denitrificationnitrification liquid circulating reactor 9) or a nitriteaccumulating intermittently aerated sequence batch reactor.…”

“…6) This means that the N 2 O emitted during the aerobic process is not a byproduct of nitrification but rather the main product of denitrification by AOB. In the anaerobic (denitrification) process, the following conditions have been found to cause N 2 O emission: (i) insufficient anaerobiosis, causing inactivation of N 2 O reductase, 7,8) (ii) the accumulation of high concentrations of nitrite, 9) and (iii) a lack of electron donors (a low COD/N ratio).…”

“…However, heavy emission of N 2 O is a drawback of the technique that must be improved upon. 9) It was long believed that denitrification is an anaerobic process, and, as such, repressed under aerobic conditions, 14) but several aerobic denitrifiers have been identified. 15,16) However, there is no study concerning aerobic denitrifiers that has examined whether they emit N 2 O under aerobic, denitrifying conditions.…”